First Report of Plumed Cockscomb ( var. ) Stem Blight Caused by in Taiwan.

spp. is a widely cultivated ornamental plant in gardens or parks in Taiwan. In September 2021, withering leaves and grayish-brown lesions were observed on the lower stem of plumed cockscombs ( var. ) in Taichung City, with an incidence of about 22% in 136 plants after continuous precipitation, impacting the aesthetic value of the landscape. Symptomatic plants were collected, surface disinfected with 70% EtOH for ~20 sec., blotted dried, and excised diseased tissues (~ 3×3 mm) were placed on 2% water agar. Four representative isolates were obtained after purification and the colonies were white with aerial and non-septated hyphae on V8 agar for 7 days. Sporangia were ovoid, ellipsoid or obpyriform, papillate, (26.3-55.9) 38.0 × 29.0 (20.1-40.6) µm (n = 200) (Ahonsi et al. 2007). Chlamydospores were spherical, terminal or intercalary, 26.0 (15.1-40.4) µm (n = 200). All isolates belong to A2 mating type with amphigynous antheridia and plerotic oospores, 21.0 (17.7-25.7) µm (n = 200), resembling the descriptions of (Erwin & Ribeiro 1996). For molecular identification, sequences of the ITS, β-tubulin (β-tub), and EF-1α regions of all isolates were amplified using ITS1/ITS4, TUBUF2/TUBUR1, and ELONGF1/ELONGR1 primers, respectively (White et al. 1990; Kroon et al. 2004). BLAST analyses of isolates cap1-2 (ITS: OQ581785; β-tub: OQ590022; EF-1α: OQ590026), cap1-3 (ITS: OQ581786; β-tub: OQ590023; EF-1α: OQ590027), cap2-1 (ITS: OQ581787; β-tub: OQ590024; EF-1α: OQ590028), and cap2-2 (ITS: OQ581788; β-tub: OQ590025; EF-1α: OQ590029) showed 100% of ITS identity, 99.5 to 99.9% of β-tub identity, and 99.4 to 99.6% of EF-1α identity with (ITS: MG865551; β-tub: MH493987; EF-1α: MH359043). Phylogenetic trees were constructed using concatenated ITS, β-tub, and EF-1α sequences based on maximum likelihood with a GTR+G model in MEGA X and Bayesian inference method in Geneious Prime 2022.2. All isolates were clustered in with similar topology, thereby were identified as . To confirm pathogenicity, 7 to 10-day-old seedlings and 6-week-old plumed cockscomb plants were inoculated in separate trials and each experiment was conducted twice. For each seedling, the lower stem was inoculated with 50 μl of zoospore suspension (10 zoospores/ml), 3 plants per isolate, and then incubated at 30±2℃ with 12 h light. For adult plants, each was inoculated with mycelial plugs from one V8 plate of 10-day-old , 5 plants per isolate, and incubated at 25±2℃ in a greenhouse. Control plants were inoculated with sterile water and V8 agar plugs, respectively. Stem and root rot were observed on seedlings 4 days after inoculation while wilting and lower stem browning were observed on adult plants 2 months after inoculation. All control plants remained healthy at the end of repeated trials and identical pathogens were re-isolated only from symptomatic plants, thus fulfilling Koch's rules. has been reported causing root rot and stem necrosis not only on cockscomb (. Hort. ex Burvenich) in Argentina (Frezzi 1950), but also infecting several ornamental plants recently in Taiwan (Ann et al. 2018). To our knowledge, this is the first report of stem blight caused by on plumed cockscombs in Taiwan. This finding suggests limited options for landscaping and the host preference of the isolates obtained in this study should warrant further studies.