Anthracnose of three-leaf akebia (Akebia trifoliata Koidzumi) caused by Colletotrichum acutatum

J Gen Plant Pathol (2004) 70:295–296? The Phytopathological Society of Japan

DOI 10.1007/s10327-004-0131-x and Springer-Verlag Tokyo 2004

Yoshinori Kobayashi · Takanori Tsukamoto Naohiko Miyai · Yoshinari Nakanishi

Anthracnose of three-leaf akebia (Akebia trifoliata Koidzumi) caused by Colletotrichum acutatum

Received: October 30, 2003 / Accepted: February 27, 2004

Y. Kobayashi (*) · N. Miyai

Tokyo-Substation, Yokohama Plant Protection Station, 2-56 Aomi,Koto-ku, Tokyo 135-0064, Japan

Tel. ?81-3-3599-1137; Fax ?81-3-3599-1140e-mail: kobayashiyr@pps.go.jp

T. Tsukamoto · Y. Nakanishi

Research Division, Yokohama Plant Protection Station, Yokohama,Japan

Abstract In October 2001, anthracnose caused by Colletotrichum acutatum Simmonds ex Simmonds was found on three-leaf akebia (Akebia trifoliata ) in Saitama,Japan. This is the ?rst report of anthracnose on three-leaf akebia caused by C. acutatum .

Key words Akebia trifoliata · Anthracnose · Colletotrichum acutatum · New disease

Three-leaf akebia, Akebia trifoliata Koidzumi, is a climbing deciduous woody plant that grows wild in mountain ?elds in Japan and is also used as a potted ornamental “bonsai”plant. In October 2001, severe leaf spot caused by Colletotrichum acutatum Simmonds ex Simmonds was found on three-leaf akebia bonsai plants during ?eld inspec-tions in bonsai nurseries in Kawaguchi, Saitama, Japan. An outline of this article was reported elsewhere (Kobayashi et al. 2003).

Symptoms. Initial symptoms appeared as small necrotic brown spots, 1–2mm diameter, on the leaf margin, central vein, and petiole (Fig. 1A). As the disease progressed the lesions expanded and coalesced, and the center of the lesions turned grayish white (Fig. 1B). Severely diseased leaves wilted and fell off. In humid conditions, acervuli containing orange to salmon-pink masses of spores emerged on lesions.

Isolation and identi?cation of the pathogen. The acervuli on lesions were subepidermal and lacked setae. Conidiogenous cells were phialidic, hyaline, cylindrical, straight or slightly

curved, and 10–20 (ave. 14.5) ? 2.5–3.0 (ave. 2.8) μm in size (Fig. 1C). Five isolates obtained by single spore isolation from conidial masses on lesions were cultured on potato dextrose agar (PDA) at 25°C under 12h of black light (FL20S-BLB 20W; Toshiba, Tokyo, Japan)/12h dark.Three isolates were used for morphological observation and inoculation tests. Conidia in cultures were aseptate, hyaline,fusiform or ellipsoid with pointed ends, and 9.5–16.4 (ave.13.5) ? 3.0–4.5 (ave. 3.9) μm in size (Fig. 1D). Appressoria that formed on a slide culture with potato-carrot agar (PCA) were one-celled, pale brown, thick-walled, ellipsoid to obovate with smooth margins, and 7.5–12 (ave. 9.4) ?4.5–8 (ave. 6) μm in size (Fig. 1E). PDA cultures were white at ?rst and subsequently became grayish white to gray and pink to reddish brown in reverse (Fig. 1F). The optimum growth temperature ranged from 26° to 28°C, and at 25°C mycelia grew 22mm in 6 days. The fungus did not form an ascigerous stage or sclerotia in culture or on the host. These morphological and cultural characteris-tics of the isolates coincided with previous descriptions of Colletotrichum acutatum Simmonds ex Simmonds (Dyko and Mordue 1979; Sato 1996; Simmonds 1965;Sutton 1980).

Pathogenicity. Wounded (with needle) and nonwounded leaves of 1-year-old three-leaf akebia plants grown in pots were sprayed with a spore suspension (1 ? 106 spores/ml of sterilized distilled water with 0.05% Tween 20). Inoculated plants were covered with polyethylene bags for 4 days. The polyethylene bags were then removed and incubated in a growth chamber (MLR–350HT; Sanyo Electric Biomedi-cal, Tokyo, Japan) at 25°C and at 70% relative humidity under 12h ?uorescence light illumination/12h dark. Six days after inoculation, small necrotic brown spots appeared on both wounded and nonwounded leaves, and the lesions enlarged and coalesced 2 weeks afterward (Fig. 1G). These lesions were similar to those observed during ?eld inspec-tions. C. acutatum was readily reisolated from the inocu-lated leaves. This is the ?rst report of the disease caused by C. acutatum on three-leaf akebia in Japan. We propose the name anthracnose of Akebia (tanso-byo in Japanese).

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References

Dyko BJ, Mordue JEM (1979) Colletotrichum acutatum . CMI Descrip-tions Pathogenic Fungi and Bacteria, No. 630. Commonwealth My-cological Institute, Kew, Surrey, UK

Kobayashi Y, Tsukamoto T, Miyai N, Nakanishi Y (2003) Anthracnose of Akebia (Akebia trifoliat a Koidzumi) caused by

Colletotrichum

Fig. 1.Symptoms and causal organism of anthracnose of three-leaf akebia (Akebia trifoliata Koidzumi). A , B Necrotic spots on leaf mar-gin, central vein, and petiole of three-leaf akebia. C Acervulus from a lesion. D Conidia formed on potato-dextrose agar (PDA). E Appres-

acutatum Simmonds ex Simmonds. Jpn. J Phytopathol 69:259(abstract, in Japanese)

Sato T (1996) Problems of taxonomy and identi?cation of Colletotrichum species. Plant Protection 50:273–280 (in Japanese)Simmonds JH (1965) A study of the species of Colletotrichum causing ripe fruit rots in Queensland. Qd J Agric Anim Sci 22:437–459

Sutton BC (1980) The Coelomycetes. Commonwealth Mycological Institute, Kew, Surrey, UK, pp 523–537

sorium formed on a potato-carrot agar slide culture. F Colonies of the isolate cultured on PDA at 25°C for 10 days. Left , surface side. Right ,reverse side. G Lesions on leaves 14 days after inoculation