Cucurbit Genetics Cooperative Report 1:33 (article 30) 1978
Genetic differences in Sex Expression and Response to Ethephon in Summer Squash, Cucurbita pepo L.
S. Shannon and R. W. Robinson
New York Agricultural Experiment Station, Geneva, NY 14456
Problems have been encountered in the commercial production of hybrid seed of summer squash when recommended rates of ethephon application were used to inhibit staminate flower production on the maternal inbred parent. The label recommendation of 88 g ethephon/ha in 370 to 940 l (100 to 250 ppm) applied once in the 2-leaf stage has often been insufficient to prevent staminate flower formation, and costly manual removal of staminate flowers has been necessary to prevent self-and sib-pollination of the maternal parent of a hybrid. Experiments were therefore conducted with different concentrations and times of application under actual commercial conditions in the field for seed production of summer squash. These tests were conducted in cooperation with the Robson Seed Co.
Three monoecious inbred lines of Cucurbita pepo differing in degree of femaleness were used as maternal parents. They included a strongly female 'Cocozelle' type, a strongly male 'Yellow Crookneck' inbred, and a 'Yellow Straightneck' line of standard monoecious type. Ethephon was applied the first year at rates of 125 to 375 ppm in 1 to 3 applications, but none of these treatments reduced staminate flower formation sufficiently to permit. hybrid seed production without manual defloration of the maternal parent. The next year one to three applications of 200 to 600 ppm was applied at different stages of seedling development. The 600 ppm rate applied at the 2 and 4 leaf stages was the most effective treatment for reducing male flower formation. None of the treatments affected seed yield or quality.
Genetic differences in responsiveness to ethephon were noted. The 'Yellow Crookneck' inbred, the most strongly male line in the tests, was the inbred least responsive to ethephon.