Studying the Impacts of Cold Temperature on Morphological and Phonological Development of Poa pratensis and Poa trivialis Regarding GDD

Poa genus has a high value for grazing and forage conservation concerning the livestock. In order to study the impacts of cold temperature and Growing Degree Days (GDD) on seedling morphological trait and phonological development of two species involving Poa pratensis and Poa trivialis, this research was conducted in laboratory and greenhouse and outdoor of Research Institute of Forest and Rangeland in Tehran, Iran. The seed samples were moist chilled at 4 °C for two weeks as compared to the control treatment. Samples of both treatments (chilling and control) were transferred into a germinator at 20±4°C for 15 days. All the pots were placed in a normal glasshouse at 20±10°C for one month. The 30th day age pots have been transferred into the cold rooms at 4°C for two weeks in comparison with control treatment. The seedling vegetative traits were measured same as the laboratory. For outdoor experiment, half of pots of greenhouse were transferred outdoor until their flowering and growth stages and GDD were recorded. In the flowering stage, morphological characteristics including stem number, stem length, peduncle length, panicle length, plants‟ fresh and dry weight of each ecotype were recorded. The collected data of each experiment were separately analyzed using factorial experiment based on completely randomized design. The results of laboratory experiment showed the significant effects of chilling (4 °C) treatment on germination percent, speed of germination in both species and vigor index for P. pratensis. Regarding P. pratensis in vegetative stage, the mean values of all of traits were higher in control treatment than those of cold treatment. Similarly, in outdoor experiment, the mean values of reproductive traits in the control treatment were higher than those for cold treatment concerning both species. P. pratensis had higher mean values for all of reproductive traits as compared to P. trivialis. Results also showed that GDD of plants which were subjected to cold treatment were lower than those for control treatment for both vegetative and flowering stages. It has been concluded that cold treatment reduced flowering dates in reproductive stage.