In vitro and in vivo antifungal activity of phosphite against Phytophthora parasitica in tomato
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Phosphite is an alkaline salt of phosphorous acid. Its antifungal properties against some phytopathogenic fungi are increasingly valued in the context of a growing concern about the detrimental environmental effects of the standard biocides used to protect plants against pests and diseases. The purpose of this work was to analyze the in vitro and in vivo effect of phosphite in the development and evolution of Phytophthora parasitica on a tomato crop. The phosphite potential to limit and control the fungus growth was first established through an in vitro assay. In a second assay, in the greenhouse, tomato plants were transplanted into pots, in a substrate previously inoculated or not inoculated with the fungus mycelium. Inoculated and non-inoculated plants were sprayed with a range of phosphite concentrations (0, 0.9, 1.4, and 1.9 mg ml-1). The in vitro growth of the fungus mycelium was progressively restricted as phosphite concentration increased in the medium, and no fungus growth was detected with a phosphite concentration of 0.9 mg/ml. In the greenhouse assay, the development of the inoculated plants improved during the culture time when treated with phosphite, as was acknowledged by their higher chlorophyll content and by the values of stress indicators when compared with untreated plants. Moreover, the dry weight of the infected plants increased as the phosphite concentration was higher, and their maximum growth was obtained at 1.4 mg ml-1 phosphite. It is also noteworthy that, when compared to healthy plants, the infected plants increased their root to total weight ratio by 31.6% when treated with the highest phosphite concentration.