Pyramiding Two Grain Weight QTLs GW2 and gw9 and their Interaction

Rice, one of the most important cereal crop in Asia is one of major food resource. In rice breeding, one of the major goal is grain yield, and the most important factors for grain yield are grain weight (GW), spikelet per penicle (SPP) and panicle number (PN). Quantitative traits loci (QTLs) for GW, GW2 and gw9 have been identified using progeny derived from crosses between the japonica cultivar Hwaseong and Oryza grandiglumis (IRGC 101154), and Hwaseong and O. rufipogon (IRGC 105491), respectively. The GW2 and gw9 alleles from wild species increased GW at two loci. This study was conducted to test whether two QTLs have epistatic interaction by phenotype and to analyze gene expression level of GW2 by quantitative real time PCR (qRT-PCR) in Hwaseong and gw9 near isogenic lines (NILs). We developed F2:3 lines by Marker assisted selection (MAS) which were developed by crossing two NILs harboring GW2 and gw9. Simple sequence repeat (SSR) markers tightly linked to the QTLs were used to check the genotype of F3 lines. F3 lines were divided into 4 groups based on their genotype at two loci, GW2 and gw9. A two-way ANOVA indicated that no epistatic interaction existed between the 2 QTLs in the F3 lines. 1000 grain weight (TGW) of homozygous plants with wild alleles at two loci was significantly higher than plants with a single QTL. These result indicate that two QTLs act addictively in distinct or complementary pathway in controlling grain weight.