Ancestral U.S. Soybean Cultivars Characterized for Tolerance to Ultraviolet‐B Radiation

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In an effort to characterize the U.S. soybean [Glycine max (L) Merr.] germplasm pool for variation in tolerance to ultraviolet‐B (UV‐B) radiation, 10 U.S. ancestral soybean cultivars were exposed in a greenhouse to a level of UV‐B radiation simulating a 25% O3 depletion. Two modern cultivars previously characterized for UV‐B sensitivity, Williams (tolerant) and Essex (sensitive), 10 wild annual soybean (G. soja Sieb. & Zucc.) accessions of diverse geographic origin were also included in the study. Significant variation was observed among the G. max cultivars in UV‐B radiation effects on leaf expansion, leaf area, height, aerial dry biomass, and seed yield. The cultivars CNS and Lincoln were consistently the most sensitive to UV‐B radiation, while the cultivars Williams, Arksoy, Richland, Mandarin, Manchu, and Mukden were most tolerant. The wild G. soja accessions as a group were about as sensitive to UV‐B radiation as the G. max cultivars, except that seed yield of G. soja accessions was not significantly reduced by UV‐B radiation. There was, however, UV‐B radiation treatment × genotype interaction for fewer growth traits among the wild G. soja accessions than among the G. max cultivars. Production of UV‐B–absorbing compounds and specific leaf weight were both implicated as important contributing factors to UV‐B radiation tolerance in G. max cultivars.