Andreas Giannopoulos

Olive trees worldwide suffer from a number of devastating fungal diseases that affect production. One such serious disease is olive leaf spot caused by Venturia oleaginea. Recently, we applied magnesium hydroxide porous micron-scale particles (PMPs) on tomatoes and observed potent antimicrobial activity, reducing the fungal load of the treated phyllosphere. To assess the effectiveness of the compound on olive fungal disease, we applied it for two consecutive seasons. One particular olive tree exhibited extreme manifestations of fungal disease and was destined for removal. A single application of Mg(OH)₂ PMP reversed all symptoms of the disease and eliminated the Venturia pathogen, curing the tree of disease. Venturia oleaginea appears to be exceptionally susceptible to treatment compared to other species in the fungal leaf community. The beneficial fungus Aureobasidium pullulans increased in relative abundance in all the sprayed trees. No toxicity and leaf loss were observed, and the compound retention exceeded 47 days. All trees sprayed showed drastic reductions in the total fungal load and compared favorably to the commercial copper compound. Spraying induced a moderate expression of key indicator genes associated with stress responses. No leaf chlorosis or shedding were observed. Overall, Mg(OH)₂ PMP treatment appears to be a highly promising tool for combating plant fungal disease.

Copper-based bactericides have appeared as a new tool in crop protection and offer an effective solution to combat bacterial resistance. In this work, two copper nanoparticle products that were previously synthesized and evaluated against major bacterial and fungal pathogens were tested on their ability to control the bacterial spot disease of tomato. Growth of Xanthomonas campestris pv. vesicatoria, the causal agent of the disease, was significantly suppressed by both nanoparticles, which had superior function compared to conventional commercial formulations of copper. X-ray fluorescence spectrometry measurements in tomato leaves revealed that bioavailability of copper is superior in the case of nanoparticles compared to conventional formulations and is dependent on synthesis rather than size. This is the first report correlating bioavailability of copper to nanoparticle efficacy.

Grey mould caused by Botrytis cinerea and Late Blight caused by Phytophthora infestans are the most important foliar and fruit diseases that affect tomato. The application of fungicides is the main control measure for these diseases. However, the development of resistance to single-site inhibitors by both pathogens necessitates research for the development of alternative products. Initially, four novel nano-copper (Cu-NPs) formulations were evaluated in vitro. The two most efficient formulations (CN_S4_X1 and CC_S4_X2) from the in vitro assay were further evaluated for their efficacy against B. cinerea and P. infestans on tomato seedling plants (cv. Belladona) during the fourth true leaf growth stage under controlled environmental conditions. To evaluate the protective and curative activity of the Cu-NPs that were tested, spray treatments were conducted 24, 48, and 96 h before (protective treatments) or after (curative treatments) the inoculation of the plants. For each plant, the disease severity value was measured as follows: 0 = no disease symptom; 1 = disease symptoms covered 20% of the leaf; 2 = disease symptoms covered 50% of the leaf; 3 = disease symptoms covered 70% of the leaf; and 4 = dead leaf. For both pathogens, disease severity on the plants that were treated curatively was higher than it was in plants that had been treated preventively. The applications of the two Cu-NPs against B. cinerea 24 h prior the inoculation led to lower disease severity with means of 1.5 and 1.3, respectively, compared to 48 h and 96 h before or after inoculation. Disease severity was significantly higher on plants treated with the commercial copper products. Similarly, the two Cu-NPs that were tested were found to be highly effective against P. infestans and resulted in lower disease severity at 24 h and 48 h pre-/post-inoculation. The results of this study are expected to contribute to the optimization of tomato disease control and to reduce the yield losses caused through the use of a new generation of biocides.