Studies On Petiole Spot In Chinese Cabbage And Its Physiological Basis Of Disease Resistance

Chinese cabbage varieties with different resistances to petiole spot were used as materials. By comparative physiology method, we studied the effect of nitrogen forms on the physiological metabolism resisted to petiole spot disease of Chinese cabbage , and the relationship of Superoxide dismutase (SOD) activity, Peroxidase (POD) activity, Polyphenoloxidase(PPO) activity, phenolics content. The results showed:(1) Both different nitrogen forms and different Chinese cabbage gene types could affect petiole spot of Chinese cabbage, when nitrate nitrogen was used as nitrogen source, the disease index lowed. and there's a remarkable rhythm between the application of ammonium nitrogen and nitrate nitrogen, except there's a bit alteration under amide nitrogen to physiological metabolism. What's more, some physiological and biochemical indexes in petiole were opposite to those in leaf blade under different nitrogen forms.(2) Petiole spot symptoms mostly occurred on the filed of outer leaf blade in the harvest stage, it appeared on different spots to different Chinese cabbage varieties. And susceptible variety had a more serious disease under higher nitrogen level. The phenol content, SOD and PPO activities in leaf petiole of the susceptible Chinese cabbage variety to petiole spot were all higher than the resistant one evidently, wherever under nitrogen treated or non - nitrogen treated in the seedling stage. On the contrary, POD activity of the resistant variety was lower than that of the susceptible one. What's more, SOD activity and the phenol content of resistant variety were lower than those of susceptible variety , and MDA content,POD and PPO activities of resistant variety were all higher than those of susceptible variety significantly during the later growth stage, especially harvesting stage. However, the difference in leaf blade wasn't remarkable.(3) The study also indicated that the capacities of self-regulating and returning to normal status of resistant variety were stronger than susceptible one. The results can be used as the physiological indexes to breeding and identification of resistance to petiole spot in the seedling stage of Chinese cabbage.(4) During the whole growing period, the differences of every phenol ingredient content were obvious for resistant cabbage variety and susceptible one in lotus period, and during this time, the most different was the content of Chlorogenic acid in leaf blade, then Caffeic acid in leaf blade and Gallic acid in petiole. And Chlorogenic acid played an important part in resisting petiole spot of Chinese cabbage.As mentioned above, the changes of protective enzymes activities (SOD﹑POD﹑PPO)and phenol content and metabolism were all related with the resistance to petiole spot of Chinese cabbage, they can be used as physiological indexes or referenced targets of the physiological seed selecting of the Chinese cabbage especially in former stage. It's important to accelerating process of seed selecting and breeding and increasing the quality of seeds.