The Distribution of Japonica

Journal of Integrative Plant Biology 29 The Distribution of Japonica Rice Cultivars in the Lower Region of the Yangtze River Valley is Determined by Its Photoperiod-sensitivity and Heading Date Genotypes Xiang-Jin Wei 1, Ling Jiang 1, Jun-Feng Xu 1,XiLiu 1, Shi-Jia Liu 1, Hu-Qu Zhai 2 and Jian-Min Wan 1,2 ( 1 State Key Laboratory of Crop Genetics and Germplasm Enhancement, Nanjing Agricultural University, Nanjing 219, China; 2 Institute of Crop Sciences, Chinese Academy of Agricultural Sciences, Beijing 181, China) Abstract There are generally four recognized classes of japonica rice cultivars grown in the lower region of the Yangtze River valley. The geographical distribution of the four classes is latitude-dependent. Variation for heading date (HD) among 29 japonica rice cultivars grown in the lower region of the Yangtze River valley and belonging to the four classes was characterized, and their sensitivity to variations in photoperiod and temperature was analyzed. All of the cultivars were sensitive to both photoperiod and temperature. A regression analysis showed that HD is closely correlated with photoperiod sensitivity (PS). The PS of the four classes increased gradually from the medium maturing middle (MMM) types, through the late maturing middle (LMM) and early maturing late (EML) types to the medium maturing late (MML) types. Crosses with tester lines established that almost all of the cultivars carry the dominant early-heading allele at Ef-1, the photoperiod insensitive allele e 2 and the PS alleles E 1 or E 1 t. Most of the MMM, LMM and MML types carry the insensitive allele e 3, while EML types have either E 3 or E 3 t.atse-1, MMM and LMM types have Se-1 e, some EML types have Se-1 e and others Se-1 n,whilethe MML types are mostly Se-1 n. The PS of some MMM, LMM and EML types is reduced by the presence of hd2. These results show that the distribution of the four rice cultivar classes from high latitude to low latitude regions depended on a gradual increase in PS, which is mainly determined by its HD genotypes. Key words: geographical distribution; genotype; heading date; japonica rice; photoperiod-sensitivity. Wei XJ, Jiang L, Xu JF, Liu X, Liu SJ, Zhai HQ, Wan JM (29). The distribution of Japonica rice cultivars in the lower region of the Yangtze River valley is determined by its photoperiod-sensitivity and heading date genotypes. J. Integr. Plant Biol. doi: 1.1111/j.1744-799.29.8.x. Available online at www.jipb.net Heading date (HD) is one of the most important traits for the adaptation of rice to different cultivation areas and cropping seasons, which can be divided into the basic vegetative phase (BVP) and photoperiod sensitivity phase (PSP). It is essentially determined by three factors: duration of the basic vegetative growth (BVG), photoperiod-sensitivity (PS) and temperaturesensitivity (TS). Several major genes for HD have been iden- Received 8 May 29 Accepted 9 Jul. 29 Supported by the National Hi-Tech Research and Development Program of China (26AA111, 26BAD1A1- and 26BAD13B1), the National Natural Science Foundation of China (3871497), Jiangsu Science and Technology Development Program (BG2631), Jiangsu Agricultural Germplasm Gene Pool Program (sx(28)g8) and the 111 Project (B82). Author for correspondence. Tel (Fax): +86 2 39 616; E-mail: <wanjm@njau.edu.cn> and <wanjm@caas.net.cn>. C 29 Institute of Botany, the Chinese Academy of Sciences doi: 1.1111/j.1744-799.29.8.x tified in rice. Ef -1 is a major gene controlling the duration of BVG, which can accelerate the switch to reproductive growth independently of photoperiod, and can also partially counteract the effects of PS genes under long day conditions (Tsai 1986; Sato et al. 1988; Kinoshita 199; Nishida et al. 22; Xu et al. 26). Other genes including E 1, E 2, E 3, Se-1, Se-2, Se-3(t), Se-4, Se-, Se-6, Se-7 and Se-9(t), are found to be responsible for PS (Okumoto et al. 1992a; Ohshima et al. 1993; Yokoo and Okuno 1993; Shen et al., 1994; Kinoshita 199; Maheswaran et al. 199; Okumoto and Tanisaka 1997). Among these genes, E 1 and Se-1 are known as major and strong PS genes and have been proven to be the most ubiquitous alleles controlling HD (Okumoto et al. 19; Ichitani et al. 1997, 1998a). In addition, the recessive inhibitor i-se-1 can inhibit the effect of Se-1, producing an early heading type even under long days (Ohshima et al. 1993; Ohshima and Kikuchi 1994; Luo et al. 22). Otherwise, a growing number of quantitative trait loci (QTLs) for HD has emerged from the analysis of various mapping populations (Li et al. 199; Yano et al. 1997, 21; Lin et al. 1998; Maheswaran et al. 2), and Several major QTLs have been isolated by

