Compost Amendments Decrease Verticillium dahliae Infection on Potato

Indigenous soil microorganisms contribute to disease suppression in cropping systems by reducing and competing with pathogen populations, thereby limiting disease severity. Various communities of indigenous microorganisms in any particular soil have adapted to the specific environmental conditions. If the soil around the plant roots could be altered to favor the indigenous soil microorganisms relative to the plant pathogen, the survival and proliferation of indigenous soil microorganisms, and thus effectiveness of biological control, may be increased. Wood chippolyacrylamide (PAM) cores were used to alter the soil environment in a greenhouse study to favor indigenous soil microorganisms in vegetable and manure compost to reduce Verticillium dahliae infection of potato (Solanum tuberosum L.) plants. Potato plants growing in soils amended with vegetable compost-wood chip-PAM cores had significantly lower visible (V_vis) and isolation (V_iso) V. dahliae infection rates than control soils and soils with dairy or vegetable compost alone. Soils amended with wood chip-PAM-dairy compost cores had significantly lower V_vis and isolation V_iso than control soils and soils with dairy compost. Soils with wood chip-PAM cores and soils with wood chip-PAM-vegetable compost had greater microbial biomass/Verticillium dahliae biomass (MB/VB) ratios in soil than control soils or in soils amended with compost alone. MB/VB ratios in wood chip-PAM cores and wood chip- PAM-vegetable compost were greater than in wood chip-PAM-dairy compost cores. V_vis correlated in a quadratic relationship with the MB/VB ratio (r²=0.76). As MB/VB ratio increased V_vis decreased. Although field studies with several crops and economic evaluations are necessary, this greenhouse study provides evidence that a wood chip-PAM or wood chip- PAM-vegetable compost soil amendment may be a viable method to control some soil diseases in high value crops.