Abstract

The influence of irradiation dose (50, 100, 200 and 300 Gray), irradiation time (July 9^th, 11^th, 15^th, 21^st and 28^th) and pollen age (0^th and 1^st days) on the pollen viability, germinability and fruit and seed-set were investigated in pumpkin (Cucurbita moschata Duchesne ex Poir.) and winter squash (Cucurbita maxima Duchesne ex Lam.). Along with increasing of irradiation dose, irradiation period and pollen age, pollen viability, germinability and fruit and seed-set decreased, significantly. Irradiated and non-irradiated pollens maintained their viability for 1 - 4 days and 4 - 7 days, respectively. Non-irradiated pollens of winter squash were germinated for 2 days and produced the highest germination rate (22.6 and 22.9%) on July 9^th and 11^th, respectively. Moreover, irradiated pollens were germinated for 2 days at 50 Gray (1.1 - 8.5%) and for one day at 100 Gray (0.6 - 10.4%). On July 9, the fruit-set rate ranged from 75.0% (at 50 Gray) to 63.0% (at 100 Gray) by pollination with 0^thday pollens in winter squash. Pollination with irradiated pollens at 50 Gray and 100 Gray gave both seeded and seedless fruits depending on irradiation periods. All fruits obtained from pollinations with non-irradiated pollens were seeded. Although irradiated pollens at 200 Gray and 300 Gray were not germinated in medium, they gave fruit more or less, but fruits were seedless. The highest fruit-set rates were determined 91.7 (57SI21) in winter squash and 26.3 (55BA01) in pumpkin, pollination with 0^th day old pollens. In all irradiation times, the percentage of fruit and seed-set of pumpkin was lower than that of winter squash.

Key words: Gamma irradiation, pollen viability and germinability, fruit and seed-set, pumpkin, winter squash.