Induced Resistance And Mechanism Of Cucumber To Anthracnose By Pieris Rapae Extract

Thirty-seven species of plant and four species of insect ethanol extracts wererespectively sprayed on the surface of cucumber leaf to investigate the induced resistanceof cucumber to anthracnose. The technique protocol was established and the biochemicalmechanism was studied for Pieris rapae extract inducing cucumber against anthracnose.Expressed genes in cucumber seedling leaf, which was inoculated with Colletotrichumorbiculare after P. rapae extract treatment and only was inoculated with C. orbiculare,were analysed by DDRT-PCR. The differentially expressed genes related to cucumberagainst anthracnose were recovered, cloned and sequenced. The result set up a solidfoundation for gene cloning and understanding their function futher.The main results in the study were as follows:1. The local and systemic resistance to cucumber anthracnose could be induced incucumber seedling leaf by the P. rapae extract.2. An optimum protocol for P. rapae extract inducing cucumber against anthracnosewas established.①The best inducing method was foliar spraying.②The proper inducing concentration of P. rapae extract was 5.0 mg/mL.③The ideal interval was 3 days between the P. rapae extract treatment andinoculation.④The effective induction could be obtained in cucumber only treated one time withP. rapae extract.⑤The optimum stage of P. rapae extract treatment was cucumber seedling phase.3. The activity of POD, PPO, PAL and SOD of the cucumber leaf treated with P.rapae extract at the concentration of 5.0 mg/mL was higher than that of the untreated ones.The peak activity of POD, PPO, PAL and SOD occurred at the 5th day, the 4th day, the 3rdday and the 2nd day with the maximum 38.9(ΔOD/g·min), 28.3(0.001ΔOD/g·s),56.4(0.01ΔOD/g·min) and 50.3(inhibitory rate/g), respectively.4. The content of proline and malefic dialdehyde was not changed evidently in thecucumber leaf treated with P. rapae extract.5. The expression of pathogenesis-related proteins could be induced in the local andsystemic leaf after P. rapae extract induction. The quantity of PRs in the leaf treated by P.rapae extract and challenged inoculation with C. orbiculare was higher than that in the leafonly treated by P. rapae extract.6. Three-anchor primers and 26 random primers were used for DDRT-PCRamplifying cucumber cDNA, which was obtained from only inoculated cucumber with C. orbiculare or the cucumber treated by P. rapae extract and challenge-inoculation with C.orbiculare. Sixty-seven differential expressed gene fragments were detected bypolyacrylamide gel electrophoresis (PAGE) and silver staining. The differential bands of89.6% among them were successfully recovered from PAGE gels. Five specific fragmentswere cloned and sequenced. Among them, the fragment D1 (344bp) had 95% homology tothe photosystemⅡCP47 protein compound that was composed of chlorophyll a and theprotein (47kD) encoded by psbB gene. The other four fragments had no homology to thegene segments registered in GeneBank.