Distribution of the F129L mutation conferring resistance to strobilurins in Alternaria solani populations in Serbia

Abstract

Alternaria solani is a fungal pathogen that causes early blight, an economically important disease of potatoes worldwide. The application of fungicides differing in mode of action are the most important control measure for early blight management. However, frequent use of fungicides may cause fungal pathogen populations to be selected for mutations conferring fungicide resistance, resulting in significant losses of fungicide efficacy. Repeated use of QoI fungicides may generate a selection pressure on A. solani populations that promotes resistant genotypes, this quality in question being because of amino acid substitutions in the cytochrome b gene. During a four-year survey, isolates of A. solani were collected from the primary potato production regions in Serbia. The cytochrome b gene region of each isolate was evaluated for the presence of the F129L substitution known to historically confer QoI resistance. Sequence analysis revealed two genotypes similar to those reported elsewhere in the world with a diverse geographic distribution in Serbia. Genotype I was dominant in the south of Serbia, genotype II was prevalent in north Serbia, and in central Serbia both genotypes were represented equally. The F129L mutation was detected in both genotypes, with a progressive shift from the wild type to mutated A. solani across years. A. solani isolates containing the F129L mutation were collected from the northern and the central Serbia in 2016 without any mutated isolates in the southern Serbia. In 2019, in all surveyed regions, a predominance of isolates with the F129L mutation was observed. The presence of two cytochrome b genotypes among A. solani isolates and significant presence of F129L mutations indicates a change in the genetic structure of this pathogens populations in potato fields nationwide, which could have a significant impact on control of early blight disease.