Response of Rhizoctonia solani to soil faunal grazing and organic amendments – different from general microbial dynamics

Abstract

In a four-month microcosm experiment, we studied the effect of enchytraeids and earthworms on dynamics of Rhizoctonia solani in soil amended with different types of organic material. Special focus was on comparing the effects with those on total microbial densities, to see if the development of the pathogen follows the general dynamics of saprophytic bacteria and fungi in the system. We found that animal effects on the density of R. solani and on the densities of culturable fungi and bacteria were dependent not only on type of animal present, but also on the amount and type of organic material available. The highest densities of bacteria and fungi were found in soil amended with fresh organic material in presence of earthworms and the lowest densities in non-amended soil with enchytraeids. While the bacteria and fungi responded similarly to animal and organic material treatments, the response of R. solani showed an opposite pattern with the highest densities observed in the treatments with the lowest densities of fungi and bacteria. These results show that R. solani does not follow the general dynamics of soil microorganisms. As the highest densities of R. solani were found in treatments with a high grazing pressure, our findings also indicate that R. solani may get a competitive advantage from soil faunal grazing