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In November 2022, symptoms of brown spot were observed in approximately 5% fruits of the Gannan navel orange (Citrus sinensis Osbeck cv. Newhall) in an orchard in Anyuan County, Ganzhou City, Jiangxi Province, China (25.13° N,115.38° E). Ten infected fruits were surface sterilized with 75% ethanol and plated on potato dextrose agar at 25 °C for 5 days. Ten isolates were obtained. Colonies of these consisted of dark green hyphae with fluffy gray spores, edges white. Ramoconidia were cylindrical, knee-like bent, septate, 8.4 to 14.7 × 3.4 to 4.6 μm (\(\overline{\mathrm x}\) = 11.8 ± 2.3 × 3.93 ± 0.4 μm, n = 30), while conidia were melon shaped to nearly oval, 3.8 to 5.9 × 2.4 to 3.3 μm (\(\overline{\mathrm x}\) = 5.93 ± 0.7 × 2.9 ± 0.3 μm, n = 30). Morphological characteristics of these isolates were consistent with those of Cladosporium tenuissimum. The internal transcribed spacer (ITS) region, actin (ACT), and translation elongation factor (TEF1-a) regions of the representative isolate (JFRL-03-759, JFRL-03-760) were amplified using primers ITS1/ITS4, ACT-512 F/ACT-783R and EF1-728 F/EF1-986R, respectively (Udayanga et al. 2015). These nucleotide sequences ITS (OQ592886, OQ592887), ACT (OQ603382, OQ603383), TEF1-a (OQ603384, OQ603385) were deposited into GenBank. The phylogenetic tree showed that the two isolates clustered with C. tenuissimum (Zhang et al. 2020). The pathogenicity test was conducted on 10 healthy fruits by inoculating mycelial plugs from a 5-day-old culture into wounds with sterile scalpels. Control fruits (n = 10) were inoculated with sterile PDA agar. All fruits were cultured at 25 °C and 85% relative humidity. Brown spots appeared all the inoculated fruits, whereas control fruits remained asymptomatic. To fulfill Koch’s postulates, the pathogen was re-isolated from all inoculated fruits and confirmed as C. tenuissimum by morphological and molecular analysis. To our knowledge, this is the first report of C. tenuissimum causing brown spot of Gannan navel orange in China.
References
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Funding
National Natural Science Foundation of China (31,560,574); National Science Foundation of Jiangxi Province (20171ACB200214); Youth Fund of Jiangxi Provincial Department of Education (GJJ190225).
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Yuan, X., Li, Z., Xiao, Y. et al. First report of brown spot of Gannan navel orange caused by Cladosporium tenuissimum in Jiangxi Province, China. J Plant Pathol 106, 287 (2024). https://doi.org/10.1007/s42161-023-01533-8
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DOI: https://doi.org/10.1007/s42161-023-01533-8