Isozyme divergence between maintainers and restorers in hybrid rice breeding programs in India

In hybrid rice breeding programs, genetic diversity between maintainers and restorers enhances heterosis. The objective was to measure the level of di versity between the two groups of rice (Oryza sativa L.) breeding lines or cultivars which were screened as potential maintainers or restorers by test -cross to WA (wild abortive) cytoplasm. Allele frequencies at 15 isozyme lo ci were compared between 51 potential maintainers and 56 potential restorer s. Differences between the two types were found at eight isozyme loci on ch romosomes 4, 6, 7, 8, 11, and 12. The majority of the potential maintainers exhibited japonica type alleles, whereas most of the potential restorers e xhibited indica type alleles. This pattern is considered to be due to retai ned associations between Rf (restorer)/rf (maintainer) genes and genetic ma rkers on chromosomes other than those carrying Rflrf genes. The diversity a s well as differentiation of indica and japonica type alleles between maint ainers and restorers should contribute to enhanced heterosis in hybrid rice .