Role of supplemental UV-B in changing the level of ozone toxicity in two cultivars of sunflower: growth, seed yield and oil quality.

Ultraviolet-B radiation (UV-B) is inherent part of solar spectrum and tropospheric ozone (O3 ) is a potent secondary air pollutant. Therefore the present study was conducted to evaluate the responses of Helianthus annuus L. cvs DRSF 108 and Sungold (sunflower) to supplemental UV-B (sUV-B; ambient + 7.2 kJ m-2  d-1 ) and elevated ozone (O3 ; ambient + 10 ppb), given singly and in combination under field conditions using open-top chambers. The individual and interactive effects of O3 and sUV-B induced varying changes in both the cultivars of sunflower ranging from ultrastructural variations to growth, biomass, yield and oil composition. Reduction in leaf area of Sungold acted as a protective feature which minimized the perception of sUV-B as well as uptake of O3 thus led to lesser carbon loss compared to DRSF 108. Number- and weight of heads plant-1 decreased although more in Sungold with decline of oil content. Both the stresses when given singly and combination induced rancidification of oil and thus made the oil less suitable for human consumption.