Confronting An Old Enemy: Deciphering Rust Diseases of Turfgrass.

Rust is a common disease of cultivated turfgrass that can cause extensive damage in heavily infested areas. Chemical control is costly and sometimes ineffective; therefore protection against rust infection is often reliant upon improved cultivar resistance. Over the past ten years, increased susceptibility has been observed among several Kentucky bluegrass (Poa pratensis L.) cultivars, particularly the ‘Midnight’ types. Once highly resistant to rust, these cultivars now experience a greater incidence of disease. It has been theorized that novel species or races of the fungus responsible for rust on turfgrass may be accountable for this recent upsurge in disease, but the data required to test this hypothesis is lacking. In the current study, we are using molecular markers to characterize races and species of rust pathogens on turfgrass. To date, 116 rust infested leaf samples have been obtained from grasses in 20 U.S. states and several countries, including the United Kingdom, Australia, Chile, and Canada. A reliable DNA extraction protocol was developed and the internal transcribed spacer (ITS) region was amplified and sequenced. Phylogenetic analysis identified Puccinia graminis, P. striiformis, and P. coronata in infested turf samples. In particular, P. coronata, the crown rust fungus, was frequently identified on many cool-season grass hosts. Using the data generated from this study, rust specific molecular markers will be designed for use in development of a real-time PCR protocol to be utilized by breeders, pathologists and diagnosticians for quick identification of turfgrass rust pathogens.