Mapping Quantitative Trait Loci for Grain Traits Using Near Isogenic Line from a Cross between Oryza minuta and O. sativa

Introgression has been achieved from wild species Oryza minuta (2n=48, BBCC, Acc. No. 101141) into O. sativa subsp. japonica cv. Hwaseongbyeo. Hwaseongbyeo was used as a recurrent parent and O. minuta as a donor parent. An advanced backcross line, WH79006 produced from a single plant from BC₅F₃ families, resembled Hwaseongbyeo, but it showed differences from Hwaseongbyeo in grain traits including 1,000 seed weight (TSW). These differences between Hwaseongbyeo and WH79006 could be attributed to the introgression of O. minuta chromosome segments into WH79006. To identify and characterize the effects of alien gene(s) introgressed into WH79006, the F₂ and F₃ populations from the cross between Hwaseongbyeo and WH79006 were developed. The 75 F₂ plants were evaluated for 8 traits in 2003 and their progeny, the 75 F₃ lines for 12 agronomic traits in 2004. Genotypes were determined for 75 F₂ plants using simple sequence repeat (SSR) markers. QTL analysis was carried out to determine the relationship between marker genotype and the traits evaluated. A total of nineteen QTLs were identified using single point analysis. Among these, 4 QTLs were detected on chromosomes 7, 10 and 11 in the F₂ population, which explained ranging from 5.7 to 12.6% of the total phenotype variation. Fifteen QTLs were detected on chromosomes 3, 5, 7, 8, 10 and 11 in the F₃ population, which explained 4.3 to 13.5% of the phenotype variation. The number of QTLs detected per chromosome ranged from 1 to 4 in both populations. Comparison of QTLs indicated that four QTLs associated with days to heading (dth), 1,000 seed weight (tsw), seed length (sl) and L/W ratio of seed (lw) were shared in both populations and the remaining 11 only in the F₃ population. Among these QTLs identified, nine QTLs have not been detected in previous QTL studies between Oryza cultivars, indicating potentially novel alleles from O. minuta. The QTLs detected in this study could be a rich source of natural genetic variation underlying the evolution and breeding of rice.