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NCER Grantee Research Project Results

Ecological Determinants Of Population Structure And Gene Flow Between Sympatric Fungal Species In The Genus Colleotrichum From Diverse Grass Communities

EPA Grant Number: F5F11594
Title: Ecological Determinants Of Population Structure And Gene Flow Between Sympatric Fungal Species In The Genus Colleotrichum From Diverse Grass Communities
Investigators: Crouch, Jo Anne
Institution: Rutgers SUNJ
EPA Project Officer: Jones, Brandon
Project Period: September 1, 2005 through August 1, 2008
Project Amount: $109,148
RFA: STAR Graduate Fellowships (2005)
Research Category: Academic Fellowships

Description:

Objective:

The fungal genus Colletotrichum contains several species infecting monocot hosts in both cultivated and natural grass communities. In monocultured agroecosystems, these fungi are often found as destructive pathogens, capable of inducing significant disease in the host plant. In contrast, my recent sampling of C. cereale in a natural tallgrass prairie ecosystem suggests that populations of this fungus living in diverse grass communities maintain a non-pathogenic lifestyle, with their presence never correlated with substantial disease. Preliminary multi-locus phylogenetic analysis supports the presence of a single lineage of Colletotrichum in the grassland environment, but transposon distribution data and RFLP patterns suggest that these populations may actually represent a hybrid zone between distinct Colletotrichum phylogenetic species. Part of this project is currently evaluating whether natural grasslands represent regions of hybridization for Colletotrichum species that inhabit Pooideae grasses.

  1. Determine species boundaries and evolutionary relationships of the Colletotrichum species inhabiting grasses of the Poaceae,
  2. Establish whether the populations of C. cereale from pooid grasses are dominated by a disproportionate proliferation of a few successful clonal lineages,
  3. Investigate the possibility that C. cereale Clade A is a recent introduction to North America and is responsible for recent epidemic levels of disease and
  4. Determine the extent to which ecological gradients in natural grasslands represent regions of hybridization between C. cereale Clade A and Clade B, potentially mitigating the potential of Clade A to initiate disease in these environments.

Approach:

Using Bayesian likelihood phylogenetic analyses of nucleotide sequences from three unlinked nuclear loci, there is now compelling evidence of sympatric, species-level phylogenetic divergence between Colletotrichum pathogenic to Zea mays and Colletotrichum specimens causing disease in grasses of the subfamily Pooideae. Data has also revealed two lineages emerging along distinct evolutionary trajectories among isolates sampled from Pooideae grasses, including several pooid species cultivated as turfgrasses. Haplotype analysis using split decomposition network analysis and compatability matrixes demonstrate reticulate patterns of evolution, suggesting recombination occurs between the lineages. Nucleotide substitution rates consistent with positive adaptive selection at the fungal mating-type gene suggest that reinforcement may have played a role in reproductively isolating these unique sibling species as they emerged in host-range restricted ecological niches. Transposon distribution patterns and RFLP fingerprint analysis extend my phylogenetic estimations, independently supporting the conclusion that several closely related cryptic species of Colletotrichum inhabit the grasses of North America.

Currently being developed is a set of microsatellite markers to generate the hypervariable genetic data needed to explore how variation is distributed spatially within Colletotrichum populations inhabiting different ecosystems. Coalescent-based population analysis of the Bayesian-defined populations will allow me to describe how genetic variation is distributed spatially within the C. cereale species range in both agroecosystems and natural grassland environments.

Expected Results:

This comparative analysis will allow us to detect historical events of interest such as population fragmentations, range expansions, and colonization in the Colletotrichum species that inhabit pooid grasses. What is learned from C. cereale populations in agronomic monocultures and prairie grasslands today may help predictions, and perhaps even prevent the next cycle of disease. Such knowledge is vitally important, especially when one considers that the host range for this pathogen includes most of our major grain crops, including wheat, oats, barley, and rye. These findings will serve as a valuable technical resource, improving the ability to predict, manage, and control the movement of high-risk phytopathogens into agroecosystems. The integration of this research promises to contribute greatly to the understanding of emerging phytopathogen systems, while also serving as an important empirical study of how ecogeographic patterns relate to spatial population structure and evolutionary history.

Supplemental Keywords:

plant disease, prairie grasslands, agroecosystems,, RFA, Scientific Discipline, Ecosystem Protection/Environmental Exposure & Risk, Monitoring/Modeling, Environmental Monitoring, Ecology and Ecosystems, plant fungus, ecological risk, genotypes, agrobiodiversity, predicting environmental change, prairie grass

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The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.

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