First record of Oidium anamorph of Podosphaera xanthii on Medusagyne oppositifolia

Abstract

Powdery mildew first appeared on mature 3-year-old bushes of ‘jellyfish tree’, Medusagyne oppositifolia (Medusagynaceae), grown from seed at Eden Project, Cornwall, England, in collaborative conservation work with the Seychelles Government. Initially, young leaves showed distortion and patches of mycelium bearing conidia. Later, light brown lesions developed and badly affected plants showed extensive leaf-drop, especially destructive in seedlings. This is the first report of powdery mildew on Medusagyne. Conidia are catenate, elliptical to doliiform, (19) 24–34(47AE5) · (13AE5) 15–18 lm with fibrosin bodies and a sinuous wrinkling pattern. Conidiophores erect with a long cylindrical straight or twisted foot-cell, 41–86AE5 (140) · (7) 9–14 (16) lm, arising towards one end of its hyphal mother cell, the lower septum occasionally raised up to 10 lm, followed by a generative cell and 2–5 maturing conidial units. Superficial hyphal cells, 25–105 · 4AE5–11AE5 lm, branched at right angles, bearing inconspicuous or slightly nipple-shaped appressoria. No chasmothecia were present, but characteristics are consistent with Oidium subgenus Fibroidium, the anamorph of Podosphaera. The short, broad germ tubes typical of the fibroidium type, brevitubus subtype narrowed the identification to Podosphaera section Sphaerotheca subsect. Magnicellulatae (Cook & Braun, 2009) with the morphology close to that of Podosphaera (syn. Sphaerotheca) fusca, apparently a ubiquitous species with a broad host range.