Screening For Resistant Mutant To Alternaria Brassicae From Radish Seeds Irradiated With ～(60)Co Gamma Ray

Radish (Raphanus sativus L.) ,also named as laifu ,is one kind of anual or biennial herbaceous vegetable belonging to cruciferae. It is one of the most popular and widely consumed vegetables in China and Japan. Because of its special flavor and medical use, radish becomes a very important vegetable in people's life. Alternaria brassicae is epidemic in spring and autumn, especially in recent years, and chemical prevention is ineffective sometimes. Disease resistance breeding becomes increasingly important.After radiation the seeds will engender some mutations in some characters. Mutants appears at different frequency when the seeds are radiated. Most mutations are recessive, while the dominant mutation frequency is definitely low. 60Co γ ray is very frequently used in radiation for its high efficiency. In this study, we aimed at obtaining dominant mutations of radish on Alternaria brassicae resistance through this strategy.The methods of identifying resistant mutants to Aternaria brassicae in vitro inoculating were studied. The radiosensitivity to 60Co γ ray was investigated on the seeds from three radish cultivars, Zhedachang, Zuixiantao and Shizhuangbai. Three generations of mutations, named as Ml, M2 and M3, were screened by the pathogen of Alternaria brassicae, and different screening methods were compared. The main results are as follows:1. It was found that the method of in vitro dropping was more stable than the in vitro spraying method in the resistant mutants screening to Alternaria brassicae. The optimal concentration of the pathogen concentration was 2500 spores per ml in the dropping inoculates.2. Radish is relatively insensitive to radiation, 'and the half lethal dose of 60Co γ ray was 1500-2000 gray. There was slight difference on radiation sensitivity among different radish cultivars.3. Two resistant lines in the cultivar of Zhedachang, 5 in Zuixiantao and 2 in Shizhuangbai were obtained after 3 generations of Alternaria brassicae screening.4. The proportion of resistant plant in the second generation could used to estimate the possible existence of dominant resistant mutants.