This study was undertaken to develop a fast and reliable nutrient solution technique to screen grain sorghum genotypes for aluminum (Al) tolerance, and to study the gene system controlling the inheritance of Al tolerance in grain sorghum. Twenty-five sorghum genotypes representing a wide range of environmental adaptation were grown in tanks (120 seedlings/tank, approximately 303.0 ml/seedling) of nutrient solution containing 148 uM liter⁻¹ Al. Relative root lengths (RRL) as well as visual symptoms of injury on roots and leaves were the parameters used in evaluating differential Al response of sorghum genotypes. A highly significant negative correlation coefficient was found between RRL and visual symptoms on roots (r = -0.96). Eleven out of the 25 genotypes behaved as Al tolerant and the remaining behaved as Al sensitive. A half-diallel cross involving three Al-tolerant and three Al-sensitive genotypes as identified through the screening test were used to study the gene system controlling the inheritance of Al tolerance in grain sorghum. The F₁ and parents data were analyzed using both Griffing's and Jinks-Hayman methods of diallel analyses. Highly significant GCA and SCA effects were observed for the Al-tolerance trait. The GCA effects were much more important than SCA effects, with the ratio of GCA:SCA being 9:1. From the Vr, Wr graphs the Al-tolerance trait showed predominantly additive genetic effects with some degree of dominance. The six parents fell into four groups according to the relative level of dominance: (1) highly dominant (AR 3010, CI 182); (2) moderately dominant (NB 9040); (3) moderately recessive (Texas Blackhull); and (4) highly recessive (AR 3001 and AR 3006). The degree of dominance was observed to be partial. F₂ populations screened for Al tolerance showed two distinct classes of tolerance with segregating ratios of tolerant:sensitive seedlings of 3:1. This segregation indicated that the Al-tolerant trait was simply inherited, but a wide range of tolerance for Al observed among the 25 genotypes suggested a more complex gene system. Heritability of Al tolerance was very high. The narrow sense and broad sense heritabilities were 77.69% and 99.54%, respectively. These results suggested that a breeding method emphasizing additive gene effects would be favorable in developing Al-tolerant inbred lines.

Recent evidence strongly suggests that aluminum toxicity is important in determining the structural and functional characteristics of freshwater communities affected by acid precipitation. To determine the effect dissolved aluminum has on lotic invertebrates previously unexposed to anthropogenic acidification, experiments were carried out in a second-order headwater stream 50 km east of Vancouver, British Columbia during August 1982. In three separate experiments, HC1 and/or A1C1₃ were added to Mayfly Creek during daylight hours, increasing acidity from pH 6.9 - 7.0 to pH 5.8 - 6.0 and total aluminum from < 0.1 mg/L to > 1.0 mg/L. Biological response was monitored by sampling invertebrate drift with 86 Mm nets. Relative to an unmanipulated, upstream control site, drift density doubled in response to added H⁺ alone (pH 5.9). When Al₃⁺ was added (pH 5.9) drift density increased fourfold. Following 48 h continuous dosing with HC1 (pH 5.9) there was an even greater response to added Al₃⁺. Ephemeroptera were able to detect dissolved aluminum and responded almost immediately (within 45 min). Similarly, Trichoptera and Chironomidae detected increased H⁺ concentrations and responded immediately. Response to augmented Al₃⁺ by Trichoptera, Hydracarina, and Chironomidae was delayed 6 h. However, pre-exposing animals to 48 h HC1 resulted in enhanced aluminum sensitivity for Chironomidae and for Simulium and Plecoptera, which had not responded within 10 h to H⁺ or Al₃⁺ alone. It is proposed that rapid increases in drift density are due to behavioral escape responses, while delayed responses are probably associated with physiological impairment. Evidence was also obtained suggesting that during early stages of morphological development Ephemeroptera and Chironomidae are more sensitive to increased Al₃⁺ and H⁺ concentrations than during later developmental stages. In laboratory experiments using artificial stream channels, Chironomidae larvae and Ephemeroptera nymphs were exposed to CI⁻ and H⁺ concentrations, equal to those during field experiments. Results showed that drift behavior in these animals is not stimulated by mildly elevated chloride concentrations. These studies demonstrate that increased dissolved aluminum concentrations intensify biological response to acidification, and confirm acid sensitivity patterns for Ephemeroptera and Chironomidae reported by others. The observed acid insensitivity of Plecoptera, simuliids, and Trichoptera also conforms to previously described patterns. Experimentally manipulating this community produced results closely resembling those obtained in similar studies for areas currently affected by acid precipitation. The major difference in results between studies is that invertebrate communities previously unexposed to acidification contain more species sensitive to mild acidification. These latter animals are particularly sensitive to the presence of elevated dissolved aluminum concentrations. / Science, Faculty of / Zoology, Department of / Graduate