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

Abstract

In the last decade, the worldwide production of kiwi fruit has been highly affected by Pseudomonas syringae pv. actinidiae (Psa), a phytopathogenic bacterium; this has led to severe economic losses that are seriously affecting the kiwi fruit trade. The available treatments for this disease are still scarce, with the most common involving frequently spraying the orchards with copper derivatives, in particular cuprous oxide (CuO). However, these copper formulations should be avoided due to their high toxicity; therefore, it is essential to search for new approaches for controlling Psa. Antimicrobial photodynamic therapy (aPDT) may be an alternative approach to inactivate Psa. aPDT consists in the use of a photosensitizer molecule (PS) that absorbs light and by transference of the excess of energy or electrons to molecular oxygen forms highly reactive oxygen species (ROS) that can affect different molecular targets, thus being very unlikely to lead to the development of microbe resistance. The aim of the present study was to evaluate the effectiveness of aPDT to photoinactivate Psa, using the porphyrin Tetra-Py-Me and different light intensities. The degree of inactivation of Psa was assessed using the PS at 5.0 μM under low irradiance (4.0 mW cm). Afterward, ex vivo experiments, using artificially contaminated kiwi leaves, were conducted with a PS at 50 μM under 150 mW cm 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, 1.2 log at 4.0 mW cm, and 1.5 log under solar radiation. However, after three successive cycles of treatment under 150 mW cm, a 4 log inactivation was achieved. No negative effects were observed on leaves after treatment. Assays using CuO were also performed at the recommended concentration by law (50 g h L) and at concentrations 10 times lower, in which at both concentrations, Psa was efficiently inactivated (5 log inactivation) after a few minutes of treatment, but negative effects were observed on the leaves after treatment.

Photodynamic inactivation of the phytopathogenic bacterium Xanthomonas citri subsp. citri

“…Complete eradication of the biofilms with cationic porphyrins was achieved without visible leaf damage (Jesus et al . 2018) as opposed to what is observed with anionic porphyrins that can cause plant cell death (Leroy‐Lhez et al . 2019).…”

“…actinidiae (Psa) with a cationic porphyrin produced an inactivation factor equivalent to that obtained in this work (6 log10) with half the concentration of a porphyrinic PS (50 µmol l −1 ) and a slightly higher light dose (Jesus et al . 2018). When a mixture of several porphyrin derivatives was used, the factor raised to 7·4 log10 with only 5·0 µmol l −1 of the PS mixture, and a light dose of 14 J cm −2 (Martins et al .…”

“…The reduction in PDI efficiency in ex vivo conditions, compared to in vitro assays, was also observed in PDI of Psa on kiwi leaves (Jesus et al . 2018) and may be related to protection and shading caused by leaf micro‐texture and sheltering provided by the stomata. Another effect may be associated with the experimental design.…”

Plant Photodynamic Stress: What's New?

“…It was reported that natural photosensitizers such as coumarins and furocoumarins or synthetic ones such as phenothiazinium and porphyrins inactivated pathogenic agents as virus (Tobacco mosaic virus), bacteria ( Pseudomonas syringae ) and fungi ( Collectotrchum abscissum, Colletotrichum gloeosporioides, Collectotrichum acutatum, Aspergillus nidulans, Fusarium oxysporum, Fusarium moniliforme, Fusarium solani ) (Table 1 ). However, when spotted on orange tree and strawberry plants, or on kiwi contaminated leaves under solar radiation, the leaves and flowers were not affected by either natural/synthetic photosensitizers excepted for strawberry leaves that were damaged upon treatment with 100 μM phenothiazinium (Orlob, 1967 ; de Menezes et al, 2014a , b ; Fracarolli et al, 2016 ; Gonzales et al, 2017 ; Jesus et al, 2018 ). In another extended context, Issawi and co-workers conceived a double target strategy that could eradicate in the same time unwanted vegetation and plant pathogens without killing plants of agronomic interest (Figure 1B ).…”

Photodynamic inactivation of Botrytis cinerea for a safe pest management of grapevine

“…PSs are classi ed in many groups such as porphyrins, chlorins, coumarins, furocoumarins, phthalocyanines and phenothiaziniums. Porphyrins and chlorins such as chlorophyllin, have been shown to be very effective against bacteria on kiwi leaves tested in vitro (Jesus et al 2018;Glueck et al 2019). Coumarins, furocoumarin and phenothiazinium were shown to be active against the plant-infecting fungi Colletrichum acuratum and Aspergillus nidulans (De Menezes et al a, b;2014;Fracarolli et al 2016).…”