Hybrid performance and genetic diversity as revealed by RFLPs in rice Oryza sativa L.)

Abstract

Information about rice heterotic patterns and genetic diversity as revealed by restriction fragment length polymorphisms (RFLPs) could assist rice breeders in selection of parents. The objectives of this study were to: (1) assess genetic diversity within and between rice subspecies; (2) elucidate heterotic patterns among southern US rices and other rice germplasm; and (3) evaluate the usefulness of RFLP-based genetic diversity measurements in predicting hybrid performance. Hybrids from a diallel cross among 20 parents representing indica, japonica and javanica groups as well as lines with inter-group ancestry were evaluated for yield and heterosis at 4 locations. Parents were analyzed for RFLPs with 3 restriction enzymes and 57 DNA probes. Fifty-two probes detected 100 loci with 253 RFLP variants. Each parent had a different RFLP profile. Genetic distances between parents, calculated from RFLP data as Modified Rogers' Distances (MRDs), were greater for parents in different subgroups than for parents within the same subgroup. Cluster analysis among the lines based on MRDs revealed two major groups representing japonica and indica subspecies, respectively, and was consistent with pedigree and morphological information. Heterosis distributions were narrower for within-group hybrids than for between-group hybrids. Indica x indica hybrids provided the highest yield and yield heterosis among hybrid groups. Javanicas produced high yield heterosis when crossed with indicas and javanicas, and were highly compatible with both japonicas and indicas. Javanica x indica hybrids are recommended for producing hybrids for the southern US. Five lines from RiceTec Inc. derived from javanica x indica crosses that clustered as indicas by RFLP data proved to be especially heterotic. Hybrid yield parameters did not correlate well with MRDs calculated from all RFLP loci together, but were improved when subsets of RFLP marker loci that were putatively linked with F1 yield were used. Correlations between yield parameters and MRDs were different with hybrid groups and locations. Results indicate that RFLP data are effective in assessing associations among rice germplasm and support the hypothesis that javanicas are a subgroup within the japonica subspecies. However, RFLP-based genetic distance measures are apparently not indicative of the performance of hybrid rice.