Genetic mapping of quantitative trait loci for the stigma exsertion rate in rice(Oryza sativa L.)

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.

Variation of rate of exserted stigma in P(T) GMS lines of rice

Rate of exserted stigmas (RES), ie. the ratio of glumes with exserted stigmas to the total glumes is one of the most important characteristics which affects the out-crossing rate of its combinations. Sixteen P(T) GMS lines with different ecotypes were used to study the variations of RES during their stable sterile period in Wuhan from 1992—1993. Ten healthy panicles were randomly selected at full anthesis. Their colour and the number of glumes showing one-side or two-side exserted of stigmas were investigated. Table 1 showed that there were a great variations of RES among the 16 lines tested in two consecutive years (c.v.=43.38%) and among the

Observation on Flowering Habit of Reverse Genic Sterile Rice FHS

[Objective] This study was to use reverse genic male sterile FHS better in field production. [Method] Low energy nitrogen ion beam was taken as a mutation source to conduct mutagenic treatment for indica rice 99-02 and the mutant FHS with special fertility that was isolated from their offspring. Some characteristics such as flowering habit and stigma exsertion rate of FHS were observed in this experiment. [Result] The reverse genic sterile rice FHS had an obvious peak flowering stage from 10:00 to 10:30, while the second peak flowering was from August 5 to August 10. Compared with PA64S, FHS flowered early and its flowering time was concentrated, showing that it is for seed propagation. The stigma exsertion rate of FHS was 85.8% and low exsertion rate was good for the purity of seed. [Conclusion] The reverse genic sterile rice FHS had good value in use, besides, it could also be used as comparison material for studying fertility alternation mechanism of photoperiod sensitive genic male sterile rice.

Thermo-sensitive genic male sterile (TGMS) rice line developed by population improvement

In this study population improvement or random polycross plus mass selection was adopted with using N8S, Huaizao4, Xiang2B and Zaoyoul as parents. To help comprehensively improve the important characters such as combining ability, grain quality, resistance, stigma exsertion rate, etc. The stigma exsertion rate of ZhunS, an elite TGMS line, is 78.6%, 72.4% higher than that of V20A. Hybrids produced by crossing ZhunS with R402, Minhui77 and Minhui63 increased the yield by 3.8%-5.8% and decreased grain chalkiness by 82.1%-84.4% compared with those from crossing V20A with the corresponding R lines.