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

Abstract

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