Stay-Green QTLs Response in Adaptation to Post-Flowering Drought Depends on the Drought Severity

Stay-green trait enhances sorghum adaptation to post-flowering drought. Six stay-green backcross introgression lines (BILs) carrying one or more stay-green QTLs (Stg1-4) and their parents were characterized under non-stress (W(100): 100% of soil field capacity (FC)) and two levels of post-flowering drought (W(75): 75% FC; W(50): 50% FC) in a controlled condition. We aimed to study the response and identify the drought threshold of these QTLs under different levels of post-flowering drought and find traits closely contributing to grain yield (GY) under different drought severity. W(50) caused the highest reduction in BILs performance. From W(100) to W(50), the GY of the recurrent parent reduced by 70%, whereas that of the BILs reduced by only 36%. W(75) and W(50) induce different behavior/response compared to W(100). Harvest index contributed to the GY under the three water regimes. For high GY under drought transpiration rate at the beginning of drought and mid-grain filling was important at W(75), whereas it was important at mid-grain filling and late-grain filling at W(50). Stay-green trait can be scored simply with the relative number of green leaves/plants under both irrigated and stress environments. QTL pyramiding might not always be necessary to stabilize or increase the GY under post-flowering drought. The stay-green QTLs increase GY under drought by manipulating water utilization depending on drought severity.