Peronospora violae . [Descriptions of Fungi and Bacteria

Abstract

Abstract A description is provided for Peronospora violae . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: Viola acutifolia, V. arvensis, V. biflora, V. calarata, V. canina, V. cornuta, V. kitaibeliana, V. palustris, V. reichenbachiana, V. riviniana, V. silvestris, V. tricolor, V. tricolor var. arvensis, V. wittrockiana . DISEASE: Downy mildew of Viola spp. (violet and pansy); the fungus is an obligately biotrophic plant pathogen. In the early stages of the disease, a light covering of sporophores may be seen on the undersurface of individual leaves, unaccompanied by a colour change in the leaf. Later yellow patches appear on the upper surface of leaves covering a part of, or the whole lobe corresponding with patches of grey down on the leaf undersurface. Infected leaves eventually turn brown and die. Not all shoots are infected. Mildew first appears in October and progresses rapidly in November if the climate is mild and damp, or more slowly if dry. GEOGRAPHICAL DISTRIBUTION: Asia: USSR (Khazakhstan). Europe: Austria, Belgium, Czechoslovakia, Denmark, Finland, France, Germany (GDR, GFR), Hungary, Italy, Norway, Poland, Rumania, Sweden, Switzerland, United Kingdom, USSR (Estonia, Latvia, Russia, Ukraine, White Russia), Yugoslavia. See CMI Distribution Maps of Plant Diseases 599. TRANSMISSION: Boudier (1987) states that 'spectacular attacks of mildew follow sprinkler watering in dry autumn weather', suggesting that dispersal of spores may occur by a water splash mechanism. No other reports have been published.