S03 - Session P1 - Stemphylium sp. in Danish spinach seed production

Authors: Birte Boelt *, Asbjorn Molmer Sahlholdt, Thies Marten Heick

Denmark holds approximately 70% of the world's spinach ( Spinacia oleracea ) hybrid seed production. Seed quality is highly important, in particular for the subsequent use for baby leaf products. Stemphylium is a necrotrophic fungi causing the disease Stemphylium leaf spot on spinach and infecting spinach seeds with risk of seed transmission (Hernandez-Perez & du Toit, 2005). Two species n S. vesicarium and S. beticola n are considered the dominant Stemphylium sp. pathogens on spinach (Liu et al., 2020; Spawton et al., 2019). Fungicides are frequently applied during seed production to avoid yield loss and deterioration of seed quality caused by infections of Stemphylium sp. . Danish farmers generally comply with the IPM principles; however, several fungicide sprays are performed under high disease pressure. As only a few fungicide products are registered in Denmark, there is a risk of fungicide resistance build-up in the pathogen population of Stemphylium , impacting their efficacy. Recently, fungicide resistance has been reported in the United States for S. vesicarium isolates from spinach in the FRAC group 11 (Spawton et al., 2019; Spawton et al., 2020) and for S. vesicarium from onion in FRAC group 7,9, and 11 (Hay et al., 2019). Here, we report on the identification of Stemphylium -isolates from 22 spinach seed lots with high incidence of Stemphylium that were produced in Denmark and Poland in 2021 using ITS-, gadph -, and cmdA -regions as templates for amplification in PCR (Woudenberg et al., 2017). In addition, we evaluated a subsample of these Stemphylium -isolates for fungicide sensitivity of commonly used fungicide mode of actions used in the Danish spinach seed production.