Fungicide Sensitivity of Paraguayan Strains of Pyricularia oryzae Isolated from Wheat

Abstract

Wheat blast caused by Pyricularia oryzae is a challenging disease to control, considering the multiple reports of fungicide resistance in triazole and strobilurin fungicides. The objective of this work was to evaluate the sensitivity of Paraguayan strains of P. oryzae to five fungicide products under in vitro conditions through determination of the median inhibitory concentration (IC50). The experiment was conducted at the Hernando Bertoni Research Center, IPTA, Caacupé. A randomized complete block design with a 5×5×8 factorial arrangement and 10 replications was used. The factors studied were five strains of P. oryzae; five fungicides (Cyproconazole 12% + Azoxystrobin 20%; Benzovindiflupyr 5% + Picoxystrobin 10%; Tebuconazole 25%; Fluxapyroxad 33.3%; Fluxapyroxad 7.7% + Pyraclostrobin 15.5% + Revysol 11.6%), and eight concentrations of each fungicide (0 (control); 0.1; 1; 5; 10; 20; 40, and 80 μg ml⁻¹). The IC50 was calculated by determining the relative growth of strains at each fungicide concentration using three-parameter log-logistic regression LL.3. Strain sensitivity and fungicide fungitoxicity were classified based on IC50 values, as well as strain sporulation through conidia ml⁻¹ counts. The strains exhibited differential sensitivity to the evaluated fungicides. None of the fungicides achieved complete inhibition of sporulation.