MORPHOTYPIC COMPOSITION AND DIFENOCONAZOLE SENSITIVITY OF APPLE SCAB PATHOGEN POPULATIONS THAT DIFFER IN THE HISTORY OF FUNGICIDE APPLICATION

Abstract

Scab is one of the most harmful diseases of the world's main fruit crop, the apple tree.
 Purpose. To evaluate the fungicide influence on the population structure of Venturia inaequalis, by its sensitivity to difenoconazole and morphotypic composition.
 Materials and methods. The study was conducted on 88 monospore isolates isolated from two populations of V. inaequalis. The baseline population, which was not treated with fungicides, was selected from natural populations of Malus orientalis. A population of commercial apple orchards was treated with difenoconazole. The sensitivity of isolates was evaluated under laboratory conditions by mycelial growth at different fungicide concentrations and expressed as effective 50% concentration (EC50). Morphotypes were distinguished by comparing photo-images of isolates with morphotype images in a database.
 Results. The populations differed in their sensitivity to difenoconazole at a high level of significance (p≤0.003), with median EC50 values of 0.5 and 2.5 mg a.i./l. The resistance factor of the orchard population had a value of 22. Morphological analysis of the isolates also showed an uneven distribution of morphotypes in the populations. Of the 15 morphotypes isolated, 73 % were unique to a particular population. A medium positive correlation between the traits "morphotype" and "fungicide sensitivity" was found.
 Conclusion. For the first time, a change in the population structure of Venturia inaequalis under the influence of a fungicide was shown not only for a trait under selection pressure (sensitivity), but also for an evolutionarily neutral trait, morphotypic composition.