Orchid mycorrhizal fungus from the Brazilian Cerrado exhibits biocontrol activity against Meloidogyne javanica.

Waitea circinata, an orchid-associated mycorrhizal fungus, was evaluated for the first time as a biological control agent against the root-knot nematode Meloidogyne javanica. The fungus was originally isolated from the roots of Epidendrum nocturnum, a rupicolous orchid to the Brazilian Cerrado. In vitro assays demonstrated that W. circinata parasitized nematode eggs, with parasitism rates of 13-15% and characteristic emergence of septate hyphae with right-angle branching. Microscopy revealed eggshell degradation, arrested embryogenesis, and juvenile deformation. A mycelial suspension (MSF) of the fungus increased juvenile (J2) mortality in a dose-dependent manner, suggesting the action of nematicidal metabolites. In greenhouse experiments, W. circinata significantly reduced the nematode reproduction factor (RF), with values dropping from above 5 in the control to below 1 at the highest concentrations. In addition, MSF application promoted plant growth, increasing root length, root mass, and shoot height. No phytotoxic effects were observed at any dose. Principal component analysis confirmed a negative correlation between nematode-related variables and plant development, reinforcing the dual action of W. circinata in nematode suppression and plant stimulation. These effects are likely mediated by a combination of mechanisms, including parasitism, enzyme activity, antibiosis, and the production of phytohormones. The results highlight W. circinata as a promising candidate for the sustainable management of plant-parasitic nematodes and the enhancement of crop performance.