Molecular marker heterozygosity and hybrid performance in indica and japonica rice
Zhang, Q., Z. Q. Zhou, G. P. Yang, C. G. Xu, K. D. Liu and M. A. Saghai Maroof. 1996. Theor. Appl. Genet. 93: 1218-1224.
ABSTRACT An essential assumption underlying marker-based prediction of hybrid performance is a strong linear correlation between molecular marker heterozygosity and hybrid performance or heterosis. This study was intended to investigate the extent of the correlations between molecular marker heterozygosity and hybrid performance in crosses involving two sets of rice materials, 9 indica and 11 japonica varieties. These materials represent a broad spectrum of the cultivated rice gene pool including landraces, primitive cultivars, historically important cultivars, modern elite cultivars and parents of superior hybrids. Varieties within each set were intermated in all possible non-reciprocal pairs resulting in 36 crosses in the indica set and 55 in the japonica set. The F1s and their parents, 111 entries in total, were examined for performance of seven traits in a replicated field trial. The parents were surveyed for polymorphisms using 96 RFLP and 10 SSR markers selected at regular intervals from a published molecular marker linkage map. Molecular marker genotypes of the F1 hybrids were deduced from the parental genotypes. The analysis showed that, with very few exceptions, correlations in the indica data set were higher than their japonica counterparts. Among the seven traits analyzed, plant height showed the highest correlation between heterozygosity and hybrid performance and heterosis in both indica and japonica data sets. Correlations were low to intermediate between hybrid performance and heterozygosity (both general and specific) in yield and yield component traits in both indica and japonica sets, and also low to intermediate between specific heterozygosity and heterosis in the indica set. Whereas very little correlation was detected between heterosis and heterozygosity (either general or specific) in the japonica set. In comparison to the results from our previous studies, we concluded that relationship between molecular marker heterozygosity and heterosis is variable depending on the genetic materials used in the study, due to the diversity of rice germplasms and the complexity of the genetic basis of heterosis.
Key words Oryza sativa, hybrid rice, predicting heterosis, diallel cross, restriction fragment length polymorphism (RFLP), simple sequence repeat (SSR)