2 Journal of Integrative Plant Biology 29 map-based cloning (Yano et al. 2; Takahashi et al. 21; Kojima et al. 22; Doi et al. 24; Xue et al. 28). The lower region of the Yangtze River valley (latitude 28 3 N) is a premier rice production area in China. It represents a transition zone between subtropical and warm temperate environments, and is suitable for planting several ecotype rice cultivars. But it has been dominated by Japonica types with a wide range of HD in recent years. Cultivars are commonly classified by their HD into medium maturing middle (MMM), late maturing middle (LMM), early maturing late (EML) and medium maturing late (MML) types, in which HDs become longer gradually, and their suitable planting areas were distributed from high latitude to low latitude regions (Lin and Min 1991). However, the research about the genetic basis of the latitude dependence distribution of those four ecotype rice cultivars is deficient. Here, the BVG, PS, TS and HD genotype of the four ecotype Japonica rice cultivars from the lower region of the Yangtze River valley were investigated. The results will be helpful in elucidating the essence for the distribution of the four ecotype Japonica rice cultivars in the lower region of the Yangtze River valley from high latitude to low latitude. Results Sensitivity to photoperiod and temperature The HD of each of the 29 Japonica rice cultivars differed markedly under short-day (SD) and long-day (LD) conditions (Figure 1). PS varied from 9.8 to 31.3 d (Table 1). Similarly, the HD of these cultivars also differed when grown under high temperature (HT) or low temperature (LT) conditions (Figure 2). The range in TS was 3.8 to 1. d (Table 1). It suggested that the Japonica cultivars in the lower region of the Yangtze River valley were sensitive to photoperiod and temperature. The relationship between HD and BVG, PS and TS There was a significant (R 2 =.94) linear correlation between HD and PS (Figure 3B), showing that the HD of these japonica cultivars was strongly influenced by their PS. However, there was little relationship between HD and either BVG or TS (Figure 3A,C). Comparing the BVG, PS and TS between the four ecotypes cultivars, we found the PS significantly become stronger from MMM type, through LMM and EML types to MML Japonica rice cultivars, but there were no significant differences for BVG and TS between the four ecotypes of Japonica cultivars (Figure 4A,B). The genotypes for major HD genes Allelic relationships at the E 1, E 2, E 3 loci The near isogenic lines EG, EG1, EG2 and EG3 all carried the PS allele Se-1 n and the dominant early-heading gene Ef-1. They differ from one another allelically at E 1, E 2 and E 3. EG is e 1 e 1 e 2 e 2 e 3 e 3, EG1 is E 1 E 1 e 2 e 2 e 3 e 3, EG2 is e 1 e 1 E 2 E 2 e 3 e 3 and EG3 is e 1 e 1 e 2 e 2 E 3 E 3 (Ichitani et al. 1997, 1998a,b; Nishida et al. 21) (Table 2), with E 1, E 2 and E 3 being dominant over the e 1, e 2 and e 3, respectively (Okumoto et al. 1992b, 19). The HDs in Nanjing of EG1, EG2 and EG3 were, respectively 19.2,., and 12.8 d longer than that of EG. The hybrids between EG1 and Zaofeng9, Wuyunjing7, Wuyunjing8, Ningjing1, Yandao8, Xudao3, Xudao4, Sidao11, Lianjing3, Nanjing4, Nanjing41, Yanjing938, Huaidao7, Wujing13, Wuxiangjing14, Suxiangjing2, Changnongjing4, Nanjing3, Nanjing43, Yanjing, Huaidao9 and Zhendao99 exhibited similar HD to hybrids between EG and them (Table 3), suggesting that all of these cultivars carried the PS allele E 1 (Table 4). While, the HD of the hybrids between EG1 and Zhendao88, Wuyujing3, Yanjingnuo1, Sidao1, Wujing1, Wuyunjing21, Huanjing2 were about 8 13 d longer than those of the between EG and them (Table 3). This result implies that Days to heading 12 1 8 6 4 2 SD LD Zhendao88 Zaofeng9 Wuyujing3 Wuyunjing7 Wuyunjing8 Ningjing1 Yandao8 Xudao3 Xudao4 Sidao11 Lianjing3 Nanjing4 Nanjing41 Yanjingnuo1 Yanjing938 Sidao1 Huaidao7 Wujing13 Wujing1 Wuxiangjing14 Suxiangjing2 Wuyunjing21 Huajing2 Changnongjing4 Nanjing3 Nanjing43 Yanjing Huaidao9 Zhendao99 Figure 1. The heading date (HD) of 29 cultivars adapted to the lower region of the Yangtze River valley under natural long day (LD) and artificially shortened day (SD) conditions. indicates that HD in SD was significantly shorter than in LD (P <.1). Values are expressed as means ± SD, n = 1.

