CARBON-DIOXIDE EXCHANGE BY INFECTED 1ST LEAF TISSUES SUSCEPTIBLE TO WHEAT-STEM RUST

An IR gas analyzer was used to measure CO2 exchange rates in healthy and infected leaf tissues (wheat [Triticum aestivum ssp. compactum] cv. Little Club) during infection by Puccinia graminis f. sp. tritici Eriks. and Henn. Rate of apparent photosynthesis at 300 ppm CO2 and chlorophyll content declined progressively 3 days after inoculation. CO2 compensation points of infected leaves increased and almost doubled that of healthy leaves at time of appearance of type IV pustules. Dark respiration increased, whereas there were no differences in rates of photorespiration between healthy and infected 1st leaf tissues. During flecking and sporulation the gradients of apparent photosynthesis/CO2 concentration relationships were lower in infected leaves compared with comparable healthy tissues.