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.

Please cite this article as: Barnett, S., Zhao, S., Ballard, R., Franco, C., Selection of microbes for control of Rhizoctonia root rot on wheat using a high throughput pathosystem, Biological Control (2017), doi: http://dx.One sentence summary: A 3-phase in planta pathosystem was used to screen large numbers of plant-associated microbes resulting in the selection of candidate strains for control of Rhizoctonia root rot on wheat. AbstractThe promise of microbial biological control of soilborne fungal pathogens of crops has yet to be fully realised with only a few strains commercialised and available to growers. One bottleneck is the availability of suitable methods to screen microorganisms for disease control efficacy relevant to controlling disease in the field. A 3-phase in planta pathosystem containing field soil was developed to screen 2,310 microorganisms for control of Rhizoctonia root rot on wheat. Test strains were added to seeds as a suspension at planting and plant growth assessed at two weeks. Strains increasing plant height and number of roots (185) were tested in a replicated Rhizoctonia pot bioassay with five wheat seedlings grown for four weeks and assessed for plant growth and root disease. Forty three strains (1.9% of strains tested) performed better than our benchmark strains and were reassessed in pot bioassays at three inoculation levels. These tested strains represented a wide diversity of microbial genotypes including fungi, (Trichoderma, Aspergillus and Cylindrocarpon) and bacteria encompassing four phyla (Actinobacteria, Firmicutes, Proteobacteria, Bacteroidetes).These results show that microbes can be successfully and rapidly screened directly for disease control on plants.