The Flowering Response of the Rice Plant to Photoperiod

The Flowering Response of the Rice Plant to Photoperiod A REVIEW OF THE LITERATURE FOURTH EDITION 1985 Los Banos, Laguna, Philippines Mail Address: P. O. Box 933, Manila, Philippines THE INTERNATIONAL RICE RESEARCH INSTITUTE First printing 1969 Partially revised 1972 Revised 1976 Revised 1985 The International Rice Research Institute (IRRI) was established in 1960 by the Ford and Rockfeller Foundations with the help and approval of the Government of the Philippines. Today IRRI is one of the 13 nonprofit international research and training centers supported by the Consultative Group for International Agricultural Research (CGIAR). The CGIAR is sponsored by the Food and Agriculture Organization (FAO) of the United Nations, the International Bank for Reconstruction and Development (World Bank), and the United Nations Development Programme (UNDP). The CGIAR consists of 50 donor countries, international and regional organizations, and private foundations. IRRI receives support, through the CGIAR, from a number of donors including: the Asian Development Bank, the European Economic Community, the Ford Foundation, the International Development Research Centre, the International Fund for Agricultural Development, the OPEC Special Fund, the Rockefeller Foundation, the United Nations Development Programme, the World Bank, and the international aid agencies of the following governments: Australia, Canada, China, Denmark, France, Federal Republic of Germany, India, Italy, Japan, Mexico, Netherlands, New Zealand, Norway, Philippines, Saudi Arabia, Spain, Sweden, Switzerland, United Kingdom, and United States. The responsibility for this publication rests with the International Rice Research Institute. Copyright @ International Rice Research Institute 1986 All rights reserved. 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ISBN 971-104-151-0 CONTENTS Foreword Introduction 1 Rice as a Short-day Plant 1 Growth Phases 2 Basic Vegetative Phase 4 Photoperiod-Sensitive Phase 5 Photoinductive Cycles 7 Reception of the Photoperiodic Stimulus and Translocation 9 Light Intensity and Quality 9 Interruption of the Dark Period 11 Days from Photoinductive Treatment to Flowering 12 Biochemical Changes During Photoinduction 12 Effect of Temperature on the Flowering Response to Photoperiod 13 Measurements and Methods of Testing Photoperiod Sensitivity 14 Date-of-Planting Experiments 15 Ecology and Photoperiodism 17 Terminology Used in Describing Photoperiod Sensitivity 20 Inheritance of Vegetative Growth Duration 23 Problems in the Study of the Rice Plant? fs Photoperiodism 25 Summary 26 Appendix 28 Bibliography 38 Foreword This review, first published in 1969, has been an important reference in understanding the rice plant. It has had a small but continuing demand. Many new reports on the flowering response of the rice plant have been published since the first edition. More than 100 publications were included in the third edition; this edition includes another 103 publications. For ease of reading, numbers have been used to cite the references. This review was prepared with the cooperation of the IRRI Library Staff and the technical assistance of Mr. Romeo M. Visperas, and edited by Ms. Emerita P. Cervantes. M. S. Swaminathan Director General Introduction Photoperiod influences several aspects of plant growth. Some of its effects on rices have been reviewed by Best (24), Gwinner (111), Katayama (192), Morinaga (316), Sircar (439), and Wagenaar (534). This review is primarily concerned with the effect of photoperiod on the flowering of the rice plant. It includes more than 500 papers on the photoperiodism of rice, most of which are available at the International Rice Research Institute library. Several contributions in Japanese have been translated into English and also are available at the International Rice Research Institute library. A bibliography is given at the end of this review; not all papers listed were cited in this review but were nevertheless included as future references for interested workers. Rice as a short-day plant Rice is sensitive to photoperiod . long-day treatments can prevent or considerably delay its flowering. Rice cultivars exhibit a wide range of variation in their degree of sensitivity to photoperiod (87, 254, 319, 357, 531, 563). Figure 1 shows these variations, ranging from the very sensitive to the nearly insensitive. 1. Response curves of three representative types of rice cultivars. 2 The flowering response of the rice plant to photoperiod Most of the wild species of Oryza and many of the primitive cultivated rices ( O. sativa L. ) are photoperiod sensitive and may be classified as short-day plants. Most papers agree on such a classification, and therefore in this review, rice will be considered as a short-day plant. It also will be classified into photoperiod-sensitive and photoperiod-insensitive types, the latter showing a low response or a slight delay in flowering with an increase in photoperiod. The present tendency is to select photoperiod-insensitive cultivars so that most of the cultivated rices may eventually become photoperiod-insensitive ones. These improved, early maturing cultivars may fit into the multiple cropping system characteristic of progressive agriculture. There have been reports of cultivars whose flowering is delayed by short-day treatments and hence are considered long-day plants (1, 98, 99, 239, 254, 276, 277, 279, 283, 284, 287, 291, 303, 398,443,444, 488). Heenati, for instance, is often referred to in the literature as a long-day plant (1). Short photoperiods have delayed its flowering by 10 d, but this delay is relatively short and may be the result of nonphotoperiodic factors, such as low light intensity or relatively high temperature. The delay caused by short-day treatments ranged from 7 to 12 d in the Charnock and Panbira cultivars using an 8-h photoperiod (443), about 9 d in B. 76 (303), and 13 d in T. N. 32 and T. A. 64 (287). Many of the reported long-day and intermediate cultivars were found to be short-day cultivars in subsequent testing (522). The apparent long-day reaction of Heenati resulted from using photoperiods shorter than the optimum, which delayed flowering (34). Some rices may have been classified as long-day plants because inadequate facilities were used in testing the photoperiod reaction. The range of photoperiods used has been limited, usually involving only two treatments. In some instances, the classification was based on field reaction to different planting dates (98). Short-day-treated plants were often compared with plants grown under natural day lengths (291, 303, 304). The difference and changes in temperature and the photoperiods used have made it difficult to interpret the data intelligently. As will be discussed later, many photoperiod response curves show that photoperiods longer or shorter than the optimum delay the flowering of photoperiod-sensitive cultivars (34, 513). Photoperiod response differs markedly among rices; this also explains the diversity of the results reported on the photoperiodism of the rice plant (see Appendix). However, more than 400 cultivars have been critically tested at IRRI (l59, 160, 161, 162, 163, 164, 166, 167, 168, 169, 170), and not one so far has shown a long-day response. Growth phases The growth of the rice plant can be divided into three stages: 1) the vegetative growth phase, from germination to panicle initiation; 2) the reproductive phase, from panicle initiation to flowering; and 3) the ripening phase, from flowering to full development of grain. In the tropics, the reproductive phase is about 35 d while the ripening phase ranges from 30 to 35 d. Both phases are relatively constant, although low temperatures have been known to prolong them and high The flowering response of the rice plant to photoperiod 3 temperatures to shorten them. The ripening phase may be prolonged to as much as 60 d. However, it is the vegetative growth phase whose duration generally varies greatly and which largely determines the growth duration of a cultivar, especially in the tropics. The vegetative growth phase can be further divided into the basic vegetative phase (BVP) and the photoperiod-sensitive phase (PSP). The BVP refers to the juvenile growth stage of the plant, which is not affected by photoperiod. It is only after the BVP has been completed that the plant is able to show its response to the photoperiodic stimulus for flowering . this is the PSP of the plant. Figure 2 shows the growth phases and the typical response of a photoperiodsensitive rice and a photoperiod-insensitive rice. Based on the BVP and PSP, varietal response to photoperiod can be classified into four types as shown in Figure 3 (105, 526). 2. Growth phases and typical responses of a photoperiod-sensitive rice and a photoperiod-insensitive rice. BVP = basic vegetative phase, PSP = photoperiod-sensitive phase. 3. Four types of varietal response to photoperiod. BVP = basic vegetative phase, PSP = photoperiodsensitive phase. 4 The flowering response of the rice plant to photoperiod The BVP and PSP are two separable growth phases controlled by different genes. Although some tropical cultivars may be classified as the D type having both long BVP and long PSP, most were probably eliminated during domestication since they would have had an unusually long growth period and could be planted only within a narrow range of dates. Such cultivars were found in Bangladesh and are known as Rayadas (105). The four types shown in Figure 3 were classified under one temperature condition. Norin 20 (Type A) has a short BVP. When grown in the tropics, however, it has a much shorter BVP than when grown in the temperate areas (Fig. 1). In classifying cultivars based on BVP, most of those from the low latitudes were found to have long BVP? fs (531, 532). Basic vegetative phase At the early growth stages, the rice plant is photoperiod insensitive so that the photoinductive treatments are usually started when the plants are 10-63 d old (13, 90, 142, 175, 186, 213, 230, 232, 273, 304, 316, 401, 512, 531). Because of this insensitivity to photoperiod, the early growth stage has been termed the basic vegetative phase; it is also referred to as the juvenile growth stage of the insensitive phase of the plant. Suenaga recognized the BVP as early as 1936. He measured it by taking the duration of the vegetative growth phase at optimum day length. The BVP also has been measured by subtracting 35 d from the growth duration (sowing to flowering) of plants grown at the optimum photoperiod (526). This assumes that the period from panicle initiation to flowering is about 35 d. Anema (13) modified the determination of the BVP by subtracting 35 d and the minimum number of photoinductive cycles needed for panicle initiation from the heading date. The resulting BVP values are smaller but this complex method would mean determining the minimum number of photoinductive cycles needed for each cultivar. The range of BVP reported in the literature has varied from 10 to 85 d (105, 175, 266, 273, 326, 381, 383, 401, 407, 445, 512). In an F 2 population, BVP? fs of more than 100 d were reported (249), but a BVP of this length has not been found in conventional rice cultivars. It is possible that such characters are eliminated during cultivar selection. The appendix shows the range of the BVP of the cultivars tested at IRRI. The indica cultivars generally have longer BVP (583). Other workers have reported or measured BVP in terms of leaf number (93, 215, 340, 413, 551, 575). The minimum number of leaves can be less than five. The need for determining the BVP of a rice cultivar before using it as an experimental plant material is obvious but is frequently overlooked especially in the study of the inheritance of photoperiod sensitivity. Several experiments showed that short-day treatments of seedlings accelerated heading (393, 401, 437, 438, 445) or delayed it (16, 273, 284, 287, 296, 426, 443, 447, 551). The results indicate the possible effect of photoperiod while the plant is in its early growth stage and the possible existence of a very short BVP. On the other hand, long-day treatments of seedlings have been reported to induce earliness in flowering (418, 427). These varied and conflicting results may have been caused by nonspecific factors. A good example is seedling vigor, which is The flowering response of the rice plant to photoperiod 5 known to affect the flowering date, especially in the weakly photoperiod-sensitive cultivars. The degree of sensitivity of rice plants has been reported to increase with age (142, 190, 195, 202, 205, 347, 512). The increase in leaf area accompanying advancement in age does not explain this increase in sensitivity (413). An increase in sensitivity with age up to 28 d and then a decrease in sensitivity with older plants (35- to 42-d-old plants) has been reported (296). The delay probably resulted from the setback from delayed transplanting and not from plant age because the plants were already 63 d old when transplanted, with some already flowering. The optimum age of responsiveness is probably the result of growthlimiting factors, such as space and nutrients and delayed transplanting. Katayama (202) indicated that the BVP, or aging effect, probably resulted from small leaf area and (or) low metabolic activity and (or) lack of a specific metabolic pattern in young plants. The substance causing response to short-day conditions is produced in too small a quantity to affect morphogenesis at the growing point, but increases gradually with increasing age. Studying this aspect, Suge (460) found that the growth inhibitors in the plant were greatly reduced as the plant grew. However, it is not known whether these inhibitory substances are essentially involved in the sensitivity of the plant to photoperiod. In some instances, the apparent low sensitivity of the younger plants may be a matter of completing the BVP. If the photoinductive cycles were given before the BVP of the plants had been completed, the effective photoinductive cycles would be less and the resulting response of the plants would be smaller. The transition from the BVP to the PSP is not well known; it could be abrupt or it could involve a gradual buildup. Using several cultivars, Best (26) found that the insensitive phase (BVP) changed to the fully sensitive phase (PSP) within a week. The following are possible explanations for the existence of the BVP (26): 1) The first leaves formed are completely insensitive to photoperiod. 2) The first leaves formed have very low sensitivity that they do not reach an adequate level of induction to evoke floral initiation before the more sensitive leaves formed at higher nodes have reached this stage. ) The first leaves formed do not attain the induced stage before the (early) senescence of these leaves. 4) The total leaf area required before the plant can react by floral initiation to the inductive photoperiod is so large that it is reached only at a relatively late stage of plant development. 