Stemphylium vesicarium: a rising threat to European horticulture

Stemphylium vesicarium is an emerging multi-host fungal pathogen that increasingly threatens European and global horticulture. Initially recognized as the causal agent of brown spot of pear and Stemphylium leaf blight of onion, the pathogen is now associated with diseases of other economically important crops, including spinach. Its broad host range, host-specialized pathotypes, host-specific toxins, and widespread fungicide resistance make disease management particularly challenging, often resulting in severe yield losses. The epidemiology of S. vesicarium is shaped by its polycyclic nature and dual reproductive strategy, with sexual ascospores colonizing alternative hosts in early spring and asexual conidia acting as the primary source of inoculum. The pathogen overwinters associated to crop residues, woody tissues, and alternative weed hosts, and can also spread through infected seeds, transplants, and thrips. Multilocus phylogenetics and whole-genome sequencing have clarified taxonomic ambiguities within Stemphylium, revealing substantial genetic diversity and complex population structures. In Europe, favourable climatic conditions, limited chemical control, fungicide-insensitive populations, and the lack of resistant cultivars in many crops underscore the urgent need for integrated disease management strategies. This review aims to give a valuable insight into the current knowledge on taxonomy, epidemiology, genetic diversity, toxin-mediated pathogenicity, and management of S. vesicarium, and identifies key research gaps to support sustainable disease control in European horticulture.