First Occurrence of Panama Disease in Two Banana-Growing Areas of South Africa.

Abstract

Fusarium wilt (Panama disease) of bananas is well established in two of the five banana production regions in South Africa: Kiepersol (near Hazyview) and southern KwaZulu-Natal. The disease is caused by a soilborne fungus, Fusarium oxysporumSchlechtend.: Fr. f. sp. cubense (E.F. Sm.) W.C. Snyd. & H.N. Hans., which is most commonly introduced into an area by infected plant material or in contaminated soil attached to vehicles, farm machinery, or footwear. In September 2000, banana plants were observed dying at an experimental site in a commercial Cavendish plantation in the Tzaneen area of the Northern Province of South Africa. Symptoms included wilting of leaves (starting from the oldest foliage) and yellow-brown discoloration of vascular tissue in the rhizome and pseudostem. These symptoms are typical of those described for Panama disease of bananas (2). Similar symptoms were observed at another experimental site in a banana plantation in the Komatipoort region of the Mpumalanga Province in November 2000. Komatipoort is currently the largest banana production region in South Africa. Panama disease has not previously been reported in the Tzaneen and Komatipoort regions. Both are at least 200 km away from the other banana production areas in South Africa. Fungal isolations were made from four diseased plants in both Tzaneen and Komatipoort, and the discolored tissue of the pseudostem was placed on potato dextrose agar amended with novobiocin (0.2 g/liter). Single-spore cultures made from developing colonies were identified as F. oxysporum based on morphological characteristics. Isolates were sent to the Cooperative Research Centre for Tropical Plant Protection (CRCTPP) in Australia for identification by means of DNA amplification fingerprinting (DAF) analysis (1). Based on DAF analysis, isolates from Tzaneen and Komatipoort were identical to those in vegetative compatibility group 0120 of F. oxysporum f. sp. cubense ("subtropical" race 4), the causal agent of Panama disease in Kiepersol and southern KwaZulu-Natal. Pathogenicity studies were performed in the greenhouse by inoculating 5-cm Cavendish banana plants with two isolates of F. oxysporum f. sp. cubense from Tzaneen and two isolates from Komatipoort. Ten plants per isolate were inoculated by submerging their roots in a suspension of microconidia (105 spores/ml). Roots of control plants were submerged in sterile distilled water. Within 6 weeks, wilting symptoms developed on the lower leaves of inoculated banana plants, and the central cylinder of the rhizomes turned reddish brown. F. oxysporum f. sp. cubense was reisolated from the diseased tissue to complete Koch's postulates. The outbreaks of Panama disease in Komatipoort and Tzaneen do not appear to have spread further. Both of the infected fields were placed under quarantine, and symptomatic plants were destroyed.