Genetic variance and molecular diversity of restorer lines in rice (Oryza sativa L.)

Estimates of genetic variance are useful in designing breeding programs, as the higher the genetic variability and magnitude of diversity, the greater the probability of heterosis. The genetic variability of restorer germplasm at PhilRice was determined by developing half-sib hybrids following the line x tester mating design involving 20 randomly selected restorers and three commercially usable CMS lines and evaluated at UPLB [University of the Philippines Los Banos, College, Laguna, Philippines] and PhilRice Maligaya. In addition, these restorers were assayed for molecular analysis using SSR [simple sequence repeats] markers to determine the molecular diversity. Analysis of variance for both locations revealed highly significant (P less than 0.01) differences among restorer lines, CMS lines and restorer lines x CMS lines for all traits. Estimates of genetic variance of restorer lines (O'2 L) for traits measured were highly significant based on F-test, except for number of productive tillers. Confidence interval estimates (O2 L) for all traits were also significantly different from zero except number of productive tillers. This indicates that estimates obtained were significant and that genetic variability exists for these traits. The 65 SSR markers were polymorphic. A total of 266 alleles ranging from 2 to 8 alleles/locus and a mean of 4.09 alleles/locus were detected. The Nei and Li genetic similarity coeficients among restorers and CMS ranged from 0.22 to 0.71. Twenty four percent of the total alleles detected were rare (63/266) and these were distributed throughout the entire chromosomes of the rice genome. Combined mean performance across locations revealed that several hybrids outyielded the best checks. Twenty-five percent (15/60) of hybrids evaluated at UPLB exhibited 16.73-44.29 percent yield advantage over the highest yielding check, PSB Rc72H. At PhilRice CES, three hybrids (5 percent) outyielded the highest yielding check PSB Rc28. Overall, the results indicate the presence of a wide range of genetic variability and molecular divergence in the PhilRice restorer germplasm, including great potential to generate outstanding hybrids for commercial cultivation.