First Report of Powdery Mildew on Azalea Cv. Mollis (Rhododendron japonicum × R. molle) in Italy

Plant Disease
A GaribaldiM L Gullino

Abstract

Rhododendron cultivation has a long history in northern Italy, where a wide selection of varieties and hybrids are grown. In summer 2001, a previously unknown powdery mildew was observed on azalea cv. Mollis (Rhododendron japonicum × R. molle) grown in several gardens in the province of Biella. Initial symptoms included chlorotic spots, followed by white fungal mycelia on both leaf surfaces. Eventually, infected leaves turned reddish and dropped prematurely. Fruit were also infected. On infected tissues, dark brown-to-black spherical cleistothecia developed, alone or in groups. The teleomorph was identified by light microscopy examination of cleistothecia. Cleistothecia measured 110 to 140 µm and were dark brown. They contained four to eight stalked or sessile asci that measured 35 to 45 µm × 40 to 55 µm, each containing six to eight ascospores. Ascospores were ellipsoid to ovoid and measured 12 to 18 µm × 20 to 25 µm. Cleistothecial characteristics were consistent with those described for Microsphaera azaleae but were different from those of the recently described species M. digitata reported in Belgium (1). The presence of conidia was rare in the specimens, so the anamorph could not be identified. To our knowledge, this is th...Continue Reading

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