Basic Vegetative Growth Research Articles

In-Frame and Frame-Shift Editing of the Ehd1 Gene to Develop Japonica Rice With Prolonged Basic Vegetative Growth Periods.

Japonica rice has become increasingly popular in China owing to its superior grain quality. Over the past decades, “indica to japonica” projects have been proposed to promote cultivation of japonica rice in low latitudes in China. Traditionally, japonica varieties were planted mainly in mid latitudes in the northeast plain and Yangtze River region. The key obstacle for introducing elite mid-latitude japonica varieties to low latitudes is the severe shortening of growth period of the japonica varieties due to their sensitivity to low-latitude short photoperiod and high temperature. Here we report development of new japonica rice with prolonged basic vegetative growth (BVG) periods for low latitudes by targeted editing the Early heading date 1 (Ehd1) gene. Using CRISPR/Cas9 system, we generated both frame-shift and/or in-frame deletion mutants in four japonica varieties, Nipponbare, Longdao16, Longdao24, and Xiushui134. When planting at low-latitude stations, the frame-shift homozygous lines exhibited significantly longer BVG periods compared with wild-types. Interestingly, we observed that minor deletion of the first few residues within the receiver domain could quantitatively impair the function of Ehd1 on activation of Hd3a and RFT1, resulting in an intermediate-long BVG period phenotype in the homozygous in-frame deletion ehd1 lines. Field investigation further showed that, both the in-frame and frame-shift lines exhibited significantly improved yield potential compared with wild-types. Our study demonstrates an effective approach to rapid breeding of elite japonica varieties with intermediate-long and long BVG periods for flexible cropping systems in diverse areas or under different seasons in southern China, and other low-latitude regions.

Genetic variation in rice (<i>Oryza sativa</i> L.) germplasm from northern Laos

We assessed genetic variation in rice germplasm in northern Laos and Vientiane province from polymorphism data of SSR markers. We classified 314 accessions into three clusters; Ia (corresponding to the lowland Japonica Group), Ib (upland Japonica Group) and II (Indica Group). The accessions of cluster Ib grew mainly in mountainous fields, and those of cluster II grew commonly in basins and along rivers. The few accessions of cluster Ia grew in only three provinces: Houaphanh, Xiangkhouang and Vientiane. Lowland cultivars in cluster II were predominant in Vientiane. Variations in heading date under short-day conditions in 2014 and long-day conditions in 2015 indicate that many accessions were sensitive to the photoperiod on account of complex genetic mechanisms underlying both photoperiod sensitivity and basic vegetative growth. A total of 219 among whole accessions were classified into 6 groups: E1–3 and L1–3. E2 and E3 were dominant in clusters Ib and II; E1 and L1–3 were minor groups. These results demonstrate characteristic distributions of the Indica and Japonica Group’s germplasms in northern Laos and their genetic variation in heading date.

The effects of phytochrome-mediated light signals on the developmental acquisition of photoperiod sensitivity in rice.

Plants commonly rely on photoperiodism to control flowering time. Rice development before floral initiation is divided into two successive phases: the basic vegetative growth phase (BVP, photoperiod-insensitive phase) and the photoperiod-sensitive phase (PSP). The mechanism responsible for the transition of rice plants into their photoperiod-sensitive state remains elusive. Here, we show that se13, a mutation detected in the extremely early flowering mutant X61 is a nonsense mutant gene of OsHY2, which encodes phytochromobilin (PΦB) synthase, as evidenced by spectrometric and photomorphogenic analyses. We demonstrated that some flowering time and circadian clock genes harbor different expression profiles in BVP as opposed to PSP, and that this phenomenon is chiefly caused by different phytochrome-mediated light signal requirements: in BVP, phytochrome-mediated light signals directly suppress Ehd2, while in PSP, phytochrome-mediated light signals activate Hd1 and Ghd7 expression through the circadian clock genes' expression. These findings indicate that light receptivity through the phytochromes is different between two distinct developmental phases corresponding to the BVP and PSP in the rice flowering process. Our results suggest that these differences might be involved in the acquisition of photoperiod sensitivity in rice.

