Over the last two centuries the atmospheric CO 2 level has exhibited a consistent rise, leading to an increase in the greenhouse effect. This level is now 35% higher than it was before the industrial revolution. On the basis of various scenarios from the Special Report on Emissions it is expected to rise from the present level of 385 ppm to 650-970 ppm by the end of the 21st century. Plant biomass and resistance of winter wheat to various powdery mildew pathotypes were investigated at normal (400 ppm) and enhanced (700 ppm) atmospheric CO 2 levels in a greenhouse. Wheat cultivars Ukrainka and Mv Hombar, and 12 lines from the mapping population developed from their cross and exhibiting different level of resistance were tested. The results showed that the atmospheric CO 2 level had little influence on the resistance of winter wheat to powdery mildew infections based on the percentage of leaf area covered whole plant percentage severity. In response to higher atmospheric CO 2 level there was an increase in the aboveground biomass of the winter wheat genotypes tested in the present work, leading to an increase in plant height and in stem and leaf weight. However, the number of tillers and the grain yield did not increase compared with the values recorded at normal atmospheric CO 2 level.
