Emergence of Severe Stemphylium Leaf Blight on Leek (Allium Porrum) During Seed Production in Türkiye

Abstract

A severe leaf blight epidemic caused by Stemphylium vesicarium was observed on cultivated leek (Allium porrum L.) in a commercial seed production field in Türkiye. The disease occurred in early summer 2025 during the second year of a biennial seed production cycle, where incidence reached 50%–75%. The extended cultivation period characteristic of seed production (12–18 months) likely served as a key epidemiological driver, enabling pathogen overwintering and extensive inoculum accumulation, in contrast to the shorter cropping period of annual vegetable production systems. The pathogen was identified as S. vesicarium based on morphological features and confirmed by maximum likelihood phylogenetic analysis of combined internal transcribed spacer (ITS) and glyceraldehyde-3-phosphate dehydrogenase (gapdh) gene sequences. Pathogenicity was verified through fulfilment of Koch's postulates using two representative isolates on healthy leek plants. This report constitutes the first confirmed occurrence of S. vesicarium on leek in Türkiye and demonstrates a shift in its epidemiological importance from a minor foliar pathogen in annual systems to the causal agent of a severe epidemic under biennial seed production conditions, highlighting the need for targeted surveillance and management strategies to mitigate disease risk in both seed and commercial leek production. © 2026 Wiley-VCH GmbH. Published by John Wiley & Sons Ltd.