Cultivar options for salinity tolerance in sorghum

Sorghum (Sorghum bicolor) is the fifth most important cereal crop of the world and is a major source of food, feed and fodder in the semi-arid tropics (SAT). It is the third most important staple food crop after rice (Oryza sativa) and wheat (Triticum aestivum) for millions of people in India. The grain molds, shoot fly and prolonged dry spells are main reasons for low productivity in India. Of all the soil mineral stresses or chemical toxicities, acidity, and associated Al3+ toxicity and salinity are probably the most important constraints to sorghum productivity in tropical environments. Saline and sodic soils cause mineral stresses on approximately 0.9 billion ha of land (Gourley et al. 1997). In addition, the problematic soils that include saline soils which constitute 15% (approx.) of total cultivable area in India, reduce crop productivity leading to food insecurity and rendering crop production non-remunerative. The increased demand for sorghum, especially for feed uses in SAT regions (Kleih et al. 2000) imposes extension of sorghum cultivation in saline soils. Soils with an ECe of <4 dS m-1 (Shannon 1997) are considered non-saline; an ECe of 4 to 16 dS m-1 are moderately saline and an ECe of >16 dS m-1 are highly saline (www.cahe.nmsu.edu). Development of cultivars tolerant to soil salinity along with appropriate management practices is required for enhanced production under saline conditions (Ramesh et al. 2005). Salinity causes reduction in germination (Igartua et al. 1994), growth (Maiti et al. 1994) and yields of sorghum (Macharia et al. 1994) and modifies the physiological and biochemical processes of the plant (Dubey 1994). Salinity causes more serious damage in the seedling emergence stage than in any other stage in sorghum (Macharia et al. 1994). Though sorghum is known to be relatively more tolerant to soil salinity than maize (Zea mays) (Igartua et al. 1994, Krishnamurthy et al. 2007), genetic enhancement of sorghum for salinity tolerance would further increase sorghum productivity in such soils