Greens-type Annual Bluegrass Resistance to Abiotic and Biotic Stresses during Winter

Unseeded annual bluegrass (Poa annua L.) is an important component of golf greens in many regions of northern countries. Although this turfgrass species has desirable playing attributes, it suffers from susceptibility to environmental and biological stresses including subfreezing temperatures, anoxia, and snow molds. During the last decade (1999-2008), we undertook a series of experiments to better understand the mechanisms of adaptation and resistance of annual bluegrass to winter biotic and abiotic stresses. When assessing freezing tolerance of three genotypes originating from North Eastern Canada and United States, we observed that the genotypes differed significantly in their freezing tolerance with an unexpected lower level of tolerance for the genotype originating from the most northern latitude, in Québec, where the depth and duration of snow cover are important factors affecting winter survival. After assessing the level of organic reserves, the results showed that the genotype originating from Québec maintained higher levels of reserves than the two other genotypes. Our studies also showed that annual bluegrass is sensitive to anoxic conditions and that its susceptibility could be linked to the reduction of organic reserves under these conditions. We observed large genetic variability for pink snow mold resistance among 29 genotypes collected on golf greens located in Québec and Ontario and concluded that snow mold disease exerts major selection pressure for the generation of genetic diversity among annual bluegrass genotypes in northern climates. Our results suggest that high level of reserves is a characteristic of annual bluegrass genotypes adapted to deep, long lasting snow cover and could be more critical for winter survival than freezing tolerance to allow plants to survive long winter period without new carbohydrate synthesis.