| Drought is one of the main abiotic constrains in rice production. Along theincreasing global water shortage and food crisis, developing of drought-resistant hybridrice has broad application potential. Normal cultivated rice varieties have low outcrossingrates. In order to increase the yield in hybrid seed production, cytoplasmic male sterility(CMS) lines with high outcrossing rates were developed by engaging high percentage ofexserted stigma as one of the key factores. In this study, the genetic mechanism of ricestigma exsertion were studied by using two F2 populations from crosses betweenHuhan1B×Ⅱ-32B and huanlB×K17. The major results were as follows:1 A genetic linkage map was constructed based on the F2 populations ofHuhan1B/Ⅱ-32B by Mapmaker/Exp3.0. The map contained 97 SSR and 3 Indel markers,and covered a total of 1163.7cM with an average interval of 11.6 cM between adjacentloci.2 Another genetic linkage map was constructed based on the F2 populations ofHuhan1B/K17 by Mapmaker/Exp3.0. The map contained 92 SSR markers, and covered atotal of 921.3cM with an average interval of 10.1 cM between adjacent loci.3 Ten QTLs distributing on the four chromosomes were detected for stigma exsertionrate based on the F2 populations of Huhan1B/Ⅱ-32B. Three QTLs were found toinfluence PSES with accumulated contribution of 21.44％, distributing separately onchromosomes 3,7 and 9. Two QTLs affecting DSES were detected on the chromosomes 3and 9, with accumulated contribution of 15.98％. Five QTLs were detected onchromosome 3, 4, 7, 9 affecting PES. The contribution rates of a single QTL varied from6.86％to 9.73％, while the total contribution was 39.42％. The additive effects playedmajor roles in most quantitative trait loci.4 In another F2 population derived from a cross between Huhan1B and K17, fivemajor QTLs were detected on chromosomes 5, 6 and 7, accounting for 53.91％of additiveeffect variance and 12.12％of dominant effect variance in total. The additive effectplayed leading role. A major QTL associated with PSES located chromosome 5, with theadditive effect variance of 10.02％. Three major QTL on chromosome 5, 6 and 7,explained 25.07％of additive effect variance affecting PDES. In addition, one major QTLof PES was detected on chromosome 6, with 18.82％of additive effect and 6.72％ofdominant effect..5 Epistasis analysis of the two F2 populations showed seven and nine pairs ofsignificant interaction sites accounted for 67.39％and 60.79％of the total phenotypic variance respectively. Most detected epistasis belongs to additive / additive interactioneffect, while a number of major QTL involved in the interactions.
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