Effects of earthworms and arbuscular mycorrhizal fungi on preventing Fusarium oxysporum infection in the strawberry plant

Background and aims Fusarium wilt is a devastating fungal disease in strawberries caused by Fusarium spp. We aimed to determine the role of earthworms and arbuscular mycorrhizal (AM) fungi in preventing Fusarium oxysporum (Fof) infection in strawberry plants. Methods AM fungi, Fof and the copy number of Actinomyces genes were determined by a quantitative real-time polymerase chain reaction. The Shannon-Wiener index for microbial communities was determined by their terminal restriction fragment length polymorphism profiles. Structural equation modelling was used to establish the relationships between the disease index and abiotic/biotic variables. Results Earthworms and AM fungi could individually or interactively prevent the infection of strawberry plants by Fof. Earthworms significantly decreased the copy number of Fof in the soil. The AM fungi increased the copy number of Actinomycetes and bacterial diversity and decreased the disease index of Fusarium wilt. Correlation analysis indicated that the root Ca and shoot Mg contents and the number of AM gene copies in plant roots had a significant negative correlation with the disease index of Fusarium wilt and the number of gene copies of Fof in plant roots. Conclusions The addition of earthworms and AM fungi to soil is a promising biological control method for the prevention of Fusarium wilt in strawberries and acts via an increase in the soil organic matter content, regulation of the soil environment, and improved root (P, Ca, Mg and Fe) and shoot (N, P, K, Ca and Mg) nutrient contents.