DETERMINATION OF OF SEMI-LETHAL (LD50) DOSES FOR MUTATION BREEDING OF WINTER SQUASH (Cucurbita maxima Duch.) AND PUMPKIN (Cucurbita moschata Duch.)

Abstract

Mutation breeding is an alternative method for the development of new plant varieties. Success in mutation breeding, but, depends on the application of an appropriate dose of the mutagen. So, the aim of the present study was to determine the semi-lethal (LD50) gamma-ray doses for the induction of genetic variation in winter squash (Cucurbita maxima Duch.) and pumpkin (Cucurbita moschata Duch.) lines. Thus, the seeds were irradiated by a Cot source at five different gamma-ray doses (50, 100, 200, 300 and 400 Gy), and the efficacy of irradiation doses was tested for seed and seedling observations. While the seeds irradiated with doses up to 200 Gy resulted in similar germination and emergence performances as non-irradiated control seeds, drastic reductions were observed in germination and emergence at 300 and 400 Gy doses. Higher radiation doses led to detrimental effects on seedling growth parameters in all winter squash and pumpkin lines. The results showed that the germination and emergence rate, and the shoot and roots length decreased with increasing the radiation doses. Similarly, the number of weak and abnormal seedlings was also determined at the higher radiation doses. The results of linear regression analyses based on the shoot and root length, the LD50 doses were predicted between 160 and 190 Gy. These LD50 doses could be safely recommended to create desirable agronomic traits for the mutation breeding efforts in winter squash and pumpkin lines.