Use of seedling growth parameters to classify soybean (Glycine max) cultivar sensitivity to sulfentrazone

Hypocotyl and root length reduction of soybean (Glycine max) seedlings when seeds were exposed to sulfentrazone during germination were used as indice s to classify cultivar response to soil-applied sulfentrazone, Seeds of "St onewall' (sulfentrazone tolerant) and 'Asgrow 6785' (sulfentrazone sensitiv e) were imbibed and allowed to germinate in 0, 1, 5, 10, and 50 ppm aqueous sulfentrazone solutions for 4 d. Hypocotyl and root lengths were reduced i n both cultivars, but the reductions were greater for Asgrow 6785 than for Stonewall. Subsequently, the relative sensitivity of 28 cultivars to sulfen trazone was independently determined by two variations of the hypocotyl red uction method (both conducted in the laboratory) and by traditional full-se ason field evaluation. Results from laboratory and field studies were in ag reement for cultivars distinctly sensitive or tolerant to sulfentrazone. Ho wever, cultivars with intermediate tolerance in laboratory studies produced variable responses in the field.