GENETICS OF HYBRID STERILITY AND HYBRID BREAKDOWN IN CULTIVATED RICE (ORYZASATIVA L.)

Authors: LI, ZHIKANG - TEXAS A&M; Pinson, Shannon; PATERSON, ANDREW - TEXAS A&M; PARK, WILLIAM - TEXAS A&M; STANSEL, JAMES - TEXAS A&M

Submitted to: Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/7/1997
Publication Date: N/A
Citation: N/A

Interpretive Summary: Hybrid sterility (F1 sterility) and hybrid breakdown (sterility and weakness of F2 and later generations) in crosses within cultivated rice (Oyrza sativa L.) are common and their genetic bases are complicated. To address this question, we initiated a mapping study using a fairly complete RFLP linkage map and F4 progeny testing from a cross between a 'widely compatible' japonica variety Lemont from southern U.S. and a Chinese indic variety, Teqing. Our results from QTL mapping and interaction analyses suggest different genetic mechanisms involved in hybrid sterility and hybrid breakdown in rice. The mechanism causing hybrid sterility appeared to be a number of putative differentiated 'supergenes' in the rice genome. Breakdown of these 'supergenes' by recombination had resulted in increased sterility, suggesting they are probably of cryptic structural hybridity. Gene(s) in the cytoplasmic genomes was found to have large effect on fertility of both male and female gametes in the F1 hybrids. There appeared a pair of complementary genes which had a very large effect on sterility and behaved like 'wide compatibility' genes. We speculate that this pair of genes and the 'gamete eliminator' (S1) or the 'egg killer' (S- 5) are probably the Rm (recombination modulating genes) which can suppress or promote the phenotypic effects of presumed 'supergenes' in hybrids. Hybrid breakdown in rice appeared to be due to the breakdown of co-adapted indica and japonica gene complexes, which consist of large numbers of complementary QTMF (quantitative trait modifying factor) loci throughout the genome.

Technical Abstract: Hybrid sterility (F1 sterility) and hybrid breakdown (sterility and weakness of F2 and later generations) in crosses within cultivated rice (Oyrza sativa L.) are common and their genetic bases are complicated. To address this question, we initiated a mapping study using a fairly complete RFLP linkage map and F4 progeny testing from a cross between a 'widely compatible' japonica variety Lemont from southern U.S. and a Chinese indic variety, Teqing. Our results from QTL mapping and interaction analyses suggest different genetic mechanisms involved in hybrid sterility and hybrid breakdown in rice. The mechanism causing hybrid sterility appeared to be a number of putative differentiated 'supergenes' in the rice genome. Breakdown of these 'supergenes' by recombination had resulted in increased sterility, suggesting they are probably of cryptic structural hybridity. Gene(s) in the cytoplasmic genomes was found to have large effect on fertility of both male and female gametes in the F1 hybrids. There appeared a pair of complementary genes which had a very large effect on sterility and behaved like 'wide compatibility' genes. We speculate that this pair of genes and the 'gamete eliminator' (S1) or the 'egg killer' (S- 5) are probably the Rm (recombination modulating genes) which can suppress or promote the phenotypic effects of presumed 'supergenes' in hybrids. Hybrid breakdown in rice appeared to be due to the breakdown of co-adapted indica and japonica gene complexes, which consist of large numbers of complementary QTMF (quantitative trait modifying factor) loci throughout the genome.