Sensitivity of two isolates of Phakopsora pachyrhizi to dithiocarmamate, chloronitril, triazoles, strobilurins, and carboxamides fungicides

Abstract

Asian soybean rust (ASR), caused by the phytopathogen Phakopsora pachyrhizi Sydow & Sydow, is a worldwide distributed fungal disease responsible for causing damages in soybean crops [Glycine max (L.) Merril] of up to 90% of its productive potential. So far, due to limited availability of resistant varieties, fungicide application is the most widely used strategy for ASR control, although some populations of the pathogen have shown reduced sensitivity to certain active ingredients. Several methods have been described to measure the sensitivity of a fungus to a given fungicide, or even the fungitotoxicity of a chemical. The most used tests are spore germination in water-agar medium and disease severity in detached soybean leaflets. Two experiments were carried out with populations of the pathogen from Uberlândia - MG and from Chapadão do Sul - MS. The results showed the reduction of benzovindiflupyr efficiency in relation to spore germination and disease severity for the MS population. The novel carboxamide Sumitomo Chemical (S2399T) was highly efficient for both populations inhibiting the pathogen at 0.1 ppm. The carboxamide fluxapiroxade (EC₅₀ = 1-10 ppm) was stable in the two commercial products (Orkestra - Fluxapiroxade and Ativum - Epoxiconazole). Multisite fungicides (chlorothalonil and mancozeb) at concentrations above 100 ppm may be used in the management of resistance in the fields of Brazil associated with strobilurins, triazoles, and carboxamides. The efficiency of the main active ingredient tested depends on the formulation and others fungicides used in the commercial fungicide.