PS and HD Genotypes Determine Rice Cultivars Distribution 3 Table 1. The heading date (HD), basic vegetative growth (BVG), photoperiod-sensitivity (PS) and temperature-sensitivity (TS) of Japonica cultivars grown in the lower region of the Yangtze River valley. Ecotype Cultivars HD BVG PS TS MMM Japonica rice Zhendao99 9.8 76.8 19. 12. cultivars Zaofeng9 9.8 76. 19.3 12.2 Xudao3 91. 77.8 13.8 7.7 Xudao4 9. 77. 18. 1.8 Zhendao88 93..3 1.3 9. Wuyunjing21 86.8 77. 9.8 9.2 Huajing2 9.8.3 17.4 6.7 Sidao11 9. 74.8 2.3 1. Lianjing3 93.8 76. 17.8 8.1 Yandao8 9..8 16.8 11.3 LMM Japonica rice Nanjing4 99.7 77.3 22.4 11. cultivars Huaidao7 9.3 7.3 2. 3.8 Yanjing 97..3 19.3 7. Huaidao9 97.8. 19.8 11. Nanjing41 9. 77.8 17.3 8.2 Sidao1 94.3 76.8 17. 1.3 Nanjing3 9.3 79.3 16. 9.7 Yanjingnuo1 98.7.8 19.9 8.2 Wuyujing3 99.3 77.7 21.6 1. Wuyunjing8 99.3. 2.8 11.8 Yanjing938 99.8 77.8 22. 1. EML Japonica rice Wujing1 11..3 23.3 12.2 cultivars Wuxiangjing14 99. 79. 2. 11. Ningjing1 11.3.7 22.6 9.9 Wuyunjing7 14.8 79.3 2. 13.7 Changnongjing4 13.3 79. 24.3 7.4 Wujing13 1..8 21.8 11.9 MML Japonica rice Suxiangjing2 19.3. 31.3.6 cultivars Nanjing43 1. 79. 26. 8.6 Values represent means. EML, early maturing late; LMM, late maturing middle; MML, medium maturing late; MMM, medium maturing middle. these cultivars carry a slightly weaker PS allele than E 1,which we have tentatively named E 1 t (Table 4). The allelic constitution at E 2 and E 3 was determined in the same manner (Table 3). All cultivars carried the photoperiod insensitivity allele e 2 (Table 4). Zhendao88, Zaofeng9, Wuyujing3, Xudao3, Xudao4, Nanjing4, Nanjing41, Yanjingnuo1, Sidao1, Huaidao7, Wujing1, Suxiangjing2, Wuyunjing21, Huajing2, Nanjing3, Nanjing43, Yanjing, Huaidao9, and Zhendao99 carried the insensitivity allele e 3, and Wuyunjing7, Wuyunjin8, Sidao11 carried the PS allele E 3. Ningjing1, Yandao8, Lianjing3, Yanjing938, Wujing13, Wuxiangjing14, Changnongjing4 carried a weak PS form of E 3, tentatively named E 3 t (Table 4). Allelic relationships at the Se-1 locus The near isogenic lines pair ER and LR differ allelically at the Se-1, with the latter harboring the sensitive allele Se-1 u, and the former the insensitive allele Se-1 e. Similarly, cv. Nipponbare harbored the PS allele Se-1 n, and NIL(Hd1) carries hd1 (synonymous with Se-1 e ) introgressed from the Indica rice cv. Kasalath into a cv. Nipponbare genetic background (Yano et al. 1997, 2; Lin et al. 2; Yamamoto et al. 1998) (Table 2). Se-1 u and Se-1 n are both dominant over Se-1 e, and the PS imposed by Se-1 u is greater than that imposed by Se- 1 n (Yokoo and Kikuchi 1977). In Nanjing, ER and NIL(Hd1) headed, respectively, 22. and 9. d earlier than LR and cv. Nipponbare. The hybrids between either ER or NIL(Hd1) and the cultivars Zhendao99, Zaofeng9, Wuyujing3, Wuyunjing7, Wuyunjing8, Ningjing1, Xudao3, Xudao4, Sidao11, Lianjing3, Nanjing4, Nanjing41, Yanjingnuo1, Sidao1, Huaidao7, Wujing1, Wuxiangjing14, Wuyunjing21, Huajing2, Nanjing3, Yanjing, Huaidao9 and Zhendao88 also headed about 22. and 9. d earlier than those of equivalent hybrids with either LR or cv. Nipponbare (Table 3), suggesting that these cultivars carried the photoperiod insensitivity allele Se-1 e (Table 4). The HDs of the hybrids between LR and Yandao8, Yanjing938, Wujing13, Changnongjing4, Suxiangjing2 and Nanjing43 were all significantly longer than the equivalent hybrids with ER, while their hybrids with cv. Nipponbare had almost the same HD as the equivalent hybrids with NIL(Hd1) (Table 3). These outcomes show that Yandao8, Yanjing938, Wujing13, Changnongjing4, Suxiangjing2 and Nanjing43 carry Se-1 n,an allele which gives a slightly weaker PS than Se-1 u (Table 4). Allelic relationships at the Ef-1 locus The tester line T6E b m headed 21.3 d earlier than T6m, because these two lines differ allelically at Ef-1 (Table 2), while the HD of the hybrids between T6E b m and 28 of the 29 cultivars (the exception was Zhendao99) did not differ significantly from those of