In order to determine the reaction of three Bromus species to drought stress, two separate experiment were conducted in both germinator and greenhouse conditions using factorial experiment based of completely randomized design with three replications in 2010 in Tehran, Iran. The drought treatments were four levels of osmotic potential (0,-0.3,-0.6 and-0.9 MPa) in germinator and four levels of osmotic potential (FC, 25% FC, 50% FC and 75% FC) in greenhouse that were made by poly ethylene glycol (PEG 6000) solution and field capacity method, respectively. Data were collected and analyzed for germination percent, root length, shoot length, seedling length, root/shoot length ratio (RSR), seedling weight, seedling dry/fresh weight ratio (DFR) and seed vigor index. In greenhouse, chlorophyll, carbohydrates and proline contents were also measured. The results showed significant differences among species, droughts levels and species by drought interaction effects for the most of traits in both conditions. However, the relationship between germinator and greenhouse, quantified using correlation was high. It was concluded that evaluation under germinator conditions is desirable for selection purposes. In both conditions all of seedling traits except RSR, DFR were increased and proline and carbohydrate content were increased by increasing osmotic potential. The results showed that the Bromus tomentellus species had higher values for the most of seedling attributes than other species. Results of probit analysis of LD 50 and LD 90 showed the same trend.

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