Effects of the cherry leaf spot pathogen Blumeriella jaapii on gas exchange before and after expression of symptoms on cherry leaves

Gas exchange in cherry leaves infected with Blumeriella jaapii, the causal agent of cherry leaf spot disease, was studied. Infection reduced net photosynthesis during all stages of disease development. Throughout the course of this study there was a continuous decrease in carboxylation and the maximum electron transport rate. Carboxylation was always the most affected parameter, and it seems likely that the infection interferes mainly with the enzymatic processes in the Calvin cycle. There was also a drastic decrease in assimilation, transpiration and stomatal conductance before any visible symptoms occurred on cherry leaves.