Exploitation of heterosis loci for yield and yield components in rice using chromosome segment substitution lines

We constructed 128 chromosome segment substitution lines (CSSLs), derived from a cross between indica rice (Oryza sativa L.) 9311 and japonica rice Nipponbare, to investigate the genetic mechanism of heterosis. Three photo-thermo-sensitive-genic male sterile lines (Guangzhan63-4s, 036s, and Lian99s) were selected to cross with each CSSL to produce testcross populations (TCs). Field experiments were carried out in 2009, 2011, and 2015 to evaluate yield and yield-related traits in the CSSLs and TCs. Four traits (plant height, spikelet per panicle, thousand-grain weight, and grain yield per plant) were significantly related between CSSLs and TCs. In the TCs, plant height, panicle length, seed setting rate, thousand-grain weight, and grain yield per plant showed partial dominance, indicating that dominance largely contributes to heterosis of these five traits. While overdominance may be more important for heterosis of panicles per plant and spikelet per panicle. Based on the bin-maps of CSSLs and TCs, we detected 62 quantitative trait loci (QTLs) and 97 heterotic loci (HLs) using multiple linear regression analyses. Some of these loci were clustered together. The identification of QTLs and HLs for yield and yield-related traits provide useful information for hybrid rice breeding, and help to uncover the genetic basis of rice heterosis.