Fungal Endophyte-Nematode Interactions in Cotton: Is the Effect Endophytic and Does It Work in the Field?

All plants including cotton host a wide range of microorganisms as endophytes. Increasing evidence suggests that many members of the plant microbiome may be beneficial mutualists that can confer protection to plants from a variety of abiotic and abiotic stressors including nematodes, pathogens and insects. In greenhouse assays, we have consistently demonstrated negative effects of two candidate endophytic fungi on root-knot nematode (Meloidogyne incognita) egg production using a seed treatment for endophytic establishment.  However, a key unresolved question was whether the negative effect of the candidate fungi was mediated by its actions when present as an endophyte versus incidental colonization of soil by spores as a result of planting treated seeds.  We conducted a seedling transplant experiment following a fungicide treatment to test for an effect of the presence of candidate fungi in the soil versus endophytically within the plant on penetration and early gall formation by root-knot nematodes. Infection levels of cotton seedling roots by nematodes were lower in endophyte-treated plants relative to untreated plants.  Importantly, the effect of the endophyte-treatment was maintained even when soil fungi were killed with a fungicide prior to nematode inoculation, suggesting that the observed negative effects on nematodes were mediated by the presence of the fungi within the plant as an endophyte. The preliminary results of field trials conducted in 2013 against both root-knot and reniform nematodes will also be discussed.