Mutualistic plant-endophyte symbioses can benefit plants by increasing host fitness through reductions in herbivory. The fungus, Chaetomium globosum strain TAMU 520, was previously isolated as an endophyte from cotton (Gossypium hirsutum) and can be re-inoculated to systemically colonize cotton plants via seed treatment. We evaluated the potential impacts of the endophyte in cotton on plant parasitic nematodes belowground, along with piercing-sucking and chewing insects aboveground. Endophytic C. globosum inhibited root-knot nematode (Meloidogyne incognita) infection and reduced female reproduction belowground. To confirm the endophytic effect of C. globosum on root-knot nematode, a contact fungicide was applied to remove soil-borne and epiphytic C. globosum Consistent inhibition of nematode activity was observed post-fungicide treatment, with positive C. globosum colonization confirmed within plant tissues. Aboveground, endophytic C. globosum also negatively affected the fecundity of both cotton aphids (Aphis gossypii) and beet armyworms (Spodoptera exigua). Faster development rates and smaller head capsule of beet armyworm larvae were observed when fed Chaetomium-colonized plants. However, no larval weight difference was found between Chaetomium-colonized and control plants. No consistent effect on plant performance was found across experiments. Our findings illustrate how a single facultative fungal endophyte can increase plant systemic resistance against a range of invertebrate herbivores in a major crop.

Studies of fungi in upland cotton (Gossypium hirsutum) cultivated in the United States have largely focused on monitoring and controlling plant pathogens. Given increasing interest in asymptomatic fungal endophytes as potential biological control agents, surveys are needed to better characterize their diversity, distribution patterns and possible applications in integrated pest management. We sampled multiple varieties of cotton in Texas, USA and tested for temporal and spatial variation in fungal endophyte diversity and community composition, as well as for differences associated with organic and conventional farming practices. Fungal isolates were identified by morphological and DNA identification methods. We found members of the genera Alternaria, Colletotrichum and Phomopsis, previously isolated as endophytes from other plant species. Other recovered species such as Drechslerella dactyloides (formerly Arthrobotrys dactyloides) and Exserohilum rostratum have not, to our knowledge, been previously reported as endophytes in cotton. We also isolated many latent pathogens, but some species such as Alternaria tennuissima, Epicoccum nigrum, Acremonium alternatum, Cladosporium cladosporioides, Chaetomium globosum and Paecilomyces sp., are known to be antagonists against plant pathogens, insects and nematode pests. We found no differences in endophyte species richness or diversity among different cotton varieties, but did detect differences over time and in different plant tissues. No consistent patterns of community similarity associated with variety, region, farming practice, time of the season or tissue type were observed regardless of the ecological community similarity measurements used. Results indicated that local fungal endophyte communities may be affected by both time of the year and plant tissue, but the specific community composition varies across sites. In addition to providing insights into fungal endophyte community structure, our survey provides candidates for further evaluation as potential management tools against a variety of pests and diseases when present as endophytes in cotton and other plants.

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A number of fungi have been shown to have negative effects on plant-parasitic nematodes. Most of these fungi have been isolated from soil, plant roots, or nematodes themselves. Fungi associated with crops can provide a diverse pool of candidates to test for antagonistic effects against plant parasites and other stressors. We used a hierarchical two-tiered approach to evaluate the efficacy and repeatability of 55 strains of fungi originally isolated as foliar facultative endophytes from upland cotton (Gossypium hirsutum) along with one commercial isolate of Beauveria bassiana for in planta antagonistic effects on root-knot nematodes (Meloidogyne incognita). All fungi were inoculated to cotton using a seed treatment. The number of root galls was quantified 3 weeks after egg inoculation of cotton seedlings. The majority of the fungi tested reduced the number of root galls relative to those on untreated control plants. To assess repeatability, 22 strains that exhibited the strongest reductions in gall numbers were further tested in replicate follow-up assays. Ninety-five percent (21/22) of these retested strains significantly reduced galling in the follow-up assay. Strains that reduced galling the most belonged to the genera Alternaria, Chaetomium, Cladosporium, Diaporthe, Epicoccum, Gibellulopsis, and Purpureocillium. On the contrary, three strains in the genera Alternaria and Curvularia significantly increased gall numbers. Our results indicate that a large proportion of the fungal strains originally isolated from cotton as naturally occurring foliar facultative endophytes are capable of reducing root-knot nematode infection when applied back to the plant as a seed treatment. These findings help establish a rich pool of candidate fungi for further evaluation as novel biological control tools against root-knot nematodes in cotton and other plants.