Studies On Control Effect Of Endophytic Actinomyces On Zucchini Powdery Mildew

Cucurbit powdery mildew was a serious problem in vegetable product in china and caused obvious yield losses.Because of its special small ecological environment, zucchini are more easily infected than other cucurbits.Biocontrol of powdery mildew, as an important alternative to chemical control, has received considerable attention due to the lack of resisitant cultivars, and increasing fungicide resisitance in population of powdery mildew and fungicide residues in the environment. In recent years, biocontrol agents were studied for the biocontrol of cucurbit powdery mildew which mainly focused on plant extracts, endophytic bacterial, ampelomyces, chemicals inducing and soil actinomyces, respectively. However, no study on biocontrol of powdery mildew with endophytic actinomyces was reported. Fifty strains of endophytic actinomycetes were screened in greenhouse pot experiments and leaf-disc test in lab. Two strains showed stable control effect on zucchini powdery mildew. Its best carbon sources, nitrogen sources and fermentation conditions were investigated according to single factor test of carbon sources selection, nitrogen sources selection and fermentation conditions optimization. Its taxonomic status was investigated according to its morphology culture properties, physiological characteristics and biochemical characteristics. Its effects were studied in the present study and the main results were as followed:1 Fifty strains of endophytic actinomycetes were screened in greenhouse pot experiments and leaf-disc test in lab. Two strains showed stable control effect on zucchini powdery mildew. In the leaf-disc test, the application of cell free filtrate of strains GKSHJA and PR1-8 showed 60.98 % and 63.22% disease control efficiency, respectively. The control effects of strain GKSHJA with application 24h before and after inoculation were 55.22% and 16.44%, respectively. The control effect of strain PR1-8 were 51.94% and 24.39% in the greenhouse potted seedlings inoculated with powdery mildew. The preinoculation application of cell free filtrate showed much higher disease control efficiency than postinoculation application. The applications of 5 times diluted cell free filtrates showed 27.81% (in GKSHJA treatment ) and 30.19% (in PR1-8 treatment) less disease index than that in untreatment control. In field experiment, the control effect of biocontrol strains GKSHJA and PR1-8 were 56.33% and 69.88% , respectively, after application of 5 times dilution of cell free filtrate on naturally infected zucchini plants. The control effect of biocontrol strains GKSHJA and PR1-8 were 73.68% and 68.13% on cucumber powdery mildew.2 According to single factor test of carbon sources selection, nitrogen sources selection and fermentation conditions optimization, the result showed the optimal carbon was glucose; the optimal inorgan and organic nitrogen sources were soybean flour and NaNO3, respectively. The optimal original pH is 6.0.The optimal culture temperature was 26～28℃. The optimal fermatation time was 5 days.The optimal inoculation volume 10%.The optimal rotating speed was 150 rpm. The control effect was 29.47% higher than before when it was incubated in optimal fermentation conditions.3 Based on the results of morphological, chemotaxonomic and physiological characteristics, strains GKSHJA and PR1-8 belonged to streptomyces.4 Optical microscopical observations indicated that the free cell filtrate of strains GKSHJA and PR1-8 have effect on spore germination of S. fuliginea. Fluorescence microscope observation indicated that the free cell filtrate of strains GKSHJA and PR1-8 have effect on mycelia growth and spread of colonies.