5) The growing point of the young plant is unable to react to the floral stimulus or the st imulus cannot reach the growing point. Photoperiod-sensitive phase The PSP or the eliminable phase (186) is the growth stage indicative of the rice plant's sensitivity to photoperiod. In photoperiod-sensitive cultivars, the PSP determines the rice plant? fs sensitivity. The PSP of photoperiod-insensitive cultivars ranges from 0 to 30 d while that of sensitive cultivars lasts from 31 d or longer. Under continually long photoperiods, 6 The flowering response of the rice plant to photoperiod some cultivars have been reported to remain vegetative even after 12 yr of growth (234). The PSP is usually determined by subtracting the minimum growth duration from the maximum growth duration of a cultivar (526). Because many cultivars remain vegetative for a long period if grown under long-day conditions, experiments are usually terminated after 200 d and the PSP of the cultivar is given the value of 200+. Besides measuring the PSP, there are many other ways . to be discussed later . of determining a cultivar? fs sensitivity to photoperiod. A rice cultivar? fs response to photoperiod may be measured by the length of the PSP, which in turn is determined by both the critical and optimum photoperiods of the cultivar. Because these two terms have been used interchangeably and in many ways, the following definitions will be adopted herein. Optimum photoperiod is the day length at which the duration from sowing to flowering is at a minimum (34). Critical photoperiod is the longest photoperiod at which the plant will flower or the photoperiod beyond which it cannot flower. Figure 1 shows that BPI-76 has an optimum photoperiod of 10 h and a critical photoperiod of 13 h. Tainan 3 has an optimum photoperiod of 12 h but no critical photoperiod because it flowered under all photoperiods. The critical photoperiod determines whether a cultivar will flower when planted at the usual time at a certain latitude, while the optimum photoperiod determines whether it will flower within a reasonable time if planted during a period with longer days than would normally occur during the growing season. With BPI-76, if the optimum photoperiod is 10 h and the delay under photoperiods longer than 10 h is great, one would expect the flowering of this cultivar to be greatly delayed when planted in the northern latitudes where the photoperiod during the growing season is about 14 h. If the critical photoperiod is 12 h, flowering will occur very late at high latitudes, and if flowering does occur, the crop will not mature in time because frost will kill it. A cultivar with a long optimum photoperiod or no critical photoperiod would have wider adaptability . it could be planted at any latitude and in any season, provided it is not too sensitive to temperature. Optimum photoperiod The optimum photoperiod differs with cultivars although many workers have observed it to be 8-10 h (39, 116, 135, 142, 311, 362, 371, 393, 512). Using intermediate photoperiods of less than and more than 10 h may reveal more important information. But this will require facilities in which a maximum of 15-min difference in photoperiods can be accurately obtained. There are also indications that the optimum photoperiod increases with increase in temperature Njoku (335) did not find any optimum photoperiod in the varieties he studied. The photoperiod he used was as short as 9 h, well below the range of natural day lengths. Cultivars with optimum photoperiods longer than 10 h have also been reported (26, 90, 320, 322, 362, 568). The less sensitivity to photoperiod, the longer is the (394). The flowering response of the rice plant to photoperiod 7 ptimum photoperiod (116, 311). However, others found no correlation between the optimum photoperiod and the photoperiod sensitivity of the many cultivars they tested (572). A photoperiod longer or shorter than the optimum has been shown to delay flowering, the delay depending upon the cultivar? fs sensitivity (311, 316, 319, 371, 393, 459, 5 13, 568). The term supraoptimum photoperiod has been used when the photoperiod is shorter than the optimum. Panicle initiation in plants receiving a photoperiod as low as 4 h has been reported (140). No flowering has resulted under a 2-h light period (140). Plants receiving 8-h light and varying dark periods from 16 to 64 h showed inhibited shoot apex conversion (219). This was ascribed to inadequacy of carbon compounds for synthesis of requisite quantity of flowering hormone. The turning point mentioned by Yu and Yao (568) is similar to the optimum photoperiod, but the photoperiod values they reported were larger because these were not the photoperiods at which growth is shortest but the photoperiods at which the first long-day effect is manifested. Critical photoperiod Scripchinsky (417), reviewing the literature on rice, indicated that the rice plants have a ? critical length of day for flowering.? h Later studies showed the presence of a critical photoperiod ranging from 12 to 14 h (175, 209, 244, 354, 478, 490, 500, 553). The critical photoperiods determined under controlled photoperiod rooms were almost the same as the day length from sunrise to sunset at 30 d before flowering under natural conditions (499). The lower the latitude of origin of a cultivar or strain, the shorter is its critical photoperiod (196, 356). The critical period is influenced by temperature (566) and lengthens as the plant becomes older (2 12). The PSP of a cultivar is probably a measure of the combined effect of photoperiod on its optimum photoperiod and critical photoperiod. The shorter the critical photoperiod, the longer is the PSP. Short optimum photoperiod is also associated with long PSP. Photoinductive cycles A photoperiodic cycle that induces the initiation of flowers on plants is called a photoinductive cycle. A 10-h photoperiod alternating with a 14-h dark period is one possible photoinductive cycle of a short-day rice cultivar. The minimum number of photoinductive cycles necessary to initiate the panicle primordium of a rice plant varies from 4 to 24. This required minimum number varies not only with cultivar, but also with the photoperiod being used (13, 21, 26, 142, 195, 292, 338, 344, 408, 449, 500, 527, 529). The number of photoinductive cycles necessary increases with photoperiod length (190, 195, 203, 204, 527). According to Katayama (190), the minimum number increases proportionally with the photoperiod used, although others (527) failed to obtain a proportional increase using a different cultivar. Katayama (190) found that the minimum number was lower in cultivars from higher latitudes than in those from lower latitudes. The flowering response of the rice plant to photoperiod Suge (463) showed that different numbers of photoinductive cycles produced different amounts of floral stimulus. He also found that Gibberellin A3 reduced the minimum number of photoinductive cycles necessary to induce flowering. However, gibberellin alone did not induce flowering under noninductive photoperiods. That a certain number of photoinductiv e cycles is required to induce flowering suggests that the stimulus produced by the treatment is cumulative and that flower induction occurs when the stimulus has reached a certain threshold level (205, 206, 208). Photoinductive cycles interrupted by noninductive cycles can negate to different degrees the effect of the photoinductive cycles (200, 206, 345). There are also indications that emergence of the panicle from the flag leaf sheath is a process separate from panicle initiation. For example, internode elongation, after the panicle has been initiated, proceeds more rapidly at shorter than at longer photoperiods (26, 37, 67, 135, 425, 451, 512, 529), and earliness is further induced if the treatment is prolonged until flowering (33, 438, 498). It is possible, however, that panicle initiation and exsertion are separate processes, but certainly the latter proceeds only after the panicle has been formed. The effect of photoperiod on exsertion may be on fuller development of the panicle, hence indirectly affecting elongation of the first internode or exsertion of the panicle. Plants subjected to insufficient photoinductive cycles sometimes form panicles but no emergence occurs (see Table 1) (92, 122, 344, 512, 526). A difference of two photoinductive cycles could make the difference between exsertion or nonexsertion of the panicle. Several workers, however, have reported that photoperiod has only a slight effect on culm elongation and panicle emergence (85, 116, 338, 473); but the cultivars used (85, 338, 473) were generally weakly photoperiodic because the differences between the control and the treated plants were relatively small (16 d at most). In another instance, the treatment was started at a later stage . 20 d before the standard heading time . at which time the plants had received sufficient photoperiodic stimulus for panicle initiation and emergence (1 16). In another experiment, long photoperiods had no effect on the terminal bud that had reached the stage of differentiation of secondary branch primordia (345). Reversals from a reproductive to a vegetative phase have been reported (54, 342). In some instances, however, the panicle is initiated and differentiated but Table 1. Response of 30-d-old BPI-76 seedlings given different numbers of 10-h photoinductive cycles. Days from sowing Days from sowing Cycles (no. ) to panicle to panicle initiation emergence 8 ** 10 47 ** 12 47 88 Continuous 46 66 *No panicle initiation 200 d after treament. **No panicle meregence 200 d after treament * The flowering response of the rice plant to photoperiod 9 does not emerge (526). The unexserted panicle ceases to grow, and instead the terminal growth is dominated by a shoot from a node below the panicle. Such a situation is not a true reversal of the growing point. In more recent histological studies, incomplete short-day treatment changed the bract pri mordium into a leaf primordium, a true reversal of some parts of the growing point (346). Reception of the photoperiodic stimulus and translocation The photoperiodic stimulus may be received by the leaves of the rice plant (24). The leaf sheaths can receive the stimulus as shown by removing the leaf blades and subjecting the plant to photoinductive treatments (26, 142, 481). More photoinductive cycles were needed to induce flowering when the leaf blades were removed (142). Defoliated plants responded to light interruption given during dark periods as well as the intact plants (142). In one cultivar, the culm received the photoperiodid stimulus (26). Evidently, the leaf most receptive to the stimulus is the youngest fully formed leaf (263). The first leaves, up to the sixth leaf, are either insensitive or have low sensitivity to photoperiod (26). It is difficult to study this aspect of leaf sensitivity because grafting experiments with the rice plant are difficult. Removing the leaves at regular intervals after the end of the photoinductive cycles showed that the floral stimulus moves gradually from the leaves to the terminal bud (142, 464). The translocation of the stimulus depends on temperature. It was also reported that the rate of translocation of the stimulus is the same regardless of the number of photoinductive cycles received by the plant (463). The question of stimulus movement from one tiller to another has also attracted the attention of several workers. When a plant was divided and half was kept under a 24-h photoperiod and the other half under an 8-h photoperiod, the half subjected to the short-day treatment flowered while that under long-day treatment remained vegetative (230, 232). The results indicate that the stimulus is not transmitted from one tiller to another. This finding has been substantiated by other workers using different cultivars and methods (263, 408, 521). Manuel and Velasco (263) concluded that the stimulus that induces flowering can be conserved in the stubble and later transferred to the ratoon but not to a neighboring tiller of the same age as the donor. Sasamura (413), however, reported that the floral stimulus goes from the main culm to its tillers. The irregularities observed in photoperiod-sensitive cultivars when planted during the off-season, for example, the high number of nonflowering tillers, have been attributed to the effect of the photoinductive cycles received by the plant and their nontranslocation to the succeeding tillers formed (521). Light intensity and quality The light intensities used to prevent or delay flowering varied from 1 to more than 200 lx. Incandescent, tungsten, as well as fluorescent bulbs have been used (69, 143, 310, 396, 484, 489, 503, 538, 565, 570, 577). The brighter the illumination, the stronger the retarding effect. 10 The flowering response of the rice plant to photoperiod Delay in flowering with light intensities varying from 10 to 100 lx and even at 1 lx (310, 484) has been reported (538, 565, 589). Extending the day length using light intensities of less than 200 lx during the first or last 3 h of the 12-h dark period did not prevent flowering (478). In another experiment, 2-h illumination at 15 lx before a 9-h dark period showed some inhibiting effect and 1-h illumination at 500 lx incandescent light before a 9-h dark period inhibited flowering (143). In correlating laboratory studies with field studies, the natural photoperiod used is usually based on the sunrise-to-sunset duration. Such measurements are unsatisfactory in assessing periods of effective light because very low light intensities have been known to effect photoperiod responses in some experiments. Civil twilight in the morning can generally delay flowering but civil twilight in the evening may or may not delay flowering (143, 196, 205, 502). Civil twilight ends when the light intensity is about 4 lx. Twilight, of course, varies with localities and within the year. The critical light that results in delayed flowering is around 5 lx and sometimes 10 lx, depending on variety and other factors (174). Twilight intensity also varies and may be higher in the morning than in the afternoon (Fig. 4). Katayama (196) attributes the greater effectiveness of the morning twilight to higher intensity. Cloudy weather affects twilight duration. Takimoto and Ikeda (478), however, concluded that the photoperiodically effective day length is equal to the astronomical day length (sunrise to sunset) because twilight (less than 200 lx) had little effect on photoperiodic induction in their experiment. Wormer (538) showed that low light intensities for 6 h (10-100 lx) given after a 12-h daylight can delay flowering. Farmers have complained that their rice plants did not flower regularly because of the electric lights installed along their fields (552). One incident has been reported in which the light from a flame of waste natural gas prevented normal 4. Change of light intensity during civil twilight (after Katayama [196]). The flowering response of the rice plant to photoperiod 11 flowering in rice. The effect of light was noticeable up to about 270 m from the flare (22). Although light from incandescent bulbs is generally used for photoperiod studies, other colors have been tried in rice. The blue-violet part of the spectrum has been shown to retard flowering (260) as has infrared light (323). The delay in flowering caused by green light is very slight, only 4-5 d later than natural day length (234). Green has, therefore, been used in light traps for the moth. Red light is the most effective in delaying flowering, while blue showed some effect only at high intensities and in the most photoperiod-sensitive cultivars (26, 146, 153, 503). The phytochrome pigment is generally regarded as the system that interacts with photoperiod or with different light qualities, such as red, far-red, and blue. Such pigment has been studied in rice coleoptile by Pjon and Furuya (378, 379). For panicle initiation, rice needs a high light intensity during the light period. The inhibition caused by low-intensity light during the light period can be overcome effectively by exposing the plant to high-intensity light immediately before or after the inductive dark period (140, 145). This phenomenon is similar to that reported in other short-day plants and is evidently a carbohydrate requirement. This requirement would explain why a 2-h light period followed by 22-h dark period did not induce flowering (140). Ikeda (145) reported, however, that plants growing in low-intensity light during the photoinductive period but briefly exposed to high-intensity light before the inductive dark period had floral induction, suggesting that light requirement for floral induction of rice is not entirely concerned with photosynthesis. In the flowering response of the rice cultivars to photoperiod, red light given during the dark period inhibited flowering (136, 146, 148, 411, 442). The effect of red light increased with intensity. Red light, as low as 10 ? EW/cm 2 given for 3 h or 290 ? EWc/cm 2 for 15 min in the middle of the dark period, inhibited flowering (146, 148, 149). Red light was most effective in inhibiting panicle initiation when given in the middle of the dark period (150). With red light, the period of exposure needed to inhibit floral development was shorter than with white light (146). The inhibiting effect of red light has also been shown in experiments involving red and far-red lights. Far-red after red nullifies the delaying effect of red light and promotes flowering (411). Far-red before a 9- or 10-h dark period promotes flowering and this effect can be reversed by red light (146, 149, 152). Far-red enhances flowering whereas blue retards flowering (185). Far-red after the critical dark period can shorten the critical dark period as well as reduce the minimum number of inductive cycles required (145). Interruption of the dark period Sensitive strains of rice respond to light interruption (26, 69, 218, 232, 260, 323, 449, 570, 577). Light given in the middle of the dark period delayed the flowering of the sensitive cultivar Shuan-chiang (570). The light intensity used was 1001x and the duration varied from a flash to as long as 15 min. The degree of delay was greater in the light interruption of a 12-h dark period (12 light and 12 dark) than of a 16-h dark period (8 light and 16 dark) (577). Interrupting the light period with darkness did not accelerate flowering. 