Stomatal Penetration of Wheat Seedlings by Stem and Leaf Rust: Effect of Light and Carbon Dioxide.

Removal of atmospheric carbon dioxide enhanced penetration of seedling wheat by stem rust Puccinia graminis in light and dark but did not materially affect penetration by leaf rust P. recondita. A concentration of 5 percent CO(2) nearly suppressed penetration by P. graminis but not by P. recondita. Thus light may promote penetration by P. graminis through photosynthetic reduction of CO(2) within the leaf and P. recondita may penetrate independently of light because it is relatively insensitive to the effects of CO(2).