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First Report of Fruit Spot of Toxicodendron sylvestre Caused by Fusarium incarnatum in China

Shen, H. F., Jiang, S. B., Lin, B. R., Zhang, J. X., Sun, D. Y., Pu, X. M.
Plant disease 2019 v.103 no.2 pp. 376
DNA primers, Fusarium incarnatum, Toxicodendron, conidia, cosmetics, culture media, disease control, ethanol, financial economics, fruit diseases, fruits, fungi, genes, growth chambers, hyphae, industry, internal transcribed spacers, medicine, microscopy, mycelium, pathogenicity, pathogens, pigmentation, polymerase chain reaction, soaking, sodium hypochlorite, sweet peppers, tissues, trees, China, Trinidad and Tobago
Toxicodendron sylvestre (Siebold & Zuccarini) Kuntze in the family Anacardiaceae, is an economically important cultivated tree in China. The extract of its fruit is widely used in medicine, cosmetics, fruit preservative, and so on. In September 2017, brown necrotic spots were first observed on the fruits of T. sylvestre in Jiaoling, Guangdong, China. This symptom occurred on approximately 21% of the T. sylvestre trees grown in a commercial field (15 ha). Infected fruits initially showed dark brown pinpoints, and the spots expanded rapidly. The fruits turned dark brown followed by the exhibition of malformed and shriveled symptoms, and they ultimately died. White mycelium appeared on the fruit surface under wet conditions. Diseased fruits were surface sterilized using 75% ethanol for 30 s and 2% NaOCl for 10 min, rinsed for three times with sterile water, and incubated for 3 days on potato dextrose agar (PDA) medium at 25°C. A fungus was isolated from all infected tissues, hyphal tips of which were subcultured on PDA for pure isolation. The mycelium was white and fluffy, and the colony pigmentation was yellowish brown. Macroconidia (20.0 to 32.2 μm in length × 3.18 to 4.83 μm in width) were dorsiventral curvature and hyaline, and they had three to five septa. Microconidia (8.1 to 10.8 μm in length × 2.7 to 3.9 μm in width) were hyaline, aseptate, and oval. These characteristics are typical of the genus Fusarium (Booth 1971). The representative isolate JLML1 (accession no. JLML1709) was deposited at South China Agricultural Research and Innovation Center. Its rDNA-ITS gene (GenBank accession no. MH537593) and TEF-1α (MH537594) gene were amplified using the primer pairs ITS1/ITS4 and TEF1/TEF2 (Cong et al. 2016), respectively. BLAST analyses of the ITS and TEF-1α sequences indicated that they shared 100 and 99% identity with Fusarium incarnatum (Desm.) Sacc. isolates HNMi (KX184815) and DEB29 (KF993975), respectively. Pathogenicity was tested by soaking 50 disease-free T. sylvestre fruits with a 30-ml mixture of macroconidia and microconidia suspension (7 × 10⁶ spores/ml) for 60 s. Another 50 fruits were soaked in sterile water for 60 s as controls. After inoculation, fruits were placed in 90-mm Petri plates with wet sterilized filter papers at the bottom and were kept in a growth chamber at 25°C. After 7 days, inoculated fruits showed diseased symptoms similar to those observed in the field. No symptom was observed on the controls. We reisolated the fungal pathogen from the symptomatic fruits and further confirmed it to be F. incarnatum by microscopy and polymerase chain reaction. F. incarnatum was previously reported to be associated with fruit disease of bell peppers in Trinidad (Ramdial et al. 2016). To our knowledge, this is the first report of F. incarnatum causing fruit spot on T. sylvestre in China. This new disease could contribute to severe economic losses for the T. sylvestre industry in China, and identification of this pathogen helps to establish the appropriate measures to control this disease.