Effects of ozone exposure or fungal pathogen on white lupin leaves as determined by imaging of chlorophyll a fluorescence

Chlorophyll fluorescence has been used routinely to investigate photosynthetic activity in plants subjected to both biotic and abiotic stresses. The aim of this work was to compare the perturbations in photosynthesis induced by ozone and by a pathogen. By using a conventional fluorometer a similar response pattern was observed in inoculated and O3-fumigated leaves. The application of chlorophyll fluorescence imaging provided further detailed information on the spatial–temporal heterogeneity of the response of white lupin leaves to fungal pathogen or to ozone fumigation. In particular, 48 h after artificial inoculation with the necrotrophic fungal pathogen Pleiochaeta setosa, the leaves showed a remarkable alteration in PSII operating efficiency (ΦPSII), which affected the whole surface. Afterwards, the infection site was surrounded by a ring of increased photosynthetic activity. The response of ozonated leaves was quite different. The reduction in ΦPSII was already evident 24 h after fumigation; moreover, a distinct heterogeneity of the fluorescence yield was observed and the major veins displayed a lowered ΦPSII.