Selection for Aluminum Tolerance in Soybeans Based on Seedling‐Root Growth1

Abstract

AbstractLaboratory techniques for screening soybean (Glycine max (L.) Merrill) genotypes for tolerance to Al would facilitate breeding programs for areas where AI toxicity limits soybean production. Genotypes from a broad‐base soybean population were screened For Al tolerance based on root growth rate of 5‐day‐old seedlings grown in solutions containing 0.4 ppm Al and 10 ppm Ca (pH 4.6). The selections were intermated to produce a second cycle. Three cycles of divergent selection were completed. The changes associated with selection were evaluated in laboratory studies and in greenhouse studies using Lynchburg sandy loam soil (Aeric Paleaquult).Tolerance to Al as measured by root growth rates proved to be heritable (0.67) with responses in each cycle of selection; however selections completely tolerant to 0.4 ppm Al in solution were not obtained. When high quality seed was used, genetic differences for tolerance were not affected by the environment used for seed production. Selection based on seedlings from individual plants was feasible. Genotypes selected for Al tolerance had less reduction in growth in soils with high exchangeable Al saturation than non‐tolerant selections; however, the differences were not as distinct as that found for the seedling root‐growth studies. Divergent selections had similar levels of metabolic intermediates in the root tips when seedlings were grown in 0 ppm Al, but pyruvate and ATP levels increased significantly under Al stress for the tolerant but not the non‐tolerant selections. Selection for Al tolerance based on growth of 5‐day‐old soybean seedlings in 0.4 ppm Al apparently identified genetic differences for tolerance in established plants as well as tolerance which appeared unique to the seedling stage.