Carbon dioxide exchange by infected first leaf tissues susceptible to wheat stem rust

Abstract

An infrared gas analyser was used to measure carbon dioxide exchange rates in healthy and infected leaf tissues (wheat cv. Little Club) during infection by Puccinia graminis f.sp. tritici Eriks. & Henn. Rate of apparent photosynthesis at 300 ppm carbon dioxide and chlorophyll content declined progressively 3 days after inoculation. Carbon dioxide 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 first leaf tissues. During flecking and sporulation the gradients of apparent photosynthesis/carbon dioxide concentration relationships were lower in infected leaves compared with comparable healthy tissues.