Verticillium albo-atrum as a parasite ofSenecio vulgaris

Many weeds, includingSenecio vulgaris, are virtually symptomless hosts ofVerticillium albo-atrum. Plants ofSenecio vulgaris were inoculated with spore suspensions ofV. albo-atrum by two different methods: root-dipping or injection. Infected plants rarely wilted but were stunted, their lower leaves died prematurely and numbers of lateral shoots were decreased.V. albo-atrum was isolated from all parts of the host including achenes. When placed on agar, infected achenes germinated more rapidly than healthy ones. Only small amounts of mycelium developed in the vessels. Severe wilting was possibly avoided because there is insufficient time for damaging amounts of mycelium to develop inSenecio which has a short period of vegetative growth. On the other hand its tolerance to infection may be attributed to the morphology of its vascular system with its narrow vessels and sparse parenchyma cells.In co-operation withH. van Geest, J. P. Overdulve andC. J. J. Richter.