Study On Artificial Innoculation And Mechanism Of Resistance To Downy Mildew In Non-Heading Chinese Cabbage

The artificial inoculation, physiological and biochemical mechanisms as well as the inheritance model of resistance to downy mildew in non-heading Chinese cabbage were studied. The results were as follows:1. Two resistant parents (001, 014) of non-heading Chinese cabbage and two susceptible parents(007, 010) were conducted to study on the artificial inoculation at the cotyledon and seedling stages. Furthmore, the correlation analysis between resistance of downy mildew at the cotyledon stage, that at the seedling stage and that at the adult stage was study in order to confirm the reliability of artificial inoculation at the cotyledon and seedling stages. As shown by the result, the optimum combination of artificial inoculation was an inoculation concentration of 2×10~5 spores/ml suspension and a inoculation volume of 10μl suspension /cotyledon at the cotyledon stage, which can adequately identify downy mildew resistance of various varieties, while the optimum combination of artificial inoculation was a inoculation concentration of 2×10~5 spores/ml suspension and a inoculation volume of 150μl suspension/plant at the seedling stage. According to identification results at the adult-plant stage and correlation analysis, R~2 between downy mildew resistance at the cotyledon stage and that of the adult-plant stage was 0.8545, while R~2 between downy mildew resistance at the seedling stage and that of the adult-plant stage was 0.9027.2. Four inbred lines of different resistance to downy mildew of non-heading Chinese cabbage were conducted in studying the relationship between the resistance to downy mildew and several characteristics of physiology and biochemistry in seedling inoculation with a aim at providing theoretical basis for selection and breeding of downy mildew resistant varieties. As shown by the result, before the inoculation, the contents of chlorophyll and lignin in healthy leaves were positive correlated to the resistance to downy mildew of inbred lines of non-heading Chinese cabbage, while the content of soluble sugar were negative correlated to it ,but there was no obvious correlation between the SOD and chitinase activities and the resistance to downy mildew of inbred lines. According to the result, after the inoculation, chlorophyll, lignin, soluble sugar, SOD and chitinase had the trend of ebb and flow which was consistent with the resistance to downy mildew of inbred lines. Above results indicated that activation of resisted potential of plants led to the increase of chlorophyll, lignin and soluble sugar contents as well as activities of SOD and chitinase, which belongs to the metabolism of inducing resistance.3. Six populations of two cross combinations (010×014,010×001) in non-heading Chinese cabbage were used to analyze inheritance of resistance to downy mildew at the cotyledon and seedling stages. As indicated by the result, resistance to downy mildew at the cotyledon and seedling stages of two cross combinations were both control by a single dominant gene without maternal effects. Therefore, in our breeding progress, there is just a resistant parent in the cross combination. Furthermore, the resistant parent can be used as not only the male parent but also the female one. It is beneficial to develop a new variety with resistance to downy mildew.