Botryosphaeria obtusa. [Descriptions of Fungi and Bacteria].

A description is provided for Botryosphaeria obtusa. Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: On Malus and Vitis. Also on Acer, Alnus, Amygdalus, Artemisia, Betula, Citrus, Crataegus, Cupressus, Diospyros, Eriobotrya, Hicoria, Juniperus, Liquidambar, Liriodendron, Lucuma, Magnolia, Melia, Nannorrhops, Nerium, Pinus, Platanus, Prunus, Rhamnus, Ribes, Robinia, Rubus, Salix, Sassafras, Tectona, Ulmus, Viburnum, Yucca. DISEASE: Causes canker and dieback on pomaceous fruits and grapevine but can live saprophytically on dead wood and bark of many woody plants. On apple, B. obtusa is responsible for three diseases: a canker (New York apple tree canker or black-rot canker); frog-eye leaf spot; and black-rot of the fruit. Cankers start as small elliptical areas of discoloured wood, often with a peripheral crack; as they grow the bark becomes roughened and black pycnidial pustules protrude. Diseased branches and twigs can be girdled and killed. Leaf spots begin as small, circular, purple spots which increase in size, developing a light brown centre, the typical 'frog-eye' symptom. Extensive defoliation may result if this stage of the disease is severe. The fruit rot usually commences at a wound or at the calyx as a dark spot, which spreads to envelope the whole fruit. Diseased fruits are firm and black but eventually shrivel and become mummified. GEOGRAPHICAL DISTRIBUTION: Widespread in the temperate areas; Europe, Southern Africa, North and South America, India, Japan, New Guinea, Western Australia, Tasmania, New Zealand. TRANSMISSION: The fungus can over-winter on mummified fruit, cankers, dead twigs and secondary hosts. Conidia and ascospores are mostly dispersed by rain-splash and perhaps by insects. Spore release is affected by relative humidity and temperature and dispersal is stimulated by night-time rain (50, 735).