12 The flowering response of the rice plant to photoperiod The earlier the interposition of the light during the dark period, the greater was the delay (449). The findings show that the flowering response of the plant is determined by the longest dark period. Days from photoinductive treatment to flowering The literature indicates that the number of days from panicle initiation to flowering is about 35. Many workers have reported that the difference among cultivars is small (7, 407, 511, 551). Others found that the number of days from panicle initiation to flowering ranges from 10 to 241 d (425). It seems obvious, however, that 10 d is too short for the full development of a panicle. Flowering may be delayed by long photoperiods after panicle initiation (176, 524). But if the plants are given photoinductive cycles beyond the minimum requirement, the subsequent photoperiods have very little effect on flowering and elongation (501, 524). Auxin application can nullify the delaying effect of long photoperiods (176). Under natural day length, the number of days from the first-bract differentiation stage to flowering varied from 27 to 46 d, depending upon the cultivar and time of sowing (14, 270). Reports vary on the number of days from the start of the photoinductive treatment to flowering. Misra (285) reported 37 d in 30-, 40-, 50-, 60-, and 70-d-old plants of the cultivar T. 36 using a 10-h photoperiod. Fuke (93) noted that the plants flowered about 28 d after treatment. The number of days from photoinductive treatment to flowering depends upon the photoperiod being used. Panicle initiation and flowering were earlier under the 10-h than under the 11- and 12-h photoperiods (527). Using 168 F 2 plants, those treated under the 10-h photoperiod took 30-47 d to flower, or a mean of 35. d (Li, unpublished data. For practical purposes, an estimate of 35 d should be workable. Thus, to obtain the BVP or the time of panicle initiation, 35 d can be subtracted from the minimum growth duration of the cultivar. In studying the effect of photoperiod on the flowering of the rice plant, the most fundamental consideration is panicle initiation because it marks the actual change from the vege tative to the reproductive phase. Instead of using this as a basis, however, most studies use the flowering date, which is only a projection of the variations of the date of panicle initiation. To a certain extent, several factors can affect the stage from panicle initiation to emergence. In some instances, panicle initiation can occur without the subsequent emergence. The panicle primordium is aborted and a vegetative shoot may dominate the growing tip (527). A methodological question might therefore arise regarding accuracy of the experiments based on flowering date. The practicality of the method, however, far outweighs the need for extreme accuracy. Biochemical changes during photoinduction Very little work has been done on the chemical changes occurring during photoinduction and panicle development in rice. An increase in the rate of respiration of rice shoot apices with each photoinductive cycle given to the eighth The flowering response of the rice plant to photoperiod 13 day, followed by a gradual decline in rate, has been reported (293). The peak of the respiration rate almost coincides with the minimum photoinductive cycles needed by the rice plant at 8 h of photoperiod. The results suggest that the photoperiodic mechanism in the flowering of rice involves a respiratory shift. This corroborates the findings of Elliot and Leopold (86) who used other plant species. The changes in carbohydrate and nitrogen content of rice plants subjected to short days were also studied by Misra and Mishra (299). Unfortunately, the difference in heading between treated and control plants was only 4 d. Khan and Misra (222) reported an increase in sugar and nitrogen content of the leaves when subjected to photoinductive cycles. Photoinduction increases the gibberellic acid activity, although the value is low (461). This immediate rice, visible after three photoinductive cycles, returns to a level lower than that of the original. The rice plant is difficult to use for studies on biochemical changes during reproduction. Perhaps it is best to leave this type of study to other short-day plants. Effect of temperature on the flowering response to photoperiod The flowering of the rice plant is mainly controlled by two ecological factors . day length and temperature . which are often interrelated. The plant may respond to temperature and photoperiod simultaneously, but the degree would vary according to the cultivar. Cultivars have been classified based on these two factors (248, 356, 530). Temperature affects both the photoperiod-sensitive and photoperiodinsensitive cultivars. Generally, high temperature accelerates and low temperature delays heading (5, 6, 90, 126, 186, 307, 339, 340, 370, 376, 409, 410, 439, 456, 531). Some reports, however, have shown that high temperature delays flowering (15, 18, 394). The acceleration of the photoperiod response by high temperature is an overall effect, but it does not indicate the specific effects on the different stages leading to flowering. The effect of temperature on the BVP, photoinductive period, panicle differentiation and development, and critical photoperiod has not been fully studied. Uekuri (506, 507) studied the effect of low temperature during the BVP and found a definite delay in attaining the PSP. The degree of extension of the BVP by low temperature varied with the cultivars used. The growing point of the shoot is the receptive organ for the low-temperature effect, not the leaf blades (506). Ahn (5) reported that high temperature reduced the BVP but had very little effect on the PSP. As early as 1931, Fuke had considered the effect of temperature during the photoinductive period. He used snow to lower the darkroom temperature, but the 5-10? †¹C decrease had little effect on heading. Temperatures above 20? †¹C to 29? †¹C accelerate panicle initiation (24, 341). Vergara and Lilis (524) showed that the vegetative primordium was converted to reproductive primordium at the same time or at the same morphological stage regardless of temperature (21-32? †¹C). 14 The flowering response of the rice plant to photoperiod Haniu et a1 (1 15) found similar results. These results contradict those reported by Noguchi and Kamata (341) and Best (24). Temperatures below 15? †¹C inhibited initiation and bud development (156). Floral induction, however, is possible at 15? †¹C (341) but not at 12 or 40oC (115). Because many test plants died in the growing process, 15? †¹ C is assumed to be near the lowest limit for rice growth (341). The optimum temperature reported for photoinduction is 30o C (1 15). The question still remains as to whether a critical temperature for photoinduction exists. The optimum temperature for photoinduction may vary depending upon the photoperiod being used. The optimum temperature tended to be higher under a longer photoperiod and vice versa (24, 364). Putting it another way, at a certain temperature each cultivar has its own optimum day length under which it flowers at the earliest date (459, 572). Detailed microscopic studies of the development of the panicle primordium have shown that high temperature accelerates panicle development (260). The critical temperature for young panicle differentiation has been reported to be 18oC (555). Best (24) has also shown that panicle development, especially in its later stages, is accelerated at high temperatures (35-37oC). On the other hand, low temperature markedly retards panicle primordium development, and, below 25oC, the panicle may not emerge completely from the flag leaf sheath (24). A night temperature of 24. 4oC was found more favorable than 29 and 35? C in accelerating the flowering of the Elon-elon cultivar (263). High night temperature accelerates flowering (220). This was attributed to increased production of florigen during the dark period. This may not be the case and dissecting plants after photoinductive treatments may reveal if it was an acceleration in panicle development and exsertion rather than in panicle initiation. Others have found that the acceleration in flowering with high temperature is the result of acceleration in panicle exsertion, which, in turn, is the result of shorter leafing interval (524). Obviously, caution should be taken in determining the time of panicle initiation by observing the heading date because the exact date of panicle initiation cannot be determined by this method. Measurements and methods of testing photoperiod sensitivity Most studies on the photoperiodism of the rice plant have been considered from two standpoints, namely, classification of the cultivar into photoperiod-sensitive and photoperiod-insensitive types and measurement of the degree of sensitivity. The classification may be relatively easy, but the measurement is rather complex (195). As a result, several methods of measuring photoperiod sensitivity have been developed. Studies on the measurement of photoperiod sensitivity are usually based on the reduction in the number of days as a result of short-day treatment (1 16, 195, 205, 327, 329, 357, 553, 574). Other methods were more specific; they measured the optimum photoperiod (40), critical photoperiod (351), or the gradient of the response curve (34, 192, 247) as the basis of sensitivity. Hara (116) was the first to measure photoperiod sensitivity using the formula: X The flowering response of the rice plant to photoperiod 15 = T . Y/Y X 100, where Y is the number of days required to head under standard conditions and T is the number of days required under an 8-h photoperiod. Several similar formulas have been used by other workers. The percentage or index obtained from such formulas, however, does not clearly define photoperiod sensitivity. The results usually apply only to the area where the rice was tested since the natural day length is usually used as the control. Chandraratna (37, 40) used second-degree polynomials to compute the minimum heading duration and optimum photoperiod; this method involved using at least three photoperiods. He showed that cultivars differ in both characters. Oka (352) and Katayama (192, 201) measured the critical photoperiod and the degree of sensitivity of several cultivars using different methods and formulas and came up with their preferred method of measurement. Both workers used the natural day length as a basis for computation and assumed that flowering occurs 30 d after photoinduction. Best (25) and Li (249), using a method similar to Chandraratna's (34, 37, 40), measured sensitivity based on response curves obtained by plotting the time from sowing to floral initiation on the ordinate and the photoperiod used on the abscissa. The method, however, requires a wide range of photoperiods. Li (249) also studied photoperiod sensitivity in terms of the BVP and the PSP. The BVP was obtained in plants grown under 10 h of light, and the PSP (which is a measure of sensitivity) by subtracting the growth duration under the 10-h photoperiod from that under the 16-h photoperiod. The PSP values obtained show the possible maximum range in growth duration as a result of extending the photoperiod. The photoperiodic characteristics of a rice plant have been described by Stewart (458) who used a different criterion based on 1) basic vegetative period in terms of degree-days (based on temperature accumulation), 2) photoinduction period in degree-days or degree-minutes (using accumulated night length), and 3) panicle development period in degree-days (based on temperature accumulation). Tests under field conditions were analyzed by this method and predictions were made on the response of the cultivar sown in different months. In Japan, the flowering response is evaluated using the floral stages (135, 463). The Japanese workers have used the scale of 0-7, based mainly on the length of the developing panicle. This destructive measurement is more accurate than the usual days from sowing to flowering or treatment to flowering. The choice of the most appropriate method of testing and describing the response to photoperiod depends upon the purpose of the experiment and the available facilities. From the physiological standpoint, however, controlled photoperiod and temperature are desired because of their advantages over natural photoperiods and temperatures. Date-of-planting experiments Day length changes rhythmically within a year and varies depending upon the latitude. The amount of change in day length during the rice cropping season differs from one latitude to another (Fig. 5). Even in locations at the same latitude the day length during the cropping season may differ because the planting dates 16 The flowering response of the rice plant to photoperiod 5. Day length changes during the cropping season at various locations in Asia. may differ greatly depending mostly on the rainfall pattern at each location. At northern latitudes (Sapporo, 43? †¹ N, and Konosu, 36? †¹ N) day ength increases and then decreases during the cropping season (Fig. 5). At lower latitudes (Taipei, 25? †¹N, and Los Banos, 14? †¹N) day length decreases during the main growing season. Near the equator (Bukit Merah, 5? †¹N) there is little change. These differences in day length during the growing season may account for the wide range of photoperiod response of rice cultivars. A rice cultivar that must have less than 12 h o daylight to flower will obviously flower too late at the northern latitudes because frost will set in before harvest. In the northern hemisphere, the longest days are in June and the shortest are in December. Taking these into account, the photoperiod response of the rice cultivars can be tested to a limited extent by planting the cultivars at a certain location at different dates. Maximum differences in growth duration can be obtained in the May and November plantings if temperatures are not too low for growth. If a rice? fs growth duration changes more than 30 d, agronomists usually consider it photoperiod sensitive or a seasonal cultivar. As Best (24) has pointed out, this criterion is