Abstract
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 (W100: 100% of soil field capacity (FC)) and two levels of post-flowering drought (W75: 75% FC; W50: 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. W50 caused the highest reduction in BILs performance. From W100 to W50, the GY of the recurrent parent reduced by 70%, whereas that of the BILs reduced by only 36%. W75 and W50 induce different behavior/response compared to W100. 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 W75, whereas it was important at mid-grain filling and late-grain filling at W50. 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.
Highlights
The global population will increase to 9 billion by 2050 and most of the increase will occur in sub-Saharan Africa [1], increasing the risk of food insecurity in this region [2]
The results indicated that harvest index (HI) contribution to the grain yield (GY) in the staygreen backcross introgression lines (BILs) was significant under the three water regimes (W100, W75, and W50) (Figure S1)
Our results indicated that HI, plant height (PH), transpiration rate (TR), and photosynthesis rate (PR) are the major traits contributing to the GY at all soil moisture levels (Table 1, Figure 6)
Summary
The global population will increase to 9 billion by 2050 and most of the increase will occur in sub-Saharan Africa [1], increasing the risk of food insecurity in this region [2]. The productivity of sorghum, the major cereal crop grown for food, feed, and fuel, is usually under threat of terminal drought, which is likely to occur in rainfed environments during grain filling [5]. Over the last 30 years, the stay-green trait has been used in breeding programs for improvement of sorghum terminal drought tolerance [11, 12]. The quantitative trait loci (QTLs) that contribute to the stay-green trait have been mapped in a range of populations, mostly derived from crosses with B35, a derivative of an Ethiopian
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