The plant growth‐promoting fungus Fusarium equiseti and the arbuscular mycorrhizal fungus Glomus mosseae stimulate plant growth and reduce severity of anthracnose and damping‐off diseases in cucumber (Cucumis sativus) seedlings

To alleviate the environmental contamination due to persistent chemical usage, approaches to integrated pest management were conceived. In this perspective, microbe–microbe interactions such as mycorrhizal relationships with other soil microbiota in the rhizosphere like the plant growth‐promoting fungi (PGPF) are particularly important. Better understanding of the interactions between beneficial microbial groups is imperative in the identification of possible synergistic or antagonistic effects to improve their practical usage as biocontrol agents or biofertilizers. In this study, the consequence of co‐inoculation of the arbuscular mycorrhizal fungus (AMF) Glomus mosseae (Gm) and the PGPF Fusarium equiseti (isolates GF18‐3 and GF19‐1) in terms of plant growth enhancement, root and rhizosphere colonisation, and development of anthracnose (Colletotrichum orbiculare) and damping‐off (Rhizoctonia solani AG‐4) diseases in cucumber plants was investigated under controlled conditions. The amendment of either GF18‐3 or GF19‐1 singly or in combination with Gm indicated a general tendency to significantly enhance the shoot dry weight (SDW) of cucumber plants at 4 weeks after planting (WAP). Similarly, Gm alone significantly enhanced SDW at 4 WAP. Gm showed a tendency to depress root colonisation by F. equiseti but such antagonistic effect was not observed in the rhizosphere soil. Both GF18‐3 and GF19‐1 significantly reduced percent root colonisation of Gm. However, these general tendencies may vary with the inoculum densities of AMF and PGPF. Both F. equiseti and Gm inoculated singly significantly increased percent of protection against anthracnose, but the combined inoculation was more effective in controlling the disease compared to single inoculation. The inoculation of the cucumber seedlings with GF18‐3, GF19‐1 or Gm, 6 or 12 days prior to damping‐off pathogen inoculation, increased percent of protection against damping‐off disease. This study shows that the co‐inoculation of F. equiseti and Gm resulted in additive effect on the suppression of anthracnose disease in cucumber.