Soil pathogen-aphid interactions under differences in soil organic matter and mineral fertilizer

Abstract

There is increasing evidence showing that microbes can influence plant-insect interactions. In addition, various studies have shown that aboveground pathogens can alter the interactions between plants and insects. However, little is known about the role of soil-borne pathogens in plant-insect interactions. It is also not known how environmental conditions, that steer the performance of soil-borne pathogens, might influence these microbe-plant-insect interactions. Here, we studied effects of the soil-borne pathogen Rhizoctonia solani on aphids (Sitobion avenae) using wheat (Triticum aestivum) as a host.In a greenhouse experiment, we tested how different levels of soil organic matter (SOM) and fertilizer addition influence the interactions between plants and aphids. To examine the influence of the existing soil microbiome on the pathogen effects, we used both unsterilized field soil and sterilized field soil.In unsterilized soil with low SOM content, R. solani addition had a negative effect on aphid biomass, whereas it enhanced aphid biomass in soil with high SOM content. In sterilized soil, however, aphid biomass was enhanced by R. solani addition and by high SOM content. Plant biomass was enhanced by fertilizer addition, but only when SOM content was low, or in the absence of R. solani.We conclude that belowground pathogens influence aphid performance and that the effect of soil pathogens on aphids can be more positive in the absence of a soil microbiome. This implies that experiments studying the effect of pathogens under sterile conditions might not represent realistic interactions. Moreover, pathogen-plant-aphid interactions can be more positive for aphids under high SOM conditions. We recommend that soil conditions should be taken into account in the study of microbe-plant-insect interactions.

Effects of conservation buffer systems on adsorption of fluorescent‐labeled Escherichia coli

“…These two properties can influence the adsorption of E. coli as a pathogen because under high SOM conditions soil pathogen interactions tend to be more positive, and the magnitude of adsorption tends to increase proportionally with soil organic fractions (Smith & Hegazy, 2006). Similarly, higher soil cation exchange capacity was a significant predictor of reduced infections (Farenhorst, 2006; Liddicoat et al., 2018; Van Gils et al., 2017). The agroforestry treatment demonstrated a better adsorption capacity (cfu g −1 ) compared with the other two treatments, which may be due to the fixation of ammonium ions (NH 4 + ) by the mineral fraction or organic fraction of the soil organic C such that they are relatively unexchangeable (Nieder et al., 2011), hence aiding in the E. coli adsorption.…”

Adsorption of fluorescent labeled E. coli in selected vegetative buffer systems

“…These two properties can influence the adsorption of E. coli as a pathogen since under high SOM conditions soil pathogen interactions tend to be more positive, and the magnitude of adsorption tends to increase proportionally with soil organic fractions (Smith and Hegazy, 2006). Similarly, higher soil CEC happened to be a significant predictor of reduced infections (Farenhorst, 2006;Liddicoat et al, 2018;Van Gils et al, 2017). The agroforestry treatment demonstrated a better adsorption capacity (cfu/g) compared to the other two treatments which may be due to the fixation of ammonium ions (NH4 + ) by the mineral fraction or organic fraction of the SOC such that they are relatively unexchangeable (Nieder et al, 2011), hence aid in the E. coli adsorption.…”