Dissection Of Combining Ability And Heterosis For Yield Traits And Fine Mapping Of QTL Associated With General Combining Ability Using Introgression Lines In Rice(Oryza Sativa L.)

Large-scale application of hybrid rice that utilizes intra- or inter-subspecific heterosis increases yield dramatically in China. The successful development of elite hybr ids depends upon the sensible selection of parents. Further analysis of combining ability(CA) is considered the most efficient tool in selecting the desirable parents for developing hybrid rice. Therefore, further study on the genetic basis of CA, characterization and identification of genes for combining ability can help facilitate the genetic improvement and breeding practice by marker-assisted selection in r ice breeding program. In this study, using a set of introgression lines derived from a cross between an elite indica restorer Shuhui527 and an indica variety ZDZ057, some important chromosomal segments controlling general combining ability and heterosis for yield and its related traits were identif ied. A major quantitative trait locus qGGY6.1 controlling combining ability for grain yield per plant(GY) were fine mapped and characterized using a set of advanced backcross introgression lines in the genetic background of Shuhui527 and their testcross populat ions(derived from the introgression lines and four types of male sterile lines including II-32 A, Jin23 A, Gang 46 A and Xieqingzao A). The main results are as follows:1. By comparison of the genotypes between two restorer lines WD34 and WD7(the parents of two contrasting hybrids with different levels of yield advantages) and their recurrent parent Shuhui527(the parent of check combination) using the whole genome scanning of SSR markers and RiceSNP50 chip, it is found that they had similar genetic background with Shuhui527. The percentage of introgressed segments of WD34 and WD7 from the donor parent ZDZ057 was 9.3% and 14.9%, respectively. Three introgressed chromosomal segments from ZDZ057 were identified in WD34. Nine introgressed chromosomal segments from ZDZ057 were identified in WD7. The results of introgression chromosomal segments are consistent with the chromosomal segments identified using RiceSNP50 chip.2. Three contrasting hybrids and their parents with different levels of yield advantages were used for systematic investigation of heterosis at the whole growth stage, confirming that heterosis is a widespread phenomenon at seedling and maturity stage in rice.3. Here, we analyzed the genetic effects and main features of three QTLs associated with heterosis for GY and two QTLs associated with GCA for GY which located in the introgressed chromosomal segments of WD34 and WD7. The results suggested that the region of RM508-RM587 on chromosome 6 was an important region controlling GCA for GY. The region of RM224 on chromosome 11 might be an important region controlling heterosis for GY.4. Four testcross populations developed by crossing a set of advanced backcross introgression lines in the genetic background of Shuhui527 with four types of widely used male sterile lines(MSL) using the North Carolina II mating design were used to conduct GCA and heterosis analysis for yield and related traits under multiple environments(2013Hefei, 2014 Hefei and 2014Changsha). The contribution rates(CR) of GCA were higher than SCA of the parents in the testcross populations for all the nine traits in all the testing environments, suggesting that the additive effect play a key role in the performances of hybrids. Furthermore, a main effect QTL qGGY6.1 controlling GCA for GY was commonly identified in all the testing environments using the advanced backcrossing introgression lines.5. Near-isogenic lines in the genetic background of Shuhui527 that were developed by backcrossing and selfing introgression line heterozygous at qGGY6.1 locus were used for fine mapping. qGGY6.1 was fine mapped to a 230.5 kb region between markers RM589 and RM588 on chromosome 6 by screening recombinant individuals and progeny test. There were 29 predicted genes in the target region. Of these, 22 genes have been reported. The other seven genes are hypothetical proteins without supporting by full-length c DNA or EST.