Physiological Effects of Solar Ultraviolet-B Exclusion on Two Cultivars ofVitis viniferaL. from La Rioja, Spain

Abstract

The response of two cultivars of <i>Vitis vinifera</i> (Tempranillo and Viura) typical of La Rioja to current levels of ultraviolet-B (UV-B) radiation was evaluated. Plants were exposed to near ambient radiation (PAR + UV-A + UV-B) or near ambient radiation 95% depleted in UV-B. At the end of the 16-day exposure, diurnal variations in photosynthetic pigment composition, soil-plant-analysis-development (SPAD) values, variables of chlorophyll fluorescence, methanol-extractable UV-absorbing compounds (MEUVAC), and sclerophylly were analyzed. The responses of the two grapevine cultivars to the reduction of solar UV-B were somewhat different. The only significant response of Viura was a decrease in MEUVAC. This response was also found in Tempranillo, together with a reduced action of the xanthophyll cycle and an increase in the concentrations of chlorophyll and carotenoids and in SPAD values. Thus, solar UV-B seems to cause slight damage in Tempranillo grapevines. This damage as compared to the almost unaltered Viura grapevines could be related to the lower capacity of Tempranillo to produce MEUVAC under solar UV-B. Given that the exclusion of solar UV-B causes only modest physiological effects, at least in the short term, both cultivars seem to be adapted to the high solar radiation typical of the Mediterranean climate, and their photosynthetic performance (derived from chlorophyll fluorescence variables) does not appear to be at risk from current levels of UV-B.