Sensitivity of Mycosphaerella graminicola isolates to demethylation-inhibiting (DMI) fungicides

Abstract

Mycosphaerella graminicola (Fuckel) J. Schrot. (anamorph Zymoseptoria tritici (Desm.) Quaedvlieg & Crous) causes Septoria leaf blotch disease of wheat. The disease can be responsible for yield losses of 30–50% and, when severe, requires management with a fungicide. Single picnidia isolates collected from different locations of Lithuania were tested in vitro for sensitivity to demethylation-inhibiting (DMI) fungicides epoxiconazole, cyproconazole and prothioconazole. Fungicide concentrations were chosen from the proposed Fungicide Resistance Action Committee (FRAC) methods. Microtitre plates with 96-wells were inoculated with suspensions of pycnidiospores taken from single pycnidia of leaves. In total, 196 isolates from 34 locations were tested over the three experimental years (2009–2011). The results showed reduced sensitivity of M. graminicola isolates to epoxiconazole and cyproconazole. The average EC 50 values over three experimental years for epoxiconazole varied between 1.02 and 3.15 mg l -1 , for cyproconazole – 1.51 and 10.66 mg l -1 . The sensitivity to prothioconazole of 64 isolates from 13 locations (2011) ranged from 0.43 to 32.28 mg l -1 . Results of field experiments (2007– 2011) showed that fungicides epoxiconazole and prothioconazole significantly reduced the area under the disease progress curve (AUDPC) values of Septoria leaf blotch compared with untreated plots in winter wheat. In most cases, a single fungicide application significantly increased grain yield and a thousand grain weight weight.