Study On Several Problem Of Genetic Differentiation And Heterosis In Rice (Oryza Sativa L.)

The extent of genetic differentiation in the parents of hybrid rice wasinvestigated at molecular level, using two sets of rice materials, i.e. a set ofdoubled haploid lines derived from a Indica/Japonica cross and another set ofIndica or Japonica lines representing a broad spectrum of the Asian cultivatedrice gene pool including landraces, primitive cultivars, historically importantcultivars, modern elite cultivars, super rice and parents of superior hybrids.1 Results showed that two major types of genotypic divergence wereexhibited, that is, qualitative and quantitative divergence. The former wasmainly existed in the second set of apparently classified Indica and Japonicalines in which more than 85ï¼…of diagnostic marker loci (DMLs) have welldifferentiated into Indica or Japonica, while the latter was mainly exhibited inDH lines in which only 51.5ï¼…of DMLs are differentiating toward Indica or48.5ï¼…are differentiating toward Japonica.2 Results of two sets of test-cross F₁ populations showed congruently that theextent of parental genetic differentiation has a relatively low impact on theheterosis of two yield components, i.e., panicle number and 1000-grain weight.But it has a great bearing on the fertility parameters, i. e., filled grains per plantand seedset. There was a peak for the distribution of fertility at the interval of 20to 25 in TDj, so was a peak for grain yield. Thus fertility was the most sensitivebut important factor influenced by the extent of parental genetic differentiation.On the other hand, our results showed that parents with moderate differentiationplayed an important role in the utilization of rice heterosis.3 Our results indicated that 87.8ï¼…of the diagnostic markers were alsohighly associated with grain yield and its components in at least one of the testcross populations, suggesting parallel relationships between the genes involvingin evolution and QTLs controlling grain yield and yield components in theprocess of differentiation of rice (O. sativa L.). Further analysis indicated thatfertility was a main factor affecting the heterosis for grain yield in inter-subspecific rice hybrids. The fertility was conditioned by both intra-locus andinter-locus gene interactions and favorable genic interactions could raise itaccordingly.