| Sclerotinia is a serious disease of cauliflower (Brassica oleracea L. var. botrytis L).The system for indentification of resistance to Sclerotinia sclerotiorum in cauliflower has not been established, and screening for germplasm sources resistance to Sclerotinia sclerotiorum in cauliflower have not been reported. In this study, five cauliflower varieties in different resistantance levels were used to establish an effective identification of resistance to Sclerotinia sclerotiorum in vivo method. The results showed that the leaves mycelial seedling inoculation method could well represent the resistance and susceptibility of detected varieties, and some resistant materials were identified. Meanwhile, the effect of BTH and Harpin on cauliflower induced resistance to S. sclerotiorum was studied and the preliminary exploration of the physiological and molecular bases was finished. The present results will provide the help for the cauliflower breeding for disease-resistant variety and improving the cultivation technology, and in-depth exploration of the molecular mechanism of Harpin and BTH induced resistance. The major study results are as following:(1) Three methods for identification of resistance to Sclerotinia sclerotiorum were compared with 5 cauliflower varieties under the same conditions for their effectiveness in the resistance identification of cauliflower. The results showed that heading stage mycelium agar disk inoculation to axil method was highly significantly correlated with field inoculation identification (r=0.8859) and it could well represent the resistance and susceptibility of detected varieties. Seedling agar disk to live leaf method can be used as reference for the rapid identification of the resistance to S. sclerotiorum. Using cauliflower variety "qingnong 45 days" as control,21 breeding materials were checked with the heading stage mycelium agar disk inoculation to axil method. Finally, Two high resistant materials'shenliang jinhua shenliang jinhua' and'changsheng 65 days'were identified.(2) The effects of benzothiadiazole (BTH) spraying on cauliflower Sclerotinia sclerotiorum were investigated in susceptible and resistant varieties, via the comparison of disease index with the inoculation of mycelium agar disk to seedling leaf. The results showed that BTH significantly reduced the size of rot tissue compared to untreated controls, and the control efficacies of BTH treatment was 83.5% and 63.8% in susceptible- and resistant- varieties respectively. The activities of defensive enzyme like POD, SOD, CAT, PAL, and PPO in BTH-treated seedlings increased after inoculation with S. sclerotiorum. The activities of CHT andβ-1,3-glucanase in cauliflower also increased in BTH-treated seedlings. The expression of two marker genes in defense signaling pathways and four pathogenesis-related protein genes were detected using semi-quantified RT-PCR. The results showed that BTH-induced resistance to S. sclerotiorum in cauliflower mainly through SA-dependent signaling pathway, the up-regulated expression of PDF1.2 showed JA/ET signaling pathway may also influenced by BTH-induced resistance in cauliflower.(3) The effects of Harpin spraying on cauliflower Sclerotinia sclerotiorum were investigated in susceptible and resistant varieties, via the comparison of disease index with the inoculation of mycelium agar disk to seedling leaf. The disease index showed induced effect is obvious with the 60 mg/L Harpin treatment。After Harpin treatment, the PAL, CAT, POD, PPO, CHT and (3-1,3-glucanas'e activities in cauliflower leaves at different times were markedly increased. Harpin inducing disease resistance may be attributed to the activation of the pathwanys of salicylic acid and jasmonic acid pathway. Harpin induced mainly through the salicylic acid pathway. After Harpin treatment, jasmonic acid pathway in induction began 3 d after inoculation.
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