First report of Stemphylium leaf spot of sugar beet caused by <i>Stemphylium vesicarium</i>

Sugar beet, a major sugar source, is subject to foliar diseases that can impact yield and quality. In 2019, three spots from two different fields were observed with atypical fungal growth. moist chamber, fungus grew these had dark conidia (average 28 × 17 μm) in irregular clusters (Figure 1). Pure cultures obtained by single spore transfer. All isolates identified as Stemphylium species (Woudenberg et al., 2017). Hanse al. (2015) reported species, later S. beticola 2017) causing yellow leaf spot, severe beet disease The Netherlands. Thus, testing was initiated on the Michigan isolates. Isolates maintained half-strength V8 (HV8) agar. For genetic testing, grown HV8 broth shaking incubator for seven days at 150 rpm room temperature. Mycelium collected, rinsed sterile distilled water, lyophilised, ground coarse powder, DNA extracted using an OmniPrep Fungus extraction kit (G-Biosciences, USA). PCR amplification used primers internal transcribed spacer (ITS) region (ITS1 4; White 1990) calmodulin (cmdA) gene (CALDF1 CALDR1; Lawrence 2013). products sequenced State University RTSF Genomics Core submitted GenBank (Accession No. ON399216 ON409524). BLAST analysis showed closest matches vesicarium (LC592362-LC592370, 98.6% MH084262, 98.8% identity). tested their ability cause germplasm lines, USDA F1042 Crystal 059. Plants commercial potting mix growth chamber 16 hr/8 hr photoperiod 26/22°C day/night temperature 8–10 stage. watered every other day fertilised Osmocote. agar 14 days. Conidia collected water plastic cell spreader concentration adjusted 1 104 spores per ml. As sticker, 5% saponin-containing extract (SBLE) added suspension (Yoshikawa 1995). SBLE made crushing leaves 50 ml of water. sprayed run-off. control plants placed humidity days, then moved back into chamber. Symptoms after 10–14 2). Leaf samples surface decontaminated 0.6% sodium hypochlorite 60 seconds plated confirm presence pathogen. caused lesions both lines. A identical isolate inoculations isolated all fungal-type lesions. No similar seen no sp. isolated. milder than those spot (Hanse 2015). has wide host range (Köhl 2009, Woudenberg but our knowledge, this first report beet.