Abstract
The fungus Cercospora beticola Sacc. is the one of the most important pathogens on the sugar beet. The frequent application of fungicides with the same mode of action increase a risk of development of resistant strains of the pathogen. Occurrence of C. beticola resistant strains has been never researched in Slovakia. In this work, C. beticola isolates were collected from 10 localities of Slovakia and analysed for fungicide resistance in laboratory conditions. Nine fungicides with different mode of action were tested – trifloxystrobin + cyproconazole, kresoxim-methyl + epoxiconazole, azoxystrobin + cyproconazole, thiophanate-methyl + tetraconazole, thiophanate-methyl, prochloraz + propiconazole, picoxystrobin, tetraconazole, and difenoconazole. The results confirmed, that occurrence of fungicide resistance in C. beticola population was established in Slovakia. Different criteria of assessment of fungicide resistance (based on EC50 and on growth rate – inhibition percentage) showed slightly different results, but both criteria confirmed resistant C. beticola strains to thiophanate-methyl, picoxystrobin and difenoconazole. Fields with higher frequency of application of these fungicides significantly supported the development of resistant strains. Assessment of any C. beticola strains have not confirmed reduced sensitivity to active ingredients tetraconazole and prochloraz + propiconazole. The lowest level of risk of fungicide resistance was confirmed in the locality Oslany. It is very important to focus on anti-resistant strategy and reduce of using fungicides on localities, where the occurrence of resistant C. beticola strains was confirmed – Dolné Saliby (thiophanate-methyl and picoxystrobin) and Senec (picoxystrobin and difenoconazole).
Highlights
Sugar beet belongs to traditional crops in Europe
Results of sensitivity test of Cercospora beticola population based on the mean of percent inhibition (PI) values showed that the mean PI value of thiophanate-methyl for each concentration achieved less than 27% for 6 of 10 localities
Cercospora beticola is a pathogen with high risk of developing of resistance
Summary
In Slovakia, it is mainly grown as a technical crop for the sugar industry. Sugar beet is currently grown on about 22 000 hectares in Slovakia. The farmers accepted the offer of sugar companies to grown more sugar beets, which helped to stabilize sugar production to satisfy consumption in Slovakia (Černý et al, 2019). An important factor in growing of sugar beet is the control of diseases and pests (Almquist et al, 2016; Černý et al, 2018). Cercospora beticola causes Cercospora leaf spot disease, which is the most important disease worldwide (Tedford et al, 2017). CBT causes the typical symptoms of leaf spots and prevents root formation. Cercospora leaf spot is economy problem for growers (Khan and Khan, 2009), because it causes decrease of assimilate transport to root. The result of disease damage is lower yield and sugar quality and high storage rots (Harveson and Bolton, 2013)
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