Plant Mechanisma Associated with Variations in Freezing Tolerance of Cool- Season Grasses

Cool-season grasses are adapted to seasonal decreases in temperature that in some areas reach well below freezing; however, despite being able to acclimate to such conditions, plants may still be susceptible to winter injury. Specifically, direct low temperature kill caused by freezing temperatures has been identified as a major component of winter injury across many plant species including turfgrasses. Although cool-season species are the grasses of choice for Northern climatic regions, a high degree of variability in freezing tolerance exists among cool-season turfgrasses. Tolerance to freezing temperatures is influenced by both the capacity of plants to cold acclimate prior to the onset of winter and the ability to withstand decreases in freezing tolerance (deacclimation) during winter and early spring months. Therefore, the objectives of my dissertation research were to (i) evaluate the physiological and biochemical modifications occurring during the cold acclimation and deacclimation process using cool-season turfgrasses that vary in freezing tolerance and (ii) determine the effects of differences in cold acclimation capacity and deacclimation sensitivity on overall freezing tolerance of cool-season grasses. Differences in freezing tolerance among the cool-season grasses evaluated were associated with variations in cold acclimation capacity and deacclimation resistance. Overall, the accumulation of protective compounds such as carbohydrates along with changes in lipid composition during cold acclimation may represent critical mechanisms to help lower cellular freezing point and improve cellular stability of cool-season grasses at freezing temperatures. In addition, decreases in freezing tolerance in response to mild warming events were minimized in plants that maintained higher levels of specific carbohydrates such as fructans. Additionally, strategies such as wilt-based irrigation may be used as a tool to enhance cold acclimation and maximize freezing tolerance of cool-season grasses. Taken together, the mechanisms identified in these studies may serve as selection criteria for the development of cool-season grasses with enhanced freezing tolerance