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The current status of research on diseases of Opuntia ficus-indica in South Africa

Swart, W.J., Swart, V.R.
Acta horticulturae 2002 no.581 pp. 239-245
Trichoderma, entomopathogenic fungi, necrosis, insect vectors, Candida, Penicillium, Ascochyta, Hanseniaspora, Mucor, vinegars, industry, plant rots, Fusarium sporotrichioides, Erwinia, Drosophila, Alternaria tenuissima, container-grown plants, yeasts, cactus pears, Neonectria, cladodes, Rhizopus, Opuntia ficus-indica, Paecilomyces, Aureobasidium, Pichia kluyveri, bacteria, South Africa, Algeria
The first systematic investigation of cactus pear (Opuntia ficus-indica) diseases in South Africa has revealed numerous species of fungi associated with the plant. A study of the epiphytic mycoflora of the fruit revealed 10 fungal genera isolated from the areole and skin of unsterilized fruit. Post-harvest rot of fruit, especially the popular red-fruited cultivar Algeria, was associated with Rhizopus sp. (34%) and Penicillium sp. (10%), with bacteria comprising 5% of the total number of tissue isolations conducted. Four species of yeasts were isolated from diseased fruit, viz., Hanseniaspora ovarum (65%), Pichia kluyveri (33%), P. membranaefaciens (3%) and Candida sp. (2%). Cladode soft rot was associated with Candida boidimi and Erwinia caratovora while dry rot or decay was mostly associated with Alternaria tenuissima. Superficial necrosis of cladodes was associated with A. alternata, Cylindrocarpon sp. and Fusarium sporotrichoides. The latter, which occurred less frequently caused the largest lesions following artificial inoculations of detached cladodes and potted plants. An investigation was also conducted to study the relationship between pathogenic fungi and insect vectors belonging to the order Diptera (vinegar flies, Drosophila spp.). Eight genera of mycelial fungi were isolated from D. melanogaster of which Mucor spp. and Fusarium spp. were most prominent. Twelve genera of mycelial fungi of which Mucor spp. were most prominent were isolated from D. hydei. Four genera, Trichoderma sp., Paecilomyces sp., Aureobasidium sp., and Ascochyta sp., were unique to D. hydei. The micro-organisms described here are of considerable significance to the emerging cactus pear industry in South Africa and they therefore justify intensive investigation.