Abstract
Abstract A description is provided for Phytophthora ilicis . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: Ilex aquifolium, I. aquifolium f. aureo-marginata . DISEASE: Produces a severe die-back disease (leaf and twig blight) of young and mature holly plants; a facultatively necrotrophic plant pathogen. Symptoms consist of black leaf spots, defoliation, twig die-back and berry infection. Limb and trunk cankers develop inside tissues. Leaf fall begins from the lower branches and progresses upwards producing shafts or pyramids of defoliation. The disease develops well in cool, wet weather but is checked during hot, dry periods. GEOGRAPHICAL DISTRIBUTION: Europe; UK (England), Netherlands. North America; USA (OR, WA). TRANSMISSION: By sporangia borne on sporangiophores which emerge through stomata on the lower surface of leaves. Sporangia are dispersed by rain-splash or by wind and infect leaves via wounds, or twigs via leaf scars. Growth of the mycelium from twigs extends into branches. Berries are infected in late winter and spring. Oospores are formed in leaf spots and in the cortex of dead twigs. They may act as perennating structures, allowing the fungus to survive over the summer and then germinate in cooler weather.
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