the equivalent hybrids with T6m (Table 3). The HD of T6E b m Zhendao99 was 1.6 d longer than that of T6m Zhendao99 (Table 3). Thus 28 of the 29 cultivars carry the dominant early heading allele Ef-1 (Table 4). Allelic relationships at the Hd2 locus NIL(Hd2) carries hd2 introgressed from cv. Kasalath in a cv. Nipponbare genetic background (Yano et al. 1997; Lin et al. 2). It headed earlier than Nipponbare under long days, but later than Nipponbare under short days, thus implying that hd2 could inhibit the effect of Hd1 (Se-1) (Luo et al. 23; Xu et al. 2). NIL(Hd2) headed 7. d earlier than cv. Nipponbare at Nanjing (Table 2). The hybrids between NIL(Hd2) and Wuyujing3, Wuyunjing8, Ningjing1, Yandao8, Sidao11, Lianjing3, Yanjing938, Sidao1, Wuxiangjing14, Wuyunjing21, Huajing2 and Nanjing3 also headed 7. d earlier than did the equivalent hybrids with cv. Nipponbare (Table 3), suggesting that all of these cultivars carried the hd2 (Table 4). In contrast, the HDs of the hybrids between NIL(Hd2) and Zhendao88,

4 Journal of Integrative Plant Biology 29 Days to heading 12 1 8 6 4 2 Zhendao88 Zaofeng9 HT LT * * * * * Wuyujing3 Wuyunjing7 Wuyunjing8 Ningjing1 Yandao8 Xudao3 Xudao4 Sidao11 Lianjing3 Nanjing4 Nanjing41 Yanjingnuo1 Yanjing938 Sidao1 Huaidao7 Wujing13 Wujing1 Wuxiangjing14 Suxiangjing2 Wuyunjing21 Huajing2 Changnongjing4 Nanjing3 Nanjing43 Yanjing Huaidao9 Zhendao99 Figure 2. The heading date (HD) of 29 cultivars adapted to the lower region of the Yangtze River valley under field (low temperature, LT) and greenhouse (high temperature, HT) conditions., indicate that HD in HT was significantly shorter than in LT (P <. and P <.1, respectively). Values are expressed as means ± SD, n = 1. HD (day) A B C 11 y = 1.8 2x - 46.198 11 y = 1.67 4x + 76.47 R 2 =.223 6 11 11 R 2 =.938 4 1 1 9 9 8 8 74 76 8 BVP (day) HD (day) 1 1 9 9 8 8 1 2 3 4 PS (day) HD (day) 11 11 1 1 9 9 8 8 y =.142 8x +.368 R 2 =.6 2 1 1 2 TS (day) Figure 3. Linear regressions between heading date (HD) and basic vegetative growth (BVG), photoperiod-sensitivity (PS) and temperature-sensitivity (TS) of Japonica cultivars adapted to the lower region of the Yangtze River valley. Zaofeng9, Wuyunjing7, Xudao3, Xudao4, Nanjing4, Nanjing41, Huaidao7, Wujing13, Wujing1, Suxiangjing2, Changnongjing4, Nanjing43, Yanjing, Huaidao9 and Zhendao99 were not significantly different from those of the equivalent hybrids with cv. Nipponbare (Table 3), suggesting that these cultivars carry Hd2 (Table 4). Segregation of HD in F 2 populations derived from crosses between testers and cultivars The frequency distributions for HD in the various F 2 populations derived from crosses between testers and cultivars are shown in Figure (take Xudao3 as an example). In the EG1 Xudao3 cross, the HD had a narrower distribution than was produced in EG Xudao3 (Figure A, B), confirming that Xudao3 carries E 1, just as EG1 does. While, the distribution of HD in the F 2 population from the EG Xudao3 was narrower than in the EG2 Xudao3 or EG3 Xudao3 (Figure A,C,D), showing that Xudao3 carries both e 2 and e 3, as does EG. The crosses ER Xudao3 and NIL(Hd1) Xudao3 produced a narrower range of HD distribution than LR Xudao3 and cv. Nipponbare Xudao3, respectively, confirming that Xudao3 carries Se-1 e (Figure E,F,I,K). Similarly, a comparison between the HD distributions from T6E b m Xudao3 and T6m Xudao3 (Figure F,G) can be taken to further confirm that Xudao3 carries Ef-1, as does T6E b m. Most of the plants in the F 2 population from the cross NIL(Hd2) Xudao3 had moderate HD, while most plants in the cross cv. Nipponbare Xudao3 tended towards late maturity (Figure I,K), confirming that Xudao3 carries Hd2. Discussion Rice can be grown under various climatic conditions, at latitudes ranging from 3 Nto4 S, by long-period introduction and

