Genotypic influence on the absorption and toxicity of manganese in Soybean

Manganese (Mn) toxicity may be a constraint for crop production in acid soils of tropical regions. However, variations of Mn concentrations in plant tissues are also related to the genotypic differences. A greenhouse experiment was carried out to evaluate Mn tolerance of three soybean cultivars [Glycine max (L.) Merrill]. Cultivars Santa Rosa, IAC-15 and IAC-Foscarin 31 were evaluated under five Mn rates (2, 100, 150, 200, and 250 [mu mol L-1) in nutrient solution (pH 5.0). The experiment in randomized blocks was a 5 x 3 factorial of five Mn doses and three cultivars, with three replications. IAC-15 and Santa Rosa leaves showed visual symptoms of Mn toxicity. At toxic Mn levels in solution, the average Mn concentration in the leaf blades was close to 1,000 mg kg(-1). Nevertheless, grain and dry matter in the aerial parts was higher for IAC-15 than IAC-Foscarin 31 (intermediate yield) and Santa Rosa (lowest yield). The greatest total root length and root dry matter yield, as well as root Mn accumulation and compartmentalization in root apoplast of IAC-Foscarin 31 contributes to explain differences in tolerance to the excess. There are, therefore, indications of genotypic differences among the soybean cultivars and that several mechanisms are involved in the tolerance to high Mn levels.