Effect of elevated ultraviolet-B on four tropical soybean cultivars: quantitative and qualitative aspects with special emphasis on gas exchange, chlorophyll fluorescence, biomass and yield

Four Indian soybean cultivars (Glycine max L. cv. JS-335, JS 97-52, PK-416 and PS-1042) were grown under field conditions in suburban area of Varanasi to evaluate the varietal differences against ambient and elevated ultraviolet-B (ambient + 7.2 kJ m⁻² day⁻¹) for two consecutive years. Elevated UV-B caused negative impact on the assessed parameters with varied magnitude amongst the test cultivars. Reductions in rate of photosynthesis and stomatal conductance were observed maximum in JS-335 and minimum in PS-1042. Elevated UV-B also affected the plant abilities to utilize sunlight and increase the photoinhibitory response, which was displayed by reduced Fᵥ/Fₘin tested cultivars. Similar results were also observed for the biomass, yield and seed quality with maximum reduction in JS-335 followed by PK-416, JS 97-52 and PS-1042. Decline in the rate of photosynthesis, extra allocation of photosynthates for repairing and change in translocation pattern of solute and nutrients are mainly responsible for the deterioration in seed quality. Cumulative stress response index (CSRI) and quality response index (QRI) also revealed the sensitivity of soybean cultivars against elevated UV-B. Indexing of cultivars suggests that JS-335 was most sensitive whereas PS-1042 was resistant amongst cultivars.