A Gamma-ray-Induced Dwarf Mutant from Seeded Bermudagrass and Its Physiological Responses to Drought Stress

Breeding for dwarf-type bermudagrass (Cynodon dactylon) with enhanced drought resistance is important for producing quality turf with reduced irrigation. A dwarf-type mutant (S-20-1) that exhibits slower vertical growth, and shorter internodes and leaf length was selected from the gamma-ray-irradiated seeds of a bermudagrass cultivar Sundevil II (S-CK). S-20-1 had slower turf coverage than S-CK. Compared with S-CK, the vertical growth of S-20-1 was more promoted by gibberellin (GA(3)) treatment. S-20-1 showed an enhanced drought resistance in greenhouse and field tests. Under drought stress, S-20-1 maintained higher relative water content and lower levels of ion leakage, malondialdehyde, and leaf firing than S-CK. Antioxidant enzyme activities and antioxidant content showed no difference between S-20-1 and S-CK under well-watered conditions, while higher enzyme activities were maintained in S-20-1 under drought stress. Free proline accumulated in response to drought stress and showed a positive correlation to the increased ion leakage, while S-20-1 had lower levels than S-CK. Our results indicated that the dwarfism in S-20-1 induced by gamma-ray irradiation might be the result of less GA3 or decrease of sensitivity to GA3 in the mutant. The improved drought resistance of the mutant is associated with maintenance of higher levels of antioxidant enzyme activities. More accumulation of proline in S-CK than S-20-1 reflected a physiological response to the drought-induced injury rather than an association with drought resistance of S-20-1.