Genetic Analysis for the Diversity of Heading Date of Cultivated Rice in China

Heading date(HD) determines the adaptability to growing regions of cultivated rice.There is a rich diversity of HDs in Chinese cultivated rice.In this study,HDs of 83 typical japonica rice and 51 typical indica rice cultivars native to different re-gions in China were investigated and their basic vegetative growth(BVG),photoperiod-sensitivities(PS) and tempera-ture-sensitivities(TS) were analyzed.A regression analysis showed that HD was closely correlated with PS and BVG.The PS and BVG of cultivars were weak in high latitude regions of China,and strong in low latitude regions.Genetic analyses of the 134 cultivars were conducted using a set of HD tester lines.The results showed that,on the whole,when the cultivars carried no-PS allele e1,the plants headed earlier with weaker PS and BVG,when the cultivars carried the PS allele E1 or E1t,the plants headed later with strong PS and BVG.When the cultivars carried the allele Ef-1,the plants headed earlier with weaker BVG,when the cultivars carried the allele Ef-1t or ef-1,the plants headed later with strong BVG.It suggested that E1 and Ef-1 are two major de-terminants of variation in heading date of cultivated rice in China.Otherwise,the distribution of different alleles of the major heading date genes in different regions of China was analysed,and the results showed that the leading alleles of the major HD genes in different regions of China was different.

Genetic Analysis of Heading Date of Japonica Rice Cultivars in Southwest China

Heading date of 26 native japonica rice cultivars in southwest China was investigated, and their basic vegetative growth (BVG), photoperiod-sensitivity (PS) and temperature-sensitivity (TS) were analyzed under artificial short-day and natural long-day conditions in Nanjing, as well as artificial high-temperature and natural low-temperature conditions in winter in Hainan. The results showed that the PS and TS varied among different cultivars. The BVG of all the japonica cultivars was well situated, but differed within cultivars. Regression analysis showed a significant correlation between heading date and PS, indicating that PS was the main factor affecting heading date of japonica cultivars in southwest China. Genetic analysis was conducted on these 26 cultivars using a set of heading date near isogenic lines as test lines. All the japonica cultivars carried the dominant early-heading gene Ef-1 or Ef-1 t, and most of these cultivars carried the dominant photoperiod sensitivity allele E 1 or E 1 t, the PS of which was slightly weaker than E 1 . For the Se-1 locus, these cultivars mainly carried recessive photoperiod insensitivity gene Se-1 e. In addition, the PS of 22 japonica cultivars could be repressed or weakened by the recessive allele hd2, inhibiting the expression of E 1 and Se-1. These results indicated that the genotypes of heading date determined different PS and well situated BVG in japonica rice cultivars in southwest China.

Extraordinary hot summer in Hokkaido decrease rice yield and satisfy growing of cultivar in Tohoku region “Hitomebore”

The summer temperature in Hokkaido in 2010 was the hottest on meteorological record and caused the crop index of rice (Oryza sativa L.) to drop below average. The mean temperature was 2.2°C higher than normal (based on the period 1981-2010) and was coincident with climate change predictions for the end of the 21st century. To investigate possible measures against the hot conditions projected in Hokkaido and the resulting reductions in yield, we tested Hitomebore, a cultivar from the Tohoku region of Japan. Although local cultivars had been used in accordance with conventional procedures, 2010 was the first year in which Hokkaido's rice yield was decreased by factors other than cold injury or strong winds. The extremely high temperature in June probably shortened the basic vegetative growth period, thus reducing the number of tillers and number of grains. However, Hitomebore grown at our experimental paddy field in Sapporo under the hot conditions of 2010 reached the heading stage during a period when it was safe from cold-induced injury, and it ripened fully to give a yield of 6300 kg/ha. Introduction of new cultivars with properties similar to those of Hitomebore will be one way of adapting to the expected climate change.

Identification of a novel gene ef7 conferring an extremely long basic vegetative growth phase in rice

A late heading-time mutant line, HS276, which was induced by gamma-irradiation of seeds of the japonica rice (Oryza sativa L.) variety Gimbozu, exhibits an extremely long basic vegetative growth phase (BVP). A genetic analysis using the F(2) population from the cross between HS276 and Gimbozu revealed that the late heading of HS276 is governed by a single recessive mutant gene. The subsequent analysis on heading responses of HS276 and Gimbozu to four photoperiods (12, 13, 14, and 15 h) and to the photoperiodic transfer treatment from a short photoperiod to a long photoperiod revealed that the mutant gene confers an extremely long BVP and increases photoperiod sensitivity under long photoperiod (14 and 15 h). The BVP durations of HS276 and Gimbozu were estimated at 30.1 and 16.0 days, respectively; the mutant gene, compared with its wild type allele, elongates the duration of BVP by 14 days. Linkage analysis showed that the mutant gene is located in the 129 kb region between the two INDEL markers, INDELAP0399_6 and INDELAP3487_2, on the distal part of the short arm of chromosome 6. None of the other BVP genes are located in this region; therefore, we declared this a newly detected mutant gene and designated it ef7. A recently established program to breed rice suitable for low latitudes, where short photoperiodic conditions continue throughout the year, aims to develop varieties with extremely long BVPs and weak photoperiod sensitivities; the mutant gene ef7, therefore, will be quite useful in these programs because it confers an extremely long BVP and little enhances photoperiod sensitivity under short photoperiod.

