QTLs for hybrid fertility and their association with female and male sterility in rice

Hybrid sterility is one of the major barriers to the application of wide crosses in plant breeding and is commonly encountered in crosses between indica and japonica rice varieties. Ten mapping populations comprised of two reciprocal F2 and eight BC₁F₁ populations generated from the cross between Ilpumbyeo (japonica) and Dasanbyeo (indica) were used to identify QTLs and to interpret the gametophytic factors involved in hybrid fertility or sterility between two subspecies. Frame maps were constructed using a total of 107 and 144 STS markers covering 12 rice chromosomes in two reciprocal F2 and eight BC₁F₁ populations, respectively. A total of 15 main-effect QTLs and 17 significant digenic-epistatic interactions controlling spikelet fertility (SF) were resolved in the entire genome map of F₂ and BC₁F₁ populations. Among detected QTLs responsible for hybrid fertility, four QTLs, qSF5.1 and qSF5.2 on chromosome 5, qSF6.2 on chromosome 6, and qSF12.2 on chromosome 12, were identified as major QTLs since they were located at corresponding positions in at least three mapping populations. Loci qSF5.1, qSF6.1 and qSF6.2 were responsible for both female and male sterility, whereas qSF3.1, qSF7 and qSF12.2 affected the spikelet fertility only through embryosac factors, and qSF9.1 did through pollen factors. Five new QTLs identified in this study will be helpful for understanding the hybrid sterility and for breeding programs via inter-subspecific hybridization.     

Identification of QTLs for hybrid fertility in inter-subspecific crosses of rice (Oryza sativa L.)

Two subspecies in rice, japonica and indica, have their own ecotypic traits. However, reproductive barriers such as spikelet sterility in hybrid progenies between subspecies have been an obstacle in breeding programs for combining desirable traits from both subspecies through inter-subspecific hybridization. The 166 F₉ RILs and two BC₁F₁s’ were analyzed for spikelet and pollen fertility with the parents and F₁ between Dasanbyeo (DS, indica) / TR22183 (TR, japonica). A frame map was constructed using a total of 218 polymorphic STS and SSR markers. In both BC₁F₁s’ of DS//DS/TR and TR//DS/TR, clusters of significant QTLs for spikelet and pollen fertility were identified on the short arm of chromosome 5 and chromosome 8. Nine and ten digenic epistatic interactions for DS//DS/TR and TR//DS//TR were identified, respectively. HF-QTLs were detected at the similar position with subspecies-specific markers and segregation distortion loci, implying that HF-QTLs might be associated with the differentiation of indica and japonica. Hybrid fertility/sterility and its relationship with other traits are discussed in relation to the reproductive barriers between subspecies of rice.