Suppression of Rhizoctonia solani AG-8 induced disease on wheat by the interaction between Pantoea, Exiguobacterium, and Microbacteria

Rhizoctonia solani AG-8 is a major wheat root pathogen; however, soils can become suppressive to the expression of disease under intensive cropping with retention of crop residues. This is in part due to the action of soil microorganisms. A step-wise approach was used to determine which microorganisms contributed to suppression of R. solani induced disease in a disease-suppressive soil. Using wheat-soil-pathogen bioassays it was determined that the interaction between 3 phylogenetically diverse groups of bacteria, Pantoea agglomerans, Exiguobacterium acetylicum, and Microbacteria (family Microbacteriaceae), was a major contributor to disease suppression. Inoculation of a sterilised soil with the combination of these groups resulted in greatly increased seedling shoot dry weight and reduced infection compared with diseased control plants with no bacterial inoculation, or inoculated with individual types of bacteria. These groups, however, did not reduce levels of pathogen DNA, although inoculation with suppressive soil (at 10% w/w) did reduce pathogen DNA. Root associated P. agglomerans and E. acetylicum promoted the growth of infected wheat plants and soil associated Microbacteria reduced root infection by R. solani.