Differential effects of two earthworm species on Fusarium wilt of strawberry

Earthworms can reduce soil-borne diseases via diverse mechanisms. The differential effects of different earthworm species on soil-borne diseases, and the mechanisms that account for the differences, however, have been largely ignored. To assess the effects of different earthworm species on Fusarium wilt in replanted strawberry and the underlying mechanisms involves, a greenhouse experiment in which plants were placed in soil with earthworms (either Metaphire guillemi (M) or Eisenia fetida (E)) or without earthworms (CK) was carried out. The disease index and biomass of each strawberry plant, along with soil microbial biomass, soil basal respiration, and the Shannon-Wiener diversity index (H′) for soil bacteria based on T-RFLP profiles and residual phenolic acids were determined. Both M. guillemi and E. fetida reduced the disease index, from 50.9 to 11.8 and 27.7 (or from 72.2 to 16.0 and 31.3 in repeated experiment) respectively, at harvest. In addition, both earthworm species increased soil microbial biomass, altered the structure of bacterial community and decreased the content of p-coumaric acid (PA), which may result in reducing the disease index. Earthworm E. fetida reduced PA from 53.22 to 30.98 (μg g−1), and M. guillemi reduced PA even more than E. fetida (from 53.22 to 13.15 (μg g−1)). Different earthworm species showed different capacities in reducing PA, a potential promoter to the growth of Fusarium oxysporum, which may lead to the different effects of the two earthworm species on the disease index.