germination characteristics of marshmallow (althea officinalis l.) as influenced by drought and salinity stress

drought and salinity are two important environmental stresses limiting the crop production. in order to study the influence of drought and salinity stresses on germination characteristics of marshmallow plant seeds, two separate experiments were conducted based on completely randomized design with four replications in controlled conditions. drought stress levels were 0, -2, -4, -6 and -8 bar in the first experiment and salinity stress levels were 0, -2, -4, -6, -8 and -10 bar in the second experiment which were accomplished using peg 6000 and sodium chloride, respectively. the results indicated a decrease in germination rate and percentage, as well as in lengths and fresh and dry weights of both plumules and radicles, as the osmotic potential was reduced in both experiments. marshmallow seeds showed an overall higher tolerance against salinity stress compared to drought stress, with germination occurring at as low osmotic potentials as -10 bars in salinity treatments, while only until -8 bar drought stress. in osmotic potentials of -2 and -4 bar the decrease in germination percentage was more sever in the salinity stress compared to drought stress; whereas in higher levels of stress (-6 and -8 bar) drought stress brought about a higher decrease in germination percentage than did the salinity stress; illustrated by the percentage of germination decrease at -6 bar, i.e. 63% for drought and 80% for salinity treatments. at the treatments of higher potential (-2, -4 and -6 bar) the decrease in radicle length was greater in response to salinity than to drought stress, but the length of plumule was more influenced by drought stress and also showed the highest sensitivity to drought, among all measured characteristics.