Determination of Cardinal Temperature of three species of Lolium genus and responses to salinity and drought stresses

In order to study seed germination responses of three species of Lolium to temperature regimes, salinity and drought stresses three separate experiment were conducted as a factorial based on completely randomized design at laboratory of ecology of Faculty of Agriculture, Science and Research Branch, Islamic Azad University in 2015. In frist experiment, factors were included three species of Lolium (poison ryegrass, Persian darnel and rigid ryegrass) and temperature at 12 levels (0, 3, 5, 7, 10, 12, 15, 20, 25, 30, 35, 40 0C). In second and third experiments effects of seven levels of salinity (0, 10, 20, 40, 80, 160 and 320 mmol) and seven levels of drought stress (0, -0.1, -0.2, -0.4, -0.6, -0,8 and -1 MPa) on germination percentage of three Lolium species were examined. Based on linear regression between germination rate and temperature, the cardinal temperatures: minimum (Tmin), maximum (Tmax) and optimum (To) were determined 2, 37 and 20ºC, for poison ryegrass, 0, 38 and 20 ºC for Persian darnel and 0, 38 and 23 ºC for rigid ryegrass, respectively. Three-parameter logestic model is well justified the relationship between different salinity and drought levels and germination percentage. Based on model, reduction of 50% of germination percentage in Persian darnel caused at intensified osmotic potential in comparison of two other species, so this species had more tolerance to salinity and drought stresses.