Abstract:

Introgression lines in crops have been proposed as an attractive and powerful way to identify quantitative trait loci (QTLs) affecting importance traits. Here we report construction of a set of contiguous segment substitution lines (CSSLs) in rice through repeated backcrossing and molecular marker-assisted selection (MAS). These CSSLs were derived from a cross between the sequenced japonica cv. Nipponbare as donor and indica cv. 9311 as recurrent parent, which is also known as an elite restorer line of super-hybrid rice in China. The advanced backcross generations (BC3 and BC4) were subjected to three rounds of MAS to select lines with single or few japonica introgression chromosomal segments. One hundred and twenty-five polymorphic SSR markers evenly distributed on rice genome were used in the MAS scheme. A set of 125 CSSLs was determined by graphical genotypes, each of lines contained a single or few chromosomal introgression segments with the indica background, all the overlapped segments covered the whole genome of japonica. The genome proportion of the recurrent parent in each of the CSSLs ranged from 93.8% to 99.9%, with an average of 98.4%. The average proportions of homozygous and heterozygous donor segments were 1.4% and 0.2%, respectively. The average length of introgression segments was 20.9 cM, ranging form 2.9 to 63.9 cM. In order to illustrate a potential application and validate these CSSLs, the phenotypic effects of the japonica introgressions on the panicle-related traits (panicle weight, panicle length, seed setting rate and degenerated spikelet of top panicle) were analyzed. Thirty-one QTLs were detected for the four panicle-related traits in two year (site) trials. The all japonica alleles at those QTLs for panicle weight and seed setting had negative effects. The set of CSSLs will provide a useful genetic stock for functional identification of genes conferring phenotypic variations between subspecies and for the subspecies breeding.

Key words: Oryza sativa L., Marker-assisted selection (MAS), Contiguous segment substitution lines (CSSLs)