Differential response of a sensitive and tolerant sugarbeet line to Cercospora beticola infection and UV-B radiation

Increased ultraviolet-B (UV-B, 280-320 nm) radiation, due to depletion of s tratospheric ozone, is an increasing threat to living organisms. Furthermor e, increased ground level temperatures as a consequence of global warming m ay favour development of pathogens, such as Cercospora beticola, that thriv e at high temperatures. This study evaluates the effect of combined UV stre ss and Cercospora leaf-spot disease on young sugarbeet plants (Beta vulgari s L.). An inoculum consisting of twelve European isolates of C, beticola Sa cc, was used in the experiments, One Cercospora-sensitive and one Cercospor a-tolerant sugarbeet line were analysed from growth regimes where plants we re grown either under visible radiation alone or with supplemental UV-B, Ph otosynthetic pigments and partial reactions of photosynthesis, including po tential yield and quantum yield under illumination, non-photochemical quenc hing (q(NPQ)) and photochemical quenching (q(P)), were measured to assess p lant response. The combination of Cercospora a and supplemental UV-B radiat ion in the sensitive line resulted in a decreased photosynthetic efficiency , shown by q(NPQ) and quantum yield under illumination as compared with tha t for either stress applied alone. The F-v/F-m was unchanged for plants sub jected to UV-B radiation without infection, although the q(NPQ) decreased, The Cercospora-tolerant line showed no significant differences under the di fferent treatments, Thus, the line tolerant to Cercospora infection also pr oved to be tolerant to UV-B radiation alone and in combination with the inf ection.