QTL mapping and loci dissection for leaf epicuticular wax load and canopy temperature depression and their association with QTL for staygreen in Sorghum bicolor under stress
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AbstractPlant waxes and staygreen are distinct phenotypic traits that have been independently implicated in heat and drought tolerance among grasses. The association between these two traits has not been fully explored, which makes the exploitation of synergy between them difficult. This study assessed the association between QTL regulating the staygreen (Stg) trait in sorghum and those regulating epicuticular wax load (WL) and associated canopy temperature depression (TD). Using a recombinant inbred line (RIL) population derived from Tx642 and Tx7000, phenotypic data were collected in three replicated field trials and one greenhouse trial. High absolute TD generally corresponded to high WL. The r2 of TD against WL was highest under non-stress conditions in the greenhouse while it was much larger in the cooler and irrigated field conditions compared to hotter, drier field trials. The genetic correlations between the two traits also followed this pattern. Composite interval mapping identified a total of 28 QTL, 15 of which had significant overlaps between different traits. Most of the wax QTL were associated with pre-anthesis drought tolerant Tx7000. However, one QTL for WL overlapped with a QTL for staygreen (Stg2) and was represented by a single, isolated marker near the centromeric region on the short arm of SBI-01. The marker is identified by a Cis-acting regulatory module and is part of a 2-kb multifunctional motif-rich region which includes core promoter and enhancer regions and transcription elements, including a drought-responsive MYB binding site. We suggest that this QTL may be pleiotropic for important stress tolerance mechanisms regulating both staygreen and leaf wax in sorghum.
