| Black spot disease of Chinese cabbage is caused by Alternaria genus not only frequently occurs in Chinese cabbage, but also widely occurs in the world. As the rapid developing of Chinese cabbage cultivated in spring and early autumn in recent years, the problem of black spot disease was increasing seriously. It is well known that disease-resistant breeding is an economical and effective way to prevent the disease popularity in Chinese cabbage, the resistance identification and disease-resistant mechanism are the foundation of disease-resistant breeding. In this research program, the disease pathogen of black spot disease in spring-summer Chinese cabbage was isolated and identified firstly, then a convenient and feasible resistant-identification method to black spot disease of Chinese cabbage was estabolished at seedling stage, the resistance of 168 Chinese cabbage lines and hybrids to black spot disease were identified at seedling stage, and the change of POD, CAT, PAL enzyme activities in leaves after inoculation were also analyzed. The main results were as follows:1. 32 single-spore-lines were isolated from the disease leaves in the main Chinese cabbage production areas of Shaanxi Province. It was determined that the A.brassicicola was the only pathogen of it according to the spore's shape and the profile of PCR amplification with special primers. The suitable temperature for the growth of A.brassicicola on PDA medium was 25～30℃. The host experiment indicated that it can infect Chinese cabbage, radish, turnip, cabbage, Chinese kale, flowering Chinese cabbage, mustard and rapeseed.2. An artificial inoculation method for black spot disease identification was estabolished, which key procedure is praying 1×104 pfu/mL spores solution on seedling with two true leaves, and placing at 25℃condition, then keeping saturation moisture and dark for 24h, and conventional condition from 2th-4th day, keeping moisture at night and opening at day from 4th-7th day, keeping moisture 24h in 8th day, then investigating disease grade. The result from the method was exact in accordance with the true resistance type of Chinese cabbage.3. 46 hybrids and 122 inbred lines of Chinese cabbage were appraised for the resistance to black spot disease at seedling stage; the result was that there were 30 resistant materials, 109 medial-resistant materials, 24 susceptible materials and 5 high-susceptible materials. the resistant materials will be used as parent in disease-resistant breeding in future, especially the line of 06S157 which disease index is only 14.6.There was not found any high-resistant and immunity materials in it, which means the road of disease-resistance breeding is difficult.4. The measurement of antioxidant activities showed that POD activity in the resistant cultivars rised earlier than in the susceptible ones after inoculation with A.brassicicala, but the highest point of POD activity in the resistant cultivars was lower than in the susceptible cultivars; The activities of CAT in the resistant cultivars raised earlier and kept a high level after inoculation with A. brassicicola, but slow and small change in the susceptible cultivars; The dynamic change of PAL activity were similar in susceptible and resistant varieties after inoculation with A.brassicicola, which was that the activities of PAL were increased after inoculation with A.brassicicola, but the activity of PAL had no significant difference between susceptible and resistant cultivars.
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