First report of <i>Erysiphe corylacearum</i> causing powdery mildew on <i>Corylus avellana</i> in Spain

In the Mediterranean basin area, powdery mildew disease on hazelnut is commonly caused by Phyllactinia guttata. The occurs in late summer-autumn causing limited damage or economic impact. April 2021, an unusual outbreak of was observed lower leaves hazelnuts (cvs, Negret and San Giovanni) leading to rapid leaf desiccation two commercial orchards (Camí de la Serra Mas Coma), both located at La Selva del Camp, Tarragona, north-eastern Spain. Unlike P. guttata, roundish spots white mycelium appeared adaxial side (Figure 1). Fruit also infected damaged. Microscopical observation amphigenous found hyaline, branched, septate hyphae, conidiophores producing single hyaline ellipsoid doliform conidia (27.2-34.0 × 17.0-23.8 μm; Figure 2). Brown chasmothecia (diameter 115–135 μm) with appendages 3–5 times tightly regularly dichotomously branched were absent time sampling but produced detached symptomatic after about three weeks 27°C. Chasmothecia contained obovoid globose asci (42.1–53.6 38.2–41.5 μm), containing 6–8 ascospores (17.5–21.7 10.2–12.0 3). Symptoms morphological characters aligned description Erysiphe corylacearum (Bradshaw et al., 2021). identification samples from different confirmed amplification sequencing ITS (PMITS1/PMITS2; Cunnington 2003) LSU regions (PM3/NL1/TW14; Mori 2000) rDNA. nBLAST analysis these sequences (GenBank Accession Nos. MZ597855-MZ597857 for ITS; MZ597843-MZ597845 LSU) revealed 100% identity E. (MW345726; MW031866; KX279887). Young healthy plants cv. Tonda Gentile detached, surface sterilised pathogenicity testing. inoculated spraying a water suspension diseased (105 conidia/ml) incubated 21°C under 12hr light cycle. After 9–12 days, whitish mycelia abundant leaves, whilst those as control, remained healthy. Dry specimens are preserved fungal herbarium University Tuscia (ECESP1 – ECESP3). To our knowledge, this first report This species, known infect Corylus heterophylla C. sieboldiana Asia 2021; Braun & Cook, 2012), reported outside 2013 significant yield losses avellana Turkey (Sezer 2017). Since then, has spread eastern countries towards western Europe, reaching northern Italy 2020 (Mezzalama 4). shows that typical traits severe invasive pathogen likely represent one most serious threats cultivation Europe. authors would like thank Mr. T. Casadó his help find trees.