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 stratospheric ozone, is an increasing threat to living organisms. Furthermore, increased ground level temperatures as a consequence of global warming may favour development of pathogens, such as Cercospora beticola, that thrive at high temperatures. This study evaluates the effect of combined UV stress and Cercospora leaf-spot disease on young sugarbeet plants (Beta vulgaris L.). An inoculum consisting of twelve European isolates of C, beticola Sacc, was used in the experiments, One Cercospora-sensitive and one Cercospora-tolerant sugarbeet line were analysed from growth regimes where plants were grown either under visible radiation alone or with supplemental UV-B, Photosynthetic pigments and partial reactions of photosynthesis, including potential yield and quantum yield under illumination, non-photochemical quenching (q(NPQ)) and photochemical quenching (q(P)), were measured to assess plant response. The combination of Cercospora a and supplemental UV-B radiation in the sensitive line resulted in a decreased photosynthetic efficiency, shown by q(NPQ) and quantum yield under illumination as compared with that for either stress applied alone. The F(v)/F(m) was unchanged for plants subjected to UV-B radiation without infection, although the q(NPQ) decreased, The Cercospora-tolerant line showed no significant differences under the different treatments, Thus, the line tolerant to Cercospora infection also proved to be tolerant to UV-B radiation alone and in combination with the infection.