Variability for freezing tolerance among 42 ecotypes of green-type annual bluegrass

Limited information exists on the extent of genetic variability for freezing tolerance among perennial biotypes of annual bluegrass (Poa annua L.) that evolved under golf greens management. We characterized the freezing tolerance of 42 ecotypes collected across the United States and in Quebec using plants hardened to low temperatures during fall and winter. We subsequently analyzed cold-induced biochemical changes in a subset of ecotypes with varied levels of tolerance. There was a large variability among ecotypes for freezing tolerance expressed as the lethal temperature for 50% of the plants (LT₅₀) with values ranging from <-27.0 to -17.0°C. Variation was observed between ecotypes originating from the same region and even the same golf course. Ecotypes from Quebec-better insulated from extreme subfreezing temperatures by reliable and abundant snow cover-developed less freezing tolerance than those evolving under milder winter climates. Signifi cant differences in the concentrations of specifi c amino acids and carbohydrates were observed among ecotypes. Only fructans of high molecular weight, however, were significantly correlated with freezing tolerance and accounted for as much as 50% of the LT50 variance. A 26-kDa polypeptide that markedly accumulated in cold acclimated crowns was more abundant in plants from Quebec. Extensive genetic variability for freezing tolerance among perennial biotypes of annual blue grass can thus be exploited to mitigate winter damage to golf greens.