Multiple alleles at Early flowering 1 locus making variation in the basic vegetative growth period in rice (Oryza sativa L.)

A recently established rice breeding program in low latitudes aims to develop varieties with extremely long basic vegetative growth (BVG) periods and weak photoperiod sensitivities. The Taiwanese japonica variety Taichung 65 (T65) harbors a recessive allele ef1 at the Ef1 (Early flowering 1) locus, thereby exhibiting an extremely long BVG period. The previous reported functional allele Ehd1 (Early heading date 1), located on chromosome 10, encodes a B-type response regulator, thereby shortening the BVG period, whereas its nonfunctional allele ehd1 greatly prolongs the BVG period. A conventional analysis using F(2) and F(3) populations and a subsequent CAPS analysis based on the amino acid sequences of Ehd1 and ehd1 showed that Ef1 and Ehd1 were at the same locus. The CAPS analysis also indicated that the Taiwanese japonica varieties with extremely long BVG periods all harbor ef1, but that ef1 does not exist among indica and japonica varieties in the low latitudes. Since ef1 has not been found in any japonica varieties outside Taiwan, this allele might have originated in Taiwan. Sequence analysis revealed that the mutant allele ef1-h, which prolongs the BVG period even more than ef1 does, harbors an mPing insertion in exon 2, which causes the complete loss of gene function. Our results indicate that both ef1 or ef1-h alleles can be used as new gene sources in developing rice varieties with extremely long BVG periods for low latitudes.

Epistasis among the three major flowering time genes in rice: coordinate changes of photoperiod sensitivity, basic vegetative growth and optimum photoperiod

Flowering time is affected not only by photoperiod sensitivity (PS) but also by basic vegetative growth (BVG) and optimum photoperiod (OP), although their developmental and genetic relationships are not well understood. The present study was carried out in rice to examine to what extent these three developmental components are modified by the three flowering time genes, Se1 (= Hd1), Ef1 and e1 (= m-Ef1), which are known to contribute to flowering time in temperate and tropical regions of rice cultivation. Photoperiodic response curves were estimated under controlled conditions of different growth regimes, using eight near-isogenic lines possessing different combinations of the alleles at the three loci. The results showed that each of the components is greatly affected by the main effect of the genes, temperature and their epistasis, indicating that none of the three genes controls flowering time by altering any single component in PS, BVG or OP. Epistasis was detected more frequently among the three genes than reported before, suggesting that epistasis contributes to flowering time by changing PS, BVG and OP differently. The comparison of the nucleotide sequences suggested that Ef1 is the same as Early heading date 1 (Ehd1). Since the two genes Se1 (= Hd1) and Ef1 (= Ehd1) are known to up-regulate the rice homolog of ArabidopsisFT, it is suggested that the detected epistasis may respond to diverse environments by modulating the CO/FT system conserved in flowering plants.

A Novel Gene ef1‐h Conferring an Extremely Long Basic Vegetative Growth Period in Rice

A late‐heading mutant line, HS169, which was induced by gamma‐ray irradiation to seeds of the japonica rice (Oryza sativa L.) cultivar Gimbozu, has an extremely long basic vegetative growth (BVG) period. A genetic analysis using the F2 population from the cross HS169 × Gimbozu showed that the late heading of HS169 is governed by a recessive mutant gene. The subsequent analysis of heading responses of HS169, Gimbozu, and six heading‐time tester lines to five photoperiods (10, 13, 14, 15, and 16 h) revealed that the mutant gene confers an extremely long BVG period by itself. A recessive allele, ef1, at the heading‐time locus Ef1 has been considered to confer an extremely long BVG period, but experimental results showed that the effect of ef1 is modified by the allelic constitution at the photoperiod sensitivity locus Se1 The allele ef1 increases the BVG period markedly only when coexisting with the nonfunctional allele Se1‐e at the Se1 locus. As a result of allelism test and subsequent trisomic analysis, the mutant gene was found to be a nonfunctional allele at the Ef1 locus on chromosome 10. We designated this mutant gene ef1‐h On the basis of the results, causal genetic pathways to flowering in rice and the significance of ef1‐h in recent rice breeding in the low latitudes were discussed.

