Fusarium wilt: A new disease of cultivated Protea in Southern Africa
A newly recorded disease of cultivated Protea, Fusarium wilt, is described and shown to be caused by Fusarium oxysporum. The disease occurs on mature plants (2-year-old) of P. aristata x repens cv. Venus, P. compacta x susannae cv. Pink Ice, P. cynaroides, P. eximia x susannae cv. Cardinal, P. eximia x susannae cv. Sylvia, P. magnifica x susannae cv. Susara and P. repens cv. Sneyd in the summer rainfall areas of the North-Western province of South Africa and in Zimbabwe. Disease symptoms first become visible as necrotic leaves. Subsequently, a dark lesion develops from the roots along the stem, usually visible only on one side of the stem. Occasionally the lesion develops in the upper part of the stem. The vascular tissue is discoloured leading to branch die-back and plant death. F. oxysporum was readily isolated from the roots, crown and vascular tissues of infected plants. Koch's postulates were proved on six Protea cultivars. Disease symptoms similar to those observed in the field developed 6 weeks after inoculation on all cultivars. The fungus was re-isolated from the roots, crown and vascular tissues of inoculated plants. This is the first record of Fusarium wilt on Protea plants.