Genetically determined fungal pathogen tolerance and soil variation influence ectomycorrhizal traits of loblolly pine.

Bridget J Piculell,Jason D Hoeksema,Lori G Eckhardt

doi:10.1002/ece3.4355

Bridget J Piculell, Jason D Hoeksema + Show 1 more

Open Access

https://doi.org/10.1002/ece3.4355

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Abstract

Selection on genetically correlated traits within species can create indirect effects on one trait by selection on another. The consequences of these trait correlations are of interest because they may influence how suites of traits within species evolve under differing selection pressures, both natural and artificial. By utilizing genetic families of loblolly pine either tolerant (t) or susceptible (s) to two different suites of pathogenic fungi responsible for causing either pine decline or fusiform rust disease, we investigated trait variation and trait correlations within loblolly pine (Pinus taeda L.) by determining how ectomycorrhizal (EM) colonization relates to pathogen susceptibility. We detected interactions between susceptibility to pathogenic fungi and soil inoculation source on loblolly pine compatibility with the EM fungi Thelephora, and on relative growth rate of loblolly pine. Additionally, we detected spatial variation in the loblolly pine–EM fungi interaction, and found that variation in colonization rates by some members of the EM community is not dictated by genetic variation in the host plant but rather soil inoculation source alone. The work presented here illustrates the potential for indirect selection on compatibility with symbiotic EM fungi as a result of selection for resistance to fungal pathogens. Additionally, we present evidence that the host plant does not have a single “mycorrhizal trait” governing interactions with all EM fungi, but rather that it can interact with different fungal taxa independently. Synthesis. An understanding of the genetic architecture of essential traits in focal species is crucial if we are to anticipate and manage the results of natural and artificial selection. As demonstrated here, an essential but often overlooked symbiosis (that between plants and mycorrhizal fungi) may be indirectly influenced by directed selection on the host plant.

Highlights

Selection on genetically correlated traits within species can create indirect effects on one trait by selection on another
To determine if EM fungal morphotype composition differed among soil inoculation sources (Question 1), permutational MANOVA was performed using the adonis function from the vegan package in R (Oksanen et al, 2015), with the response variable being a Bray–Curtis dissimilarity matrix generated using the vegdist function from the vegan package (Oksanen et al, 2015), and the predictor variables Soil (MS, GA, AL), Genetic Category, TA B L E 2 Morphological characteristics of the four dominant ectomycorrhizal fungal morphotypes found on loblolly pine (Pinus taeda L.) seedlings
The studies presented here lend evidence that several traits of loblolly pine that govern its interaction with members of the fungal community are likely genetically correlated

Summary

| INTRODUCTION

Selection on genetically correlated traits within species can create indirect effects on one trait by selection on another. Several studies have shown variation among loblolly pine genetic families in their susceptibility to both fusiform rust disease (Isik et al, 2008; Li, McKeand, & Weir, 1999) and pine decline (Singh, Anderson, & Eckhardt, 2014) Studies such as these demonstrate the potential for evolution of pathogen tolerance in response to artificial and natural selection, but what we do not know is how selection on these traits might influence other important traits of loblolly pine, such as those mediating interactions with other species or communities, such as the soil borne mycorrhizal fungal community. The experiment utilized multiple genetic families of loblolly pine previously determined to be either tolerant or susceptible to two different suites of pathogenic fungi responsible for causing either pine decline or fusiform rust disease, and exposed those families to different mycorrhizal fungal inoculation regimes. How do other traits (host plant relative growth rate [RGR], root– shoot ratio, and number of root tips colonized by EM fungi per cm root) respond to host genetic variation in pathogen tolerance and does this depend on origin of the fungal community?

| MATERIALS AND METHODS

Findings

| DISCUSSION