Mapping Quantitative Trait Loci for Heading Date and Awn Length Using an Advanced Backcross Line from a Cross between Oryza sativa and O. minuta

An advanced backcross line, WH29001, was produced from a single plant from BC5F3 families derived from a cross between Oryza minuta (2n = 48, BBCC, Acc. No. 101141) as a donor parent and the O. sativa subsp. japonica cv. Hwaseongbyeo as a recurrent parent. Although WH29001 resembled Hwaseongbyeo, several traits were different from those of Hwaseongbyeo, including awn length and heading date. These differences between Hwaseongbyeo and WH29001 could be attributed to the introgressed O. minuta chromosome segments into WH29001. SSR analysis enabled to identify thirteen O. minuta-specific chromosome segments in WH29001 genome. To map and characterize QTLs for awn length and heading date, an F2:3 population from the Hwaseongbyeo/WH29001 cross was developed. The 197 F2 plants and 197 F3 families were evaluated for the two traits and the genotypes of the 197 F2 plants were determined using eighteen SSR markers located in the introgressed segments from O. minuta. QTL analysis identified two QTLs each for days to heading and awn length on chromosomes 6 and 9, respectively. The total phenotypic variance explained by these four QTLs ranged from 8.1% to 51.0% in the F3 population. Interestingly, QTLs for heading date and awn length were colocalized on chromosomes 6 and 9, respectively. Among these QTLs identified, the QTLs for heading date (dth9) and awn length (awn6) had not been detected in previous QTL studies between Oryza cultivars, indicating the existence of potentially novel alleles from O. minuta. The QTLs detected in the present study could become a valuable source of natural genetic variation underlying the evolution of rice.