Pyramiding seed dormancy genes to improve resistance of semi-dwarf varieties to pre-harvest sprouting in rice

The quantitative trait locus SD1-2 for seed dormancy (SD) is identical to the semi-dawrf1 (sd1) gene prevailing in high-yield varieties of rice. However, sd1 alone appeared not sufficient to overcome the preharvest sprouting (PHS) problem in crop (or hybrid seed) production. This research aimed to address some genetic issues that may impact pyramiding of SD genes to improve semi-dwarf varieties for the PHS resistance. The isolated SD1-2, SD8, and SD10 loci were also associated with plant height (PH), awn or flowering time (FT), with the dormancy-enhancing alleles reducing stem elongation, increasing awned seeds, and promoting flowering, respectively. Allelic variants at SD1-2 and SD8 or SD10 were assembled in the same background as two digenic systems, each consisting of all the nine digenic genotypes. The two systems of plants were evaluated for the four traits and phenotypic data used to model trait correlations and the component additive, dominance, and epistatic effects of the two loci. FT was correlated with PH and germinability, but the correlations were opposite in direction between the two systems. Both additive and non-additive effects contributed to the variation for SD. All the three loci had effects on FT and PH in the digenic system(s). The SD10 alleles altered directions for effect on SD, with the late-flowering allele reducing germinability in the SD1-2 and SD10 system. This research demonstrated that genetic improvement of semi-dwarf cultivars for the PHS resistance involves proper selections for dormancy genes, recipient’s genetic backgrounds, and agronomic traits.