Disease Resistance and Yields of Transgenic and Traditional Summer Squash

Abstract

Kentucky vegetable growers exploiting a fall-harvested market window for summer squash (Cucurbita pepo L.) usually encounter severe virus and fungal disease pressure resulting in serious yield and quality reductions. Twenty-five summer squash varieties or advanced breeding lines (9 zucchini, 8 yellow straightneck, and 8 crookneck entries) were evaluated in a late summer planting for yield, quality, and disease resistance at the Univ. of Kentucky South Farm in Lexington. Both genetically engineered virus-resistant materials and new resistant/tolerant varieties from traditional breeding programs were compared with our recommended hybrids. Border rows of a virus-susceptible variety were planted alongside and between each of the four blocks to enhance virus spread throughout the trial. Virus incidence was determined visually before and after final harvest and leaf samples were collected for virus assays. Virus symptoms were absent or difficult to see on zucchini squash plants during most of the trial but became obvious near the final harvest date. Varieties from traditional breeding programs having virus tolerance were among the highest yielding zucchini types. Traditionally-bred cultivars with the precocious yellow gene and two transgenic lines were in the highest yielding group of yellow straightneck squash—in spite of high virus incidences in precocious yellow cultivars. Transgenic cultivars were clearly superior in terms of yields among yellow crooknecks with yields nearly double those of the lowest yielding traditional hybrids. Cultivars and breeding lines varied considerably in color, shape, overall appearance, and potential marketability.