not specific enough for research on photoperiodism, and caution should be taken in evaluating the data obtained. These phenological data, however, are important to breeders in selecting ecotypes. This method of testing sensitivity to photoperiod has been followed in Australia (245), Brazil (l03, 579), China (44, 356, 582), India (98, 99, 101, 214, 220, 295, 298, 423), Indonesia (467), Japan (533, 548), Korea (247, 466), Malaysia (74, 77, 244), Philippines (91, 512), Russia (452), Senegal (66), Sierra Leone (68, 536), Sri Lanka (112, 259, 402), Thailand (381), Trinidad (325), and United States of America (177, 180). The flowering response of the rice plant to photoperiod 17 These experiments strongly confirm the existence of wide cultivar differences in the effect of planting date on flowering date. Many of the results obtained from this type of testing, however, are not applicable to identical cultivars grown at different latitudes. A cultivar can be insensitive to day length in Malaysia but sensitive in Taiwan. Results of field tests at a certain latitude are, therefore, not always applicable at another latitude. Some published papers on the use of this testing method failed to mention latitude or the place where the tests were conducted. Under natural conditions very small differences in day length can affect the rice plant. In Malacca (Malaysia), the difference between the maximum and the minimum day lengths is only 14 min and yet the cultivar Siam 29 takes 329 d to flower when planted in January and only 161 d when planted in September (76). Another instance showing the sensitivity of the rice plant to small differences in day length was reported in a date-of-planting experiment in Malaysia (244). There was a difference of as much as 156 d in the growth duration of photoperiodsensitive cultivars when planted in the same month but in different years (Table 2). This presumably resulted from differences in weather during the critical periods. Cloudy weather early or late in the day shortens the twilight hour, thus shortening the day length. Toriyama et al (490) tested rice cultivars involving not only monthly planting but also sowing at different latitudes (Sri Lanka, Taiwan, and Japan). This gives a better idea of the photoperiodic response of the cultivars but involves much work and cooperation. Ecology and photoperiodism Rice can be grown over a wide range of environmental conditions, from the equator to about 53? N latitude, leading to the differentiation and establishment of various ecotypes and forms. The great diversity in photoperiod sensitivity from one latitude to another or within a latitude probably indicates that the rice cultivars predominantly cultivated in each area are those that have been selected on the basis of local adaptability (that is, adaptability to the temperature of the rice-growing season, day length, and duratio n of the growing season) to assure the full development of the plant and the best possible balance between vegetative and reproductive growth (423, 530, 532, 584, 585). Table 2. Growth duration (days from sowing to flowering) of photo. period-sensitive cultivars when planted in January 1962 and 1963 at several localities in Malaysia (244). Cultivar Locality Jan 1962 Jan 1963 Difference Engkatek Telok Chengai 136 292 156 Kota Bahru 146 243 97 Kuala Lumpur 134 97 37 Subang Bukit Merah 270 224 46 lntan 117 Kuala Lumpur 171 138 33 Kota Bahru 276 176 100 18 The flowering response of the rice plant to photoperiod A major problem in studying the ecology of the rice plant, especially in reference to photoperiodism, is that cultivars in farmers' fields keep changing. For example, Hara reported in 1930 that Japanese cultivars were more sensitive than the cultivars from mainland China and Taiwan. He concluded that the lower the latitude of the region of the native habitat, the less sensitive were the cultivars there. Wada (531), using 134 cultivars, showed contrasting results . the cultivars from the northern region of Japan had lower photoperiod sensitivity than those from the southern region. Recent papers, however, generally agree that among the photoperiod-sensitive cultivars, the lower the latitude ofdistribution, the higher the sensitivity (351, 352, 356, 531, 583). The cultivars in the tropics or lower latitudes are usually late maturing (long growth duration). Many studies show that the late cultivars are more sensitive to photoperiod than the early ones (116, 248, 357, 511, 563, 583). In the tropics, where rice can be grown any time of the year provided there is sufficient water, photoperiod sensitivity presents certain problems. During the off-season, when the day length during the early growth stage is increasing, the sensitive cultivars are uneconomical to use because they take a very long time to produce any grain. For wider adaptability, cultivars should have low photoperiod sensitivity (53, 70) and thus have little differences in growth duration when planted at different times of the year or at varying latitudes. Insensitive cultivars have been successfully grown at different latitudes where rice is used as a crop (45, 351, 352, 511, 532, 568. This indicates that it should not 6. Growth duration of IR8 planted in June or July at 12 sites in Asia. La Trinidad and Kanke are high-altitude areas (52). The flowering response of the rice plant to photoperiod 19 e difficult to introduce new photoperiod-insensitive cultivars to different ricegrowing areas or to culture them year-round in the tropics. The plant breeders, as the varieties coming out indicate, are developing more photoperiod-insensitive cultivars. Extensive testing in various rice-growing areas of the world has established the wide adaptability of photoperiod-insensitive cultivars. In general, the longer the BVP the less variation ingro wth duration and the stronger the PSP the greater the variation in growth duration (581). The wide adaptability and the stable growth duration of IR8, a photoperiod-insensitive cultivar, are indicated by the data furnished by cooperators in various parts of the world. IR8? fs growth duration varied within a range of 20 d at latitudes from 11o to 27oN except at high altitudes where low temperatures prevailed during part of the growing season (Fig. 6). A more illuminating example of the effect of temperature comes from monthly planting at Los Banos, Philippines, and at Joydebpur, Bangladesh (Fig. 7). A comparison between the monthly mean temperatures and mean photoperiods shows that the more variable heading pattern at Joydebpur is more closely associated with temperature rather than with the prevailing photoperiod. The effect of low temperature on the improved tropical cultivars becomes more obvious in photoperiod-insensitive cultivars. 7. Mean monthly temperatures and day length in relation to the growth duration of IR8 at Los Banos, Philippines, and Joydebpur, Bangladesh (52) 20 The flowering response of the rice plant to photoperiod Sensitivity to photoperiod of rice cultivars in the deep water areas is an important characteristic for survival (104, 520). The floating rice cultivars are highly photoperiod sensitive. They are planted early in the season when the soil can still be worked and without danger of submerging the young seedlings. Flowering occurs when the floodwater peaks or starts receding. If the cultivar flowers when the floodwater is still rising, it would mean the complete loss of the crop if the panicles are submerged. Elongation ability ceases after panicle emergence. Harvesting is usually done when the floodwaters have receded. The maturity of floating rice cultivars coincides with the receding of the annual floodwaters which may be 150-270 d after sowing. Such a long growth duration requires a photoperiod-sensitive cultivar. So far, there is no known tropical cultivar that has a long growth duration and is not sensitive to photoperiod. Photoperiod sensitivity may work as a safety mechanism when precise planting dates are not followed and environmental conditions such as water level cannot be effectively controlled. If the date of sowing or transplanting is delayed because of insufficient rainfall, a photoperiod-sensitive cultivar may still mature at its usual time (352, 382). Plants are not seriously damaged if left in the seedbed for prolonged periods because the growth duration of the main crop is sufficiently long for the plants to adjust. Thus, land preparation and transplanting can be staggered (382). Maturation of the crop at the same time. as with photoperiod-sensitive cultivars planted at different dates, may reduce rat and insect damage in any one field. Also, harvesting and drying are simplified. If the soil is not sufficiently fertile, a photoperiod-sensitive cultivar will continue its compelled vegetative growth until the short days come. This would give the plant enough time to reach a reasonable plant weight and accumulate enough carbohydrates before flowering (528). Thus, a photoperiod-sensitive cultivar generally may be more resistant to unfavorable conditions. Long-growthduration cultivars (essentially photoperiod sensitive) are least affected by strong soil reduction (549). Most upland rice cultivars have short growth duration and are photoperiodinsensitive (11, 12). However, in areas where the rainfall pattern is bimodal, as in northern Thailand, the cultivars are of medium growth duration and are photoperiod-sensitive . possibly another indication of the greater specific adaptability of long-growth-duration cultivars to adverse conditions. The sensitivity to photoperiod of wild species has also been studied in relation to their ecological distribution. Most of the wild rice materials tested were sensitive (191, 201, 205, 209, 353). They suggested that this sensitivity favors the wild rice plants and is perhaps essential to their survival. Terminology used in describing photoperiod ensitivity There is confusion in the terms used to describe the response of the rice plant to day length (515). Often, the terms used for growth duration are also used for response to photoperiod (see Table 3). As early as 1912, Kikkawa pointed out that The flowering response of the rice plant to photoperiod 21 Table 3. Some terms used in describing the growth duratio n and day length response of rice cultivars. Terms References Response to day lengths: date fixed vs period fixed season fixed vs period fixed season bound vs period bound timely fixed vs periodically fixed short-day plant vs long-day plant ensitive vs indifferent sensitive vs insensitive sensitive vs less sensitive short-day plant vs indifferent plant strongly photoperiodic vs weakly photoperiodic sensitive vs photosensitive vs photononsensitive day length sensitive vs day photoperiodic photoperiodic insensitive length nonsensitive early, medium, and late long-aged vs short-aged early flowering vs late flowering late maturing vs early maturing Season of planting: aman vs non-aman yala vs maha winter vs summer main-season vs off-season first crop vs second crop wet vs dry season aus, aman, boro, rabi, kharif Growth duration: 33 7 214, 511 308 1, 99, 336 3 68, 352, 353 21, 98, 449, 538 563 51 1 195, 352 339 574 91, 276, 277, 281 259 158 3, 230, 374 427 112 444 Malaysia, Indonesia, an d Thailand China Philippines Bangladesh, India it is meaningless to classify the rice cultivars of the world into such groups as early, medium, late, aus, or aman. He said, however, that this classification is useful in districts where the climates are similar. The use of the terms photoperiod-sensitive and photoperiod-nonsensitive in reporting the flowering response of a rice cultivar to changes in day length has been suggested (515). Weakly photoperiod-sensitive is sometimes used in place of photoperiod-nonsensitive because the existence of a completely photoperiod-nonsensitive cultivar is difficult to prove. Weakly photoperiod-sensitive is also used to describe cultivars whose flowering is delayed by as many as 70 d by long photoperiods. However, those types can be planted any month of the year in the tropics and can be expected to flower within the crop season. The terms short-day plant and long-day plant are not satisfactory because most rice cultivars today are short-day plants. Sensitive and insensitive, sensitive and indifferent, and sensitive and less sensitive are ambiguous terms. Because the response being described is a response to light period and not only to light, the terms photosensitive and photononsensitive are inappropriate. 22 The flowering response of the rice plant to photoperiod 8. Effect of four photoperiod treatments on the seeding-to-heading period of seven rice cultivars. Chang and Vergara (51, 52, 53) classified rice cultivars into four types using the length of the BVP and PSP as criteria (Fig. 8). Their classification was based on duration of plants grown in the greenhouse. Under this classification, the Japanese varieties, such as Fujisaka 5 and Norin 20 (Appendix), do not fall under any category because they have a short BVP and short PSP. Also, at least four photoperiods (10, 12, 14, and 16 h) are needed to classify the cultivars. A more practical grouping could be as follows (using also the length of the BVP and PSP). 1. Photoperiod nonsensitive . very short PSP (less than 30 d) and BVP varying from short to long. 2. Weakly photoperiod-sensitive . arked increase in growth duration when photoperiod is longer than 12 h; PSP may exceed 30 d, but flowering occurs under any long photoperiod. 3. Strongly photoperiod sensitive – sharp increase in growth duration with increase in photoperiod; no flowering beyond critical photoperiod; BVP usually short (not more than 40 d). Cultivars tested under only two photoperiods, such as 10 and 14 h, can also be classified according to these groupings (1 1). Agronomists and farmers would tend to use these groupings. The flowering response of the rice plant to photoperiod 23 Inheritance of vegetative growth duration The inheritance of the duration from seeding to heading in cultivated rices has been studied by many research workers, but the findings have resulted in diverse interpretations. Three categories of genetic postulates were generally offered: 1) monogenic or digenic control of heading date, with earliness dominant to lateness; 2) monogenic or digenic control of flowering date, with lateness being a dominant trait; and 3) multiple-factor inheritance in which the F 2 population showed a continuous and often unimodal distribution and in which the same population might produce a bimodal distribution when grown in a different season (44, 509). In experiments where photoperiod sensitivity was recognized, delayed flowering under a long photoperiod was generally inherited as a monogenic or digenic dominant trait (38, 242, 406, 424, 567). In several crosses involving distantly related parents, sensitivity to photoperiod appeared to be a recessive trait (242, 406). The continuous and transgressive segregation in several F 2 populations involving photoperiod-insensitive parents was ascribed to multiple genes, which indicated dominance of earliness (41, 95, 96, 97, 333, 389, 469, 554). However, in crosses among varieties in Yunnan Province in China, photoperiod sensitivity appeared to be a recessive trait in some F 1 hybrids (252). Some of the divergent interpretations just mentioned resulted partly from failure to recognize the composite nature of the vegetative growth period from seeding to panicle primordium initiation, partly from failure to control the interaction of the environmental factors (mainly photoperiod and air temperatures) and the different genes controlling the vegetative growth period, or from failure to relate the phenotypic expression with the revailing environment. Recent studies at IRRI (48, 161, 162, 163, 164, 165, 167, 168, 249) have demonstrated physiologically and genetically the feasibility of partitioning the vegetative growt

