Abstract
SummaryUnlike most of the important food crops, sesame can survive drought but severe and repeated drought episodes, especially occurring during the reproductive stage, significantly curtail the productivity of this high oil crop. Genome‐wide association study was conducted for traits related to drought tolerance using 400 diverse sesame accessions, including landraces and modern cultivars. Ten stable QTLs explaining more than 40% of the phenotypic variation and located on four linkage groups were significantly associated with drought tolerance related traits. Accessions from the tropical area harboured higher numbers of drought tolerance alleles at the peak loci and were found to be more tolerant than those from the northern area, indicating a long‐term genetic adaptation to drought‐prone environments. We found that sesame has already fixed important alleles conferring survival to drought which may explain its relative high drought tolerance. However, most of the alleles crucial for productivity and yield maintenance under drought conditions are far from been fixed. This study also revealed that pyramiding the favourable alleles observed at the peak loci is of high potential for enhancing drought tolerance in sesame. In addition, our results highlighted two important pleiotropic QTLs harbouring known and unreported drought tolerance genes such as SiABI4, SiTTM3, SiGOLS1, SiNIMIN1 and SiSAM. By integrating candidate gene association study, gene expression and transgenic experiments, we demonstrated that SiSAM confers drought tolerance by modulating polyamine levels and ROS homeostasis, and a missense mutation in the coding region partly contributes to the natural variation of drought tolerance in sesame.
Highlights
Sesame (Sesamum indicum L., 2n = 26) is a traditional oilseed crop with one of the highest oil contents and qualities amongst the major oil crops
The genotypic dataset resulting from the data cleaning pipeline and imputation was composed of 1 000 939 SNPs covering all the 16 linkage groups (LGs) of the sesame genome
The LG14 encompassed the lowest number of SNPs (23 371) while the LG3 had the highest number (103 814)
Summary
Sesame is grown in arid and semi-arid areas characterized by high temperatures, high levels of solar radiation, high evaporative demand and unpredictable drought episodes which greatly impair the productivity (Hassanzadeh et al, 2009; Witcombe et al, 2007). Several traits of the plant have been reported to be affected by drought stress including the germination rate, plant growth, flowering, number of capsules per plant, seed yield as well as oil yield and quality (Bahrami et al, 2012; Boureima et al, 2016; Hassanzadeh et al, 2009; Kassab et al, 2012; Sun et al, 2010). Sesame seed yields are generally low (300–400 kg/ha) in most of the arid and semi-arid areas (Islam et al, 2016)
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