Cucurbit Genetics Cooperative Report 10:104 (article 54) 1987

Cold Tolerance in the Cucurbitaceae

R. W. Robinson

Horticultural Sciences Department, New York State Agricultural Experiment Station, Geneva, NY

All cultivated cucurbits prefer warm temperature. They are subject to chilling injury and are very sensitive to frost. A very light frost, not sufficiently cold to injure other tender crops such as beans and tomatoes, may blacken the leaves of squash plants. Numerous accessions of wild species of Cucumis, Cucurbita, Citrullus and other genera of the Cucurbitaceae have been grown at Geneva, New York in recent years but none was found to have a useful degree of frost tolerance that might be transferred by conventional breeding techniques to a cultivated cucurbit. One cucurbit, however, that proved to be remarkably frost tolerant is Ecballium elaterium (L.) A. Rich. A frost 10 hours long and as low as -40°C killed all other cucurbits in the field but did not injure the foliage of this species, although it caused the fruit to lose their capacity to forcibly eject seed. Two months later, when the ground was covered by snow in December, the foliage of E. elaterium was still green and showed no evidence of injury from the cold. The plants did not survive the winter, but volunteer plants from overwintering seed were abundant the next season.

Cucurbita ficifolia Bouché, a native of high elevations, appears to be well adapted to low temperature. Although it appeared to be equally sensitive to killing frost, it was more tolerant than other Cucurbita species to temperatures between 0 and 10°C. The onset of cold weather in the fall caused other Cucurbita species to cease floral and vegetative development, but C. ficifolia continued to grow vigorously and flower profusely. Most accessions of this species are short day plants and do not flower at Geneva, NY until shortly before frost, too late to make crosses in the field. It was possible, however, to make interspecific crosses in September by pollinating C. pepo plants in the greenhouse with pollen from field grown C. ficifolia. The C. ficifolia plants produced abundant, functional pollen despite the chi11ing temperatures during microsporogenesis. The fruit of C. ficifolia are tolerant of chilling temperature. When fruit of C. ficifolia and different cultivars of C. pepo, C. maxima, and C. moschata were stored at 5°F, all except C. ficifolia quickly rotted. Fruit of C. ficifolia have a very long storage life; fruit remained in sound condition for over a year when stored at room temperature, but storage life was shortened by prolonged exposure to chilling temperature.

Cyclanthera pedata (L.) Schrad. has edible fruit that may be eaten raw, like cucumber, or cooked like summer squash. It grows well at low temperature, and continued to be productive in the fall after fruit production of cucumbers and summer squash was curtailed by low temperature.