Express Yourself Through Music Essay

It is clearly the most powerful tool used for expression. It doesn’t judge or discriminate, and there’s always a piece for you. This, of course, is music, which might be the greatest invention known to humans. Music has become an important part of society throughout the world as people use it to express themselves. All it takes is to listen to the very different and contrasting genres of music we have today. Each different type of genre conveys different meanings. Jazz is associated with relaxation, the blues with sorrow, and so on. Whatever instrument it may be, your voice, or a piano, you are expressing yourself. Music provides a great source of communication. For example, if speech was the only form of communication, and there was no smiling, sign language, or music, life would prove to be very dull and unfulfilling. Most music has a purpose, in which the composer/performer is trying to relay a message to their audience. This is especially noticed on the radio, with song after song, each displaying its very own message. Some artists use lyrics in their songs to express explicit messages or to make people think about life and its various lessons. Others want to inspire people, invoking the emotions within, while others are use their demeanor and emotions to relax their listeners. Many songs I have heard have accomplished their goal of seizing the listener. No other song I’ve been in touch with has taken hold of me like Billy Joel’s â€Å"Piano Man†. I believe it to be a classic song and never tire from listening to it. The magnificent and captivating vocals and the smooth flow of the piano brings a sense of happiness and joy about me that is incomparable. Expressing yourself through music can help you keep in touch with how you are feeling. It can also release a lot of tension that you may be carrying around with you. Music can help prevent your feelings from bursting out in situations or ways that are embarrassing and inappropriate. This happens when people get out of touch with their feelings, something that music can help solve. Everyone needs some time to themselves to reflect on their feelings, which can easily be done while listening to music. Being able to express how you feel through music may help you make better decisions about what is right for you now. Your feelings and expressions are closely associated with music. I personally don’t know of anything else (outside of first hand interaction with other human beings) that can affect me the way music does. You can either express the way you feel and get out of that trap, or you can just drown in your problems by playing the sorry blues. All my life I’ve been involved with music and I also realize that music is a difficult, but beautiful thing that people should take more time to appreciate. It is often overlooked as being unimportant, but I know how useful it can be in expressing oneself. In fact, in life, there’s nothing that makes me feel more at peace than music.

