Isolation, identification and evaluation of rhizosphere actinomycetes for control of peanut southern blight

Peanut southern blight is a fungal disease which is caused by the pathgen Sclerotium rolfsii Sacc., and seriously restricts the quality and yield of peanut. In this study, 116 strains of actinomycetes were isolated and purified from rhizosphere soil of Achyranthes bidentata by dilution coating method, and the strains that can control peanut southern blight were screened and identified. Two strains, Soil-1-5 and Soil-3-28, with good and stable antifungal activity, were screened by the plate confrontation test, and their inhibition rates were 80.43% and 92.34%, respectively. Morphological observation, physiological and biochemical tests, and 16S rRNA gene sequence analysis identified strains Soil-1-5 and Soil-3-28 as Streptomyces scabiei and Streptomyces luteogriseus, respectively. The inhibition of aseptic fermentation filtrate of antagonistic strains on plant pathogens was measured by mycelium growth rate method. The results showed that after 5 times dilution of aseptic fermentation filtrate of strains Soil-1-5 and Soil-3-28, the inhibit rates of S. rolfsii were 73.67% and 57.11%, respectively, and the two strains had different degrees of inhibition effects on the six plant pathogens including Fusarium graminearum. In addition, the two strains of aseptic fermentation filtrate also had good antagonistic effects on the sclerotinia germination and sclerotinia formation. The results of pot experiment showed that the control effects of strain Soil-1-5 and Soil-3-28 on peanut southern blight were 51.92% and 31.74%, respectively, and strain Soil-3-28 could promote the growth of peanut. In conclusion, strains Soil-1-5 and Soil-3-28 had better control efficacy on peanut southern blight, and had potential application value.