First record of powdery mildew on Homalocladium platycladum in the Czech Republic

Homalocladium platycladum (Syn. Muehlenbeckia platyclada; tapeworm plant or ribbonbush) has a worldwide distribution as an ornamental plant and in tropical regions is used in parks and as a hedge plant (Hanelt et al., 2001); in Europe it is used mostly as a pot plant. Beginning in March 2005 in greenhouses ("Fata Morgana") of the Botanical Garden of Prague (Prague-Troja), powdery mildew symptoms on Homalocladium were observed and were observable periodically thereafter. Symptoms were white irregular colonies on the upper and lower surfaces of leaves; stems were symptomless.

To observe powdery mildew morphology, fuchsin staining was used (Shin, 2000). Mycelium was white, superficial, branched, with hyphae 5-6.5 µm in diameter; conidia were cylindrical, lacking fibrosin bodies, length 31.72 – 51.24 mm (mean 39.97 µm), width 10.98 – 15.86 µm (mean 13.39 µm), shape index 2.16 – 4.2 (mean 3.00), with germ tube arising from the end of the conidium, often broadened at its apex and the appressoria appearing slightly-lobed to lobed. Conidiophores were erect, with foot-cells followed by 2-3 distal cells; conidia were formed singly (pseudoidium type). The teleomorph was not observed. Voucher specimens are being kept in the Department of Botany collection at Palacký University in Olomouc, Czech Republic.

The anamorph was thus identified as Oidium subgen. Pseudoidium, imperfect state of the genus Erysiphe. Braun (1995) reported only one Erysiphe on members of the Polygonaceae: Erysiphe polygoni. This powdery mildew has with a wide distribution in Europe, Asia, Africa, North and South America and has been reported on Homalocladium platycladum in Great Britain, Romania, Finland and former Soviet Union (Braun, 1995).