Common foliar fungi of Populus trichocarpa modify Melampsora rust disease severity

Abstract

Summary Nonpathogenic foliar fungi (i.e. endophytes and epiphytes) can modify plant disease severity in controlled experiments. However, experiments have not been combined with ecological studies in wild plant pathosystems to determine whether disease‐modifying fungi are common enough to be ecologically important. We used culture‐based methods and DNA sequencing to characterize the abundance and distribution of foliar fungi of Populus trichocarpa in wild populations across its native range (Pacific Northwest, USA). We conducted complementary, manipulative experiments to test how foliar fungi commonly isolated from those populations influence the severity of Melampsora leaf rust disease. Finally, we examined correlative relationships between the abundance of disease‐modifying foliar fungi and disease severity in wild trees. A taxonomically and geographically diverse group of common foliar fungi significantly modified disease severity in experiments, either increasing or decreasing disease severity. Spatial patterns in the abundance of some of these foliar fungi were significantly correlated (in predicted directions) with disease severity in wild trees. Our study reveals that disease modification is an ecological function shared by common foliar fungal symbionts of P. trichocarpa. This finding raises new questions about plant disease ecology and plant biodiversity, and has applied potential for disease management.

Dimensions of biodiversity in the Earth mycobiome

“…leaves by some common endophytic fungi, such as Cladosporium spp. and Alternaria spp., caused up to an 85-fold variation in the severity of rust disease 91 . Similarly, increasing evidence suggests that communities of endophytic fungi contain wood decomposer fungi that are present in a latent state prior to plant death.…”

A Multiscale Approach to Plant Disease Using the Metacommunity Concept

“…Empirical data support the utility of the metacommunity framework in this context. For example, coinfection of hosts by a suite of common foliar fungi alters disease severity in Populus trichocarpa by Melampsora rust disease and also may alter the probability of among-host pathogen transmission (29). Pathogen diversity (i.e., coinfection) within hosts also has been documented to increase with host size (86,87,124,125), possibly because larger hosts tend to be longer lived, thus accumulating pathogens over a longer time period.…”

“…Recent work using next-generation sequencing and culture-based tools to quantify the substantial microbial diversity within plants underscores the likelihood that within-host microbial population growth and interactions play an important role in mediating among-host microbial transmission (29). Concomitant with our ability to quantify the diversity of plant microbiomes is a growing realization that community ecology, microbial ecology, the ecology of infectious disease, and plant pathology are tightly aligned fields (20,50,112).…”

Ecological patterns of seed microbiome diversity, transmission, and assembly

“…In addition, the composition of the plant microbiota can enhanced host resistance to aboveground [6,7] and belowground [8,9] pathogens. The promise of plant benefits from plant microbiota opens new possibilities for increasing plant productivity or wellness through manipulation of the composition of these assemblages.…”