First report of benzimidazole, DMI and QoI-insensitive Cercospora beticola in sugar beet in Morocco.
Cercospora leaf spot, caused by Cercospora beticola, is of the major foliar diseases of sugarbeet (Beta vulgaris) in Morocco. During the 2016-17 growing season, symptomatic sugarbeet leaves were collected from the 4 major sugarbeet producing regions (Berkane, Doukala, Ghareb and Tadla) to evaluate the sensitivity of C. beticola to thiophanate-methyl, difenoconazole, epoxiconazole, tetraconazole, azoxystrobin and trifloxystrobin fungicides. The results showed that all isolates were resistant to thiophanate-methyl. For difenoconazole 41% of isolates were sensitive and 59% were resistant while for tetraconazole and epoxiconazole 27.3% of isolates were resistant, 66.7% with medium resistance and 6% were sensitive. Furthermore, the mycelial growth inhibition with QoI was less effective with azoxystrobin compared to that obtained with trifloxystrobin. There were at least 54.54% of isolates which demonstrated resistance to azoxystrobin. This is the first report of benzimidazole-DMI and QoI-insensitive C. beticola isolates in Morocco.