Submitted to: PLoS One
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/22/2014
Publication Date: 5/19/2014
Citation: Beirn, L., Clark, B., Crouch, J. 2014. Influence of host and geographic locale on the distribution of Colletotrichum cereale lineages. PLoS One. 9(5):e97706. doi:10.1371/journal.pone.0097706. Interpretive Summary: Anthracnose diseases are caused by fungal-like parasites that cause significant damage to crop plants in the United States. Severe outbreaks of anthracnose disease destroy turfgrass across North America each year. This research describes the distribution of fungi responsible for turfgrass anthracnose disease using DNA-based tools. This research shows that the distribution of turfgrass anthracnose pathogens is impacted by geographic location, with populations of the fungus in warmer southern regions of the continent structured differently than populations of the fungus in cooler northern regions. These results suggest that climate may influence the spread of anthracnose disease fungi in North America.
Technical Abstract: Colletotrichum cereale is an ascomycete inhabitant of cool-season grasses of the Pooideae subfamily. The fungus has increased in frequency over the past decade as a destructive pathogen of Poa annua and Agrostis stolonifera cultivated as turfgrass. DNA fingerprinting has revealed two distinct C. cereale lineages, designated clade A and clade B. Little is known about the distribution of these clades in natural environments, or what role the subdivision of C. cereale may play in the trajectory of recent disease outbreaks. In this study, our objective was to determine the frequency of C. cereale clades A and B in the environment. To rapidly discriminate between the two C. cereale clades, a dual-labeled hydrolysis probe-based real-time PCR assay was developed based on eight adjacent SNPs situated within a 103-bp segment of the Apn2 gene. The assay was used to genotype a sample of 701 C. cereale pathogens and endophytes of 20 Pooideae grass genera. C. cereale was detected from 98.4% of the samples. The assay was 100% accurate in diagnosing clade affiliation, with the Sanger-sequenced genotypes of 85 C. cereale isolates matching data from the real-time PCR assay. Overall, 87% of the C. cereale sample was identifed as part of clade A, 11.7% was identified as part of clade B, and 1.3% was identified as a mixture of clades A and B. The overabundance of clade A was observed from both modern samples (<36 years old) and fungarium specimens (75-105 years old). On average, C. cereale isolates from turfgrass hosts in North America were most commonly members of clade A (81%). The overabundance of clade A in turfgrass isolates of C. cereale was directly attributable to the dominance of this lineage from southern sampling sites, where 97.5% of the 154 isolates were members of clade A, regardless of host origin. In contrast, the 111 C. cereale isolates made from northern sampling sites were evenly distributed between clades A and B. Only 28% of the C. cereale isolates made from A. stolonifera at northern sampling sites were part of clade A. These data show that environmental factors such as geographic location and host identity likely played a role in the distribution of the major C. cereale clades in North American turfgrass.