PS and HD Genotypes Determine Rice Cultivars Distribution A 3 PS (day) 3 2 2 1 I 1 MMM LMM EML MML II IV 74 76 8 82 BVG (day) III B PS (day) 3 3 2 2 1 1 II MMM LMM EML MML IV 1 1 2 TS (day) I III Figure 4. The basic vegetative growth (BVG), photoperiod-sensitivity (PS) and temperature-sensitivity (TS) of medium maturing middle (MMM), late maturing middle (LMM), early maturing late (EML) and medium maturing late (MML) cultivars adapted to the lower region of the Yangtze River valley. I, II, III and IV indicate the distribution of the four cultivar types. Table 2. Genotypes and heading date (HD) of the tester lines grown under natural long day conditions in Nanjing Locus Test lines Heading date E 1 E 2 E 3 Se-1 Ef-1 Hd2 EG e 1 e 1 e 2 e 2 e 3 e 3 Se-1 n Se-1 n Ef-1Ef-1 71.2 ±.6 EG1 E 1 E 1 e 2 e 2 e 3 e 3 Se-1 n Se-1 n Ef-1Ef-1 9.4 ±.7 EG2 e 1 e 1 E 2 E 2 e 3 e 3 Se-1 n Se-1 n Ef-1Ef-1 76.7 ± 2.2 EG3 e 1 e 1 e 2 e 2 E 3 E 3 Se-1 n Se-1 n Ef-1Ef-1. ± 1.6 ER E 1 E 1 e 2 e 2 E 3 E 3 Se-1 e Se-1 e Ef-1Ef-1 8.7 ± 1.3 LR E 1 E 1 e 2 e 2 E 3 E 3 Se-1 u Se-1 u Ef-1Ef-1 12.7 ± 1. T6E b m e 1 e 1 E 2 E 2 E 3 E 3 Se-1 e Se-1 e Ef-1Ef-1 7.6 ± 1.6 T6m e 1 e 1 E 2 E 2 E 3 E 3 Se-1 e Se-1 e ef-1ef-1.9 ± 1.7 Nipponbare E 1 E 1 e 2 e 2 e 3 e 3 Se-1 n Se-1 n Hd2Hd2 86.9 ± 1. NIL(Hd1) E 1 E 1 e 2 e 2 e 3 e 3 Se-1 e Se-1 e Hd2Hd2 77.4 ± 1. NIL(Hd2) E 1 E 1 e 2 e 2 e 3 e 3 Se-1 n Se-1 n hd2hd2 79.9 ± 1. Values are expressed as means ± SD, n = 1. domestication, although it is a short-day plant (Lu and Chang 198). HD is critical for adaptation to specific cultivation conditions and cropping seasons, which can be divided into the basic vegetative phase (BVP) and the photoperiod sensitivity phase (PSP). The length of the BVP is decided by the temperatures, but the PSP is decided by the photoperiod during the growing period (Chang et al. 19). The genotype of major HD genes has specific rules for different ecotypes of rice cultivars in different environments. Earlier studies have shown that allelic variation at Se-1 is particularly important for the climatic adaptation of Japanese rice (Okumoto et al. 1992a, 19; Ichitani et al. 1997, 1998b). The insensitive allele Se-1 e predominates in the high latitude (41 4 N), southeastern (36 41 N) and some lower latitude (21 3 N) regions of Japan, while the sensitive allele Se-1 n is restricted to the southwest (31 36 N). Cultivars from Hokkaido carry the insensitive allele e 1 (Okumoto et al. 19), while those from Taiwan have both ef-1 and Se-1 e, which ensures that these cultivars have a long BVP and a weak PS (Tsai 198; Okumoto et al. 1992b). Most of the Medium indica cultivars grown in the central and lower regions of the Yangtze River valley carry hd2, which inhibits the expression of both E 1 and Se-1, if present (Xu et al. 27). Cultivars from northeastern China are uniformly fixed for Ef-1, and carry at most one PS allele (at either E 1 or Se-1), and some cultivars even carried the recessive allele hd2, resulting in the cultivars having short BVP and weak PS, being able to adapt well to the short and cool summer with a long natural day-length (Wei et al. 28). The lower region of the Yangtze River valley located at the transition region between a subtropical and warm temperate zone, the day-length increased gradually and the mean temperature gradually decreased from low latitude to high latitude during the rice growing season. The planting area of Japonica

6 Journal of Integrative Plant Biology 29 Table 3. Heading date (HD) (in days) of hybrids between tester lines and cultivars HD of hybrids of test lines crossed with tested cultivars (d) Cultivars EG EG1 EG2 EG3 ER LR T6m T6E b m Nipponbare NIL(Hd1) NIL(Hd2) Zhendao88 8. 88. 86.1 97.4. 16.2 94.3 92.7 77. nd 8.1 Zaofeng9 89. 9.7 97.3 17. 88. 16. 13.1 1.3 87. 81.8.8 Wuyujing3 82.3 9.3 91.8 12.7 79.4 1.6 14. 97.2 88.1 77. 83.3 Wuyunjing7 89.7 9.2. 92. 86.7 14.3 14. 13. 97.7 nd 9.7 Wuyunjing8 86. 9.3 93.2 89.9 8.1 1.2 97.7 98. 97.6 91.1 93. Ningjing1 93. 9. 1.7 98.6.2 1. 1.8 11.3 98. 91.2 92. Yandao8 92.2.1. 99.1. 97. 97. 9.9 8.7 87. 8. Xudao3 8.3 8.4 87.2 98.3 81.9 99.9 94.6 91.1.4 79.4 81. Xudao4 79.6 86.7 86.2 98.1 82.7 1.1 9. 89.7.6.7 81.7 Sidao11 9.8 97. 