| Rice production is limited by many environmental factors, of which drought and salinity are the most important abiotic stresses which greatly constrain yield and planting area of rice. Development of drought and salinity tolerant (DT, ST) variety is a most effective method to solve this problem.In the present study, using BC3F5 introgression populations derived from an elite indica variety Feng-Ai-Zhan 1 (FAZ1) as the recurrent parent and indica varieties Guang-Hui 122, Bg 94-1, Jiang-Xi-Xi-Miao and japonica varieties Yuan-Jing 7 and Shen-Nong 89366 as donor parents, four high yield (HY) and DT lines and four HY and ST lines were selected and used for pyramiding of HY, DT and ST. As compared with the pyramiding parents, DT, ST and HY were selected from the four pyramiding F2 populations, getting 27~46 extreme DT, ST and HY individuals with a selection intensity of 7.5%~12.7%, respectively. The selected populations from pyramiding F2 were used to analyse the effect of selection of HY, DT and ST on yield-related traits and identify QTLs affecting HY, DT and ST related traits under irrigation, drought and salt stress conditions. QTLs which stably expressed under different genetic backgrounds and different environments were identified and used for marker-assisted selection (MAS) breeding. The main results were summarized as follows.1. In the three target-trait selected populations from HY and DT pyramiding F2 populations, the average grain yield (HY) were 27.2g ~ 32.5 g, significantly higher than the control FAZ1 and their respective parents. The selected offspring showed good salt tolerance, significantly stronger than the control FAZ1 and parents in survival days of seedlings (SDS), especially for those selected from ST pyramiding populations. Seven promising lines, QP9, QP25, QP31, QP32, QP47, QP49, QP154 were obtained from the pyramiding populations of HY and DT and 1 line (QP75) from pyramiding populations of HY and ST through repeated or intercross screening for HY and ST selected lines, whose DT, ST and yield greatly were enhanced compared with FAZ1 and the parents.2. In HY, DT and ST selected populations, yield-related traits all presented significant variation, showing much difference from the recurrent parent with earlier heading date (HD), reduced panicle number per plant (PNP), increased filled grain per panicle (FNP) and seed setting rate (SSR). It indicated that it is possible to develop new high yielding varieties with stronger DT or ST.3. Correlation analysis of yield-related traits of the target traits selected populations from the four pyramiding F2 populations showed that HY was significantly positively correlated with FNP, PNP respectively. It was suggested that FNP and PNP are the two key component traits to develop high yielding varieties with DT or ST.4. The Chi-square statistical analysis showed that QTLs affecting HY, DT and ST related-traits detected in the four pyramiding populations were 13, 9, 7 and 7 respectively, locating in all 11 chromosomes except 10. Genetic overlapping regions affecting HY, together with DT or ST detected in all pyramiding populations were mainly distributed in chromosomes 1, 3 and 6. One-way ANOVA using the integrated populations derived from different target traits selection in each pyramiding F2 partially validated the QTLs detected by Chi-square analysis with estimation of gene effects of QTLs.5. QTLs affecting HY and ST related-traits closely associated with the regions of RM302~M297 on chromosome 1, RM424 on chromosome 2, RM55 on chromosome 3, RM3 on chromosome 6 and RM108~RM553 on chromosome 9 detected in two or more integrated background populations are important to pyramid different favorable alleles in MAS-based pyramiding breeding.
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