Interactive effects of two heading-time loci, Se1 and Ef1, on pre-flowering developmental phases in rice (Oryza sativa L.)

The interaction between the Se1 and the Ef1 loci, which chiefly control the photoperiod sensitivity (PS) and the basic vegetative growth (BVG) period of rice (Oryza sativa L.) respectively, was investigated using four tester lines different in genotype for the two heading time loci from each other. The four tester lines were grown under 10, 13, 14, 15, and16h day lengths to estimate their BVG period and PS. The Taiwanese cultivar Taichung 65(T65), one of the tester lines, has an extremely long BVG period that has been considered to be conferred by a late heading-time allele ef1 at the Ef1 locus. Experimental results, however, showed that the extremely long BVG of T65was conferred not by a single effect ofef1 but by a complementary effect ofef1 and Se1-e, a photoperiod insensitivity allele, at theSe1 locus. It was also found that a complementary effect of a PS allele Se1-n at the Se1 locus and ef1stimulates the PS of rice. Gene analysis for heading time under an optimum daylength (10 h) as well as under natural day length confirmed the presence of the complementary effect of the two nonallelic genes on BVG, which was found only with homozygosity of both the genes. Based on these results and earlier reports on the Se1 locus, the roles of the Se1 andEf1 loci on the durations of pre-flowering developmental phases in rice were discussed.

A Novel Gene Conferring an Extremely Long Basic Vegetative Growth Period in Rice

A late-heading mutant line, HS169, which was induced by gamma-ray irradiation to seeds of the japonica rice (Oryza sativa L.) cultivar Gimbozu, has an extremely long basic vegetative growth (BVG) period. A genetic analysis using the F2 population from the cross HS169 × Gimbozu showed that the late heading of HS169 is governed by a recessive mutant gene. The subsequent analysis of heading responses of HS169, Gimbozu, and six heading-time tester lines to five photoperiods (10, 13, 14, 15, and 16 h) revealed that the mutant gene confers an extremely long BVG period by itself. A recessive allele, ef1, at the heading-time locus Ef1 has been considered to confer an extremely long BVG period, but experimental results showed that the effect of ef1 is modified by the allelic constitution at the photoperiod sensitivity locus Se1 The allele ef1 increases the BVG period markedly only when coexisting with the nonfunctional allele Se1-e at the Se1 locus. As a result of allelism test and subsequent trisomic analysis, the mutant gene was found to be a nonfunctional allele at the Ef1 locus on chromosome 10. We designated this mutant gene ef1-h On the basis of the results, causal genetic pathways to flowering in rice and the significance of ef1-h in recent rice breeding in the low latitudes were discussed.

Identification of an Early Heading Time Gene Found in the Taiwanese Rice Cultivar Taichung 65.

An early heading time gene tentatively designated as 'v' and nonallelic to E1, E2, E3 and Ef-1 was detected in the Taiwanese rice cultivar Taichung 65 (T65) (Okumoto et al. 1992b). This gene remarkably accelerated heading time. The allelism test of this gene to a photoperiod insensitivity gene Se-1e at the Se-1 Iocus was performed using the progenies from reciprocal crosses between T65 and a heading time tester line ER. The role of this gene in the rice cultivation in Taiwan was also discussed on the basis of photoperiod responses of T65, ER and a heading time tester line LR. T65 was found to have the genotype E1E1E2E2E3E3 vv ef-1ef-1, while ER and LR had the genotypes E1E1e2e2E3E3Se-1eSe-1eEf-1Ef-1 and E1E1e2e2E3E3Se-1uSe-1uEf-1Ef-1, respectively. ER also carried a rice blast resistance gene Pi-zt closely linked to Se-1e on chromosome 6. E1, E2, E3 and Se-1u were all photoperiod sensitivity genes, and ef-1 at the Ef-1 Iocus remarkably increased the duration of the basic vegetative growth period (BVG). In the F2, rio distinct transgressive segregants appeared, and the three genotypes (Pi-zt Pi-zt, Pi-zt+, ++) for the Pi-z locus in the F2 exhibited almost the same range and the same mean for heading time. These facts imply that 'v' is identical with Se-1e. T65 exhibited a far longer BVG than the two tester lines. The critical day-lengths (CDLs) of T65 and ER were longer than 16 h, while the CDL of LR ranged between 14 h and 15 h : the CDL of LR was shorter than those of T65 and ER. When compared to LR, T65 and ER exhibited a small retarding effect under super optimum photoperiod (RES), and did not differ in RES. These results indicate that the low photoperiod sensitivity of T65 is due to the action of 'v' (=Se-1e). Since the long BVG of T65 is attributed to the action of ef-1, it is considered that 'v' (=Se-1e) and ef-1 are very important genes for rice cultivation in Taiwan, where natural day-length is short even in summer and seasonal changes are negligible.

