Bigenic epistasis between QTLs for heading date in rice analyzed using single segment substitution lines

Accumulating evidences suggested that epistasis, interactions between genes, is an important component of the genetic determination of quantitative traits. In present study, four F2 populations derived from pair wise crosses between 5 single segment substitution lines in the HJX74 background, harboring single QTL for heading date including Hd3a, RFT1, OsFTL13, OsMADS50IR64 and OsMADS50Lemont were used to characterize the epistasis between QTLs and QTL-by-environment interaction (QEI). Epistasis was found to be present between Hd3a and OsMADS50IR64, Hd3a and OsMADS50Lemont, and RFT1 and OsMADS50IR64. The interaction between Hd3a and OsFTL13 was not detected by single environment analysis but detected by across-environment combined analysis. Genetic analysis using a bigenic model showed that the additive and dominant effects were more important than the overall epistatic effects for all pairs of QTLs. The additive-by-additive and additive-by-dominant effects were more important than the dominant-by-dominant effect. QEIs were significant for Hd3a, RFT1, OsMADS50IR64 and OsMADS50Lemont but not for OsFTL13. The additive-by-environment and dominant-by-environment interaction effects were significant while the epistasis-by-environment interaction was not. Utilization of the known major QTLs for heading date in breeding through gene pyramiding needs take epistasis into consideration.