Exobasidium siroboe Nagao, S. Ogawa & S. Kurogi, 2023

Nagao, Hideyuki, Kurogi, Shuichi & Ogawa, Seiji, 2023, Exobasidium siroboe sp. nov. (Exobasidiaceae) causing Exobasidium fruit deformation on Symplocos myrtacea in Japan, Phytotaxa 579 (3), pp. 219-224 : 219-221

Exobasidium siroboe Nagao, S. Ogawa & S. Kurogi , sp. nov. FIGURE 1

MycoBank no.: 847125

Type: — JAPAN. Kagoshima Prefecture, Kumage-gun, Yakushima-machi, Yodogou-tozanguchi , 20 July 2005, Nagao & S. Kurogi INM-2-17577-055270, acc. nos. LC656026 / LC656021 , culture MAFF239964 .

Additional specimens examined: — JAPAN, immature fruits of S. myrtacea : Fukuoka Prefecture, Onga-gun, Okagakimachi, Kuroyama , 20 June 2001, S. Ogawa TSH-B 0088 ; Kagoshima Prefecture, Aira-gun, Makizono-cho, Onamiiketozanguchi , 19 July 2005, Nagao & Kurogi INM-2-17564-052435, acc. nos. LC656022 / LC655200 , culture MAFF239959 ; Kagoshima Prefecture, Kirishima-shi, Karakuni-dake , 19 July 2005, Nagao & S. Kurogi INM-2-17566-055265, acc. nos. LC656023 / LC656018 , culture MAFF239960 ; Kagoshima Prefecture, Kirishima-shi, Karakuni-dake , 19 July 2005, Nagao & S. Kurogi INM-2-17568-055268, acc. nos. LC656024 / LC656019 , culture MAFF239961 ; Kagoshima Prefecture, Kumagegun, Yakushima-machi, Yodogou-tozanguchi , 20 July 2005, Nagao & S. Kurogi INM-2-17571-052437, acc. nos. LC656025 / LC656020 , culture MAFF239963 ; Kagoshima Prefecture, Kumage-gun, Yakushima-machi , 20 July 2005, Nagao & S. Kurogi INM-2-17582-052445 .

Different from E. symploci-japonicae var. caprogenum by narrower basidiospores [(14–)15–26 × 3–6(–7) µm] and fewer septal numbers in basidiospores [0–3(–5)].

The hymenium composed of basidia with 2–4 sterigmata and conidia. Basidia were clavate to cylindrical, 35–40 × 6–7 µm ( FIGURES 1A, B ), emerging directly from the host surface or through stomata. Sterigmata were 4–8 × 1.5 µm, developing outwardly and tapering toward the tip ( FIGURES 1A, B , 3A, B ). Basidiospores were ellipsoid, (14–)15–26 × 3–6(–7) µm, hyaline, smooth, one-celled when formed, becoming septate with 3(–5) septa ( FIGURES 1C , 3C, D, E ). Septate basidiospores germinated after placing on culture media for 18–24 h ( FIGURE 3F ). Germ tubes of the basidiospores emerged from several cells and produced conidia at the tip of germ tubes 24 h after release ( FIGURES 2 , 3G ). Germ tubes grew into pseudohyphae and branch. Conidia were lacrimiform, subfusiform, and clavulate, 5–13 × 1 µm. Colonies on potato dextrose agar (PDA) composed of partially elongated pseudohyphae and conidia. The colony surface corrugate without a farinose appearance and pink to pale pink, the same as the reverse of the colonies. Dark pigment was not produced on PDA. Colonies were glutinous and did not fix on the agar surface.

Etymology: —Referring to the local name of the host plant, S. myrtacea , by the Yakushima dialect.

Symptom: —On infected fruit of S. myrtacea , white powdery hymenia appeared entirely on the swollen part of the fruit ( FIGURE 4A ). Size of the infected fruit was apparently larger than the healthy ones and the color was pale green or whitish green ( FIGURES 4B, C ). Infected fruit showed thickened mesocarp and cavities. The symptom was different from the pocket caused by Taphrina species. All seeds were sterile ( FIGURE 4D ). Hymenium formation was not observed on leaves, twigs and branches.

Phylogenetic analysis: —Bootstrap values on neighbor-joining and support values of Quartet Puzzling on maximum likelihood trees were highly supported (100/100), so that this new species is distinguished from the two previously described varieties of E. symploci-japonicae .

Figures

FIGURE 1. Basidia andbasidiosporesof Exobasidium siroboe on infected fruit of Symplocosmyrtacea.Basidia (A1,A2,A3), basidiospores (B) and germinated basidiospores (C) collected in Kagoshima Prefecture (INM-2-17577-055270). Scale bar: 3 µm. Illustrated by Hideyuki Nagao.

FIGURE 2. Basidiospore germination of Exobasidium siroboe (TSH-B 0088) on potato dextrose agar after 24 h of incubation. Some of the basidiospores produced conidia on the germ tubes (arrows). Scale bar: 3 µm. Illustrated by Hideyuki Nagao.

FIGURE 3. Basidia and basidiospores of Exobasidium siroboe on infected fruit of Symplocos myrtacea collected in Kagoshima Prefecture (INM-2-17577-055270). Basidium with 4 sterigmata (arrow) (A) or with 3 sterigmata (arrow) (B), basidiospores ovoid (C) to fusiform (D, E), one-celled when formed, becoming septate with 3 septa (arrows) (C). Basidiospore germination of E. siroboe on potato dextrose agar after 24 h of incubation (F); conidia (arrows) were produced on the germ tubes that emerged from basidiospores after 24h (G). b: basidiospore. Scale bars: A–E = 3 µm, F,G = 20 µm. Photographed by Hideyuki Nagao.

FIGURE 4. Symptoms of Exobasidium fruit deformation of Symplocos myrtacea by Exobasidium siroboe. A. Fruit deformation covered with white hymenia observed in July 2005 in Kagoshima Prefecture. B. Appearance of fruit deformation (center and right) and healthy (unaffected) fruit. Development of fruit deformation was not necessarily uniform. Parts of infected fruits apparently looked healthy (arrow). C. Example of symptom development of Exobasidium fruit deformation (TSH-B 0088). H: healthy fruit, IN: infected fruit, IN-A: swollen infected fruit, IN-B: decayed swollen infected fruit. D. Vertical section of infected fruit (TSH-B 0088). Asterisk indicates thick mesocarp and arrow indicates aborted seed in the cavity. H: healthy fruit, IN: infected fruit, INS: vertical section of infected fruit. Photographed by Hideyuki Nagao.