1.3 Agricultural advantages

1.3.1 Salt tolerance

Sorghum is characterized as moderately tolerant to salinity (Almodares and Sharif, 2005; Almodares and Sharif, 2007). Salinity reduces sorghum growth and biomass production. Salinity greatly reduced sorghum growth and this effect was more pronounced at 250 mM than at 125 mM NaCI (Ibrahim, 2004). However it was reported that sorghum growth was significantly reduced at all salinity levels from 50 to 150 mM (El-Sayed et al., 1994). Imposition of salt stress resulted in decreases in the percentage of seeds germinated (Almodares et al., 2007), although the strongest decline in germination occurred at the highest salt concentration (Table 2). Nevertheless, the development of high-yielding salinity tolerant sorghums is the best option to increase the productivity in soils (Igartua et al. 1994). Similarly, Gill et al. (2003) observed a great reduction in germination rate due to salt stress, in sorghum seeds at 37 °C in NaCl (-1.86MPa).

Relative percent germination(%)in osmotic potential (Mpa)created by NaCl

According to Prado et al. (2000), the decrease in germination may be ascribed to an apparent osmotic ‘dormancy’ developed under saline stress conditions, which may represent an adaptive strategy to prevent germination under stressful environment. Germination time delayed with the increase in saline stress and root growth was more sensitive to salt stress than was germination (Gill et al., 2003). It seems that grain weight is related to salt tolerance in sweet sorghum. It showed that higher total seedling dry weight was obtained with larger seed size in 18 sweet sorghum cultivars under salt stress (Table 3 and Fig. 1). The presence of large genotypic variation for tolerance to salinity is reported in sorghum (Maiti et al, 1994). Sorghum seems to offer a good potential for selection, as intraspecific variation for germination under saline conditions (Table 2) or in the presence of other osmotic agents that has already been reported. Selection of salt tolerant cultivars is one of the most effective methods to increase the productivity of salinity in soils (Ali et al., 2004). By using these salt tolerant plants in breeding they produced progranuned an improved plant having higher chlorophyll concentration, more leaf area, early and better yield potential etc. The advancement of salinity tolerance during the early stages of sorghum growth been successfully accomplished through selection.

Genotypes possessing salt tolerance characteristics will help in boosting up plants production in salt-affected soils (Ali et al., 2004). Azhar and McNeilly (1988) found that, for salinity tolerance of young sorghum seedlings, both additive and dominant effects were involved, the latter being of greater importance. Attempts have been made to evaluate salt tolerance at the germination and emergence stages in sorghum (Igartua et al., 1994). In fact, the variation in whole-plant biomass responses to salinity was considered to provide the best means of initial selection of salinity tolerant genotypes (Krishnamurthy et al, 2007). The presence of large genotypic variation for tolerance to salinity reported in sorghum (Krislmamurthy et al., 2007). There are large genotypic variations for tolerance to salinity in sorghum (Table 4). The other possible solution could be either using physical or biological practice (Gupta and Minhas, 1993). Sudhir and Murthy (2004) reviewed both multiple inhibitory effects of salt stress on photosynthesis and possible salt stress tolerance mechanisms in plants. Salinity reduced relative growth rates and increased soluble carbohydrates, especially in the leaves of salt sensitive genotype (Lacerda et al., 2005). In addition salt-stressed sorghum plants additionally accumulate organic solutes, like proline, glycinabetaine, sugars, etc. (Lacerda et al., 2001). The total soluble sugar increased in sorghum sap with increasing salinity level (Ibrahim, 2004; Almodares et al., 2008a). Sucrose content of plant parts is an indicator of salt tolerance (Juan et al., 2005). The imposition of strong water or salt stresses in sorghum has been demonstrated to be accompanied to an increase in the sugar levels of embryos, which may help in osmoregulation under stress conditions (Gill et al., 2003). The fructose level is always higher than glucose and sucrose levels in response to various salinity treatments (Gill et al., 2001; Almodares et al., 2008a).