Assessment of seed chilling, GA3 foliar application, girdling, and grafting as affecting transition to functional flowering in pumpkin

ABSTRACT Temperature is a factor governing the transition for pumpkin (Cucurbita spp. L) from vegetative to reproductive growth that is necessary for fruit and seed production. Under high-temperature plants may not flower at all. An experiment investigated functional flowering induction of a recalcitrant-to-flower cv. El-Zarka (C. maxima Duchesne) in response to foliar GA3 application, pre-sowing seed chilling, vine girdling, and grafting on rootstock of the ready-to-flower cultivar cv. Kafr El-Battikh (C. moschata Duchesne ex Poir.). The recalcitrant cv. flowered when subjected to all treatments. The best responses were GA3 at 10 mg∙L−1, seed imbibed for 36 h and subjected to chilling (4–5°C) for 12 d, vine girdling of 30-day-old plants, and grafting onto rootstock of 7–10-day-old plants of the ready-to-flower cultivar. Transition to flowering in the ready-to-flower and recalcitrant-to-flower cvs. was consistently accompanied by an elevation in leaf total sugar content. Female flower percent was positively associated with enhanced fruit yield and flesh quality. Isozyme analyses exhibited shared bands for seed chilling with application of GA3 and another between girdling and grafting. The common consistent elevation of leaf total sugar content indicates flowering may be mediated via sugar signaling plus carbohydrates availability (response limiting factor). The methods tested appear to control flowering recalcitrance in pumpkins.