Drought and UV-B Radiation Effects on Soybean Early Seedling Growth.

Soybean growth and development are highly susceptible to global climate change components such as drought and ultraviolet-B (UV-B) radiation. Water is an increasingly limited resource, and water availability limits soybean productivity in many parts of the U.S. and the world. On the other hand, due to damage of the stratospheric ozone layer, the level of UV-B radiation reaching the biosphere is increasing causing detrimental effects on soybean productivity.  The objective of this study was to study the effects of soil moisture stress and UV-B radiation on soybean early seedling growth and root morphology and to understand the genotypic variation among those cultivars. The experiment was conducted in controlled sunlit chambers using 64 soybean cultivars representing maturity groups III, IV, and V. Two soil moisture regimes including 100 and 50% evapotranspiration based irrigation and two levels of UV-B, 0 and 10 KJ were employed. Plants grown at +UV-B and 50% ET produced shorter plants, smaller leaf area, and reduced total dry matter. The production of phenolic compounds was increased under UV-B radiation. UV-B radiation had more adverse effects on soybean seedlings than drought according to the physiological and morphological parameters measured. Total stress response index (TSRI) for each cultivar, developed from the cumulative sum of response indices of vegetative and physiological parameters, varied among the cultivars. The 64 cultivars were classified as tolerant, intermediate and sensitive to combined environmental stresses. Out of the 64 soybean cultivars, REV38R10 was identified as the most sensitive and NKS55Q3 as the most tolerant to combined drought and UV-B stresses. The differences in sensitivity identified among the soybean cultivars imply that there may be options for selecting cultivars with tolerance to drought and UV-B stresses projected to occur in future climates.