9. 88. 8. 1. 93.7 91.3 93. 82. 82. Lianjing3 91. 9.4 97.3 98.3 79.8 97.. 92.2 91.9 83.3 82.7 Nanjing4 83.3 86. 91.3 14 77.1 14.7. 97. 8.9 8.7. Nanjing41 81.1 86.6 89.7 9.3 83.3 11. 93. 9.8 88.6 82.4 86.3 Yanjingnuo1 83. 94. 93.3 11. 87. 16.8 1.4 99.7 87.1 81.8 nd Yanjing938 91.. 98.3 99.3 87..6 98. 97.3.4 91.9 88.3 Sidao1 86.2 9.6 94. 97.1 82.4 98. 91.7 87.4 9.7 82.3 81. Huaidao7 83. 88.3 89. 11.7.7 1.7 9.6 9 86. 79.8 83.3 Wujing13.3 99.3 11.9 13.3 9. 99. 11.6 99.9 89.2 92. 92.3 Wujing1 82. 9.3 9.7 11. 8.8 17.3 1.4 98. 88.3 82.8 86.2 Wuxiangjing14 9.1 1.8 12.6 13.8. 11. 11.7 11. 99.3 93.6 91.6 Suxiangjing2 11. 16.3 18.7 11. 98. 16.3 19. 1. 11.7 98. 98.8 Wuyunjing21 83.3 93.4 9.1 94.9 8.9.4 89.4 87. 89.2 83. 82.2 Huajing2 83. 9. 87.9 99..7 13..7 9. 87.1 79. 81.6 Changnongjing4.2 1.7 12.1 14. 89. 1.3 12.7 11. 99.3 9.8 9.6 Nanjing3 94. 98.4 11.3 13.8 83. 18.3 92.6 89.9.4.3.6 Nanjing43 92.8 99. 99.1 18.3 9.6 16.8 18.3 14..7 93. 99.1 Yanjing 81.2 87.7 89.6 99.1 83.1 11.4 9.7 94. 8.2.7.6 Huaidao9 8. 88.7 92. 14.4 87.3 13.1.4 9. 86.2 79.7. Zhendao99 8.4 87.4 87.6 98.8 8.4 1.8 19. 93. 8.7 8. 82.8 Values represent means. rice cultivars accounted for 8% of the total paddy planting area of the lower region of the Yangtze River. These Japonica rice cultivars were divided into four ecotypes, which were MMM, LMM, EML and MML Japonica rice cultivars. The HD of the four ecotypes increased gradually, and the suitable planting regions of them distributed from high latitude to low latitude. Here, variation in HD among a set of Japonica rice cultivars grown in the lower region of the Yangtze River valley and belonging to the four ecotypes was characterized, and the contribution of photoperiod and temperature to this variation were analyzed. Both photoperiod and temperature influence HD. The HD and PS have a significantly linear correlation, and the PS increased gradually in the four ecotypes cultivars. Almost all of the cultivars carry the dominant early-heading gene Ef-1, photoperiod insensitivity allele e 2 and PS allele E 1 or E 1 t. Most of MMM, LMM and MML varieties carried the photoperiod insensitivity allele e 3, while EML ones carried the PS allele E 3 or E 3 t.atse-1 locus, MMM and LMM types have the photoperiod insensitivity gene Se-1 e, EML ones have either Se-1 e or Se-1 n, while most MML ones are Se-1 n. The PS of some MMM, LMM and EML cultivars is weakened by the presence of hd2. Thus, the japonica cultivars grown in the lower region of the Yangtze River valley tend to be sensitive to photoperiod and there is a trend of increasing PS from MMM through LMM and EML to MML types, which is the real reason for their distribution from high latitude to low latitude with increasing HD. Although rice can be grown under a variety of climatic conditions, adaptation to a rather specific environment is common, generally because of a requirement for a particular combination of day length, temperature and farming system. An example of this specialization occurs in the lower region of the Yangtze River valley, where LMM types are suited to areas south of 34 N, EML types south of 32 3 N, and MML ones south of 31 6 N (Jin and Xia 1998). If the rice cultivars from low latitude

PS and HD Genotypes Determine Rice Cultivars Distribution 7 Table 4. The heading date (HD) genotypes of Japonica cultivars grown in the lower region of the Yangtze River valley HD genotypes Ecotypes Cultivars E 1 E 2 E 3 Se-1 Ef-1 Hd2 MMM Japonica rice cultivars Zhendao99 E 1 E 1 e 2 e 2 e 3 e 3 Se-1 e Se-1 e ef-1ef-1 Hd2Hd2 Zaofeng9 E 1 E 1 e 2 e 2 e 3 e 3 Se-1 e Se-1 e Ef-1Ef-1 Hd2Hd2 Xudao3 E 1 E 1 e 2 e 2 e 3 e 3 Se-1 e Se-1 e Ef-1Ef-1 Hd2Hd2 Xudao4 E 1 E 1 e 2 e 2 e 3 e 3 Se-1 e Se-1 e Ef-1Ef-1 Hd2Hd2 Zhendao88 E t t 1 E 1 e 2 e 2 e 3 e 3 Se-1 e Se-1 e Ef-1Ef-1 Hd2Hd2 Wuyunjing21 E t t 1 E 1 e 2 e 2 e 3 e 3 Se-1 e Se-1 e Ef-1Ef-1 hd2hd2 Huajing2 E t t 1 E 1 e 2 e 2 e 3 e 3 Se-1 e Se-1 e Ef-1Ef-1 hd2hd2 Sidao11 E 1 E 1 e 2 e 2 E 3 E 3 Se-1 e Se-1 e Ef-1Ef-1 hd2hd2 Lianjing3 E 1 E 1 e 2 e 2 