An Overview of Research on Diseases of Cactus Pear in South Africa

Since 1996, the primary objective of the New Crop Pathology Program at the University of the Free State has been to conduct a systematic survey of diseases occurring in cactus-pear [Opuntia ficus-indica (L.) Miller] orchards throughout the country and to investigate possible relationships between disease-causing microorganisms and various insects, specifically Drosophila sp. Numerous fungal genera, of which the most prominent were Alternaria, Rhizopus, and Fusariu, were isolated from the exterior tissue layer of nonsterilized fruit. Two genera, Rhizopus and Penicillium, were isolated at frequencies of 34% and 10%, respectively, from rotting fruit. Alternaria tenuissima has been isolated from symptoms on cladodes that include small, superficial, chlorotic spots on the cuticle, which coalesce to form raised grey scabs. Lasiodiplodia theobromae (teleomorph: Botryosphaeria rhodina) has been isolated from roundish, black cankers on cladodes characterized by black gum exudation from the perimeter of the canker. A clear association between Drosophila species and mycelial fungi was identified.