Isolation Of Phyllosphere Actinomycetes From Cucumber And Biocontrol On Cucumber Grey Mold And Target Leaf Spot

Botrytis cinerea and Corynespora cassiicola have been the main threats to the cucumber planting, especially in the green house. As the need of green vegetable has been increasing these years, the biofungicide, especially the microbial fungicide has been the hot spot for studing to control the cucumber diseases. This study was carried out with tissue separation method, in order to screen the strains those have inhibitory effects on the tomato grey mold and cucumber target spot. Besides, the inhibitory activities of the fermentation filtrates of the antagonistic isolates and the characteristics of the isolates were also studied, for assessing their potential of being applied.In spring and autumn, there are some differences in terms of the quantity of the microbes that isolated from cucumber. In spring, 7.345×10~7 cfu/g of the microbes were isolated from the cucumber phyllosphere, compared to 1.333×10~6 cfu/g in autumn; 3.189×10~7 cfu/g of the microbes were isolated from the endogenetic cucumber leaves compared to 9.054×10~4 cfu/g in autumn.8 strains and 6 strains that showed significant antagonism against B. cinerea and C. cassiicola respecitively were selected as candidates, of which XN-1 and XN-22 both indicated high antagonistic effects on the two target pathogens. The inhibition rate of XN-22 and XN-1 were 67.37% and 69.88% for tomato grey mold, and 74.10% and 63.54% for cucumber target leaf spot, respectively.The primary concentration of fermentation filtrates of XN-22 and XN-1 also showed greatly inhibitory effects on the spore germination. The germination inhibition rate of B. cinerea under the treatment of Strain XN-22 and XN-1 were 96.20 % and 92.41%, respectively. The germination rate of C. cassiicola of the two strains were 90.84% and 84.56%. In addition, the germs of the spore became inflated and breached after the treatment of the two antagonistic strains.The fermentation filtrates of the two strains were both stable in the range of 50-80℃, whose stability sustained between pH5.0 and pH9.0. The antifungal compounds showed the highest activity between pH7.0 and pH8.0 and became declined with the decrease or increase of pH values. Both the strains also showed stable under the exposure of UV, whose filtrates turned declined with the length of exposure time but still kept a relatively high level.In order to test the range of antifungal spectrum, 10 pathogens were used to test the antagonistic activity of XN-22 and XN-1. The inhibition ranges of zone were all upon 6mm, which showed that the two tested strains had broad antifungal spectrum.