SENSITIVITY BASELINE AND ORCHARD POPULATIONS OF VENTURIA INAEQUALIS TO THE SUCCINATE DEHYDROGENASE INHIBITOR FUNGICIDES (SDHI)

Abstract

Background. Scab plays the leading role in terms of significance and harmfulness among apple-spotted spots. The use of fungicides with a highly specific mechanism of action against the pathogen can lead to the development of resistance in the pathogen. Purpose. To assess the sensitivity of monospore isolates of Venturia inaequalis from a population with different histories of interaction with fungicides to the active substances of the SDHI chemical class boscalid and fluxapiroxad in vitro. Materials and methods. The in vitro sensitivity of isolates was assessed by mycelial growth at various concentrations of boscalid and fluxapiroxad and expressed as an effective 50% concentration (EC50). Results. Boscalid EC50 values for all populations ranged from 0.04 to <300 mg a.i./l, and the average value was 16.27 mg a.i./l. The resistance factor (RF) for boscalid in various garden populations varied from 2 to 8, and the proportion of resistant isolates was not high. The population mean EC50 of fluxapiroxade was 0.259 mg a.i./l. The RF for fluxapiroxad did not exceed 4, and for two garden populations it was only 2, which indicates a slight shift in sensitivity in these populations relative to the "initial". Conclusion. For the first time in the world, the EC50 value of the boscalid was obtained for the initial population. The activity of fluxapiroxad against the pathogen was higher than that of boscalid. For all orchards populations, a decrease in sensitivity to the investigated fungicides was shown in comparison with the original population. It is assumed that a relatively low shift in sensitivity to carboxamides for the studied populations is due to the use of these DIs in the region in the form of mixed preparations with fungicides that have a different mechanism of action.

Keywords

• sensitivity
• venturia inaequalis
• baseline population
• ec50
• resistance factor