E t t 3 E 3 Se-1 e Se-1 e Ef-1Ef-1 hd2hd2 Yandao8 E 1 E 1 e 2 e 2 E t t 3 E 3 Se-1 n Se-1 n Ef-1Ef-1 hd2hd2 LMM Japonica rice cultivars Nanjing4 E 1 E 1 e 2 e 2 e 3 e 3 Se-1 e Se-1 e Ef-1Ef-1 Hd2Hd2 Huaidao7 E 1 E 1 e 2 e 2 e 3 e 3 Se-1 e Se-1 e Ef-1Ef-1 Hd2Hd2 Yanjing E 1 E 1 e 2 e 2 e 3 e 3 Se-1 e Se-1 e Ef-1Ef-1 Hd2Hd2 Huaidao9 E 1 E 1 e 2 e 2 e 3 e 3 Se-1 e Se-1 e Ef-1Ef-1 Hd2Hd2 Nanjing41 E 1 E 1 e 2 e 2 e 3 e 3 Se-1 e Se-1 e Ef-1Ef-1 Hd2Hd2 Sidao1 E t t 1 E 1 e 2 e 2 e 3 e 3 Se-1 e Se-1 e Ef-1Ef-1 hd2hd2 Nanjing3 E 1 E 1 e 2 e 2 e 3 e 3 Se-1 e Se-1 e Ef-1Ef-1 hd2hd2 Yanjingnuo1 E t t 1 E 1 e 2 e 2 e 3 e 3 Se-1 e Se-1 e Ef-1Ef-1 Wuyujing3 E t t 1 E 1 e 2 e 2 e 3 e 3 Se-1 e Se-1 e Ef-1Ef-1 hd2hd2 Wuyunjing8 E 1 E 1 e 2 e 2 E 3 E 3 Se-1 e Se-1 e Ef-1Ef-1 hd2hd2 Yanjing938 E 1 E 1 e 2 e 2 E t t 3 E 3 Se-1 n Se-1 n Ef-1Ef-1 hd2hd2 EML Japonica rice cultivars Wujing1 E t t 1 E 1 e 2 e 2 e 3 e 3 Se-1 e Se-1 e Ef-1Ef-1 Hd2Hd2 Wuxiangjing14 E 1 E 1 e 2 e 2 E t t 3 E 3 Se-1 e Se-1 e Ef-1Ef-1 hd2hd2 Ningjing1 E 1 E 1 e 2 e 2 E t t 3 E 3 Se-1 e Se-1 e Ef-1Ef-1 hd2hd2 Wuyunjing7 E 1 E 1 e 2 e 2 E 3 E 3 Se-1 e Se-1 e Ef-1Ef-1 Hd2Hd2 Changnongjing4 E 1 E 1 e 2 e 2 E t t 3 E 3 Se-1 n Se-1 n Ef-1Ef-1 Hd2Hd2 Wujing13 E 1 E 1 e 2 e 2 E t t 3 E 3 Se-1 n Se-1 n Ef-1Ef-1 Hd2Hd2 MML Japonica rice cultivars Suxiangjing2 E 1 E 1 e 2 e 2 e 3 e 3 Se-1 n Se-1 n Ef-1Ef-1 Hd2Hd2 Nanjing43 E 1 E 1 e 2 e 2 e 3 e 3 Se-1 n Se-1 n Ef-1Ef-1 Hd2Hd2 EML, early maturing late; LMM, late maturing middle; MML, medium maturing late; MMM, medium maturing middle. regions were introduced to high latitude regions, the HD will be prolonged, resulting in the occurrence of low temperature stress at later growth stages; similarly, if the rice cultivars adapted to high latitude regions were introduced to low latitude regions, they will suffer a yield penalty because their HD will be too short. An understanding of the genetic basis of this adaptation is important for the rational exploitation of natural genetic variation in the context of improving the efficiency of breeding optimally adapted cultivars. Materials and Methods Plant materials The following plant materials were used: (i) a set of tester lines, comprising the HD near-isogenic lines EG, EG1, EG2, EG3, ER, LR, T6m and T6E b m (Yamagata et al. 1986; Ichitani et al. 1997, 1998a,b; Inoue et al. 1998) and the HD QTL near-isogenic lines NIL(Hd1) and NIL(Hd2), which have been constructed in a background of cv. Nipponbare (Yamamoto et al. 1998; Lin et al. 2) (Table 2); (ii) a panel of 29 cultivars, including 1 MMM (Huajing2, Lianjing3, Sidao11, Wuyunjing21, Xudao3, Xudao4, Yandao8, Zaofeng9, Zhendao88 and Zhendao99), 11 LMM (Huaidao7, Huaidao9, Nanjing3, Nanjing4, Nanjing41, Sidao1, Wuyujing3, Wuyunjing8, Yanjing, Yanjing938 and Yanjingnuo1), six EML (Changnongjing4, Ningjing1, Wujing13, Wujing1, Wuxiangjing14 and Wuyunjing7), and two MML (Nanjing43, Suxiangjing2) Japonica rice cultivars grown in the lower region of the Yangtze River valley, and cv. Nipponbare; and (iii) the hybrids and derived F 2 populations from a set of crosses between the cultivars and genetic stocks. Photoperiod-sensitivity analysis The 29 cultivars were grown under both artificial short-day (9 h of sunlight per day [h/d], SD ) and natural long-day (LD)

8 Journal of Integrative Plant Biology 29 Number of plants 3 3 2 2 1 1 9 4 3 3 2 2 1 1 9 4 3 3 2 2 1 1 9 2 1 1 9 3 2 2 1 1 9 2 2 1 1 A B C D E F EG 9 EG2 ER Xudao3 EG1 12 EG3 12 12 12 18 LR 18 12 18 12 18 12 12 18 12 12 18 12 12 Days to heading 2 2 1 1 9 16 14 12 1 8 6 4 2 9 3 2 2 1 1 9 4 3 2 1 9 3 3 2 2 1 1 G H I J T6E b m NIL(Hd1) K 9 Nipponbare NIL(Hd2) 12 12 18 12 12 18 12 12 T6m 18 12 12 18 12 18 12 Figure. Frequency distribution for heading date (HD) in F 2 populations derived from crosses between tester lines and Xudao3. A, EG Xudao3; B, EG1 Xudao3; C, EG2 Xudao3; D, EG3 Xudao3; E, ER Xudao3; F, LR Xudao3; G, T6E b m Xudao3; H, T6m Xudao3; I, cv. Nipponbare Xudao3; J, NIL(Hd1) Xudao3; K, NIL(Hd2) Xudao3.

