First report of shoot blight of Japanese maple caused by Diaporthe eres in China
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Japanese maple (Acer palmatum Thunb.) nursery plants in Nanjing, exhibiting shoot blight were observed from 2014 to 2017, with an incidence of up to 20%. To determine the causal agent of the disease, small fragments (5 × 5 mm) of symptomatic twigs were surface-sterilized with 0.5% NaOCl, washed in sterile distilled water, placed on potato dextrose agar (PDA) plates and incubated at 24 °C for eight days in the dark. Globose to subglobose pycnidia, 330 to 370 μm in diameter formed and released two types of hyaline, aseptate conidia, alpha (8.8 to 9.2 × 2.1 to 2.9 μm) and beta (17.8 to 30.9 × 1.6 to 2.1 μm). The fungus identified as causal agent of the disease could be related to Diaporthe eres (Udayanga et al. 2014). To confirm the identity at the molecular level, the internal transcribed spacer region, translation elongation factor 1-alpha, and actin were amplified using the respective primers (Carbone and Kohn 1999; White et al. 1990). The sequences (GenBank accession Nos. MG767199-MG767201) matched those of D. eres in BLAST and molecular phylogenetic tree analyses. Pathogenicity was confirmed by scratch inoculation of Japanese maple twigs (2 cm in diameter, n = 3) removed from a tree with sterilized knife and covered with 5-mm mycelial discs. Control plants were covered with empty PDA discs. The same symptoms seen in the field were shown after 14 days by inoculated plants only, from which D. eres was re-isolated. To our knowledge, this is the first report of shoot blight of Japanese maple caused by D. eres in China.
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