Introgression of dwarfing allele dw1 reduced seed dormancy and increased pre‐harvest sprouting susceptibility in grain sorghum converted lines

Abstract

Grain sorghum (Sorghum bicolor L. moench) stands as a globally significant cereal crop but theadversity of pre-harvest sprouting (PHS) caused by reduced grain dormancy and moist conditionsprior to harvest remains unsolved. Here, we identified a dormancy QTL using a Redlan×IS9530RIL population, where parent lines are low in tannins and early flowering but otherwisecontrasting in grain dormancy and plant height. We phenotyped this population in 2 years withinformative PHS-related traits (grain germination index, embryo sensitivity to abscisic acid and inone year the actual natural sprouting), revealing a robust dormancy QTL in chromosome 9(qDOR-9). This signal overlapped with associations found for plant height (caused by the dw1locus, used for decades in sorghum improvement) and time to flowering. The effect of qDOR-9was validated with independent near isogenic lines carrying the IS9530 “dormant” allele whilemaintaining the Redlan dw1 “short” allele. Additional analyses on Yellow Milo, from which thedw1 allele originated, implied that a low dormancy allele close to dw1 was introduced to Redlan—as well as to many other currently productive lines—by breeding efforts aimed at decreasingplant height, thus illustrating a new instance of genome erosion canalised by crop breeding.However, the introgression of qDOR-9 could enhance PHS tolerance in cultivated dw1-carryingbackgrounds without affecting plant stature.