Postharvest cold tolerance in summer squash and its association with reduced cold-induced ethylene production

Tolerance to postharvest chilling injury (PCI) is becoming an ever more essential trait for export-oriented vegetables requiring refrigerated transport and/or storage. Summer squash, Cucurbita pepo, is highly subject to PCI. We screened a collection consisting of 80 long-fruited accessions of morphotypes zucchini, cocozelle, and vegetable marrow for cold tolerance. Of these, we selected the most cold tolerant and some of the least cold tolerant for further scrutiny. Fruits from each accession were stored for 7 and 14 days at 4 degrees C before evaluating PCI, weight loss (WL) and ethylene production. Several accessions, including CpCAL003, CpCAL053 and CpCAL051, showed tolerance to PCI, with a lower percentage of the fruit surface suffering injury and WL at 4 degrees C. The mode of inheritance of tolerance to PCI index and WL was investigated by crossing the tolerant accession designated CpCAL003 with the susceptible CpCAL112, and observing their filial-and backcross-generation progenies. The results indicate that cold tolerance is not conferred by a single gene, but rather is quantitatively inherited trait. Cold-induced ethylene production co-segregated with PCI susceptibility. Thus, ethylene production under cold storage can be used as physiological indicator in selecting for PCI tolerance in summer squash.