Salinity and waterlogging co-exist in the lower reaches of several river basins throughout the world, affecting agricultural production and the livelihoods of the affected communities (Wichelns and Oster, 2006). Efforts being made to overcome salinity and waterlogging problems by consist of engineering solutions such as installation of a drainage system to manage the drainage effluent generated by irrigated agriculture. This is a long term strategy; however drainage installation is expensive. The areas under salt-affected and waterlogged soils are expanding because of inappropriate on-farm water and soil management. Selection and cultivation of high-yielding salt-tolerant varieties of different crops is a potential interim strategy to fulfill the needs of the communities relying on these soils for their livelihoods (Ayers and Westcot, 1989). Many crops show intraspecific variation in response to salinity. Sorghum is moderately salt-tolerant. Generally, substantial genotypic differences exist among sorghum cultivars in response to salinity stress (Sunseri et al., 2002; Netondo et al., 2004).

1.1.1 Screening methods based on growth or yield

Screening large numbers of genotypes for salinity tolerance in the field is difficult, due to spatial heterogeneity of soil chemical and physical properties, and to seasonal rainfall distribution. Frequently, short-term growth experiments have revealed little difference between genotypes that differ in long-term biomass production or yield. Many short-term growth experiments measuring whole shoot biomass revealed little difference between plant genotypes in their response to salinity, even between those known to differ in long-term biomass production or yield (Rivelli et al., 2002). Longer-term experiments are necessary to detect genotypic differences in the effects of salinity on growth: it is necessary to expose plants to salinity for at least two weeks, and sometimes several months (Munns et al., 1995). Even with rice, a fast growing and salt sensitive species, it is necessary to grow plants for several weeks to be confident of obtaining reproducible differences in salinity tolerance between genotypes (Zhu et al., 2001).