The endophytobiome of wild Rubiaceae as a source of antagonistic fungi against the American Leaf Spot of coffee (Mycena citricolor)

Aims: The American leaf spot, caused by Mycena citricolor, is an important disease of coffee (Coffea arabica), mostly in Central America. Currently, there are limited pathogen control alternatives that are environment friendly and economically accessible. The use of fungi isolated from the plant endomycobiota in their native habitats is on the rise because studies show their great potential for biological control. To begin to generate a green alternative to control M. citricolor, the objectives of the present study were to (i) collect, identify, screen (in vitro and in planta), and select endophytic fungi from wild Rubiaceae collected in old-growth forests of Costa Rica; (ii) confirm endophytic colonization in coffee plantlets; (iii) evaluate the effects of the endophytes on plantlet development; and (iv) corroborate the antagonistic ability in planta. Methods and results: Through in vitro and in planta antagonism assays, we found that out of the selected isolates (i.e. Daldinia eschscholzii GU11N, Nectria pseudotrichia GUHN1, Purpureocillium aff. lilacinum CT24, Sarocladium aff. kiliense CT25, Trichoderma rifaii CT5, T. aff. crassum G1C, T. aff. atroviride G7T, T. aff. strigosellum GU12, and Xylaria multiplex GU14T), Trichoderma spp. produced the highest growth inhibition percentages in vitro. Trichoderma isolates CT5 and G1C were then tested in planta using Coffea arabica cv. caturra plantlets. Endophytic colonization was verified, followed by in planta growth promotion and antagonism assays. Conclusions: Results show that Trichoderma isolates CT5 and G1C have potential for plant growth promotion and antagonism against Mycena citricolor, reducing incidence and severity, and preventing plant mortality.