Interactions Between Clonostachys rosea f. catenulata, Fusarium oxysporum and Cucumber Roots Leading to Biological Control of Fusarium Root and Stem Rot

Abstract

Clonostachys rosea f. catenulata (Gliocladium catenulatum) strain J1446 (formulated as Prestop WP) suppressed Fusarium root and stem rot caused by Fusarium oxysporum f. sp. radicis-cucumerinum on greenhouse cucumber plants. In culture, C. rosea produced chitinase and β-1,3-glucanase enzymes on chitin or laminarin as a sole carbon source, respectively, and caused localized degradation of Fusarium hyphae. These enzymes were also induced by growth on Fusarium mycelial fragments and homogenized cucumber roots in vitro. Cucumber root extracts from C. rosea-colonized plants had significantly higher levels of glucanase at 7 days post-application compared to untreated controls. Reverse-transcription polymerase chain reaction using primers designed to amplify a β-1,3-glucanase gene confirmed C. rosea glucanase expression on roots. Following transformation of the biocontrol agent with Agrobacterium tumefaciens strain AGL-1 containing the hygromycin resistance (hph) and β-glucuronidase (uidA) genes, blue-stained mycelia could be seen growing on the surface and within epidermal and cortical cells of roots, stems and shoots 3 weeks after treatment. Application of C. rosea preceding inoculation with Fusarium significantly reduced pathogen populations on roots compared to plants inoculated with Fusarium alone, while densities of the biocontrol agent appeared to increase in the presence of the pathogen. Colonization of infection sites by C. rosea in the root zone is one of the mechanisms by which pathogen development and disease incidence is reduced.