Molecular analysis and infectivity of Puccinia species pathogenic to turfgrass

Rust (Puccinia spp.) has become an increasingly prevalent disease of cool-season turfgrasses over the past two decades. Unlike the cereal rust pathosystem, pathogen biology, populations, races, and species of rust fungi associated with turfgrasses have not been well studied. In this thesis, isolates of turfgrass rust fungi from the United States and four other countries were evaluated for genetic variation within the ribosomal internal transcribed spacer (ITS) region and were identified using phylogenetic analysis. Three rust species were revealed in the sample collection: Puccinia coronata, P. graminis, and P. striiformis. P. coronata was frequently found in association with Kentucky bluegrass (Poa pratensis), a host/pathogen relationship that has not been previously reported. Since the ITS region exhibited sufficient nucleotide variation for the identification of turfgrass rust species within the sample collection, this region was used to design species-specific primers and probes for the development of an accurate, reliable, real-time PCR assay to rapidly diagnose rust fungi from diseased turfgrass tissue. Accurate, reproducible species identifications were made using as few as 50-150 urediniospores, even in mixed infections. This protocol was designed so that diagnosticians, pathologists, and turfgrass breeders who may have limited molecular training can identify rust species on turfgrass with relative ease. This study represents the first DNA-based evaluation of turfgrass rust fungi and provides a quick and reliable sequence-based protocol as an alternative to error-prone field-based identification techniques. However, research and breeding efforts are still impeded by the inability to rapidly screen new turfgrass germplasm for resistance to rust and difficulty in obtaining pure isolates of rust fungi for genotyping analysis. By adapting and modifying a protocol designed for cereal rust fungi, an inoculation procedure was developed for two turfgrass rust species prevalent in temperate regions: P. coronata and P. graminis. Uredinia of both species were induced on Kentucky bluegrass cultivars Bewitched, Diva, and Ulysses 14 days after inoculation. The molecular, diagnostic, and infectivity studies described in this thesis will serve as a foundation for future research on the rust fungi that attack turfgrass.M.S.Includes bibliographical referencesIncludes vitaby Lisa A. Beir