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First Report of Stem Die-back on Platanus × acerifolia Caused by Neofusicoccum parvum in China

Yu, L., Liu, J. N., Chen, Z. B., Xu, S. G., Ren, Z., Wang, D. K., Geng, K. Y., Zhang, Q., Pei, W. H., Kong, C. S.
Plant disease 2018 v.102 no.7 pp. 1446
Neofusicoccum parvum, Platanus acerifolia, bark, blight, cambium, conidia, culture media, dieback, discoloration, ethanol, fungi, greenhouses, internal transcribed spacers, leaves, mycelium, ornamental plants, pathogenicity, peptide elongation factors, pycnidia, ribosomal DNA, seedlings, sodium hypochlorite, stems, tap water, translation (genetics), trees, urban areas, wilting, woody plants, China
London plane tree (Platanus × acerifolia) is an ornamental plant species of urban environments, and is widely planted in China and many other countries. In August 2014, symptoms of stem blight were observed on P. × acerifolia in Kunming, Yunnan Province, southwest China. Symptoms included stem dieback and branch blight. The inner bark and the cambial region of affected tissue were discolored bluish gray, and 10 to 15% of trees were damaged. Samples from plants with symptoms were washed with running tap water, surface sterilized with 2% sodium hypochlorite and then 70% ethanol, rinsed in sterile distilled water, plated on potato dextrose agar (PDA), and incubated at 28°C. Fungal isolates developed copious white aerial mycelium that became dark gray after 4 to 6 days, and formed black pycnidia after 25 days. Conidia forming on PDA were one-celled, fusiform to ellipsoidal, externally smooth, and thin walled, with dimensions of 16.0 to 23.0 × 5.2 to 7.8 (average 18.5 × 5.7 μm). Identity was confirmed by analysis of the rDNA internal transcribed spacer region (ITS1-5.8S-ITS2) and the translation elongation factor 1-alpha (EF1-α). GenBank BLAST searches showed a high identity with reference sequences (ITS, 99%; EF1-α, 100%). Representative sequences of both regions were deposited at GenBank (ITS, Accession Nos. KP140963 to KP140965; EF1-α, Accession Nos. KR349969). Morphological and molecular results confirmed this species as Neofusicoccum parvum. Pathogenicity tests were conducted by stem inoculation of 2-year-old P. × acerifolia seedlings. Mycelial plugs (4 mm in diameter) from actively growing colonies of N. parvum (PDA) were applied to same-size bark wounds on the middle point of the stems. Inoculated wounds were wrapped with Parafilm. Control seedlings received sterile PDA plugs. Inoculated and control seedlings (5 each) were kept in a greenhouse and watered as needed. After 5 to 6 days, tissue discoloration that developed on the inoculated plants extended 2.8 ± 0.2 cm. After 3 weeks, all of the inoculated but none of the control P. × acerifolia seedlings showed leaf wilting and dark, vascular stem tissue. Neofusicoccum parvum was reisolated from symptomatic tissues, thus fulfilling Koch’s postulates. No symptoms were visible in the control seedlings. Neofusicoccum parvum is a member of Botryosphaeriaceae, commonly associated with dieback and cankers of woody plants (Moricca et al. 2012; Cheon et al. 2013; Yu et al. 2013). To our knowledge, this is the first report of N. parvum on P. × acerifolia in China.