Comparison of Young Seedling Growth and Sodium Distribution among Sorghum Plants under Salt Stress

Young seedlings of 22 Sorghum cultivars including sorghum, sudangrass and sorghum-sudangrass hybrids, were examined for their growth characteristics and sodium ion accumulation in different plant parts, under salt treatment. The salt treatment was started with 100 mM NaCl and increased to 150 mM during the experiment. The plant dry weight decreased under NaCl treatment in all cultivars, and especially the dry weight of leaf blade decreased markedly. The cultivar difference in the plant dry weight under salt stress was affected by that in relative growth rate which was mainly changed by net assimilation rate (NAR). Cultivars that maintained higher NAR under salt stress had a smaller specific leaf area and higher nitrogen content per unit leaf area. Sorghum plants under salt stress retained Na+ mainly in roots preventing the distribution of excess amount of Na+ to leaves, but the root dry weight was increased by salt stress. It was therefore considered that thicker leaf blades and apparent increases in root dry weight were the main contributors to the maintenance of dry matter yield and enhanced the growth of Sorghum cultivars under NaCl treatment.