effects of salinity stress on seed germination characteristics of two medicinal species thymus kotschyanus and t. daenensis

the genus thymus is perennial medicinal plants belong to the lamiaceae familythat is used for different propose in pharmaceutical industry. environmental stresses,particularly salinity, are considered as the major factor reducing plant growth. the purpose ofthis study was to investigate the effects of salt stress on germination characteristics andseedling morphology in two medicinal species of t. kotschyanus and t. daenensis. a factorialexperiment was conducted using completely randomized design with four replications andseven salinity levels. the salinity factor were included of 0, 50, 100 150, 200, 250 and 300mm nacl. data were collected for germination percentage, germination rate, time means ofgermination, radicle length, plumule length, seed vigor, and allometry ratios. the overallmeans of germination percentage, germination rate, radicle length, and seed vigor were lowerfor t. daenensis as 41.44, 0.28, 1.15 and 1.87 than those for t. kotschyanus as 54.32, 0.37,1.81 and 2.8, respectively, indicating more tolerant to salinity for t. kotschyanus than that fort. daenensis. results showed that by increasing salinity, the germination percentage, rate ofgermination, plumule length, radicle length, and seed vigor were reduced in both species. theslop of reduction was higher for t. daenensis than t. kotschyanus. in other words, t.kotschyanus was more tolerate to salinity than t. daenensis. it was concluded that this genuscould be cultivated in environments, which plants are not in expose to salinity.