First Report of Leaf Blight Caused by Cladosporium perangustum on Livistona chinensis in China

Livistona chinensis (Jacq.) R.Br. ex Mart. belonging to monocotyledonous Palmaceae, is widely distributed in Eastern Asia, and a common ornamental plant in Southern China (Li et al. 2019, Wu et al. 2019). In November 2019, epidemics of leaf blight were discovered on aged leaves of L. chinensis in the campus of Sichuan Agricultural University, where disease incidence was up to 90% among the cultivated plants, but without resulting in the death of the host. Initial symptoms appeared chlorotic spots on the upper part of leaves, then spots expanded and turned brown. Subsequently, the enlarged spots developed necrotic tissues in the center with brown to dark brown margin. At later stages, conidia and conidiophores were observed on the surface of lesions with the aid of a microscope. As the disease progressed, multiple lesions usually coalesced to cause extensive tissue necrosis at third or more parts of the leaf. Three isolates were obtained from diseased leaves with a single spore isolation referred to Chomnunti et al. (2014), and cultured on potato dextrose agar (PDA) under a 12-h photoperiod and 25±1℃. The colonies were gray to gray-olivaceous with an olivaceous-black reverse side, and measured approximately 7 cm in diameter after 6 days. The conidiophores were macronematous, semimacronematous or micronematous, erect, straight or slightly flexuous, filiform to narrowly cylindrical-oblong, occasionally branched, pale olivaceous-brown, wider at the base, 1 to 8 septate, 14-104 × 3-6.8 µm (x̅ =57.7 × 4.9 µm, n=30). Conidiogenous cells were integrated, terminal, intercalary or pleurogenous, cylindrical-oblong, 9-21 × 4-5.9 µm (x̅ =15 × 4.9 µm, n=20), thick walled, usually aseptate, occasionally 1-2-septate, with 1-5 apically crowed loci. Ramoconidia were almost oblong, aseptate, 4-8.4 × 3-5.7 µm (x̅ =6.9 × 4.6 µm, n=20). Conidia were numerous, catenate, in branched chains, small terminal conidia, subglobose or ovoid, and intercalary conidia were ovoid, limoniform, fusiform, aseptate, 2.9-5.5 × 2-5 µm (x̅ =4 × 3.5 µm, n=20). The representative isolate SICAUCC 20-0007 was used for Genomic DNA extraction, and the internal transcribed spacer (ITS), translation elongation factor 1 alpha (TEF 1-α) and partial actin (ACT) regions were amplified using the primer pairs ITS5/ITS4 (White et al. 1990), EF1-728F/EF-2 (O'Donnell et al. 1998, Carbone et al. 1999) and ACT-512F/ACT-783R (Carbone et al. 1999), respectively. Nucleotide BLAST in GenBank revealed identity with those of C. perangustum, the ITS (MT427730) had 100% identity with MF473185 and MF473177, TEF 1-α (MT441922) had 100% identity with HM148379 and MF473595, ACT (MT441917) had 100% identity with HK521577 and MH047335. The phylogenetic tree combined with ACT, ITS, and TEF 1-α genes (Fig. 1) and morphological characteristics confirmed the identification as C. perangustum defined by Bensch et al. (2010). To determine pathogenicity, five potted plants were inoculated with conidial suspensions (10⁵ conidia/ml) prepared from 1-week-old cultures of the isolate SICAUCC 20-0007 onto the wounded sites via pin-prick inoculation (five to eight leaves per plant with roughly 1 to 2-year-old), and the same amount of healthy plant was sprayed with distilled water as controls. Plants were sprayed regularly with distilled water every day and placed under a 12-h photoperiod and 25±1℃. About fifteen days later, faint yellow to yellowish-brown spots were found on inoculated leaves and were similar to those previously observed and no symptoms developed on the control plants. After a month, leaf blight was observed and the pathogenic fungus was re-isolated from the inoculated tissues. Previous reports have shown that C. perangustum causes leaf spot on Myrica rubra (Lour.) Siebold & Zucc. in China (Lu et al. 2015). To our knowledge, this is the first report of C. perangustum causing leaf blight of L. chinensis in the world. This disease potentially reduces the ornamental value under favorable conditions, and proper control strategies should be implemented.

Keywords: Causal Agent; Cladosporium perangustum; Crop Type; Fungi; Livistona chinensis; Trees; ornamentals.