Efficacy loss of strobilurins used in protection against apple scab in Czech orchards

Abstract

The apple scab caused by Venturia inaequalis is important apple disease in temperate zone. Economical losses caused by the pathogen are effectively reduced by intensive chemical protection and breeding. Occurrences of pathogen resistence to strobilurin fungicides were noted in some Czech orchards in the past. In 2007–2011, collection of 136 isolates V. inaequalis was tested with the aim to detect presence of single-point mutations of cytochrom b (cytb) gene causing efficacy loss of strobilurins. Consequently occurrence of beta-tubulin (beta-tub) gene mutation causing resistance to benomyl was studied with the aim to obtain comparative data about frequency of mutation in non-selective environment. Therefore simple and highly repeatable PCR based mutation detecting methods were optimised. Analysis brought knowledge about high similarity of cytb and beta-tub genes mutations occurrence. Whilst the frequency of the G143A substitution in cytb gene was 65% the E198A substitution of beta-tub gene occurred in 54% within pathogen population. This high frequency of resistant population necessitates revision of the way of strobilurins use in apple scab management.