A QTL on chromosome 17 identified by Genome-Wide Association Mapping controls postharvest cold tolerance of Cucurbita...

The worldwide cultivated Cucurbita pepo L. is one of the most diverse species in the plant kingdom. In this study, chilling tolerance over a wide range of cultivars was characterized to discover the allelic variants to improving the postharvest quality of the immature fruit during cold storage. For this purpose, fruits from 126 accessions of worldwide origin have been evaluated for weight loss and chilling injury after 3, 7 and 14 days of cold storage, classifying them into tolerant, partially tolerant, and sensitive accessions. To verify this classification, antioxidant capacity and lipid peroxidation (MDA) of contrasting accessions (tolerant vs. sensitive) were assessed. The antioxidant capacity significantly decreased during cold storage in the sensitive accessions, while it was maintained in tolerant accessions. Additionally, the sensitive accessions presented a higher accumulation of MDA during this period. Finally, a GWAS analysis using GBS data available in CuGenDBv2, combined with weight loss percentage data, led to the identification of a candidate QTL located on chromosome 17 that regulates postharvest cold tolerance in zucchini. The region contains four SNPs whose alternative alleles were significantly associated with lower weight loss percentage and chilling injury indices during cold storage. Two SNPs are located in the 3' UTR region of the gene CpERS1, a gene involved in ethylene perception. The other two SNPs generate missense mutations in the coding region of a Pectin methyl esterase inhibitor gene (CpPMI). The role of this QTL and these variants in chilling tolerance is discussed.