Effect of seed priming on seedling growth of barely (Hordeumvulgare L.), under salinity stress in phytogel

Seed emergence and seedling growth can be major factor limiting the establishment of plants under saline conditions (Patade et al., 2009; Jafar et al., 2011). Salinity can affect germination and seedling growth either by creating an osmotic pressure that prevents water uptake or by toxic effects of sodium and chloride ions (Jafar et al., 2011). Seed priming is a technique in which seeds are partially hydrated until the germination process begins, prior to radicle emergence (Patade et al., 2009; Rehman et al., 2011). Priming allows the metabolic processes necessary for germination to occur without actual germination. In addition, primed seeds usually exhibit an increased germination rate, greater germination uniformity, greater total germination percentage (Patade et al., 2009; Rehman et al., 2011; Jafar et al., 2011). Gel chamber technique is new method for root study in early stage (Bengough et al., 2004).
Two experiments were carried out evaluate the effect of seed priming to improve salinity stress on seedling growth of barely. First experiment was conducted as factorial based on completely randomized design with four replications. Treatments were included two cultivars of barely (Yusef and Maquie) and four levels of nitrogen priming (2, 4, 6 and 8 gN.L-1 of urea) and hydropriming with un-prim seeds.
Before priming, seeds staid on hypochlorite 2.5% for 5 min then washed with distilled water three times. Disinfected seeds were in the room temperature for 24 hours. In following, barely seeds were soaked for 6 hours with hydropriming and nitrogen priming levels. Twenty seeds were put in glass Petri dishes adding 10 ml distilled water. Petri dishes placed into germinator with 20ºC and dark condition. Finally, germination percentage, time to get 50% germination and seedling vigor index was measured.
In second experiment, hydropriming, priming with 0.002 (w/v) N (Best treatments of one experiment) with un-prim seeds were used. Salinity stress levels of 0, 200 and 300 mM induced by Sodium chloride used in preparation stages of phytogel and each cultivar investigated in separated factorial experiment based on a completely randomized design in gel chamber condition.
Chambers were constructed from two plates (generally with one black polyviniychloride, one transparent Perspex), each measuring 215×300×3 mm. strips of Perspex (3mm thick) were used as spacers around each plate, giving a plate separation of 6 mm, leaving three gaps, each approximately 25 mm long, along the top surface, to allow gas exchange with surrounding atmosphere and unimpeded shoot extension. Each Perspex plate was covered with a layer of phytogel approximately 1.5 mm deep, sandwiching an air gap of approximated 2.5 mm width between the plates in which root growth occurred (Bengough et al., 2004). Roots grown within the air gap to avoid problems of poor aeration.
After priming, seeds placed to germinator for 24 hour. Uniform seedling barley were placed to gel chambers and fixed into phytogel. Afterward, gel chambers were placed to germinator with 12/12 light and dark at 12ºC. After 21 days, plumule length, fresh and dry weight of plumule, green area, radicle length and volume, fresh and dry weight of radicle was measured
Results of first experiment showed that seed priming led to significant increment of radicle length, plumule length and seedling vigor index and on the contrary, reduced time to get 50% germination (T50). By increasing the nitrogen concentration of two percent, in most of traits didn’t show statistical difference and even had negative effect on measured traits.
Results of second experiment were indicated a positive significant effect of utilized two priming treatments on plumule length, fresh and dry weight of plumule, green area, radicle length and volume, fresh and dry weight of radicle at different levels of salinity stress in Maquie cv. In Yusef cv., seed priming was improved all studied traits except radicle volume. Both barely cultivars didn’t show similar reaction to seed priming. In Yusef cv. by increasing salinity to 300 mM, hydropriming and priming with 0.002 (w/v) N led to significant enhancement in most of traits, than control. While positive and considerable influence of priming on Maquie cv. was to salinity level of 200 mM, 11, 8 and 19 percent, respectively.
In addition, priming with nitrogen were enhanced two barley germination characters and 0.002 w/v was best treatment. In salinity stress, priming influenced growth of barley seedling.