Physiological basis for the differential tolerance of Glycine max to sulfentrazone during seed germination

Glycine max cultivars exhibit differential tolerance to soil-applied sulfen trazone. The intent of this study was to determine the physiological basis for this differential tolerance by evaluating sulfentrazone absorption and metabolism during the earliest stages of G. max development (i.e., germinat ing seeds, and germinal seedlings). Imbibed seeds (24 h) of the sulfentrazo ne-tolerant cultivar 'Stonewall' absorbed 37% less sulfentrazone than the s ulfentrazone-sensitive cultivar 'Asgrow 6785'. Similarly, germinal seedling s (i.e., 60 h from start of imbibition) of the sulfentrazone-tolerant culti vars Stonewall and 'Pioneer 9593' absorbed 22% less sulfentrazone than the sulfentrazone-sensitive cultivars Asgrow 6785 and 'Carver' when exposed to sulfentrazone-containing solution for either 24 or 48 h. The amount of root -absorbed C-14-sulfentrazone that was translocated into cotyledon or hypoco tyl tissues did not exceed 11% of the amount absorbed and was similar for a ll four cultivars. Sulfentrazone metabolism by both imbibed seeds and by ge rminal seedlings was independent of cultivar. Increasing the sulfentrazone concentration in the seed imbibition solution and increasing the temperatur e resulted in greater seedling height reduction at 10 d in Asgrow 6758 than in Stonewall. Results indicate that differential absorption during the ear liest stages of development is the basis for the differential response amon g G. max cultivars. Comparatively limited sulfentrazone absorption by Stone wall, as reflected in acceptable seedling injury, remained relatively consi stent across the range of concentrations and temperatures evaluated.