Dissection of combining ability for yield and related traits using introgression lines in the background of a key restorer line in rice (Oryza sativa L.)

Combining ability analysis is commonly used to obtain information for designing more efficient hybrid breeding strategies in rice. However, genetic basis of combining ability is less studied. Two hundred and twenty eight testcross combinations developed by crossing 57 introgression lines derived from two donor parents with four types of widely used male sterile lines were used to conduct combining ability analysis and dissect the genetic basis of combining ability for grain yield and eight related traits. The variances of general combining ability (GCA) and special combining ability (SCA) for all nine traits were highly significant in both years. A total of 32 and 45 main effect QTL controlling GCA and SCA for the nine traits were identified across the two years, respectively. Only six QTL were commonly identified for GCA and SCA. Twenty one of the GCA QTL had the positive alleles from the recurrent parent, Shuhui527. Only 11 and six QTL were commonly detected in the two years, and in the two populations classified by the donor parents, respectively. As for SCA, 22 out of the 45 QTL were commonly identified in the two years and 25 QTL had positive effects. A total of 92 epistatic QTL pairs for GCA were identified. The Shuhui527 alleles at the markers RM508 and RM587 on chromosome 6 had the largest effects on GCA for GY and thus played important roles in making Shuhui527 a key parent in hybrid rice breeding. The ZDZ057 alleles at markers RM4584 on chromosome 7 and RM224 on chromosome 11 could be used to further improve GY GCA of Shuhui527.