Tapping into the Cotton Fungal Phytobiome for Novel Nematode Biological Control Tools

An increasing number of fungi have been shown to have nematicidal properties. Most of these fungi were isolated from soil, plant roots, or nematodes themselves. We used a two-tiered approach to evaluate the efficacy and repeatability of 56 strains of fungi originally isolated as foliar endophytes from cotton (Gossypium hirsutum) for antagonistic effects on root-knot nematodes (Meloidogyne incognita). All fungi were inoculated to cotton using a seed treatment. A majority of the fungi tested had negative effects on root-knot nematode galling three weeks after egg inoculation of cotton seedlings. Across replicated greenhouse assays, 40% percent of the strains exhibited consistent statistically significant negative effects. Strains with consistent negative effects belonged to the genera Chaetomium, Cladosporium, Epicoccum, and Phomopsis. Three strains in the genera Bipolaris, Chaetomoium, and Phomopsis had an opposite effect and significantly increased gall numbers. Our results indicate that a large proportion of naturally-occurring fungal endophytes in cotton are capable of conferring some degree of resistance to the plant from root-knot nematode infection. These findings help establish a rich pool of candidate fungi derived from cotton for further evaluation as novel biological control tools against root-knot nematodes in cotton and other plants.