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An insight on photodynamic approach versus copper formulations in the control of Pseudomonas syringae pv. actinidiae in kiwi plants.

Abstract

In the last decade, the kiwifruit worldwide production has been highly affected by Pseudomonas syringae pv. actinidiae (Psa), a phytopathogenic bacterium, responsible for severe economic losses that is seriously affecting kiwifruit trade. The available treatments for this disease are still scarce, being quite frequent to spray the orchards with copper derivatives, in particular cuprous oxide (Cu2O). However, copper should be avoided due to their high toxicity and, therefore, it is essential to search for new approaches of controlling Psa. Antimicrobial photodynamic therapy (aPDT) can be an alternative approach to inactivate Psa. aPDT forms highly reactive oxygen species (ROS) that affect different molecular targets which makes it very unlikely that the microbes can develop resistance. The aim of this work was to evaluate the effectiveness of aPDT to photoinactivate Psa, using porphyrin Tetra-Py+-Me and light at different intensities. Initially, the degree of inactivation of Psa in vitro was assessed using the PS at 5.0 μM under low irradiance (4.0 mW cm-2). After, ex vivo experiments, using artificially contaminated kiwi leaves, were done with a PS at 50 μM, under 150 mW cm-2 and sunlight irradiation. A reduction of 6 log in the in vitro assays after 90 min of irradiation was observed. In the ex vivo tests, the decrease was lower, approximately 1.8 log reduction at an irradiance of 150 mW cm-2, 1.2 log at 4.0 mW cm-2 and 1.5 log under solar radiation. However, after three successive cycles of treatment under 150 mW cm-2, a 4 log inactivation was achieved. No negative effects were observed on leaves after treatment. The highly CuO2 tested at the recommended concentration by law (50 g hL-1) and at 10 times lower; it efficiently inactivated Psa (5 log) after a few min of treatment, but negative effects were observed on leaves. Overall, it was demonstrated that aPDT with the porphyrin Tetra-Py+-Me under natural solar radiation is effective to inactivate Psa, does not damage the plant and can be applied by spraying.

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Publication details

The article was received on 11 Aug 2017, accepted on 27 Nov 2017 and first published on 28 Nov 2017


Article type: Paper
DOI: 10.1039/C7PP00300E
Citation: Photochem. Photobiol. Sci., 2017, Accepted Manuscript
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    An insight on photodynamic approach versus copper formulations in the control of Pseudomonas syringae pv. actinidiae in kiwi plants.

    V. Jesus, D. Martins, T. Moura, N. Valério , M. D. G. P. M. S. Neves, M. A. Faustino, L. Reis, E. Barreal, P. Gallego and A. Almeida, Photochem. Photobiol. Sci., 2017, Accepted Manuscript , DOI: 10.1039/C7PP00300E

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