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First Report of Pestalotiopsis theae Causing Leaf Spot of Ixora chinensis in China

Mukhtar, I., Li, H., Quan, X., Chou, T., Jiang, S., Chen, B., Wen, Z., Xie, B.
Plant disease 2019 v.103 no.2 pp. 370
Ixora chinensis, Pestalotiopsis, appendages, color, conidia, conidiomata, conidiophores, culture media, defoliation, disease incidence, ethanol, flowering, fungi, genes, internal transcribed spacers, leaf spot, leaves, loquats, mycelium, ornamental plants, ornamental value, pathogenicity, plant growth, tea, China
Ixora chinensis is a flowering ornamental plant widely grown in tropical counties including China. Visible leaf spots with concentric rings were observed in March 2018 on I. chinensis in Fuzhou, China. In some areas, disease incidence was up to 60% of the plants. Initially, tiny circular brown spots were observed on leaves, and over time the spots expanded to become large and irregular lesions, surrounded by a dark brown or yellow border. Mostly with shaded leaves, lesions spread over the surface, resulting in defoliation. Leaf spots contained concentric rings dotted with acervuli of up to 250 μm diameter. For fungal isolation, infected leaf surfaces were disinfected with 70% alcohol; small pieces (0.5 cm²) were cut from the lesions, inoculated onto 2% potato dextrose agar (PDA), and incubated at 25 ± 2°C for 3 to 4 days. When pure, fungal colonies were white with cottony aerial mycelium, margin undulated, and the reverse of the colony was slightly yellow. Black conidiomata were irregularly distributed in mature colonies. Conidiomata were globose to oblate, immersed in mycelia, 250 to 800 μm diameter, and dark greenish brown to black in color. Conidiophores were reduced to conidiogenous cells. The conidiogenous cells were separate, colorless, smooth walled, straight to slightly curved, ampulliform or subcylindrical, and 6.0 to 13.5 × 1.3 to 3.0 μm (n = 100). Conidia were five-celled-clavate fusiform, ellipsoid to subcylindrical, slightly constricted at septa, 18.5 to 32.0 × 5.0 to 8.0 μm (n = 100); obconical basal cell was hyaline with or without a truncate base, thin walled, and 3 to 5 μm long. A single tubular, unbranched, knobbed, centric or excentric, 3 to 6 μm long appendage was attached to the basal cell. Three median cells were 12 to 18 μm long, doliiform, brown to light brown, or olivaceous in color. Septa were darker than the cells. The apical cell was 3 to 5 μm long, hyaline, cylindrical to subcylindrical, with two to four tubular, filiform, knobbed, 18 to 35 μm long apical appendages. On the basis of morphological characteristics, the fungus was identified as Pestalotiopsis theae (Sawada) Steyaert (Chang et al. 1997). Internal transcribed spacer ITS1-5.8S-ITS2 regions and partial EF-1a gene were amplified for different isolates. ITS sequences (MH470249, MH470257, and MH472583) and EF-1a sequences (MH479105 and MH479106) were 99 to 100% similar to many P. theae (e.g., KJ503818, JQ683743, and KX895203) and Pseudopestalotiopsis species, respectively, in GenBank. For the pathogenicity test, eight healthy, detached I. chinensis leaves disinfected with 70% ethanol were placed into separate moist plastic boxes. Conidia produced on PDA were used to prepare a spore suspension of 2.0 × 10⁷ conidia/ml. The suspension was sprayed onto each leaf, followed by incubation at 25°C. For the control, sterile water was sprayed on a set of eight leaves. After 15 days, typical symptoms appeared on all inoculated leaves, whereas control leaves remained symptomless. The same fungus was reisolated from lesions and identified. This disease reduces plant growth and reduces the ornamental value of the plants. Previously, P. theae has been reported causing gray leaf blight of tea and loquat in China (Chen et al. 2013; Lu 1995). To our knowledge, this is the first report of P. theae causing leaf spot on I. chinensis worldwide.