Pg. 2-4 Armillaria Rot of Litchi Trees (Litchi Chinesis) in South Africa

Armillaria rot is causing considerable losses to litchi (Litchi chinensis) plantings in the high rainfall area of the Northern Transvaal in South Africa. Initial symptoms of the disease are a loss of vigour and the absence of new growth, which is followed by defoliation and the death of the trees. Aboveground symptoms characteristically develop on sections of the trees first. Young plants often collapse suddenly during the warm rainy summer period, when the pathogen is most active and rapid girdling of the trunk occurs. Infected large trees may deteriorate for several years showing symptoms
of a slow decline. The pathogen enters and kills major roots first and later invades the trunk. The disease typically spreads in a circle in the orchard and is more severe in stressed trees, such as plantings in lands with a high water table. No fruiting bodies of the fungus have been observed on any of the infected trees, but abundant white mycelial sheet production under the bark and rhizomorph development on the roots have been recorded. Most isolates in this study have produced rhizomorphs in axenic culture.