Genetic Analysis Of Heading Date Of Japonica Rice Cultivars In Southwest China And Late Season Japonica Rice Cultivars From Tai Lake Region

Heading date (HD) is one of the most important traits for the adaptation of rice to different cultivation areas and cropping seasons. It is essentially determined by three factors, i.e. duration of the basic vegetative growth (BVG), photoperiod-sensitivity (PS) and temperature-sensitivity (TS). PS are found to be responsible for heading date of cultivars with strong PS. Several major genes for HD have been identified in rice. Among these genes, E1and Se-1are known as major genes have been proved to be the most ubiquitous alleles controlling HD. Under optimum photoperiod and temperature conditions, the heading time of rice is now considered to be chiefly determined by the length of the basic vegetative growth (BVG) period. Ef-1is a major gene controlling the duration of BVG. Because of the special ecological conditions in Southwest China and Tai Lake Region, it is of great significance to find out the HD genetype of rice cultivars grown in these two aeras.So in this study, BVG, PS and TS of japonica cultivars from these two areas were analyzed under artificial short-day (9h L/15h D) and natural long-day conditions (14h L/lOh D) in Nanjing, as well as artificial high temperature and natural low temperature conditions in winter in Hainan. Genetic analyses were conducted on these cultivars using a set of heading date near isogenic lines:EGO～EG3, ER, LR, T65m, T65Ebm and NIL (Hdl)、 NIL (Hd2) as tester lines. The main conclusions are as follows:1. Analysis of japonica rice cultivars native to Southwest China showed that PS and TS varied markedly in different cultivars. The BVG of all the japonica cultivars was well situated, but also differed in cultivars. Regression analysis showed a significant correlation between heading date and PS, indicating PS was the main factor affecting heading date of japonica cultivars in Southwest China.2. The genetic analysis showed that all these japonica cultivars of Southwest China carried the dominant early-heading gene Ef-lor Ef-l’, and most of these cultivars carried the dominant photoperiod sensitivity allele Ej or E1t, the PS of which was slightly weaker than E1. For the Se-1locus, these japonica cultivars mainly carried recessive photoperiod insensitivity gene Se-le. In addition, the PS of22japonica varieties can be repressed or weakened by the recessive allele hd2, inhibiting the expression of E1and Se-1. These results indicated that the heading date genotypes determined the different PS and well situated BVG of japonica rice cultivars grown in Southwest China.3. Analysis of late japonica rice cultivars native to Tai Lake Region showed that all the cultivars had strong PS. Besides, most of the cultivars in this study had strong TS and short BVG. Regression analysis showed a significant correlation between heading date and PS, indicating PS was the main factor affecting heading date of late season japonica cultivars from Tai Lake Region.4. Genetic analyses on20late japonica rice cultivars of Tai Lake Region showed that almost all these japonica cultivars carried both the dominant photoperiod sensitivity allele E\and the dominant early-heading gene Ef-1. At the E2and E3locus, most of the late season japonica varieties carried the photoperiod insensitivity allele e2and e3, but some carried the photoperiod sensitivity allele E2and E3or E3. For the Se-1locus, late season japonica cultivars mainly carried recessive photoperiod insensitivity gene Se-le, others carried Se-ln. In addition, some of the late season japonica varieties carried the recessive allele hd2, inhibiting the expression of El and Se-1.