Impact of individual and combined antagonist application towards Rhizoctonia solani on lettuce and on indigenous microbial rhizosphere community

Abstract: The soil-borne pathogen Rhizoctonia solani Kühn is responsible for serious damageson a wide range of important crops worldwide. Efficient control strategies against R. solani areurgently required. Application of individual biocontrol strains has often resulted in inconsistentperformance in the field. Consequently biocontrol activity was assessed by combining biocontrolstrains with different modes of action to overcome this problem. The bacterial antagonistPseudomonas jessenii and the mycoparasite Trichoderma viride were selected as promisingcontrol agents against R. solani the causal agent of bottom rot on lettuce. Growth chamberexperiments were performed to investigate the biocontrol efficacy of individual and coinoculationtreatments of these biocontrol agents in the presence and absence of R. solani onlettuce. Additionally, the impact of the inoculants on compositions of bacterial and fungalcommunities in the rhizosphere of lettuce was studied by analyzing with 16S rRNA and ITSbasedfingerprinting methods. Biocontrol efficacy was improved in co-inoculants treatment ofP. jessenii and T. viride compared to individual inoculant application. DGGE analysis revealed amore pronounced effect on the bacterial and fungal community in the treatment with bothinoculants compared to individual bacterial and fungal inoculant application. In summary, theapplied cultivation-independent methods provided insights into the complex interaction inresponse to the pathogen presence and to biocontrol strains inoculation.