Nerson, H., Department of Vegetable Crops, Agricultural Research Organization, Newe Ya'ar Research Center, P. O. Box 1021, Ramat Yishay 30095, Israel

Greenhouse experiments were conducted in the Newe Ya'ar Research Center, Israel, during the autumn and winter of 1999-2000, to examine whether muskmelons (Cucumis melo L.) are capable of setting parthenocarpic fruits without external induction. The cultivars CNY and CKR differed markedly in their ability to produce pistillate flowers under the experimental conditions. Nevertheless, both cultivars did set parthenocarpic fruits spontaneously, after emasculation and covering of the female flowers. In the autumn (late November), parthenocarpic fruit-set was promoted by cool night temperatures. However, the unfavourable winter climate (late January) limited fruit set in both parthenocarpic and pollinated treatments. There were no significant differences in fruit number per plant or in mean fruit weight between plants subjected to active hand pollination and those that underwent passive (covering pistillate flower without emasculation) self-pollination, but the plants in each of these treatments produced more fruits than those in the parthenocarpy treatment. As expected, parthenocarpic fruits had no viable seeds. Fruits developed by passive pollination had significantly fewer seeds than those developed by active pollination treatments, but their seeds were larger and exhibited inferior germination. Pollen source (self or cross) had no significant effects on fruit set or on fruit weight, but it significantly affected the number of fully developed seeds in CKR in the autumn experiment. Comparison between the data on numbers and weights of seeds and fruits in the passive and in the active pollination treatments suggest that there is no cause-effect relationship between seed and fruit development in muskmelons.