First report of powdery mildew on Sedum alboroseum in Europe

T. Jankovics* and O. Szentiványi

Plant Protection Institute, Hungarian Academy of Sciences, H-1525 Budapest, PO Box 102, Hungary

*tjan@nki.hu

Accepted for publication 06/04/05

In the autumn of 2004, symptoms of powdery mildew infection were observed on striped sedum (Sedum alboroseum cv. ‘Mediovariegatum’, syn. Sedum erythrostichum f. variegatum), sold as potted ornamental plants in Budapest. The diseased plants came from a Hungarian commercial nursery, where most plants were infected with powdery mildew. White powdery mildew colonies and abundant sporulation were apparent on both surfaces of leaves and also on petioles and stems (Fig. 1). Initially the pathogen appeared on older leaves and then spread upward, causing severe defoliation (Fig. 2).

Figure 1: Sedum alboroseum infected with powdery mildew

Conidia were cylindric-to-doliiform, measured 27-45 x 10-18 µm and were produced singly on conidiophores (Fig. 3); consisting of a foot-cell measuring 30-50 x 6-9 µm, followed by two or three shorter cells of 15-36 µm length. Germ tubes were formed apically. Hyphal appressoria were nipple-shaped to lobed or multi-lobed. The teleomorph stage was not found. Based on these morphological characteristics, the pathogen was identified as a powdery mildew anamorph belonging to the genus Oidium subgen. Pseudoidium as defined by Cook et al. (1997). Herbarium specimens were deposited in the herbarium of Martin Luther University, Halle, Germany (HAL 1844 F).

Figure 2: Defoliation of a potted striped sedum plant caused by powdery mildew	Figure 3: A conidiophore of the powdery mildew anamorph found on S. alboroseum (bar represents 20 µm)

Pathogenicity of the pathogen was confirmed on healthy potted sedum plants, inoculated by touching them with mildew-infected leaves. Non-inoculated plants served as controls. Both inoculated and non-inoculated plants were kept separately in a greenhouse. One week after inoculation powdery mildew colonies appeared on the infected plants, while no symptoms appeared on the controls.

Three powdery mildew species, Erysiphe sedi, E. umbilici (syn. Microsphaera umbilici) and Golovinomyces orontii (syn. E. orontii) have been reported to infect Sedum spp. in different parts of the world (Braun, 1987, 1995; Kiss & Daughtrey, 2001). Two of them, E. sedi and E. umbilici, produce their conidia singly, similar to the pathogen reported here. According to Braun (1987), E. umbilici is known from Asia only. E. sedi is an Asian species which has expanded its area of distribution to Eastern Europe (Braun, 1995) and has also been found in North America (Kiss & Daughtrey, 2001). To our knowledge, this is the first report of the occurrence of a powdery mildew on S. alboroseum in Europe.

Acknowledgements

The authors would like to thank Dr. Levente Kiss for his helpful comments.

Braun U, 1987. A Monograph of the Erysiphales (Powdery Mildews). Beihefte zur Nova Hedwigia 89, 1-700.

Braun U, 1995. The Powdery Mildews (Erysiphales) of Europe. Jena, Germany: Gustav Fischer Verlag.

Cook RTA, Inman AJ, Billings C, 1997. Identification and classification of powdery mildew anamorphs using light and scanning electron microscopy and host range data. Mycological Research 101, 975-1002.

Kiss L, Daughtrey ML, 2001. First report of Erysiphe sedi on Sedum spectabile in North America. Plant Disease 85, 1207.

The British Society for Plant Pathology