GROWTH TRAITS AMONG SORGHUM GENOTYPES IN RESPONSE TO ALUMINUM

Aluminum (Al) has many detrimental effects on plant growth, and shoots and roots are normally affected differently. A study was conducted to determine differences among sorghum [Sorghum bicolor (L.) Moench] gen otypes with broad genetic backgrounds for growth traits of plants grow n at 0, 200, 400, 600, and 800 mu M Al in nutrient solutions (pH 4.0). Genotypes were categorized into ''Al-sensitive'', ''intermediate Al-t olerant'', ''Al-tolerant'', and SC 283 (an Al-tolerant standard). As A l increased, shoot and root dry matter (DM), net main axis root length (NMARL), and total root length (TRL) became lower than controls (0 Al ). Aluminum toxicity and/or nutrient deficiency symptoms become more s evere, and shoot to root DM ratios and specific RL (TRL/root DM) value s also changed as Al in solution increased. Root DM had greater change s among genotypes than shoot DM, and NMARL at 400 mu M Al, and TRL at 200 mu M Al had greater differences among genotypes than root DM, rati ngs for toxicity and/or deficiency symptoms, and other DM and RL trait s. The wide differences among genotypes for NMARL and TRL could be use d more effectively to evaluate sorghum genotypes for tolerance to Al t oxicity than the other growth traits.