freezing tolerance of grass species under controlled conditions

background and objectives: cold stress is one of the most important limiting factor for growth and development of grasses in temperate regions. freezing tolerance is highly different between plant species and between regions. the importance of grasses is due to widespread application in lawn beautifying, animal feeding, and erosion control. there are many differences between grass species in regards to freezing tolerance as well. researchers have used several traits such as lethal temperature 50 percent (lt50), electrolyte leakage, plant height, and leaf area to identify more freezing tolerant plant species. due to little information exists about freezing tolerance of grasses, this experiment was conducted in order to identify more tolerant species of grasses using some physiological and morphological traits.materials and methods: in order to evaluate the freezing tolerance of some grass species under controlled conditions, an experiment was conducted at faculty of agriculture, ferdowsi university of mashhad, as a completely randomized design using factorial arrangement with three replications in 2009. treatments were included 14 freezing temperatures and six grass species. grass seeds were sown in plastic pots (10 cm in diameter) in late september. in order to induce cold acclimation, plantlets were grown to 4-6 leaves stage in natural conditions. pots were irrigated 24 h prior to be transferred to thermogradient freezer. such traits as crown and leaf membrane stability, survival percentage, dry matter per plant, lt50, rdmt50, and tiller number were evaluated.results: the results showed that freezing temperature significantly (pconclusion: in overall, it seems that lt50, rdmt50, survival percentage and membrane stability index are suitable indices to determine freezing tolerant of grasses. based on the results, bermudagrass and festuca arundinacea (var. starlet) have known as freezing tolerance grass species.