Effects of Powdery Mildew and Water Stress on CO(2) Exchange in Uninfected Leaves of Barley.

Net photosynthesis is stimulated in third seedling leaves of barley plants whose lower two leaves are heavily infected by Erysiphe graminis f.sp. hordei Marchal. Stimulation is greater in water-stressed than in well-watered plants. In stressed, but not in well-watered plants, stimulation is associated with the maintenance of high leaf water potential and high leaf conductance. A small part of the changes in net photosynthesis is attributable to changes in respiratory metabolism in the third leaf, and other possible causes are discussed.