Screening Sorghum for Aluminum Tolerance in Nutrient Solutions¹

Abstract

Abstract Identification of Al tolerant sorghum [ Sorghum bicolor (L.) Moench] is important if this crop is to be grown successfully on acid, Al‐toxic soils. A rapid method for screening genotypes for Al tolerance was developed by growing over 100 plants in the same container of relatively small volume (50 ml/plant). Mineral element conditions that gave good differential responses for Al tolerance were 148 µmol liter− 1 Al, 64 µmol liter− 1 P, 7.4 mmol liter− 1 Ca, 1.6 mmol liter− 1 Mg, 3.9 mmol liter− 1 K, 24.7 mmol liter− 1 N (8 NO 3 −:1 NH 4+ ), light (17 hours)/dark (7 hours) temperatures of 28/23 C, and solution pH values below 4.0. Mineral element levels or temperatures higher or lower than these resulted in poorer differential responses of genotypes to Al, either because Al had essentially no effect or Al effects were too severe. Nitrate as a single N source could not be used to screen for Al tolerance because the solution pH increased as plants grew and Al in solution was inactivated. A mixture of NO 3 − or NH 4+ gave better genotypic separation than NO 3 − or NH 4+ alone. Visual Al toxicity symptoms on roots were noted within 10 days, and seminal root lengths could be used to assess Al tolerance of sorghum genotypes. Differences in root and top dry matter yields did not distinguish sorghum genotypes for Al tolerance.