Dry Matter Accumulation and Remobilization in Grain Sorghum Genotypes (Sorghum Bicolor L. Moench) Under Drought Stress (Report‪)‬

Introduction Drought stress is a major constraint factor affecting crop production in arid and semi arid climates. It has been shown that stem and leaf sheath of small grain cereals are the organs that reserve photosynthetic assimilates (Slafer and Savin, 1994; Yang et al., 2007). During grain filling, occurrence of different biotic and abiotic stress factors such as water deficit decreases current photosynthesis (Bdukli et al., 2007). Under this condition demand rate for utilization of the stem accumulation increases and remobilization of stem reserves is an important supporting process that can largely compensate grain yield decrease (Palta et al., 1994). Moreover, leaf photosynthesis is decreased as a result of various stresses such as drought, heat stress, and leaf diseases (Bdukli et al., 2007) and consequently, grain filling becomes largely dependent on the vegetative source or photosynthesis of ear tissue (Paponov et al., 2005). One of the appropriate ways to achieve reasonable yield is to assess remobilization rate of carbohydrates and protein that are produced under stressful condition and considered as an effective physiological index in yield formation. The decrease of photosynthetic capacity is a fundamental yield limiting factor, thus, lower photosynthetic capacity of canopy leads to decreased yield by shortening duration of grain filling period (Blum et al., 1994). The best-known agents to stimulate leaf senescence are chlorate magnesium (Blum et al., 1983), potassium iodide (Nikolas and Turner, 1993) and potassium chlorate (Bdukli et al.,2007) that are used in field to screen drought-tolerant genotypes at post-anthesis stage. These compounds are highly efficient and have low toxic effects. By applying chemical substances involved in leaf senescence, current photosynthesis is disturbed, resulting in significant decrease in yield and yield components. Genetic variation for assimilation and remobilization under drought stress as well as disturbance in current photosynthesis has been reported (Royo and Blanco, 1999). A simple and effective method for determining the amount of remobilized dry matter is to measure the differences in stem weight between anthesis and maturity stages (Ehdaie et al., 2007). Sorghum (Sorghum bicolor L. Moench) is an important summer season crop in low rainfall areas. Sorghum is better able to tolerate drought stress compared with other crops and is known as an index for drought resistance of agronomic crops (Beheshti, 1997). A better understanding of the performance of sorghum cultivars in terms of dry matter accumulation and remobilization of photosynthetic assimilates under optimal and stressful condition will assist to select new varieties, which are suitable for cultivation in semiarid areas.