Germination percentage (%)
The effect of drought stress induced by mannitol on the germination percentage % of barley cultivars (Giza-126, Giza-2000, Giza-118 and Giza-121) is presented in Table (5). Grains germination and seedling development in lab conditions have been recognized as testing procedure in barley and it is well known that with the increase in mannitol concentrations, the germination rate and growth of seedlings got decreased (table 5). The highest germination rate was recorded at control followed by the lower mannitol treatments (125 mM). Giza-126 and Giza-2000 cultivars recorded the lowest germination percentage (%) on 250 mM treatment while Giza-118 and Giza-121 gave the lowest percentage of germination on the high concentration of mannitol (500 mM). The Giza-126 cultivar showed more germination at the higher concentration of mannitol (500 mM) in comparison with control and the other treatments. Also, between investigated cultivars, the Giza-126 showed low germination rate reduction with increasing mannitol concentration than the other genotypes.
Khazayi et al. (2008) in their study concluded that negative potentials between -0.4 and -0.8 MPa are the best condition for studying germination features of different genotypes of plants under drought stress. The results are in agreement with the earlier study Ansari and Sharif-Zadeh (2012) who reported the significant reduction in the germination as well as growth of Rye. Also, earlier reports (Patade et al., 2011; Ansari and Sharif-Zadeh, 2012 and Rouhi et al., 2011) have shown positive effect of priming in relation to seed performance, germination percentage and seedling indices. Root and shoot length reduced by mannitol induced drought and similar findings have been reported by many scientists (El-Midaoui et al., 2003 and Parmar and Moore, 1965).
Almaghrabi, (2012) reported that environmentally confined seedlings in laboratory experiments would appear to be suitable for screening large population to improve drought tolerance prior to yield testing. Usually the drought tolerant genotype will have the highest germination rate and better survival. The higher germination rates of the tolerant germplasm may be due to their capability to absorb water even under mannitol induced water stress. Hegarty, (1997) and Turk et al, (2004) reported that water stress at germination stage delayed or reduced or hinder germination completely. However, once the grain attains a critical level of hydration it will lead to full seed germination. If, the physiological changes happen below the critical level it lead to complete inhibition of seed germination.
Strong negative relationship was noted between root length and mannitol concentration. Roots are the primarily effected plant part under drought conditions than any other parts (Ghafoor, 2013). Root and shoot traits of all varieties provided useful information against different levels of mannitol and this is very important attribute to study the drought stress. The genotypes which has better growth under stressed environment may have drought tolerance mechanism and these plants may have capability of holding a homeostasis under stressed conditions (Abdel-Raheem et al, 2007 and Saxena and Toole, 2002). Several reports indicated that better growth under stress conditions as a trait to select germplasm to improve the yield (Richards, 2000).
Conclusions: It is concluded from the present studies that shoot and root length of both the genotypes was decreased as the level of the stress increased. Further, the effect of drought on shoot and root length was linear but on roots the effect was sever at first stress and later on the effect of stress was decreased which maybe because of the greater carbohydrates accumulation in the roots as compare to the shoots.
Germination percentage (%)