Abstract: In order to screen beneficial microorganisms for effectively controlling peanut southern blight caused by Sclerotium rolfsii, Trichoderma spp. was isolated from peanut rhizosphere soil by soil dilution method, the strain with the highest biocontrol effect on S. rolfsii was screened by dual culture method and pot experiment and identified by morphological and molecular biological techniques. Its biocontrol mechanism against peanut southern blight and biological characteristics were determined. The results indicated that strain GH-20 was screened from 132 isolates of Trichoderma and had significant inhibition activity to S. rolfsii, with the rate of 89.93%. The strain was identified as Trichoderma asperellum. During dual culture, antagonism index of GH-20 to the S. rolfsii was grade I. After the strain GH-20 completely cover the colony of the pathogen, GH-20 mycelium can wrap and invade the pathogen hyphae, resulting in mycoparasitism, and gradually digest and reduce its mycelium, resulting in inability of the pathogen to produce sclerotia. The inhibition rates of volatile gas (VOG) and non-volatile gas (non-VOG) produced by GH-20 against the pathogen were 59.95% and 79.49%, respectively. Pot experiment showed that the biocontrol efficacy of GH-20 on peanut southern blight was 79.64%. Under conditions of fructose as carbon source, yeast extract as nitrogen source and the optimal pH value of 7, GH-20 was more conducive to growth and development. Continuous light was conducive to GH-20 mycelial growth, while alternating light and dark conditions were conducive to spore production. In conclusion, T. asperellum GH-20 could effectively control the peanut southern blight mainly through competition, hyperparasitism and antagonistic substances.

Key words: peanut southern blight, Trichoderma asperellum, biocontrol, mechanism, biological characteristics