A Family’s Influence in “Death of a Salesman”

Death of a Salesman by Arthur Miller depicts the life of a salesman named Willy Loman and his family in 1950’s New York. Willy Loman reflects on his life in his old age with dissatisfaction, and at the close of the play ends up taking his own life. A family can emotionally hurt each member of it’s content more than any other person because of their closeness and similar thinking, as is shown throughout the play through the Loman family. Arthur Miller uses vividly portrayed flashbacks from Willy’s life to explain how one’s family can influence a person to feel like a failure. One way the author portrays Willy’s regrets is by introducing his older brother, Ben Loman. Ben ventured to Alaska to seek out a fortune and have an adventure, and although he invited Willy, he declined to stay in New York and become a salesman. Willy tells his Boss â€Å"I was almost decided to go when†¦ I realized that selling was the greatest career a man could want. † (p. 1859) He then goes on to say that although it was once a great business, the times have changed and instead of personality and friendship in the job, the people do not know him anymore. Willy also complains to his son, Happy, that he should have gone with Ben and made a fortune, rather than staying behind. â€Å"Why didn’t I go to Alaska with my brother Ben that time! That man was a genius, that man was success incarnate! What a mistake! † (p. 1839). Miller is telling through these passages that older siblings are able to make one feel inferior, when comparing your own successes to theirs. Ben overshadowed Willy with his accomplishments, feeling like he did not live up to expectations from his family. Older siblings create a standard for younger siblings to live up to, and if one does not live up to these standards just like Willy Loman, there is a sense of inferiority and failure. Willy Loman once had a strong relationship with his boys. Miller contrasts Willy’s past relationship with his two sons, Happy and Biff, with their current relationship to illustrate how your children’s dissapproval and strained relationship will affect one’s sense of failure. In Act I, Willy gets lost in a daydream where his boys are laughing and joking with him and hanging on his every word. When he tells them of his travels, they ask to be taken along, and offer to carry his bags. (p. 1835). Miller uses the small gesture of the boys asking to carry their Father’s bag to show that they had a true respect for him once, and would offer to do the smallest things to please him. This instance is contrasted when Biff is speaking to his Mother about Willy’s well being and yells â€Å"I know he’s a fake and he doesn’t like anybody around who knows! † (p. 1848). Throughout their lives, their relationship has become strained and Biff no longer feels the same respect for his Father as he did once before. Willy outwardly resents Biff every time they come in contact, but in reality he is resenting himself inwardly as Biff tells him the things he is starting to believe are true about himself. When a parents child has ceased to believe that their parent is magical and true in every way, that person will feel as though they have failed to teach their children, just as Willy Loman felt he had failed to teach Biff and Happy. The relationship between husband and wife is crucial to a family’s foundation and ultimate happiness. While Linda and Willy Loman have a seemingly wonderful relationship, Willy has an affair with a character simply called The Woman. The author portrays Willy’s deep guilt towards Linda during a daydream when The Woman is introduced. Willy flirts with The Woman, with her saying that he is funny and generous. Willy gives her a new pair of stockings, and she tells him while he kisses her â€Å"You just kill me, Willy. And thanks for the stockings. I love a lot of stockings. † (p. 1838) The scene then changes to Linda mending a pair of old stockings, telling Willy it is because they are so expensive. Willy lashes out at her quickly, telling her to throw them out. Miller uses this contrast between the two women in Willy’s life to portray the guilt he feels towards the affair, and illustrating that his heart does not completely lie in the marriage he is in. Both women are offering Willy adoring comments, but while he is able to buy The Woman new pairs of stockings, his wife is at home mending an old pair. Willy had become unhappy at home, and had therefore tried to find his happiness somewhere else in another woman, offering her new things rather than his wife. The author is telling his audience that marital relationships are very important, and if it is not strong then the rest of the family will continue to suffer, and eventually feel the effect of their failed relationships. In another essay by Arthur Miller, he states that Willy â€Å"gave his life, or sold it, in order to justify the waste of it. † (p. 1892). The failed family relationships from his wife and children, as well as the shadow of his brother hanging over his head, had led Willy to believe he was worth more dead than he was alive. A person’s family has more influence on a person’s self esteem and worth more than any other factor, and can either lead to great self esteem, or in the case of Willy Loman, a sense of intense failure.

Auer waffeln an austrian company's tale of growth,globalization and Essay

Auer waffeln an austrian company's tale of growth,globalization and decline - Essay Example Business organizations rely on the effectiveness of their marketing strategies, which should always determine the potential of the market thereby informing the subsequent production process of the organization. An effective marketing process should inform the production thereby preventing the organization from incurring losses (Solomon et al, 2009). SWOT analysis The marketing process relies on a number of organizational analyses key among which is the SWOT analysis. This is a business tool used in analyzing the potential of the business organization in sustaining the market demands. The first two components of the analysis are the Strengths and weaknesses of the business organization while the last two are opportunities and threats of the business. The first two elements are therefore within the organization and the organization can manipulate them to ensure it sustains its profitability. The last two on the other hand exist externally; they are part of the market forces implying th at the business organization cannon manipulate them. They therefore determine the profitability of the business. ... The growth if the business portrays a number of management success resulting from bold management strategies. However, the business later stifled away following a number of management lapses and the inability to maintain its market share. The success of the business depends on the effectiveness of the business idea and the nature of the execution of the idea. Guenter Auer identified a potential need for the foodstuff in the Austrian market. The business later flourished following the effectiveness of the business idea. Apparently, the Austrian market had lacked such a business thereby creating a loud that the Waffeln business seamlessly filled. Market entry strategies After identifying an effective business idea, the nature of executing the idea becomes essential in safeguarding the success of the business. Auer identified a gap within the market and therefore decided to fill it thereby developing a market of its own. The idea was unique and therefore took the market by surprise. The business therefore developed a sizable market for itself. However, Auer knew the nature of the market and the amount of potential it had. He therefore began by operating his business in a small scale within the small local market. This did not only provide adequate profitability but also provided the organization with an effective market research opportunity (Ghauri & Cateora, 2010). Through the small local market, he determined that the business could grow to become a national and progressively an international business. He therefore realized the need for a more qualified manager for the business a factor which compelled him to send his son to some of the best schools from where he studied manage net among other operational courses related to production.

Cash Flows in Business Organisations Coursework - 1

Cash Flows in Business Organisations - Coursework Example On the other hand, net cash flow can be defined as the difference between the cash that is brought in and that goes out of a company. First, to understand the underlying factor causing the difference in these two major accounting items, it is imperative to be known that the determination of a company’s net profit for the financial period depends on some criteria as provided by the GAAP (Eisen 2007, pp. 101-110). Unlike net profit, cash flow determination is not affected by any criteria. Second, the difference is brought about by the fact that some expenditure considered as non-cash such as the depreciation costs are deducted from the revenue in order to obtain the net income. On the other hand, these non-cash costs are added back to obtain the net cash flow. Third, the difference may be caused by the rules regulating the recognition of revenues and expenditures, which do not apply to a cash flow statement but to the profit and loss account. Consider a company with a net income of $ 1,117,500. To obtain the company’s cash flow, some costs such as the amortization ($ 101,100) are added back to the net income to obtain the net cash flow. Therefore, $ 1,117,500 + 101,100 + (or less other items) will result in a higher value of net cash flow as compared to the net income (Gilbertson & Lehman 2009, pp. 428). As provide in the international accounting standards 7, the indirect method of cash flow presentation involves beginning with the net income, which is then adjusted to obtain the net cash flow. On the other hand, the direct method specifically shows the cash inflows that make up the operating activities as shown in appendix 1a and 1b (Jury 2012, pp. 228-230). Operating activities: The extracts of operating activities of the two companies are available under appendix 2. In the year 2011 and 2012, the following are the cash flow analysis: Viacom has net earnings of $ 2,173,000 and

IT Doesn't Matter Essay Example | Topics and Well Written Essays - 750 words

IT Doesn't Matter - Essay Example An example of the technology is that involved in sharing tasks in building a railway so that the rail is completed in time. Proprietary is the technology that is able to give a company a competitive advantage as long as there is protection in the production rights that the company operates on. This leads to generation of higher profits than the rivals. IT was compared to transport system as it transmits digital information the same way as it is in transport system. The comparison is with the other modes of transport including power grids that carry electricity and railroads that carry goods. IT is more replicable and this makes it be compared to a more valuable commodity than just a byte of data. The comparison of IT to a commodity is not false, the comparison is right as the transformation that is made on the commodities can be made in IT (Harvard Business Review, 2003). Commodities are accelerated in terms of developments. Introduction of internet accelerated commoditization of IT through provision of a perfect generic application for the delivery channel. The first argument that is given comparing IT to a commodity is that IT is a transport process that transmits digital information just like the other forms of transport such as roads and rails. IT just like the transport system is effective when shared than when it is used in separation by an individual. The second argument that makes IT compared to a commodity is that it is highly replicable. It is hard to imagine a more perfect commodity than just a byte of data. When it is combined with technical standardization, there is production of more economical value. The concept can also be argued by through consideration of the arrival of internet that has accelerated the commoditization of IT. The last argument that is given by Carr is that IT is subjected to rapid deflection in prize. He links this to when Gordon Moore made a prescient assertion that the density of

A guide to taking a patient's history Essay Example | Topics and Well Written Essays - 750 words

A guide to taking a patient's history - Essay Example ‘A guide to patient’s history obtaining Nursing’ article by Lloyd and Craig investigates the approach of gathering history of a patient. The guide identifies the procedure and reason of patient’s history obtaining, the significance of environment preparation and how efficient skills of communication aid in the taking of accurate history. Article summary Correct patient history is crucial because it provides the doctors or nurses and healthcare management with the effective information required in carrying out their assignments. The environment preparation offers patient safety, correctly equips them and eliminates any form of patient or nurse distractions during history taking process. The patient may feel uncomfortable talking over some sensitive matters if some distractions occur in the environment, or the nurse seems not to be attentive. The setting should be private to make the patient confident to give private information without reservation. The nurse should ensure respect for the patients, which involves respecting the values and beliefs and privacy, confidentiality and dignity of the patients, and the capacity to be non-judgmental and highly professional throughout the process. Effective communication skills are crucial to allow obtaining of a comprehensive history, while the medical practitioner should obtain patients consent before the commencement of the intervention. After obtaining the patient consents, the nurse should follow the below overall standards when collecting patient’s information. First, Introductions are crucial for the creation of patient-nurse relationship and mutual trust and to help set an interview process tone, and investigate how the patient prefers to be addressed. Pay attention to the patient’s history as this provides a systematic order of information. Closed questions offer additional information and enlighten patient’s story. Clarification, which entails recalling back to the parson and comprehension of the history, comments and disease symptoms, is crucial. After complaint presentation, the nurse should take the medical history of the patient and investigate other related histories and records of the patient. It also provides crucial health information background such as cancer history and about diagnosis, sequence, disease management and dates. Mental health history investigates whether the patient has experienced any mental challenges in the past. Investigate the present coping mechanisms of the patients including anxieties over health challenges (malignancy suspicions, future surgery, test outcomes) or advanced mental challenges like bipolar disorder. Medication history is crucial to investigate the previous and current medication that the patient may be using. For instance, the source and form of medicine used, whether the medicines were prescribed by a doctor, bought from pharmacy or acquired from other sources such as herbal medicine and homeopath ic remedies. Family history should be established because it can provide a significant source of familial conditions like cerebral malaria, dementia history, asthma and diabetes history, which might aid direct patient healthcare management. Social history – experts agree that a person’s capacity to cope with health alterations depends on his social welfare. The nurse should investigate the function level and any long-term functional change due to illnesses, (Lloyd & Craig, 2007). The nurse should investigate the patient’s family relationship, social membership and other social support networks. Sexual history covers sexual health, and some of the sexual infections that the patient may have experienced. For instance, in men investigate about past infections of urinary tract and STIs and possible treatments offered. In females, explore date of menstruation, menarche regularity and characteristic of pregnancies, abortion, life births and periods as well as risks of STIs infections, (Lloyd & Craig,