稲作北限地域の不感光性イネ品種に見出されたSe-1座の感光性遺伝子

Heading trait mainly determined by photoperiod sensitivity and basic vegetative growth greatly contributes to the climatic and regional adaptability of rice (Oryza sativa L.) cultivars. In Hokkaido of Japan (42-45°N), the northern limit region of rice cultivation, extremely early maturing (heading) cultivars with photoperiod insensitivity are planted. In the present study, the gene analyses of 12 Hokkaido cultivars for the important photoperiod sensitivity locus Se-1 were made, and the genetic factors responsible for the photoperiod insensitivity of Hokkaido cultivars were discussed. Experimental results unexpectedly showed that eight of 12 cultivars examined carried a photoperiod insensitivity gene Se-1e and four of them carried a photoperiod sensitivity gene Se-1n. Unlike a photoperiod insensitivity gene e1that most of the Hokkaido cultivars carry at the E1 locus, Se-1e was considered not to be necessarily required in realizing the photoperiod insensitivity of Hokkaido cultivars. It was also suggested that some genetic factor(s) suppressing the expression of Se-1n is present among Hokkaido cultivars. This factor was considered to take part in establishing Hokkaido cultivars together with e1. Further analysis on identifying this factor will be required for the efficient breeding of rice adapting to the northern limit region of rice cultivation.

Effects of Se1 gene on basic vegetative growth of rice

Effects of Se1 gene on basic vegetative growth of rice

Basic Vegetative Growth and Photoperiod Sensitivity of Heading-time Mutants Induced in Rice.

Out of a large number of heading-time mutants artificially induced from a rice variety Gimb6zu, 83 mutants covering the heading dates from 3 weeks earlier to 2 weeks later than the original variety, were selected without a biased distribution of heading time. These mutants were grown together with the original variety and 32 important Japanese varieties in two kinds of artificially controlled environments, a high-temperature (30°C-short-day-length (10h) and a high-temperature (30°C)-long-day-length (14h): their basic vegetative growih (BVG), which was expressed by the days to heading under 30'C0h, and photoperiod sensitivity (PS), which was expressed by the difference between the days to heading under 30°C-14h and that under 30°C-10h, were estirnated. The estimated BVG and PS were then analyzed for their genetic variations and their relationships with the heading time under the natural conditions in a paddy field in Kyoto (N. L. 35°C01'). The extremely-early-heading varieties cultivated in Hokkaid6 showed small BVG and small PS, the early-heading varieties mainly cultivated in Tohoku and Hokuriku districts generally showed large BVG and small PS, and the intermediate- or late-heading varieties cultivated in the region from Kant6 to Kytish{i districts showed small BVG and large PS (Table 1, Fig. 2).

Further analysis of geographical variation of heading response to daylength in foxtail millet (Setaria italica P. Beauv.).

Using materials differing in heading response from the previous study (TAKEI and SAKAMOTO 1987), the variations in the effects of daylength and temperature on floral initiation and panicle development in foxtall millet (Setaria italica P. BEAUV.) were investigated. Type I strains, those from Europe and Afghanistan, initiate the floral buds without short-day stimulus. In these strains, floral initiation rather depends on the degree of vegeta-tive growih, although panicle development is accelerated by short-day and high temperature conditions. The number of days to heading depends consequently on temperature conditions. Strains from Okinawa, Batan Is., and Lan-Yu Is. which showed sensitivity to daylength, did not necessarily need short-day stimulus for panicle initiation, but panicle development was accelerated by short day. Type II strains, those from low latitudinal areas have a long basic vegetative growth period and the duration of this period is reduced by high temperature conditions. In addition, these strains need many cycles of short-day to induce the floral buds. The requirement of short-day cycles for floral initiation and morphological development is reduced by aging. The heading of the strain from Halmahera Is. (2°N), the representative of Type II, is accelerated by 10 hrs. of light, but floral initiation does not necessarily take place as a response to the subtle change of daylength of this low latitude locality. The strain from Thailand is sensitive to a wide range of daylength. It should be identified as the fourth type, Type IV, characterized by a long basic vegetative growth period and high sensitivity to daylength. The strains from the Temperate Zone are sensitive to changes of daylength. The strain 403, from Kochi Prefecture, which is a representative of Type III and is an obligate short-day plant, shows a striking response to daylength only one week after sowing, and only a few cycles of short-day stimulus are enough for floral inductlon.

