DISTRIBUTION OF ZIMBABWEAN ARMILLARIA GROUPS AND THEIR PATHOGENICITY ON CASSAVA

Disease surveys carried out between 1989 and 1992 showed Armillaria to be restricted to the northern and eastern parts of Zimbabwe and to be absent from the western and southern parts. Armillaria disease is of local economic significance especially in fruit and clonal pine seed o rchards. Pathogenicity studies showed significant differences in infec tion of cassava (Manihot esculenta) variety Zanaga (Ccv1) between isol ates belonging to the three Zimbabwean Armillaria groups (I, II and II I), but there were no significant differences in the infection of anot her cassava variety, Zcv1, from Zimbabwe. The group II isolates failed to cause any infection on the cassava clones. Rhizomorphs were the ma in means of infection in the pathogenicity studies, although they ape rare in nature in Zimbabwe. Results using detached cassava tubers to a ssess pathogenicity proved to be inconsistent. Periderm restoration re sponses, which have been observed in woody plants and are presumed to function by restricting pathogen ingress, were observed in cassava inf ected with Armillaria.