Art History Essay Example | Topics and Well Written Essays - 750 words - 7

Art History - Essay Example ticle focuses on modernism and the author has turned to present day practitioners whose work are not only the most powerful being done currently, but as well is a wholly committed to the modernist project. The author has used other author’s examples throughout his work in giving examples on how modernism begins and how postmodernism comes in and changes the way a human being lives. The use of descriptive language style in this context has made the author draw the reader’s attention which is a better method of retaining readers and making an article more interesting. The author has also applied the use of speech; this clearly shows how the author has invited other people’s work in this particular article. The author has also used descriptive and vivid language in order to add depth to this article. This appeal to mankind senses to deepen any reader’s well understanding of this article (Morris, Tony, Anthony, Watt and Michael 65). To foster this, the author has included some photographs to support some of his facts. These pictures help any reader to visualize the content being talked about at the back of his or her mind. According to the author, within modernist practice, artists will always reach for signs that function as algorithms of the structural or medium within which they occur. As the center or core of that particular structure, such as a sign, secures the unity or singularity of the task itself, a unity that had been named â€Å"aura† in a different era. The author has also elaborated modernity with most trending lifestyle things such as cars and electronic gadgets majorly. Constitutive heterogeneity may as well define the latest work of a modernist in most part of the article (Cahoone and Lawrence 111). The author has not talked much about himself about modernism which leaves the reader to wonder what type of option he has decided to take. It is until the last sentence of the article that the reader realizes that when the author reveals that the

Essay on Process Improvement Example | Topics and Well Written Essays - 1250 words

On Process Improvement - Essay Example Following a lengthy process, the recruitment process conducted by TS takes too long resulting in some interested candidates getting taken away by other companies. Within the framework of the company itself, some employees appear very dissatisfied with the services rendered by the company. The level of input appear to be dwindling among the employees of Talent Seek, reaching levels of failing to cooperate with the newly appointed manager of the Business Analysis and Improvement team. Objectives of the improvement process The purposes of performing a process improvement include identifying the processes that require improvement, analyzing the identified processes, and finally implementing the desired changes aimed at improving the processes. The processes reviewed for improvement ought to present a surmountable impact on the customer satisfaction or competitive advantage. While numerous reasons exist, for implementing process improvement, the case of Talent Seek would mainly aim at imp roving customer satisfaction with the services offered. The improvement of customer satisfaction, required by the company, remains reducing the time taken to complete requested recruitments. This duration appears to cause some qualified candidates to lose interest in the employment opportunities offered. Reducing the duration, therefore, remains essential to the overall improvement of the process and ensuring the recruitment of the best candidates within the specified job market. The improvements Disconnects could be defined as elements that appear to inhibit the efficient and proper functioning of a process (Rummler, 1996). They form the basis upon which improvements should target, as handling disconnects improves the entire process. Proper handling of the prevalent disconnects remains essential in ensuring improvement of the entire process. Within the TS recruitment process, majority of the delays result from processes considered protocol within the company. Majority of these â₠¬Ëœprotocol’ stages could be eliminated in order to quicken the process, hence improvement of the operations. In the preparation stages of the process, the client-end managers could be handed the task of determining terms and conditions for the various vacancies. This would efficiently cut the consultation period utilized when the TS team determines the terms, and the client-end managers have to counter-check before the process can proceed. A cost effective method for implementing such changes would be charging for the services of drawing conditions and terms. Companies willing to have conditions determined by TS would pay for the service, effectively; the TS Company would cater for the remunerations of the individuals performing the job through these payments, while making a profit. Within the recruitment process, TS could limit the duties performed by the recruitment panelists. The roles of the panelists could be reduced to only conducting the vis-a-vis interviews. The aspe ct of having the panelists’ review the applications could be done away with as it only consumes time. Since panelists must be sourced once applications have been received, the roles played by these individuals need to remain minimized to reduce the duration. The role of the panelist in the actual recruitment ought to remain limited to conducting the interview, on the specified period. Being expatriates, retaining panelists for long periods could prove costly to the recruiting company. In managing the costs

Environmental Engineer Essay Example for Free

Environmental Engineer Essay For an Environmental Engineer, it is very important to know the jurisdiction that one will be working in. Not only is thorough knowledge of the natural characteristics such as geological and meteorological aspects of the jurisdiction to scientifically cater to the unique environmental concerns of a certain area, but it is also essential that one also knowledge of the social and judicial aspects of the jurisdiction for easier cooperation with the citizens and more efficient applications of environmental impact assessments and mitigations or development of environmental policy and regulation, for example. The Northwest Territories and Nunavut are unique in many aspects that concern Environmental Engineering practice. In general, the Northwest Territories and Nunavut are already geared towards environmental safety, conservation, and regulation. For example, in the Northwest Territories, programs are already in place to ensure sustainability of forest use, regulation of wildlife protection and use, etc. In Nunavut, their Department of Environment actively apply what they call Avatittinnik Kamatsiarniq, or environmental stewardship, to conserve their vast natural resources and promote sustainability, a principle that is based on the Inuit culture and must be respected by any Environmental Engineer who plans to practice in that territory. In fact, one must have good knowledge of that culture as the Inuit populace of Nunavut make up the majority of the demographic and thus their culture and belief system have a great influence on governmental policies, considering that the self-governing system of the Inuit is unique to Nunavut and issues such as land claims are a constant concern. Similarly, the agencies of the Northwest territories also make use of the traditional knowledge of the Inuit concerning the natural resources and the relationship between man and environment. As North American Indians comprise the majority of the population in the Northwest Territories, they appreciate the value of this knowledge and these are taken into consideration in the making of public policies which include environmental engineering law. To work in the Northwest Territories, one must be aware of programs such as the NWT Protected Areas Strategy, that utilizes a community-based process as it makes sure to respect Aboriginal rights to balance conservation and economic development. The programs already in place and the social set-up of the jurisdiction are only part of the concerns of an Environment Engineer, of course the physical aspects of the territories are also important. The weather is an important part of the culture of the Aboriginal people, not only are the weather extremes (such as the record-breaking Arctic heat in Nunavut) and the natural hazards serious concerns, climate change is also a much monitored phenomenon. The geological makeup and position of Nunavut and the Northwest territories make them very vulnerable to climate change effects, such as the possible melting of permafrost. In the Northwest Territories, their use of their abundant mineral resources have caused a great strain in the environment such as the giant earth scars left by diamond mines or the hazardous tailings pond spills, and the Environmental Engineer should not only be aware of these for future mining operations but could also work together with other agencies to alleviate these prior issues. Furthermore, the geology of Nunavut can span most of Earths history with great economic potential yet it is still very underdeveloped, and yet, they are actively advertising extreme sports tourism which could cause environmental as well as safety concerns. In all, there is a balance in the naturalistic Aboriginal-based society and community and the raw environment of this jurisdiction that gives the Environmental Engineer a unique practice.

