Chemically Induced Parthenocarpy in Certain Horticultural Plants, with Special Reference to the Watermelon

Abstract

No parthenocarpy, vegetative or stimulative, other than that due to hormone treatment, occurred in the watermelons and other spp. of Cucurbita tested, excepting cucumber and pepper. A very limited number of pollen grains did not cause the watermelon to set fruit. By adding a growth substance, however, mature fruits were obtained. Treated watermelon flowers which did not develop and mature parthenocarpic fruits yet persisted on the vine, apparently because the substances prevented the formation of an abscission layer. No apomictic seed of any sort developed in the parthenocarpic fruits produced from growth substances. A mixture of 2 growth substances gave better results than one alone; e.g., indolebutyric acid, acenaphthene. and sulfanilamide induced parthenocarpy when employed alone, but gave more favorable results when mixed with other substances. Indolebutyric acid (1-5%), acenaphthene (10%), and sulfanilamide (1.5%) in lanolin paste failed to induce parthenocarpic development in watermelon. Naph-thaleneacetic acid had a greater effect on parthenocarpic development than its K salt and other growth substances. There were great variations in fruit size and seed-coat development among the parthenocarpic fruits. Normal-sized hard seed coats were occasionally present in some fruits; however, seedless fruits of normal size which lacked seed coats were present in many spp. or certain vars. within the same horticultural group. Pre-treatment of watermelon seeds with proper dosage of colchicine prevented development of integuments into seed coats on parthenocarpic fruits. Mixing the colchicine with a growth substance in the paste applied to the cut style did not prevent such seed-coat development.