Submitted to: Rice Technical Working Group Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: February 1, 1996
Publication Date: N/A
F1 sterility and hybrid breakdown (sterility of F2 and later generations) in crosses between distantly related rice varieties are common though their complicated genetic basis remains controversial. We conducted a RFLP mapping study using a F4 progeny testing from 'Lemont', a 'widely- compatible' javanica, and 'Teqing', a Chinese indica and found 7 QTL and a large number of putative quantitative trait modifying factors (QTMFs) whic appeared to affect spikelet sterility. We propose four different genetic mechanisms which appear to work jointly in determining the hybrid sterility and hybrid breakdown in rice. 1) The presence of 'supergenes' was suggested from the increased sterility associated with heterozygosity in four genomic regions. Recombination within these putative supergene regions appeared to result in significantly reduced fertility. 2) Impact by cytoplasmic gene(s) was indicated by the fact that spikelet sterility of fthe reciprocal F1 hybrids differed significantly (by 33%). This differenc was largely explained by the effect of Lemont (widely compatible) cytoplasmic gene(s) on the fertility of the F1 female gametes. 3) There appeared to be a pair of complementary genes which behaved like 'wide compatibility' genes and appeared to influence the phenotypic effects of presumed 'supergenes' in hybrids. 4) Hybrid breakdown appeared to be largely due to incompatibilities between indica and japonica alleles at many unlinked epistatic loci. These proposed mechanisms may partly account for the complicated nature of the post-reproductive barriers observed in rice and may also influence reproductive isolation in other plants and animals.