Photodynamic Inactivation of plant pathogens part II: fungi

Abstract

The constantly increasing demand for agricultural produce from organic and conventional farming calls for new, sustainable, and biocompatible solutions for crop protection. The overuse of fungicides leading to contamination of both produce and environment and the emergence of plant pathogenic fungi that are resistant to conventional treatments warrant the need for new methods to combat fungal infections in the field. We here deliver the follow-up study to our research on the Photodynamic Inactivation (PDI) of plant pathogenic bacteria (Glueck et al. in Photochem Photobiol Sci 18(7):1700–1708, 2019) by expanding the scope to fungal pathogens. Both fungal species employed in this study—Alternaria solani and Botrytis cinerea—cause substantial crop and economic losses. Sodium magnesium chlorophyllin (Chl, approved as food additive E140) in combination with Na2EDTA and the chlorin e6 derivative B17-0024 holding cationic moieties serve as eco-friendly photoactive compounds. Effectiveness of the antifungal PDI was measured by inhibition of growth of mycelial spheres (average diameter 2–3 mm) after incubation with the photosensitizer for 100 min and subsequent illumination using a LED array (395 nm, 106.6 J cm−2). One hundred micromolar Chl combined with 5 mM Na2EDTA was able to successfully photokill 94.1% of A. solani and 91.7% of B. cinerea samples. PDI based on B17-0024 can completely inactivate A. solani at 10 times lower concentration (10 µM); however, for B. cinerea, the concentration required for complete eradication was similar to that of Chl with Na2EDTA (100 µM). Using a plant compatibility assay based on Fragaria vesca, we further demonstrate that both photosensitizers neither affect host plant development nor cause significant leaf damage. The plants were sprayed with 300 µL of treatment solution used for PDI (one or three treatments on consecutive days) and plant growth was monitored for 21 days. Only minor leaf damage was observed in samples exposed to the chelators Na2EDTA and polyaspartic acid, but overall plant development was unaffected. In conclusion, our results suggest that sodium magnesium chlorophyllin in combination with EDTA and B17-0024 could serve as effective and safe photofungicides. Graphical abstract

In Vitro Photoinactivation of Fusarium oxysporum Conidia with Light-Activated Ammonium Phthalocyanines

“…Thus, although the photosensitization of fungal structures requires higher PS concentrations, the cellular targets of photosensitization with PS 1 may be sufficiently diverse to support the prospect of a broad-spectrum (multiorganism) phytosanitary approach applicable to plant nurseries. The effectiveness of the two PSs against pathogenic fungal microbes in vitro showed their promising application in an in vivo approach, such as the one presented by Plaetzer and coworkers, who used strawberry leaves and solar light as a green irradiation source [ 51 ].…”

Efficacy of Oil and Photosensitizer against Frankliniella occidentalis in Greenhouse Sweet Pepper

“…Photosensitizers have been observed as effective against bacteria [ 18 ], fungi [ 19 ] and insects such as mosquitoes, ticks and Thrips tabaci Lindeman [ 31 , 32 ]. Glueck et al [ 18 ] reported that the sodium salt of chlorophyllin (Chl, E140), the active ingredient present in SUN-D-06 PS in this study, is effective in controlling the Gram-positive bacterial plant pathogen Rhodocccus fascians and Gram-negative Xanthomonas axonopodis and Erwinia amylovora .…”

“…Due to their unique mode of action, photosensitizers could also play an important role in IPM as reduced risk pesticides. Recently, Photodynamic Inactivation (PDI) has emerged as a powerful tool to control both Gram-negative and Gram-positive bacteria, as well as fungi [ 18 , 19 ]. PDI is characterized by the use of a photosensitizer (PS), that when activated by a light source in the presence of molecular oxygen produces reactive oxygen species (ROS) and singlet oxygen.…”

“…These reactions target multiple sites, causing extensive damage leading to rapid cell death and subsequent insect death ( Figure 1 ). To date, no known resistance to PDI has been recorded [ 19 ]. It is highly unlikely that any organism could develop resistance against photosensitizers since their mode of action targets multiple sites at the same time and they become exhausted after light-activation.…”

“…The ideal structure of a PS used in horticulture differs considerably from its counterpart used in human medicine. Whilst repeated medical photodynamic therapy may make patients sensitive to light, photosensitizers as applied in horticulture are safe to use, not cytotoxic, nor genotoxic or mutagenic to human and animal life [ 19 , 20 ]. Indeed, the sodium magnesium chlorophyllin (Chl, E140) photosensitizer formulation evaluated in this study ( Figure 2 ) is derived from natural molecules, and has been widely approved as food additive E140, “natural green”.…”