Spatial and temporal dynamics of Collembola (Isotomiella minor) and plant pathogenic fungi (Rhizoctonia solani) interactions

The mechanistic and spatial dynamics of microarthropod-plant pathogen interactions remain understudied, despite the importance of these interactions in plant disease control. We conducted three complementary laboratory experiments using the plant-pathogenic fungus, Rhizoctonia solani, and the Collembola Isotomiella minor. The dominant mechanism (consumption vs. dispersal) of these interactions was investigated over 5 days in a controlled environment. The dominant mechanism observed was consumption, with I. minor decreasing R. solani growth by up to 58 %. There was no evidence of pathogen dispersal, however, there was potential for R. solani dispersal by I. minor as there were viable pathogen structures on the cuticle and in the frass. I. minor effects on R. solani mycelial growth rate were then determined using race tubes over 14 days. I. minor decreased R. solani mycelial growth rate by up to 23 %. Soil environment effects were explored over 5 days in a controlled environment using mineral substrate to mimic a 3-dimensional soil environment, both with and without organic matter (alfalfa) additions. In the soil without organic matter, the high I. minor abundances decreased R. solani growth compared to the low and no I. minor abundances by 23 % and 22 % respectively. In the soil with organic matter, I. minor did not affect R. solani growth. These findings suggest that organic matter in soils may be diminishing collembolan control of plant pathogens in field settings.