Photosynthesis Limitations of Grapevine after Treatment with the Fungicide Fludioxonil

The aim of this work was to determine the major limitations to photosynthesis induced by the fungicide fludioxonil (fdx) on nontarget grapevines using cutting as a model. The fdx treatments (1.2, 6, and 30 mM) induced a net photosynthetic rate (Pn) decrease without changes in stomatal conductance, suggesting a nonstomatal limitation. Fdx effects on Pn were related neither to photosynthetic capacity alteration in leaves nor to loss in PSII activity. The mechanism underlying photosynthesis reduction differed according to the concentration. Fdx at 6 mM led to an increase of light requirement for photosynthesis while 30 mM fdx induced an increase in the respiration rate in the light. Pn decrease after 1.2 mM fdx could rather be related to wetness caused by the spraying than to fungicide toxicity. Pn recovered 10 days after treatment, meaning that fdx had little deleterious effect on plant physiology or that grapevine has a great capacity to overcome this temporary stress.