Two Contrasting Patterns and Underlying Genes for Coadaptation of Seed Dormancy and Flowering Time in Rice

Association between seed dormancy (SD) and flowering time (FT) may generate a synergy in plant adaptation. This research aimed to identify patterns and underlying genes of the association in rice (Oryza sativa). Four F₂ and two BC₁F₁ populations from crosses of weedy/cultivated rice, and two families of progeny lines from backcrosses were evaluated for variations in time to flowering and germination ability. The two measurements were correlated negatively in the F₂ and BC₁F₁ populations, but positively in advanced generations of the progeny lines. The negative correlations were resulted from linkage disequilibria between SD and FT loci at 7-40 cM apart. The positive correlations arose from co-located SD and FT loci undetectable in the BC₁F₁ population. Two independent sets of co-localized loci were isolated as single Mendelian factors, and haplotypes that promote flowering and reduce germination derived from weedy and cultivated rice, respectively. The presence of negative and positive correlations indicates that the rice complex has maintained two contrasting patterns of SD-FT coadaptation, with the positive being "recessive" to the negative pattern. Modeling with isogenic lines suggests that a negative pattern could generate a greater synergy (difference between haplotype variants) than the positive one for seedbank persistence, or enhanced plant adaptation to seasonal changes in temperature or moisture. However, the early-flowering dormant genotype of a positive pattern could also have a selective advantage over its counterpart for weeds to avoid harvesting. The isolated haplotypes could be used to manipulate cultivars simultaneously for germination ability and growth duration.