Wild trees in the Amazon basin harbor a great diversity of beneficial endosymbiotic fungi: is this evidence of protective mutualism?

It has been shown that the disappearance of, or drastic changes in, ancestral and indigenous (or native) endosymbiotic microbiota can lead to many adverse health consequences. However, the effects of changes in beneficial endosymbionts in plants are poorly known (except for mycorrhizal and rhizobial associations). We sampled and compared endophytes from hundreds of trees belonging to the economically important genus Hevea, the source of natural rubber, in their native range in the Amazon basin and in plantations. We also conducted antagonism tests to determine the potential effects that some of these endophytes may have on selected plant pathogenic fungi. The natural and indigenous endosymbiotic mycota of the rubber tree (Hevea) contains a high diversity of beneficial fungi that may protect against pathogens (protective mutualism). In contrast, plantation trees have a reduced and different diversity of these beneficial fungi. We propose that abundance, and not just presence, of competitive fungal strains and species (i.e., Trichoderma and Tolypocladium) create a protective effect against pathogens in wild trees. This study provides support for the importance of mutualistic endosymbionts in plant health and ecosystem resilience, and calls for awareness of their potential loss by human-related activities.