Earthworms affect decomposition of soil-borne plant pathogen Sclerotinia sclerotiorum in a cover crop field experiment

Earthworms provide important ecosystem services in agricultural systems. However, little is known with regards to which extent earthworms feed on soil-borne plant fungal pathogens, thereby potentially reducing pathogen infection of crops. Using a food choice arena in the laboratory, we examined (i) whether the hardened resting structures (i.e., sclerotia) of white mould (Sclerotinia sclerotiorum (Lib.) de Bary) are consumed by the earthworm Lumbricus terrestris L. (Lumbricidae) and (ii) to what extent this consumption is affected by a possible hydration of sclerotia. We found that earthworms fed on sclerotia, preferably when sclerotia were hydrated. After 13 weeks of sclerotia hydration, on average, 61.1 ± 26.0% were consumed. In field plots, we further tested the interaction between earthworms, cover crops (mustard (Sinapis alba L.), oilseed radish (Raphanus sativus subsp. oleiferus M.), oat (Avena sativa L.), grass pea (Lathyrus sativus L.)) and sclerotia. After eight months, the number of remained sclerotia was lower when earthworms had access (51 ± 19%) than when earthworm had restricted access (79 ± 11%; Sidak; P = 0.01). Oilseed radish increased earthworm abundance, however cover crops did not directly reduce sclerotia. Our findings indicate that sclerotia can be reduced by supporting cover crops that favour earthworms rather than having bare fallow.