| Spring dead spot (SDS) is a destructive disease of bermudagrass throughout the transition climatic zone of the United States, New Zealand, and Australia. Three ectotrophic root-rotting fungi (Ophiosphaerella herpotricha, O. korrae, and Leptosphaeria narmari) cause SDS. One objective of my research was to investigate the phylogenetic relationships among these species by studying the nucleotide sequence of the ITS region of the rDNA. High levels of sequence similarity were observed among the species and they clustered into a distinct clade that was distant from other Leptosphaeria and Phaeosphaeria species. Based on sequence data and morphological characteristics of these species, I propose a taxonomic transfer of L. narmari to O. narmari . The second objective of my research was to assess the distribution and genetic diversity of the three Ophiosphaerella spp. by systematically sampling two golf courses in Oklahoma and one in Kansas. PCR primers, specific for each Ophiosphaerella spp., aided in the identification of non-sporulating isolates collected. Of 5 13 isolates collected from the three courses, 445 were O. herpotricha, 47 were O. korrae, and 21 were O. narmari. This is the first report of O. narmari in North America and the first finding of O. korrae in the Great Plains region on bermudagrass. The amplified fragment length polymorphism (AFLP) technique was used to investigate intraspecific genetic diversity. Overall, genetic diversity in O. herpotricha and O. narmari were greater than in O. korrae isolates assessed. The majority of the O. herpotricha and O. narmari isolates were distinct haplotypes, suggesting that sexual recombination was occurring. However, some haplotypes represented multiple isolates, indicating that these fungi were also propagating asexually. The genetic diversity within O. korrae was much less since identical haplotypes were collected from wide geographic regions including western and northern North America and Australia. Finding identical haplotypes within a species over wide geographic areas suggests that these pathogens maybe moved via vegetatively propagated sections of their respective host turfgrass species. |
