Characterization of Boron Toxicity Tolerance of Two Soybean (Glycine max L.) Varieties

Soybean (Glycine max L.) is one of the most widely grown oilseed crops worldwide. Little is known about boron tolerance of soybean and although some authors state that it is a moderately tolerant species, they do not report its tolerance range. Therefore, the aim of this study was to assess the effect of increasing boron concentrations in irrigation water on germination, growth and root anatomy of two soybean varieties (M 6210 and NS 8288). Standard germination and pot experiments, using different boron concentrations (0.5, 1.0, 2.0, 4.0 and 8.0 mg.L-1) were performed. Radicles obtained from germination assays were used to make cross sections that were examined under the microscope. Increasing boron concentrations reduced germination percentages (in NS 8288) and most of the growth variables evaluated, with significant differences between varieties. Symptomatology was observed above 1.0 mg.L-1 B and was particularly pronounced in M 6210, which exhibited high leaf senescence and abscission. Maximum diameter of xylem vessels showed a gradual decrease in response to increasing boron concentrations in M 6210. This is the first study evaluating in detail the impact of boron toxicity on soybean varieties. Increasing boron concentrations cause a decrease in germination, growth and in the diameter of the xylem vessels. We suggest that the range of tolerance of the varieties here evaluated is lower than the one proposed by some authors for soybean and thus, further studies including more varieties is needed.