Evaluation of Methods to Quantify Populations of Rhizoctonia in Soil

The best method to quantitatively determine populations of Rhizoctonia in soil from soybean fields undergoing rice and soybean rotations was determined for use in a large-scale spatial study to be done over multiple fields and years. The methods evaluated were the toothpick-baiting method, the multiple-pellet soil sampler, and the pour-plate method using elutriated organic matter from soil or surface residue. The toothpick-baiting method was calibrated using the multiple-pellet soil sampler and determined to assay an approximate soil volume of 15.43 cm3. The radius of isolation with the toothpick-baiting technique was approximately 1 cm. In 2009 and 2010, the toothpick method was determined to be the most reliable method for assaying soils, with the most isolates across space and greater recovery of Rhizoctonia solani AG1-IA, R. solani AG11, and R. oryzae, the major Rhizoctonia spp. in these fields, when quantified as propagules per volume of soil or organic matter. In 2011, the recovery of these three gr...