Diversity and fungicidal resistance of Cercospora beticola

Abstract

The fungus Cercospora beticola Sacc. belongs to the most important pathogens on sugar beet. The Cercospora leaf spot disease is important problem for growers in all growing areas of sugar beet. This study was focused on the morphological diversity of C. beticola isolates and occurrence of their fungicidal resistance in Slovakia. Isolates involved in this work were collected from sugar beet leaf during 2016-2018. Average growth rate of the tested C. beticola isolates on five different media showed the major role of cultivation temperature. The fastest growth was measured by 30°C on TE medium, followed by PDA, SBLEA, AWSBL, and V8. The colour of aerial mycelium varied from olive-green to grey with white powdery appearance, per grey colour with wrinkled texture, to black colour. There is no significant correlation among isolates origin, colony morphology parameters and growth rate. The highest sporulation rate was recorded at cultivation temperature 25°C by using of TE growth medium, the lowest one by V8 medium. The inhibition effect of azoxystrobin + cyproconazole was significantly different among the tested isolates from different localities and years. The results showed reduced sensitivity of C. beticola population in Slovakia strictly depending of the locality. The most reduced sensitivity was measured on localities Hronovce and Nové Zámky, followed by localities Mojmírovce, Senec, and Dolné Saliby with similar values. There is no positive correlation between inhibition effect and mycelial growth rate. The results showed increasing fungicidal resistance of C. beticola to azoxystrobin + cyproconazole in some localities of Slovakia.