Geographical variation of heading response to daylength in foxtail millet (Setaria italica P. Beauv.).

The variations of the heading response to daylength in foxtail millet (Setaria italica P. BEAUV.) were investigated. Twenty strains of foxtail millet collected from various parts of Eurasia including islands of Southeast Asia were cultivated under three daylength conditions : Short-days (10 hrs. light +14 hrs, darkness), natural daylength (14.5 hrs-11.5 hrs. light+9.5hrs. -12.5hrs. darkness) and long-day (16 hrs. light+8hrs. darkness). Based on the variations of the response, three types were identified. Type I : early maturing strains indifferent to daylength condition ; Type II : very long basic vegetative growth period ; Type III : short basic vegetative growth period and high sensitivity to daylength: Type I is represented by strains from areas of a higher latitude such as Europe, Central Asia and northern part of East Asia. Type II is represented by strains from low latitudinal areas such as Halmahera Is., Indonesia and Luzon Is., Philippines. Type III is found in late maturing varieties growing in areas of a latitude of around 30 ??, such as "Shimokatsugi", a landrace of mountainous villages on Shikoku Island, Japan. The other strains were scored as intermediate between these types. These findings suggest that there is a relationship between the types of heading response to daylength and the geographical distribution which determines the planting season in traditional cultivation practices of foxtail millet.

Studies on Meteorological Fluctuation in the Growth of Rice Plants. : V. Regional Differences of Thermo-Sensitivity, Photo-Sensitivity, Basic Vegetative Growth and Factors Determining the Growth Duration of Japanease Varieties.

Thermo-sensitivity(X1), photo-sensitivity(X2) and basic vegetative growth(X3) of 70 rice varieties in Japan were obtained by growing plants in growth cabinets under possible 4 combinations of different daylength and temperature : short(SD:10h) or long(LD:14h) daylength and low(LT:20'C) or high(HT:30'C) tempcrature. The X1, X2 and X3 are expressed by nSDLT-nSDHT, nLDLT-nSDLT and nSDHT, respectively, where nSDLT Stands for the number of days from sowing to headlng under 10h and 20 C and so on. Duration (Y) from sowing to heading of the same varieties was examined in a paddy field with three different sowing dates. Multiple correlations between duration(Y) and a set of X1, X2 and X3 of early, medium and late maturing varieties in all sowing dates were highly significant, showing thatvarietal differences in duration(Y) could be largely explained by the combination of the three factors.

Studies on Meteorological Fluctuation in the Growth of Rice Plants : IV. Factors Affecting Duration from Sowing to Heading under Different Temperature Levels ad Sowing Times.

Heading tirne of rice varieties are known to be controlled by three factors, thermo-sensitivity(X1)' photo-sensitivity(X2) and basic vegetative growth(X3)' Degree of contribution of the three Lactors to the determination of growth duration from sowing to' heading was investigated. In the first experiment, 44 rice varieties were grown in a growth cabinet, the temper-ature of which was controlled so as to give a constant difference from the temperature of the open air. The measure of the three factors was obtained by growing plants in a growth cabinet with short(S:10h) or long(L:14h) daylength and low(L:20'C) or high(H:30'C) temperature. X1, X2 and X3 are expressed by nSL-nSH, nLL-nSL and nSH, respectively, where nSL Stands for the number of days from sowing to heading in case of 10h and 20'C, and so on. Multiple correlation between growth duration(Y) and a set of X1, X2 and X3 was. highly significant in all temperature levels, showing that the most part of varietal diffe-rences in growth duration can be explained by the three factors in combination. The standard partial regression coeffcient of Y on X1, X2 and X3 revealed that photo-sensiti-vity(X2) is most important in determining growth duration, followed by basic vegetative growth(X3), thermo-sensitivity(X1) showing no influence.