Photosynthetic Response of Wheat to Stress Induced by Puccinia Recondita and Post-Infection Drought

To quantify photosynthetic response of wheat to the combination of a fungal brown rust infection and a post-infection drought, four treatments were compared: no stress (control), fungal stress (FS), water stress (WS), and twofold stress (WS×FS). Predawn leaf water potential (_wp) was similar in FS and WS treatments over a 3-week period. In the WS treatment, net photosynthetic rate (P _N) and stomata CO₂ conductance (g _s) diminished concomitantly with a constant intercellular CO₂ concentration (C _i) close to 200 µmol mol^–1. In the FS treatment, a reduction of P _N occurred with an increase in respiration rate (doubling of the CO₂ compensation concentration) and in C _i but with no water loss modification. Healthy leaves of infected plants (FS) showed a reduction of P _N as well, with constant g _s and increased C _i. In the twofold stress treatment (WS×FS), leaves showed reduced P _N in relation to the lower _wp. Deleterious effects of both drought and fungal infection on the final area of leaves and dry matter were additive.