EFFECTS OF ALUMINUM ON GROWTH AND MINERAL NUTRITION OF SORGHUM GENOTYPES

Sorghum {Solrghum bicolor (L.) Moench} genotypes were grown in nutrient solutions with varied levels of Al under growth chamber and greenhouse conditions to determine differences in root lengths, fresh and dry matter yields, plant-induced solution pH changes, intact root phosphatase activities, and plant mineral element uptake and accumulation. At 74 (mu)M Al, net seminal root length (NSRL) and length of the longest adventitious root (LARL) gave the widest differences among Al-tolerant (NB9040 and SC369-3-1JB), moderately Al-tolerant (CK60), and Al-intolerant (TX415, Martin, SC33-9-8E4, and NB3494) genotypes. Differences in fresh and dry matter yields among genotypes were not as wide as root length measurements. A close relationship between final solution pH and degree of Al tolerance was noted among the genotypes grown in nutrient solutions with varied levels of Al. The more Al-tolerant genotypes did not reduce the pH to as low a level as the more Al-intolerant genotypes. Intact root phosphatase activities (Pase) expressed on a per unit root dry weight basis did not differ among treatments and decreased with plant age. However, Pase expressed on a total root basis increased with plant age and decreased with Al treatments. The decreases noted for Al-intolerant genotypes were greater than those for Al-tolerant genotypes. Pase on a total root basis correlated better with total root length (r = 0.92(\u27**) for Martin and r = 0.75** for NB9040) than with total root weight (r = 0.89(\u27**) for Martin and r = 0.36 ns for NB9040). Increased concentrations of macronutrients were observed in the tops of plants grown at lower levels of Al, except for Mg concentrations which decreased as Al increased in solution. Decreases in Mg concentrations in the tops of Al-intolerant genotypes were larger compared to the Al-tolerant genotypes. Except for S concentrations that remained unchanged and P concentrations that increased, concentrations of the macronutrients in the roots decreased with Al. The contents of macronutrients followed the pattern of the dry matter yields, except for Mg contents which decreased in the tops and roots. Aluminum-intolerant genotypes had higher concentrations of Al in the roots than the Al-tolerant genotypes. However, the contents of Al of Al-intolerant genotypes were equal to or lower than those of Al-tolerant genotypes. A dilution effect from growth might have occurred in the roots of Al-tolerant genotypes and could have accounted for most of the Al concentration differences noted among genotypes. Decreased concentrations of Mn, Fe, and Cu in the tops and roots, decreased concentrations of Zn and Mo in the tops, and increased concentrations of Zn and Mo in the roots were observed for plants grown with increased levels of Al. The Al-intolerant genotypes had more pronounced changes than the Al-tolerant genotypes. The severity of an Al-induced interveinal chlorosis (typical Fe deficiency symptoms) on the upper leaves of Al-intolerant genotypes agreed well with the decreases in Fe concentrations of the tops (except for \u27SC33-9-8E4\u27 and \u27CK60\u27). Except for Zn in the roots, the contents of micronutrients in the tops and roots decreased more in Al-intolerant than in Al-tolerant genotypes. Regardless of the female parent used, F(,1) hybrids derived from the Al-tolerant \u27NB9040\u27 \u27SC369-3-1JB\u27 or \u27SC500-6-1\u27 were tolerant to Al in nutrient solutions. Relative length of the longest adventitious root was a more reliable parameter to quantify Al tolerance differences among sorghum hybrids than the visual rating system used to estimate Al toxicity symptoms on roots. Good agreement between laboratory screening data and field-grown plants on Al toxic, acid soils was obtained