The Study Of Biological Control Against Cucumber Downy Mildew And Cucumber Powdery Mildew

At present the efficient measures to prevent cucumber downy mildew and cucumber powdery mildew are planting resistant varieties and controlling the disease by chemical agents.But there is a too long time by planting resistant varieties.Repeated use of chemical agents is easy to produce drug resistance and pollute the environment.Therefore,biological control strategies become the new direction in preventing these two plant diseases.1.Isolation and screening of the antagonistic bacteria303 bacteria strains were isolated from cucumber different microenvironment.The ability index of each strain was measured as follows:production protease,chitinase,cellulase activity and production addicted ferrite.While Phytophthora capsici,Botrytis cinerea and Pythium ultimum were used to determine antagonistic activity.Assessment value was given to each strain according to their enzyme activity and antagonistic activity.Finally,potential biocontrol bacteria were screened out for greenhouse and field experiments according to their assignment evaluation and cluster analysis.2.Evaluation of biocontrol potentiality of antagonistic bacteria 26 strains were selected for greenhouse study according to assessment value andcluster analysis.We also selected 9 strains from the BCA library in our lab.Inoculated pathogenic fungi 20 d later,the control efficiency of antagonistic bacteria against cucumber downy mildew ranged 8.74 to 69.04%and the control efficiency of antagonistic bacteria against cucumber powdery mildew ranged 16.96 to 68.49%.The correlation analysis showed that there was a positive correlation between the results of assignment and the control efficiency.The correlation coefficients were 0.81 and 0.82.Strains can also promote plant growth effectively.In greenhouse experiment,the highest increase of plant biomass growth was 27.94%.In the nature field of 2013,the control efficiency of antagonistic bacteria against cucumber downy mildew ranged 36.09 to 51.78%.There was a significant difference between the treatment group and the control group.3.Biocontrol efficiency of different biocontrol agents against cucumber downy mildew in natural fieldThis study aimed to study the biocontrol efficiency of different biocontrol agents against cucumber downy mildew and the yield promotion.In natural field,at the day of 7,22 and 37 d after second treatment,the biocontrol efficacy of seven biocontrol agents DYW14?DS22+1BS4?3BS3+1BS4?2BS5+ HS10?HYW4+HS10?3BY4+DYW14+3BS3 and DS22+ HS10+ DYW14 were over 40%.All of the treatments could improve the yield of cucumber.The yield promotion of three biocontrol agents 3BY4+DYW14+3BS3?3BY4+DYW14+1BS4 and DS22+7ze3+3BY4 were over 40%.Composite agents were better than single agents in biocontrol efficacy and yield promotion.4.ConclusionIn this study,a few strains of the potential to control cucumber downy mildew and cucumber powdery mildew are found through a series of indoor and outdoor screening strategies.We also found that composite agents were better than single agents in biocontrol efficacy and yield promotion.