Genotypic Rankings for Aluminum Tolerance of Soybean Roots Grown in Hydroponics and Sand Culture

Abstract

Screening methodology remains a practical barrier in the breeding of Al‐tolerant soybean [ Glycine max (L.) Merr.]. Our objectives were to (i) develop a repeatable sand‐media culture method for Al tolerance screening of plants, (ii) compare Al response of genotypes in sand culture to a standard hydroponics‐based seedling culture, and (iii) establish a practical guide for the use of hydroponics and sand‐culture screening methods in the selection of Al‐tolerant soybean. We developed a sand‐media culture method and imposed 0 and 450 μ M Al 3+ activity treatments upon 10 diverse soybean genotypes. The experiment employed a randomized complete block design with nine replications. Root weight and relative root surface area (RRSA) were determined at 18 d after transplanting (DAT). In hydroponics, the genotypes were compared for taproot elongation after 3 d of exposure to 0, 2, and 5 μ M Al 3+ activity treatments in a split plot design with six replications. Aluminum stress was imposed successfully (approximately 57% of the growth in control) in hydroponics and sand culture, but discrepancies between methods were apparent. The hydroponics‐based seedling screen produced an inflated range of genotypic response and altered Al tolerance rankings in comparison with sand culture. ‘Perry’, which was tolerant to Al in sand culture, was remarkably sensitive to Al in hydroponics. Despite the discrepancies, seedling‐based screening successfully identified three (PI 417021, PI 416937, and Biloxi) of the four genotypes that were most tolerant to Al in sand culture. Results suggested that seedling screens can play a practical role in breeding. However, their application to a specific breeding population should be validated with older plants and solid media. The RRSA appeared to be a promising measure of A1 tolerance for soybean roots.