Wheat and signal grass blast populations from Minas Gerais are sensitive and can be controlled with DMI, QoI and SDHI fungicides

Fungicides play an important role in wheat blast management in Brazil, but the variable and inconsistent responses to some active ingredients have been associated with fungicide resistance, among other factors. To determine whether the reported patterns of fungicide resistance are present in Pyricularia oryzae populations from wheat and signal grass grown in Minas Gerais state, Brazil, we characterized the sensitivity of 64 fungal isolates to seven fungicides belonging to DMI (tebuconazole and epoxiconazole), QoI (azoxystrobin and pyraclostrobin and SDHI (bixafen, fluxapyroxad and benzovindiflupyr) groups. We further assessed if the differential sensitivity of selected isolates affected disease control using commercial doses of the fungicides applied protectively (prior to inoculation) on the heads of potted wheat plants. Despite founding relatively low levels of in vitro sensitivity to some of the fungicides (e.g. azoxystrobin, fluxapyroxad and bixafen), control efficacies (percent reductions in head blast severity and sporulation on the rachis) were generally not affected by the sensitivity of the strain to all fungicides but azoxystrobin. The levels of head blast control for most fungicides (> 70%) in the greenhouse were similar or higher than previously reported in the field. The molecular data for a set of isolates representing different fungicide sensitivity levels were generally not predictive of the phenotype. The wheat-infecting isolates were less sensitive than signal grass-infecting isolates to all fungicides including azoxystrobin. Our findings suggest that at least one active ingredient, within each of the three chemical groups (e.g. tebuconazole, pyraclostrobin and benzovindiflupyr), is capable of successfully controlling the disease.