Abstract:

Abundant heterosis is manifested from the cross of two genetically diverse parent lines. Therefore, it is essential to reveal genetic relationships among varieties with unknown pedigree. In the present study, genetic divergences among 66 rice (Oryza sativa L.) varieties, including 5 photoperiod/thermo-sensitive genic male sterile lines, 7 cytoplasmic male sterile lines, 53 restorers and one wild rice variety, were analyzed by using 36 SSR (simple sequence repeats) primer pairs which disperse on 12 chromosomes. A total of 300 polymorphic bands were detected among 66 varieties, and on average 8.33 distinguishable bands were observed after amplification with each primer pair. Genetic divergences between all possible pairs of varieties were defined by Nei M method with genetic distance (GD), calculated from SSR data by the equation GD=－ln[2M_XY/(M_X+M_Y)], where MXY is the total number of bands common to varieties X and Y, and M_X and MY are the total number of bands present in x and y respectively. 66 cultivars were clustered based on GD by Unweighted Pair Group Method using Arithmetic Average (UPGMA). The results were concluded as follows: (1) Sixty-five out of sixty-six varieties were distinguished obviously, different ecotypes were also defined using SSR markers, which were consistent with the relationship of their pedigrees, and were similar with the result of phenotype analysis. (2) Indica, japonica and wild rice were discriminated based on GD=0.73，and some indica cultivars bearing japonica or wild rice consanguinity were discriminated based on GD=0.63, indicating that SSR markers are sensitive and precise for classification on indica, japonica and wild rice. Otherwise, ten specific primers were screened and selected to identify subspecies between indica and japonica. (3)Twelve male sterile lines and more than fifty restorers were divided into eight ecotypes based on GD=0.56，and many parents of hybrid rice used in large scale were classified in multiple ecotypes, suggesting there were great genetic divergences between the parents of elite hybrid rice. Parents’ selection of hybrid rice will get benefit from the classification on both male sterile lines and restore lines.

Key words: Hybrid rice, Classification, SSR marker, Heterosis ecotype, DNA fingerprint