The efficiency of hybrid rice seed production can be improved by increasing the percentage of exserted stigmas. To identify quantitative trait loci （QTLs） for this trait, we conducted QTL mapping using 75 chromosome segment substitution lines （CSSLs） developed from a cross between the donor parent, Xieqingzao B （XQZB）, a maintainer line which has high stigma exsertion and the recurrent parent, Zhonghui 9308 （ZH9308）, a restorer line which has low stigma exsertion. Atotal of nine QTLs （qSSE5, qSSE10, qSSE11, qDSE10, qDSE11, qTSE5, qTSE6, qTSE10, and qTSE11） for single stigma exsertion （ssE）, dual stigma exsertion （DSE） and total stigma exsertion （TSE） were assessed in two environments （Hainan and Zhejiang）. Six of these QTLs （qSSE10, qSSE11, qDSE10, qDSE11, qTSE10, and qTSE11） were found in both environ- ments, while one QTL （qTSE6） was found in only Hainan, and two QTLs （qSSE5 and qTSE5） were found in only Zhejiang. The qSSE10, qSSE11, qDSE10, qDSE11, qTSE6, qTSE10, and qTSE11 alleles, which are derived from the parent XQZB, exhibited a positive additive effect. In contrast, the qSSE5 and qTSE5 alleles, which are derived from the parent ZH9308, exhibited a negative additive effect. The SSE, DSE and TSE traits were significantly correlated with each other in an en- vironmentally dependent manner. These results indicated that the lines showing higher values for SSE were more likely to exhibit increased values for DSE, which would ultimately increase TSE. To evaluate the advantage of exserted stigmas for cross-pollination, single, dual and total stigma exsertion should be considered separately in future attempts at genetic improvement to achieve increased production of rice hybrid seeds. This study also provides information for fine mapping, gene cloning and particularly marker-assisted selection （MAS）, on the latter and with an emphasis the phenotypic effects and implications of the QTLs for practical use in hybrid rice breeding.
We conducted a quantitative trait locus （QTL） analysis of 165 rice recombinant inbred lines derived from a cross between Zhonghui 9308 （Z9308） and Xieqingzao B （XB） in Hainan and Hangzhou, China. Grain thickness （GT）, brown rice thickness （BRT）, hull thickness （HT） and milling quality were used for QTL mapping. HT was significantly and positively correlated with GT and BRT. Twenty-nine QTLs were detected with phenotypic effects ranging from 2.80% to 21.27%. Six QTLs, qGT3, qBRT3, qBRT4, qHT6.1, qHT8 and qHT11, were detected repeatedly across two environments. Inherited from XB qHT6.1, qHT8 and qHT11 showed stable expression, explaining 9.92%, 21.27% and 10.83% of the phenotypic variances in Hainan and 9.61%, 6.40% and 6.71% in Hangzhou, respectively. Additionally, the QTL cluster between RM5944 and RM5626 on chromosome 3 was probably responsible for GT and milling quality. The cluster between RM6992 and RM6473 on chromosome 4 played an important role in grain filling. Three near isogenic lines （NILs）, X345, X338 and X389, were selected because they contained homozygous fragments from Zhonghui 9308, corresponding to qHT6.1, qHT8 and qHT11, respectively. The hull of XB was thicker than those of X345, X338 and X389. In all the lines, qHT6.1, qHT8 and qHT11 that regulated rice HT were stably inherited with obvious genetic effects.
LUO Li-liZHANG Ying-xinCHEN Dai-boZHAN Xiao-dengSHEN Xi-hongCHENG Shi-huaCAO Li-yong
