A. Almodares1, M. R. Hadi2 and Z. Akhavan Kharazian1

1Department of Biology, University of Isfahan, 2Department of Biology, Sciences and Research Branch of Fars,

Islamic Azad University, Iran

1. Introduction

Soil salinity is one of the main problems for plant growth in agriculture, especially in countries where crops should be irrigated (Ahloowalia et al., 2004). Soil salinity has been considered a limiting factor to crop production in arid and semi arid regions of the world (Munns, 2002). Saline soils are estimated about 5 — 10% of the world’s arable land (Szabolcs,

1994) , and the area affected by salinity is increasing steadily (Ghassemi et al., 1995). Salt — affected soils are distributed throughout the world and no continent is free from the problem (Brandy and Weil, 2002). Globally, a total land area of 831 million hectares is salt — affected (Kinfemichael & Melkamu, 2008; FAO, 2000). However, soil salt accumulation can change with time and place, as a function of soil management, water quality (Almodares & Sharif, 2005), irrigation method, and the weather conditions. Salt accumulation is mainly related to a dry climate, salt-rich parent materials of soil formation, insufficient drainage and saline groundwater or irrigation water (Almodares et al., 2008a). Salts in soils are chlorides and sulfates of sodium, calcium, magnesium, and potassium that among them sodium chloride has the highest negative effect on the plant growth and development. Salinity causes slow seed germination, sudden wilting, and reduce growth, marginal burn on leaves, leaf yellowing, leaf fall, restricted root development, and finally death of plants. The inhibitory effects of salinity on plant growth include: (1) ion toxicity (2) osmotic influence (3) nutritional imbalance leading to reduction in photosynthetic efficiency and other physiological disorders. Among agricultural crops, sorghum (Sorghum bicolor L. Moench) is naturally drought and salt-tolerant crop that can produce high biomass yields with low input. Also, it can thrive in places that do not support corn, sugarcane and other food crops. In addition, sweet sorghum has potential uses (six F) such as: food (grain), feed (grain and biomass), fuel (ethanol production), fiber (paper), fermentation (methane production) and fertilizer (utilization of organic byproducts), thus it is an important crop in semi-aired and aired regions of the world. Sorghum is grown on approximately 44 million hectares in 99 countries (ICRISAT, 2009). An estimation of the world-wide tonnage produced in 2007-2008 is shown in Table 1. The increasing cost of energy and deplete oil and gas reserves has created a need for alternative fuels from renewable sources. The consumption of biofule may reduce greenhouse gases. Also it can be replaced with lead tetraethyl or MTBE (Methyl tert-butyl ether) that are air and underground water pollutants,

respectively (Almodares & Hadi, 2009). Plants are the best choice for biofule global demands. Currently, ethanol production is based on sugar or starch of crops such as sorghum, corn, sugarcane, wheat and etc. In comparison with other crops, carbohydrate content of sweet sorghum stalk and its grain starch is similar to sugarcane and corn, respectively but its water and fertilizer requirements are much lower than both sugarcane and corn. Thus, in many tropical and temperate countries where sugarcane and corn cannot be grown, a growing interest is being focused on the potential of sweet sorghum to produce bioethanol feed stock (Almodares et al., 2006, 2008d). Sweet sorghum biomass has rich fermentable sugars such as sucrose, glucose, and fructose so it is an excellent raw material for fermentative production (Almodares et al., 2008d). The total soluble sugars can be increase in sweet sorghum with increasing salinity level and sucrose content could be an indicator for its salt tolerance. (2008b). Salt-stressed sorghum plants additionally accumulate organic solutes, like proline, glycinabetaine, sugars, etc. (Lacerda et al., 2001). These organic solutes may contribute to osmotic adjustment, protecting cell structure and function, and/or may serve as metabolic or energetic reserve (Hasegawa et al., 2000). Inorganic and organic solutes concentrations maintained during salt stress, therefore, they may be important during the salt stress recovery period (Pardossi et al., 1998). Since sweet sorghum is more salt tolerant than sugarcane and corn which currently are the main sources of bioethanol production. Therefore, it is suggested to plant sweet sorghum for biofule production in hot and dry countries to solve problems such as increasing the octane of gasoline and to reduce greenhouse gases.