Effect of drought, salinity and freezing on seed germination characteristics of Rapistrum rugosum L

Three experiments were conducted to evaluate the effect of different levels of plant stresses (drought, salinity and freezing) on the germination characteristics of upper (the upper piece) and lower (the lower piece) position of turnip weed (Rapistrum rugosum) silicle at the laboratory of Faculty of Agriculture at Ferdowsi University of Mashhad. Treatments included seed type (upper and lower), different levels of drought (0, -2, -4, -6, -8 and-10 bar) and rates of salinity (0, 10, 40, 80, 120 and 200 mM). Results showed that decreasing in water potential was companion with a liner decreasing in germination rate and percentage, plumule length, fresh weight of plumule and radicle compared to the control. However, the radicle length of the first seed type increased until -6 and the second seed type up to -4 bar, and then decreased. The rate and percentage of germination increased with increasing salinity up to 10 mM and then decreased, compared to control. However, germination rate of second seed type showed a linear decrease when salt was applied from the beginning of treatment. The effect of freezing temperatures had no significant reduction of germination rate in the first seed type up to -5º C and on second seed type up to -15º C. With increasing salinity up to 10 mM, the parameters studied were not significantly different compared to the control plants, although the germination rate between seed type of upper and lower in 10 mM NaCl was significantly different.