First Report of Trunk Canker of London Plane Tree Caused by Botryosphaeria dothidea in China

In June 2025, trunk canker symptoms were observed on London plane trees (Platanus × acerifolia (Aiton) Willd.) in green spaces of Kashi City, Xinjiang, China. A survey of more than 1,000 trees at 20 urban green-space sites in Kashi City revealed a disease incidence of 6.0%. Symptoms appeared as dark brown, slightly sunken trunk lesions that expanded longitudinally into elongated cankers. Beneath the bark, the phloem and cambial tissues showed dark brown necrosis, and transverse sections revealed irregular brown discoloration extending into the xylem. Severe cankers were occasionally associated with branch decline. Bark tissues from lesion margins were cut into 5 × 5 mm pieces, surface-disinfested in 75% ethanol for 30 s and 1% sodium hypochlorite for 1 min, rinsed three times with sterile distilled water, placed on potato dextrose agar (PDA), and incubated at 25°C in the dark. Five representative symptomatic samples were collected for pathogen isolation, from which fungi with similar colony morphology were obtained. Three representative isolates, BdK05, BdK12, and BdK18, were purified by hyphal-tip isolation and used for morphological and molecular identification. Colonies on PDA were initially white and cottony, becoming gray to dark gray. Sporulation was induced on 2% water agar containing autoclaved pine needles at 25°C under near-ultraviolet light with a 12 h light/12 h dark cycle. Conidia were collected from mature pycnidia and were hyaline, aseptate, fusiform to ellipsoid, measuring 11.52 to 19.33 × 3.55 to 6.10 μm, with an average size of 15.59 ± 1.47 × 4.73 ± 0.58 μm (n = 50), consistent with Botryosphaeria dothidea (Phillips et al. 2013). The internal transcribed spacer region (ITS), partial translation elongation factor 1-α gene (tef1-α), and partial β-tubulin gene (tub2) were amplified from BdK05, BdK12, and BdK18 using ITS1/ITS4, EF1-728F/EF1-986R, and Bt2a/Bt2b, respectively (White et al. 1990; Carbone and Kohn 1999; Glass and Donaldson 1995). GenBank accession numbers were PZ587174 to PZ587176 for ITS, PZ687083 to PZ687085 for tef1-α, and PZ687089 to PZ687091 for tub2. Bayesian phylogenetic analysis was performed using MrBayes v3.2.7 based on the combined ITS, tef1-α, and tub2 sequence dataset (1,210 bp). The three isolates clustered with B. dothidea reference strains CMW7999 and CMW8000 with a Bayesian posterior probability of 0.9. Based on morphology and multilocus phylogeny, the isolates were identified as B. dothidea. Pathogenicity tests were conducted using healthy one-year-old London plane seedlings. Stems were disinfected with 75% ethanol and wounded with a sterile 5-mm cork borer. Three seedlings were inoculated with 5-mm mycelial plugs from the margin of an actively growing PDA colony of BdK05, with one wound per seedling; three controls received sterile PDA plugs. Sites were covered with moistened sterile cotton, sealed with Parafilm, and maintained under natural field conditions. Five days after inoculation, all inoculated stems developed dark brown, sunken necrotic lesions resembling early field symptoms, whereas controls remained asymptomatic. The fungus was re-isolated from symptomatic tissues but not from controls and confirmed as B. dothidea by morphology and ITS sequencing. The assay was performed twice with similar results, fulfilling Koch’s postulates. B. dothidea causes canker, dieback, and fruit rot on many woody plants (Marsberg et al. 2017). Neofusicoccum parvum causes stem dieback of P. × acerifolia in China (Yu et al. 2018). To our knowledge, this is the first report of trunk canker of London plane caused by B. dothidea in China. As London plane is an important ornamental and shade tree in the urban green spaces of Kashi, this finding provides useful information for trunk canker diagnosis, surveillance, and management.