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First Report of Cladosporium perangustum Causing Leaf Spot of Myrica rubra in China

    Authors and Affiliations
    • L. M. Lu , Citrus Research Institute of Zhejiang Province, Huangyan 318020, China
    • B. P. Cheng , Plant Protection Research Institute, Guangdong Academy of Agricultural Sciences and Guangdong Provincial Key Laboratory of High Technology for Plant Protection, Guangzhou 510640, China
    • Z. X. Pu
    • X. R. Hu
    • D. C. Du
    • G. Q. Chen , Citrus Research Institute of Zhejiang Province, Huangyan 318020, China.

      Chinese bayberry (Myrica rubra Siebold & Zucc.) is an economically important fruit tree widely cultivated in southern China. During autumn 2013 and 2014, surveys were conducted to identify the causal agent of a leaf spot of M. rubra cv. Dongkui in Huangyan City (121°27′ E, 28°64′ N) and Xianju City (120°73′ E, 28°85′ N) of Zhejiang Province. Disease incidence was 5 to 30% in various orchards covering about 300 ha. Initial symptoms appeared as tiny taupe spots on the upper or lower leaf surface, while no visual symptoms were observed on the opposite side. As the disease progressed, the spots expanded into round lesions 1 to 5 mm in diameter. Olivaceous bulges (i.e., hyphae) were usually observed on the surface of lesions, and round reddish brown spots with yellow halos developed on the opposite leaf surface. At later stages, conidia and conidiophores were frequently observed on the lesions, and multiple lesions usually coalesced, causing extensive tissue damage. Diseased samples were surface-sterilized with 0.5% NaClO and then cultured on potato dextrose agar (PDA) in the dark at 25°C. Fourteen isolates from 10 samples from Huangyan orchards and eight isolates from seven samples from Xianju orchards, at least one isolate from each sample, were finally obtained. The 22 isolates were morphologically indistinguishable. Their colonies were gray to gray-olivaceous with an olivaceous-black reverse and measured 5.2 cm in diameter after 10 days of culture. Conidiophores were macronematous or micronematous, erect, filiform to cylindrical, 1 to 6 septate, and 45.0 to 160.0 × 2.0 to 4.0 μm in size. The ramoconidia were cylindrical or oblong, 0 to 2 septate, and 26.5 to 45.0 × 2.8 to 4.2 μm in size. Secondary ramoconidia were cylindrical to oblong, 0 to 2 septate, 7.0 to 32.0 × 2.0 to 3.2 μm in size, with 2 to 5 distal conidial hila. Intercalary conidia were ovoid to ellipsoid, 0 to 1 septate, 4.5 to 16.5 × 2.0 to 3.2 μm in size, with 1 to 3 distal hila. Terminal conidia were ovoid to subglobose and 2.0 to 4.5 × 1.8 to 2.5 μm in size. Conidiogenous loci and hila were 1 to 1.5 µm in diameter. These cultural and morphological characteristics matched the description of Cladosporium perangustum (Bensch et al. 2010). The internal transcribed spacer (ITS, GenBank Accession No. KM485631) and translation elongation factor 1 alpha (tef1 alpha, KM485632) genes of the fungus were sequenced and showed 100 and 99% identity with those of C. perangustum from Brazil (JN698599 and KC484658). To determine pathogenicity, 25 healthy leaves on eight 2-year-old potted M. rubra cv. Dongkui plants were wound inoculated with sterilized water (control) or conidial suspensions (106 conidia/ml; 15 μl on each wounded site) and maintained in an environmental chamber at 90% relative humidity at 25°C with a 12-h photoperiod. Assays were performed twice. Inoculated leaves showed symptoms identical to those observed in the field after 20 days. C. perangustum was reisolated from the lesions on inoculated plants. No symptoms were visible on the four control plants and no fungus was isolated from them. Previous reports showed that C. perangustum causes leaf spot on Syagrus oleracea (Oliveira et al. 2014). To our knowledge, this is the first report of C. perangustum causing leaf spot of M. rubra in China. This disease may potentially cause considerable economic losses under favorable conditions, so proper control strategies should be implemented promptly.