Influence of elevated CO2 and ozone concentrations on late blight resistance and growth of potato plants

Potato plants (Solanum tuberosum L. cv. Indira) with high susceptibility to the late blight pathogen Phytophthora infestans were exposed for 4 weeks to two different CO2 concentrations (400/700 ppm) combined with ambient and double ambient ozone concentrations (first experiment) and with 1/5 ambient and ambient ozone concentrations (second experiment) in climate chambers. Leaves of the potato plants were then inoculated with Phytophthora infestans zoospores. Plants from the high CO2 variant showed a significantly increased resistance to the pathogen, verified by visual evaluation and quantitative real-time PCR, whereas plants treated with double ambient ozone were slightly more susceptible. An increase in the constitutive activities of the PR-proteins beta-1,3-glucanase and osmotin in leaves of plants exposed to 700 ppm CO2 correlated with the increase in resistance at this CO2-concentration. Biomass parameters were barely affected by the elevated CO2-concentration but decreased with increasing ozone concentrations. Biochemical analyses revealed that the content of starch as well as the content of soluble sugars in leaves were highest at the double ambient ozone/700 ppm CO2 variants pointing to an ozone-induced inhibition of assimilate allocation from leaves to tubers. Leaf C/N-ratio increased at elevated CO2-concentrations due to a decrease in N-content. The effect of the ozone- and CO2-induced biochemical changes on the resistance response of potato towards Phytophthora infestans is discussed. (C) 2007 Elsevier B.V. All rights reserved.