Priming effects of gamma radiation on the mitigation of drought stress: The morpho-physiological responses of Oenothera speciosa Nutt

Radiation-induced priming is a potent method for improved stress tolerance under adverse conditions, such as drought. Therefore, this experiment was conducted to investigate the morphological and physiological responses and drought tolerance indices of Oenothera speciosa genotypes exposed to different doses of gamma rays and to determine the appropriate dose of radiation for the use in drought stress tolerance programs in this species. Seeds from three genotypes of O. speciosa were exposed to different levels of gamma radiation, including 50, 100, 200, and 300 Gy for 21' 22'', 42' 44'', 85' 28'' and 128' 12'', respectively. Then, treated seeds were sown in pots, grown in the greenhouse, and transferred to the field. The field experiment was carried out based on a randomized complete block experimental design with three replications for 3 months. The plants were irrigated weekly under normal conditions until the early flowering stage. Afterward, irrigation continued to maintain the minimum soil moisture at 50 % (normal condition) and 15 % (drought condition) of field capacity for two months. The growth and physiological traits associated with tolerance to drought stress of plants were examined from the flowering stage onward. The study revealed a notable rise in plant height, fresh weight, thousand-grain weight, flowers per plant, seed yield, total carbohydrate content, DPPH radical scavenging capacity, anthocyanin content, ascorbate and glutathione contents, oil content, and a significant drop in electrolyte leakage, H2O2, and malondialdehyde contents in all 3 genotypes of O. speciosa, exposed to all gamma irradiation levels, under both drought and normal irrigation conditions. In addition, OS3 was the best genotype responding to gamma irradiation related to its higher seed yield and plant dry weight-based drought tolerance indices. According to the results of the present study, it is concluded that the impacts of O. speciosa seed priming with gamma radiation may result in a significant increase in tolerance to drought stress conditions.