Examining the evolutionary interactions of loblolly pine with both beneficial and pathogenic fungi
Genetic correlations between traits may influence how species evolve under multiple, conflicting selection pressures, which may constrain or enhance the adaptation of species to each other and to other sources of selection. Loblolly pine (Pinus taeda) is important both as an economic crop and as a wide-ranging dominant species throughout the southeastern United States. It is subject to natural selection from both biotic and abiotic sources, as well as artificial selection for favorable economic traits. Using a combination of field and laboratory studies, we investigated the underlying genetic structure of multiple adaptive traits in loblolly pine. Specifically, we ascertained mycorrhizal colonization on the root systems of 140 loblolly genotypes (each clonally triplicated) in a pedigree population to determine i) the narrow-sense heritability of above-ground and below-ground traits, including susceptibility to pathogenic fungi and compatibility with symbiotic fungi and ii) the degree to which these traits are genetically correlated with one another and with SNPs in loblolly candidate genes. Additionally, we conducted a laboratory experiment using loblolly families either tolerant or susceptible to different fungal pathogens, assessing mycorrhizal colonization when planted in different field soil types to determine iii) variation among these P. taeda families in compatibility with different mycorrhizal communities.
In the field study, we found measurable narrow-sense heritability for both above- and below-ground pine traits, including susceptibility to the disease-causing fusiform rust (Cronartium fusiforme), resistance to attack by tip moth (Rhyacionia sp.), compatibility in forming mycorrhizae with particular fungal species, and overall mycorrhizal fungal diversity. We also determined genetic correlations between these traits, and associations between these traits and SNPs located in loblolly candidate genes. In the laboratory experiment, we observed differences in the mycorrhizal fungal community in different field soils, and genetic variation in patterns of association with different mycorrhizal fungi by P. taeda. While the abundance of certain fungi was determined solely by soil type, we also found correlations between susceptibility to pathogenic fungi and compatibility with certain symbiotic fungi. These results shed light on the underlying genetic structure of coevolving traits and how it may affect the evolution and adaptation of species. In addition, understanding the genomic architecture of how important adaptive traits are related to one another is an essential component of successful breeding and management strategies.