Importance Of Stretching Before Exercise Physical Education Essay

Importance Of Stretching Before Exercise Physical Education Essay Stretching before participation in athletic activities is typical practice for all levels of sports, competitive or recreational. Athletes, coaches, trainers, physiotherapists, and physicians recommend stretching in an effort to both prevent injury and enhance performance. Several papers have been published which has produced a significant body of evidence that stretching may not be the way to improve performance and decrease risk of injury. Recent research demonstrates that stretching prior to physical activity decreases performance. However, these stretching bouts are not representative of athletes during warm up procedures, as they are usually time consuming. The aim of the this study is to examine whether the duration of acute static stretching is responsible for losses in sprint times compared to increased/decreased flexibility.   Research has shown the reduction of peak flow force when using static stretching but research has also shown the reduction of injury and the improve ment of flexibility in the long term which also assists in sprinting performance. Research in this area has sometimes been vague involving the time of the static stretched used. Bandy (1997) used 57 subjects from the age of 21 to 37 years old, 40 of these being male and 17 female with all participants having limited hamstring flexibility. These participants were randomly assigned to four groups. Three groups stretched 5 days per week for 15, 30, and 60 seconds, Group four served as a control group, and did not stretch. The test was ran over a six week period. The results showed that holding a stretch for 30 seconds was optimal as it had a greater effect on range of motion than the 15 seconds and control group and the same effect as the 60 seconds. Bandy (1997) concluded that because there was little difference between no stretching and 15 seconds coaches and athletes must raise the question of the effectivness of static stretching for periods less than 30 seconds. Although this study supports its hypothesis it is very specific to the hamstring and lower body. Muscle such as the gasrtocnemuis may show different results due to the higher percentage of fast twi tch muscle fibres which performs larger, more powerful movements REF. The study did not show the acute effects of static stretching so we cannot assume these results would or would not enhance range of motion/flexibility gains prior to any sporting events. Also this study is excessively narrow in subject focus and as all participants had limited amount of range of flexibility within the hamstring, with a higher majority of subjects being men. Therefore this makes the results only valid to this population. Due to the length of the study and the uncontrolled environment I would have to question the suitability of the research design and the effectiveness of the data collection. The subjects were only tested once after the six week period, therefore subjects were subjected to outside environmental factors during the six weeks which may have affected results. Testing and monitoring constantly throughout the six weeks would improve the reliability of this study. A more controlled study was done by Shirer (2005). This study focused on muscle performance rather than flexibility. He conducted a study using males from a university population who were pre and post tested for isometric force and surface electromyography activity. (Shirer 2005 pg 22) tests were performed on only lower limb muscles, range of motion in seated hip flexion, prone hip extension, ankle planter and dorsi flexion, no-counter movement jump height, and ground contact time. Male participants were tested 30, 60, 90, and one120 seconds after static stretching. The group partake in an 18 minute static stretch routine for the lower body (hamstrings, quadriceps, and planter flexors). 45 seconds was the protocol stretch time used for each muscle group and was repeated four times with a 15 second break in-between. Shirier (2005) found differences in the acute (just before exercise) and regular stretching (over a period of time). Results stated that there was no significant benefit o f acute stretching on isometric force production, isokinetic torque, or jumping height. In addition, (Shirer 2005 pg 25) concluded by saying that regular stretching after exercise may improve strength, jump height, and running speed. As a result these findings imply that acute stretching before exercise had no positive effects on strength and power while regular stretching after training or competition improved strength and speed. Results did not relate to the acute effects of static stretching but only the acute effects of isometric force. Again this study provides significant evidence for the effects of stretching on performance, however the time frame used for the stretches in this study was 45 seconds and 30 seconds has been proven in the previous study to be the optimal time. This extended period of time could therefore affect the force production and therefore the results. A similar study by Fowles (2000) that supports Shirer (2005) body of evidence showed the effect of stretching on muscular strength over time. (Fowles 2000 pg 1179) Subjects performed 13 stretches of the plantar flexors, holding each stretch for 135 seconds during a time frame of 33 minutes. Maximal voluntary isometric contraction (MVIC) was assessed 6 times during the ensuing 60 minutes. Fowles (2000) concluded that an intense extended stretch (of the plantar flexors) reduces MVIC for up to 1 hour after stretching. Although this evidence supports that of Shirier (2005) it is not relevant to sports performance as proven by Bandy (1997) the time for both holding the stretch and time spent on stretching is too long and therefore is not specific to sports performance and is not relevant. A more sport specific study was done by (Sayers AL 2008) who performed a study using 20 female football players to determine which phase of the 30 meter sprint (acceleration and or maximum velocity) was affected by performance static stretching. Participants were assigned at random to either a stretch or no stretch condition on two non-consecutive days. The athletes in the no-stretch condition completed a standard warm-up protocol and then performed three 30-m sprints, with a 2-minute rest interval between. The athletes in the stretch condition performed the standard warm-up protocol, completed a stretching routine of the lower limbs which included calf, quadriceps, and hamstrings and then without delay performed three 30-m sprints, also with a 2-minute rest between each sprint. The groups would then reverse the next day, and indistinguishable procedures were followed. A considerable statistical difference in acceleration maximal-velocity sprint time, and overall sprint time between the stretch and no-stretch conditions was seen. (Sayers AL 2008 pg 1420) concluded by stating that static stretching before sprinting resulted in slower times in all three performance variables. Although this study proves that static stretching diminishes spitting performance it does not state the time held with the stretches. Again this study is gender specific and as studies has proven significant differences between male and females relating in flexibility and spots performance we cannot assume these results are relevant for both genders. Favero (2009) took this further by relating flexibility to performance investigating the effect of stretching on sprint performance and baseline flexibility. 10 trained male subjects (age 22 to 23 yrs) were randomly designated to Rest and Stretch conditions. (Favero 2009 pg 52) A low intensity 5 min running warm-up procedure was followed by either 12 min of inactivity (Rest) or lower-limb stretches. No statistically significant difference in measures of sprint performance between conditions were seen, however there was a significant correlation between baseline sit-and-reach scores and mean change in mean velocity between conditions. There was an preference for stretching to a harmful affect on sprint performance in subjects with moderately high baseline flexibility. (Favero 2009 pg 54) concluded by saying an acute bout of stretching does not exert a significant effect on sprint performance under prescribed conditions. This research therefore disputes previous studies which state tha t stretching effects sprinting performance. Unlike the previous studies Favero (2009) compared the difference in flexibility compared to the sprinting performance, therefore making the results specific, reliable and valid. Unfortunately there is a lack of evidence and current data to support this conclusion. Kistler (2008) conducted a similar study to see what would happen to these performance effects at longer distances such as those seen in competition.(Kistler 2008 pg. 2281) This study investigated the effects of passive static stretching vs no stretching on the 60- and 100-m sprint performance of college track athletes after a dynamic warm-up. Results discovered a considerable slowing in performance with static stretching in the second 20 (20-40) m of the sprint trials. Following the first 40 m, static stretching exhibited no added affect on performance in a 100-m sprint. However, even tho there was no further time loss, athletes never retrieved back the time that was initially lost in the first section of the trials. Therefore, in strict terms of sporting performance, it is probable that including static stretching will have a diminishing affect of sprinting performance up to 100 meters. (Kistler 2008 pg. 2283) went on to say that the study found no additional inhibition during the final 60 m of a 100-m dash, therefore it is possible that performance in even longer events could actually benefit from static stretching. This study supports that of previous literature and supplies solid evidence to propose that static stretching has an effect on sprinting performance at short distances; however many athletes use stretching as a method of injury prevention and increase range in motion, and this study does not provide any information about the effectiveness of static stretching in this regard. Summary All but 1 study found that an acute bout of stretching diminished performance tests of sprinting, or jumping performance Even though most studies used a randomised cross-over design some studies used a pre-post design. Results were in general constant across designs. Static stretching was used in most of the studies, even tho there are many other appropriate methods used to stretch. Affects were however was observed with other forms of stretching as well. The review showed body of evidence suggesting that these affects were consistent across different types of stretching for isometric force, isokinetic torque, and jump height. Even though different types of stretching in running produced incompatible results, the main methodological difference was the duration of stretch, which was inconsistent and had no explanation for the use of the time used. As a result it was found that longer stretch produced worse results. In relation there was limited research on acute effects after stretching in relation to range of motion and flexibility. A huge variable to consider was the subject population as most studies found similar results across age, gender and level of athletic ability. This may suggests the results are due to fundamental physiological adaptations that occur in the muscle, a hypothesis that is supported by the critical science evidence on stretch-induced muscle damage and stretch-induced hypertrophy (Morgan 1999). Possible improvements in performance may be at the expense of an increased risk of injury. Therefore the advantages and disadvantages of stretching need to be considered for individual athletes, together with but not partial to competition level, competition timing (e.g., early or late in the season). Although different forms of performance were tested in these studies, including isokinetic, isometric force, jump height, jump velocity, acceleration, and sprint speed, these do not account for all aspects of performance. In addition, stretching may be a method of relaxation for athletes, and may possi bly affect performance. If this were a method to improve performance, then stretching should be compared with other methods of relaxation for quantifiable effectiveness. In summary, the literature suggest that for athletes who take part in sports that require power, strength, and explosive movements need to consider that static stretching before activity may cause a short-term decline in sprinting performance. Conversely, frequent stretching will advance the results for all activities. This is comparable to the fact that stretching directly prior to exercise does not diminish the possibility of injury, nevertheless regular stretching may reduce the risk of injury. Therefore, athletes should stretch after exercise, or at a time not associated to exercise. Further research is necessary to ascertain both the degree of pre-stretching necessary to cause a damaging effect, and the time-course between the preservation of the increased range of motion and the prolongation of the capacity to generate maximal power. Methodology The focus of this study was to test the length of time taken with a stretch and compare this to the performance of both sprinting and flexibility. 30 male participants were recruited from Cheddar Football club. Subjects were required to read and complete a health questionnaire and sign an informed consent document. The appropriate institutional ethics committee approved the study. The participants were not informed of the results until the study was completed. A convenience sample was used as a high volume of participants were readily available and allowed basic data and trends to be obtained without the complications of using a randomised sample. All participants regular play football and are subjected to sprinting. This makes my sample specific and relative to athletic performance where as an ideal sample results may differ due to gender, age, and athletic ability differences. A secondary observer was used to record the results and help time the pre stretches. This ensured subject were monitored, and therefore helped ensure the test procedure was followed correctly. The 30 males partaked in both a pre sit and reach flexibilit y test and a 40 meter sprint. Participants were subjected to a 5 min protocol warm up prior to the pre test comprising of jogging 400 m, forward skips 2 x 60 m, side steps 4 x 20 m, backwards skips 2 x 60 m. Participants only had 1 attempt at each of the pre test. To minimise variation in climatic conditions, all sprints were performed on an indoor track using running trainers. The sprints were initiated from a standard stationary split stance with the dominant foot to the front and foot behind the starting line, with no rocking movements and were timed with (Omoron electronic timing gates). Timing gates were used to ensure the most accurate readings as the difference in times will be minimal, therefore this will ensure there is no room for human error, therefore making the results more reliable. The time would start as soon as the participant travels through the first beam and then would stop when the participant travels through the beam 40 meters from the starting line. To control for error, the laser beam was positioned so the height above the ground approximated the height of the runners waist. The sit and reach test was then performed 2 minutes after the 40 meter sprint. A modified sit and reach test was used to control for the variable lengths of peoples arms and legs, which is a limitation of the standard test. The equipment was set up that, the zero mark is adjusted for each individual, based on their sitting reach level. This ensured that the result would be a positive number which is necessary for a statistical analysis. An (Acuflex) modified flexibility sit and reach test box was used to record the test. Procedure Three different stretch protocols were used, with each protocol being performed on a different day. Group 1 would hold the stretch for 30 seconds, group 2 for 15 seconds and group 3 would stretch for 5 seconds. All groups were given the same protocol warm up as the pre test. The stretching activities were ones that the athletes normally used in their daily warm-up rituals. All groups then stretch their hamstrings, quadriceps, and gastrconemuis for their given times. For each activity, the range of motion was increased until the person acknowledged a stretch-induced discomfort similar to that normally felt during their daily stretching activities. At this point, the stretch was maintained for their given times. The first stretch was a hamstring stretch. The subjects laid down in a supine position on the floor with a leg extended. The opposing leg was flexed at the patella at 90 degrees and hip 45 degrees, with the sole of the foot planted tightly on the floor. From this pose, the extended leg was raised to an upright position. The second was a quadriceps stretch. The participant adopted a vertical position, standing on one leg with the other leg flexed with the heel pulled close to the glutes with the help of the hand. The last stretch was the glastocnemius. The participant adopted a split stance shoulder width apart with the front leg slightly bent. The body weight is transferred forward whilst keeping the heel of the back foot on the ground. All stretches were performed in the order mentioned above, in accordance of a 30 second rest interval dividing each different stretch. Once this sequence of stretches was finished, the leg was rested for a further 30 seconds and then the sequence was repeated until all muscles were equally stretched 3 times. One full cycle of stretches on one leg was performed before changing legs. Following the stretching regime, the athletes were told to relax for 3 minutes before beginning the 40 meter sprints. The modified sit and reach test followed the 40 meter sprint. The test involved sitting on the floor with legs stretched out straight ahead. Footwear was removed. The soles of the feet were placed flat against the box. Both knees were locked and pressed to the floor with the palms facing downwards, and the hands on top of each other or side by side, the subject then reached forward along the measuring line as far as possible. The hands had to remain at the same level, not one reaching further forward than the other. The subject then reaches out and holds that position for two seconds while the distance is recorded.  Groups repeated the test 1week later changing the time of the stretch. 1 week wash out time was given to ensure significant time to recover. This was again repeated the following week with the groups changing the times once again. I have used repeated measure as it ensured the experiment was more efficient and helped keep the variability low. This therefore helped to ke ep the validity of the results higher, while still allowing for smaller than usual subject groups. It also allowed the experiments to be completed more quickly, as only a few groups need to be used to complete the entire experiment. It is important to make sure the experiment is completed quickly as changes in participants may occur due to practice effects. The two pre- and two post-sprint times were averaged. Data was analysed using qualitative measures. The reliability of the 40 meter times for each stretch condition was calculated using an intraclass correlation coefficient on pre test measures. A one-way analysis of variance (ANOVA) with repeated measures was used to compare the times for each stretch condition. I have used this method of testing as it will reduce the likelihood of a false positive (type 1 error). For this reason using the ANOVA will help me compare three means. In addition to the above analysis on the average 40 m sprint times, a post-hoc analysis was done on the best time for each trial. I have used these methods of testing as they have been used in many of the reviewed literature. Therefore I know these methods are applicable and will therefore allow me to easily compare my results to previous literature. To prove my hypothesis, I have used a common alpha value of 0.05 (5%). Parametric (anova) or non Parametric