Department of Plant Pathology, University of the Free State, P.O. Box 339, Bloemfontein 9300, South Africa
ARC Institute for Industrial Crops, Private Bag X2075, Rustenburg 0300, South Africa
Kenaf (Hibiscus cannabinus L.) is a fast-growing, bamboo-like annual plant belonging to the Malvaceae. The stem, which ranges from 1.5 to 4 m, presents a source of high-quality cellulose fibers. The plant is being investigated in South Africa with a view to commercial production. In April 2001, at least 50% of 4- to 5-month-old kenaf plants grown from seed in trials near Rustenburg, Northwest Province, South Africa, were observed as having powdery mildew. Signs included extensive growth of white, superficial mycelium and emergent conidiophores on the abaxial leaf surface, followed by partial defoliation. On older leaves, the abaxial leaf surface was completely covered by powdery mildew, and chlorotic and necrotic patches were clearly visible on the adaxial surface. Symptoms were observed on all five planted cultivars (Everglades 41, Cuba 108, El Salvador, SF459, and Tainung 2), and no difference in disease severity was noted among cultivars. Leveillula taurica (Lév.) Arnaud (anamorph Oidiopsis taurica [Lév.] Salmon) was subsequently identified by the presence of endophytic mycelia, often branched conidiophores, and dimorphic conidia borne singly or in short chains (1). In 100 measurements of each type, pyriform conidia averaged 69 ± 5 × 18 ± 2 μm and cylindrical conidia averaged 62 ± 6 × 16 ± 2 μm. The teleomorph was not observed. The source of L. taurica for this reported outbreak is unknown, and powdery mildew was not observed in a field of mature cotton (Gossypium hirsutum L.) growing within 10 m of the kenaf plot. L. taurica was reported on kenaf in Texas in 1992 (2) and in Italy in 1995 (3). The pathogen can cause significant losses in seed yield and reduce seed quality in susceptible kenaf cultivars. Although L. taurica has been reported from Hibiscus sabdariffa in Egypt (4), to our knowledge this is the first report of the pathogen occurring on kenaf in Africa.
References: (1) H. J. Boesewinkel. Bot Rev. 46:167, 1980. (2) C. G. Cook and J. L. Riggs. Plant Dis. 79:968, 1995. (3) S. Frisullo et al. Inf. Fitopatol. 45:37--41, 1995. (4) M. Khairy, et al. Phytopathol. Medit. 10:269--271, 1971.