In Vitro and In-Soil Suppression of Soybean Cyst Nematode by Fungi Isolated from Cyst Mycobiome.

Soybean cyst nematode (SCN; Heterodera glycines Ichinohe) is recognized as the most destructive soybean pathogen. Biological control of SCN using fungi associated with cyst nematodes (Heteroderidae) could be a promising strategy. In this study, we screened 75 fungal isolates representing 55 species associated with different cyst nematodes to assess antagonistic effects on SCN. A rapid 24-well plate in vitro assay was used to evaluate fungal cell-free filtrates for their effect on SCN egg viability and hatch. Filtrates of 14 isolates significantly reduced egg viability and hatch by inducing "vacuole-like" structural aberrations in SCN eggs. The 14 fungal isolates were further tested for their effect on SCN second-stage juvenile (J2) viability and direct egg parasitism. Filtrates of Alternaria tenuissima, Fusarium solani, Purpureocillium lilacinum, Debaryomyces hansenii, Plectosphaerella cucumerina, Arthopyrenia salicis, and Cosmospora lavitskiae resulted in the most significant reduction in egg viability. Filtrates of C. lavitskiae, D. hansenii, F. acaciae-mearnsii and F. solani were the most toxic to SCN J2 in the mortality assay. Trichoderma virens, A. tenuissima, F. acaciae-mearnsii and Pochonia chlamydosporia had the highest degree of SCN egg parasitism. Based on in vitro assays, 10 promising fungal isolates were selected for evaluation in a soil-based experiment. Trichoderma virens, P. lilacinum, and P. chlamydosporia significantly reduced SCN cyst and egg densities, while Talaromyces ramulosus, P. cucumerina, and C. lavitskiae provided moderate SCN suppression. These findings highlight the potential of nematophagous fungi isolated from cyst nematodes for SCN management and offer a screening approach for identifying potent fungal biocontrol agents.