Effect of drought stress and cold treatment on germination and seedling growth of Poa pratensis and Poa trivialis under germination and greenhouse condition

Poa genus has important role for livestock grazing and forage production. To evaluate the effects of both drought and cold treatments on seed germination and seedling growth, 6 genotypes of Poa pratensis and Poa trivialis were examined in laboratory and greenhouse using a factorial experiment based on completely randomized design in three replications. Drought levels (0, -0.3, -0.6, -0.9 and -1.2 MPa), made by PEG 6000 solution, were related to the germinator experiment. For green house experiment, five drought levels of 20, 40, 60, 80, 100% field capacity (FC) were made by weighting of wet and dried soil. Data were collected and analyzed for seed germination percent, speed of germination, root/shoot length ratio, seedling length, vigor index and seedling weight. Results showed significant differences between drought treatments, species, genotypes within species and interaction effects between drought and species for most of traits. No seeds were germinated in -0.9, -1.2Mpa, indicating low to moderate resistance of two species to drought stress. Seed germination traits were decreased by increasing drought stress. In contrast, the shoot/root length ratios (R/S) and dry/fresh seedling weight ratio (D/F) were increased. For -0.3MPa stress, the means of seed germination percent, root and shoot length were 11, 10 and 16% lower than those for control, respectively. In greenhouse, for 20% FC, the average values of root and shoot lengths were decreased by 34 and 23% than those for control. The R/S values were increased to maximum values by increasing drought stress. Therefore, it was suggested as a good indicator for screening of drought resistant genotypes. In comparison between control and cold pre treatment (4°C), results showed significant effects of cold treatments for some of seed germination characteristics in laboratory. It was concluded that genotype Astaneh (24066), belonging to Poa pratensis, had higher values for most of seed characteristics and vigor index than those for other five genotypes in both environments and it was recognized as superior genotype for breeding improved varieties.