BSAseq analysis reveals two major QTLs contributing to postharvest cold tolerance in Cucurbita pepo

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Zucchini has a subtropical origin, therefore, physiological disorders such as chilling injury (CI) appear when the fruit is stored at low temperatures. This affects the quality and shelf life of these commodities. Cold tolerance throughout this period depends on the variety; Natura and Sinatra are contrasting cultivars for this trait, and abscisic acid (ABA) is a key metabolite conferring this resistance in zucchini. Physiological differences between these cultivars have been previously reported, but the complete regulation and molecular mechanisms that control this trait are still unknown. Thus, this work aimed to identify genomic regions and genes involved in the postharvest cold tolerance of zucchini fruit. NxS segregating populations were evaluated for weight loss (% WL) and chilling injury (CI Index). The observed segregation ratio (1:2:1) suggests that postharvest chilling tolerance in Natura is controlled by at least one semidominant gene. QTL analysis was performed using BSAseq of two contrasting DNA bulks for postharvest cold tolerance. The results revealed two major QTLs on chromosomes 5 and 18 controlling postharvest cold tolerance in Zucchini squash. Fine mapping validation of QTLs indicated that each contributed to a percentage of the phenotypic variation observed in the segregating population. Therefore, QTL5 and QTL18 exhibited additive effects on the postharvest chilling tolerance of the fruit. Candidate genes in these QTLs, including those involved in cell wall remodeling, such as two CpXTH genes, along with two genes involved in the biosynthesis of cold tolerance-related metabolites ( CpC4H , CpPGK ). In addition, two WRKY family transcription factors showed differential expressions between fruits of both cultivars. The putative function of these candidates in the postharvest cold tolerance of zucchini is discussed. • The evaluation of the NxS offspring reveal segregation for % WL and CI Index. • ABA levels are negatively correlated with %WL in the NxS segregating population. • Two QTLs in chromosomes 5 and 18 are controlling postharvest quality. • Both QTLs contribute additively to %WL and CI Index, with QTL5 higher influence. • Candidate genes identified, including those with genetic variants, are discussed.

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