Construction of chromosomal segment substitution lines and genetic dissection of introgressed segments associated with yield determination in the parents of a super-hybrid rice

Heterosis is a phenomenon whereby hybrids of inbred lines produce favourable phenotypes that exceed those of their parents. Traits of interest are higher yield and stronger stress tolerance. The two-line super-hybrid rice ‘Liangyoupei9’ (LYP9) shows superiority to both its elite inbred line ‘93-11’ and ‘Pei'ai64s’ (‘PA64s’) parents and conventional hybrids. However, the genetic basis of its hybrid vigour, especially yield determination, remains elusive. In the present study, a set of 156 chromosome segment substitution lines (CSSLs) carrying overlapping segments from ‘PA64s’ in a genetic background of ‘93-11’ were constructed and planted in six environments. Three major agronomic traits, viz. panicle length (PL), heading date (HD) and plant height (PH), and five yield-related traits, viz. grain weight per panicle (GWP), number of grains per panicle (GPP), 1000-grain weight (TGW), seed set (SS) and number of panicles of per plant (PPP), were evaluated over 3 years. Quantitative trait loci (QTL) analysis was conducted using a likelihood ratio test based on stepwise regression. Forty-six putative QTL distributed on 11 chromosomes were detected in more than one year. Remarkably, GWP of four CSSLs carrying positive yield QTL outperformed the recurrent parent ‘93-11’ by more than 15%, in at least two environments. These results indicate that CSSLs are effective in identifying yield-associated traits, and lines harbouring such QTL will be rich in resources for future molecular breeding programmes.