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Kentucky bluegrass (Poapratensis L.) is a widely used, facultatively apomictic, cool season turf and forage grass, with many known cultivars. Previously these have been classified on the basis of morphological traits in field tests. However, these determinations are lengthy, sensitive to environmental variations, and there are few traits that can be tested. Molecular markers provide an alternative way to classify these cultivars. Important advantages of molecular markers include lack of sensitivity to changes in environmental conditions, as well as a nearly unlimited potential number of markers and speed of the marker assays as compared with field tests. They can also provide additional information such as the amount of genetic divergence between Kentucky bluegrass cultivars and other genotypes, the amount of agreement between morphological and marker-based classification, and the amount of genetic variability between seedling replicates of genotypes. Random amplified polymorphic DNA (RAPD) marker data was collected from three replicates each of 123 Kentucky bluegrass cultivars, plant introductions (PIs), experimental breeding lines, and interspecific hybrids between Kentucky and Texas bluegrass (Poa arachnifera Torr.). From these data multidimensional scaling (MDS) plots were created, and ANOVA tests of significant differences between germplasm sources were performed. The Pis were the most genetically divergent from the cultivars, while the interspecific hybrids were not as distinct. Members of two morphological trait-based types were found to be genetically similar, and there was a wide range of genetic variability among germplasm sources. The genetic divergence of the PIs, combined with their potentially high turf utility reported in earlier studies, indicates their potential as a genetic resource. All but two of the morphological trait-based types contained genetically diverse individuals, so that cultivar blends of all but these two types would be morphologically similar yet genetically diverse. The rather high within-cultivar genetic variability could be due to a relatively high proportion of potentially sexually produced off-types. Thus, this study provides further evidence for the utility of RAPD markers for turfgrass genetics, as well as important genetic information for turf breeders and managers. [ABSTRACT FROM AUTHOR]

Typhula incarnata, the causal agent of gray snow mold, is an important winter pathogen of turfgrasses in the northern United States. The relative susceptibility of cultivars of three bent-grass species (creeping, colonial, and velvet bentgrass) to Typhula incarnata and the aggressiveness of 15 T incarnata isolates obtained from infected turfgrasses on golf courses in Michigan, Minnesota, and Wisconsin were evaluated under controlled conditions. A hypersensitive type of resistance response to T incarnata was not observed in any cultivar. Disease severity increased with higher inoculum concentration of T. incarnata. Colonization by gray snow mold gradually decreased with increasing plant age from 11 weeks after seeding in most cultivars tested, suggesting that age-related resistance was expressed over time. There were significant differences in disease severity among the three bentgrass species, particularly between tetraploid (creeping and colonial) and diploid (velvet) species, and among cultivars within each species, indicating varying levels of susceptibility to T. incarnata. All 15 isolates were pathogenic on bentgrass and were significantly different in aggressiveness, but aggressiveness was not related to geographic origin. Therefore, turfgrass breeders should be able to use one or a few virulent representative isolates of the pathogen to screen for resistance. [ABSTRACT FROM AUTHOR]

Snow molds are psychrophilic fungi that grow under snow cover by taking advantage of carbohydrate-depleted, dormant plants. Typhula snow molds caused by Typhula incarnata, T. phacorrhiza, and T. ishikariensis are the most important winter diseases of perennial grasses and winter cereals in the United States. Colonized turfgrass samples with sclerotia were collected from 135 golf courses in Wisconsin, Utah, Michigan, and Minnesota in spring 2001 and 2002. Species and varieties from a total of 2,864 samples were identified using Typhula spp.-specific polymerase chain reaction markers. All three species were found throughout the states sampled, except T. phacorrhiza, which was not found in Minnesota. T. incarnata was distributed in areas of shorter snow cover duration and higher mean temperature than T. ishikariensis. Canonical correspondence analysis indicated that snow cover days and mean temperature were significantly correlated with frequency of Typhula spp. and T. ishikariensis varieties infecting turfgrasses on golf courses in Wisconsin, and that T. incarnata, T. phacorrhiza, and T. ishikariensis were ecologically distinct based on the 2001 data. However, because these two variables accounted for a relatively small proportion of total variation, other environmental variables also may be important in characterizing the distribution of these pathogens and require further study. [ABSTRACT FROM AUTHOR]