PS and HD Genotypes Determine Rice Cultivars Distribution 9 Temperature ( C) 4. 3. 3. 2. 2. 1. HT NJ LT 1. 1 2 3 4 6 7 8 9 1 Days from seeding Figure 6. Daily mean temperatures from seeding to heading in the greenhouse (high temperature conditions, HT) and in the field (low temperature conditions, LT) during the winter in Hainan province, and natural high temperatures in the summer at Nanjing (NJ). conditions in the field near Nanjing (32 N) in 26. Initial sowing was carried out on 2 May, and 1 seedlings of each entry were transplanted into the field on 1 June, with an interplant separation of 13.3 cm and an inter-row separation of 26.7 cm. The natural photoperiod between May and August ranged from 13.2 h/d to 14.2 h/d. Mean temperatures experienced by the plants grown under artificial SD and natural LD conditions were almost identical (Figure 6). The photoperiod sensitivity (PS) of each entry was calculated from the difference in HD between SD and LD. Crop management followed commercial practices. Temperature-sensitivity analysis The 29 cultivars were grown both in greenhouse (high temperature, HT) and under field conditions (low temperature, LT) during the winter at a site in Hainan Province (18 29 N). Sowing was completed on 2 November 2 and 1 seedlings of each entry were transplanted on 1 December into both the field and the greenhouse, with an interplant separation of 13.3 cm and an inter-row separation of 26.7 cm. Daily mean temperatures in both the HT and LT experiments are shown in Figure 6. The photoperiod experienced by plants grown in the HT and LT conditions ranged from 11. h/d to 11.9 h/d. The temperature sensitivity (TS) of each entry was given by the difference in HD between HT and LT grown plants. Crop management followed commercial practices. Genotypes analysis of heading date hybrids and F 2 populations were derived from crosses between each of the 29 cultivars and each of the testers EG, EG1, EG2, EG3, ER, LR, T6m, T6E b m, NIL(Hd1), NIL(Hd2) and cv. Nipponbare. The parents of each along with the corresponding F 2 population were grown in the field at the Institute of Food Crops of Jiangsu Academy of Agricultural Sciences in Nanjing in 26. Sowing and transplanting occurred on17 May and 16 June, respectively. Ten parental and 1 plants per cross, along with approximately 2 F 2 individuals, were transplanted into the field with an interplant separation of 13.3 cm and an inter-row separation of 26.7 cm. Crop management followed commercial practices. Statistical analysis Heading date was defined by the date on which the leading panicle had emerged about 1 cm beyond the leaf sheath of the flag leaf, and was expressed as the number of days from seeding to heading. The BVG of one cultivar was represented by the HD under SD conditions. T-test was used to estimate the significance of difference of the HD between LD and SD or HT and LT. Regression analysis was conducted using Microsoft Excel software. Acknowledgements We are grateful to Drs K. Ichitani and M. Yano for provision of the testers EG, EG1, EG2, EG3, ER, LR and QTL NILs, and to Dr Tsai Kuo Hai for the isogenic lines T6m, T6E b m. References Chang TT, Li CC, Vergaram BS (19). Component analysis of duration from seeding to heading in rice by the basic vegetative phase and photoperiod-sensitive phase. Euphytica 18, 79 91. Doi K, Izawa T, Fuse T, Yamanouchi U, Kubo T, Shimatani Z et al. (24). Ehd1 a B-type response regulator in rice, confers shortday promotion of flowering and controls FT-like gene expression independently of Hd1. Genes Dev. 118, 926 936. Ichitani K, Okumoto Y, Tanisaka T (1997). Photoperiod sensitivity gene of Se-1 locus found in photoperiod insensitive rice cultivars of the northern limit region of rice cultivation. Breed. Sci. 47, 14 12. Ichitani K, Okumoto Y, Tanisaka T (1998a). Genetic analysis of the rice cultivar Kasalath with special reference to two photoperiod sensitivity loci E 1 and Se-1. Breed. Sci. 48, 1 7.

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