First Report of Fusarium moniliforme Causing Cassava Root, Stem, and Storage Rot. W. Msikita, International Institute of Tropical Agriculture, BP. 08-0932, Cotonou, Benin. P. E. Nelson, Pennyslvania State University, University Park 16802; J. S. Yaninek, M. Ahounou, and R. Fagbemissi, International Institute of Tropical Agriculture, BP. 08-0932, Cotonou, Benin. Plant Dis. 80:823. Accepted for publication 13 May 1996. Copyright 1996 The American Phytopathological Society. DOI: 10.1094/PD-80-0823D.
Storage roots of cassava (Manihot esculenta Crantz) are left in the field as unharvested plants, or are harvested, peeled, and dried in the sun to form a product referred to as "cassava chips." Fifty-five samples consisting of rotted cassava crowns and roots (storage and feeder, derived from wilted and/or lodged plants) and discolored chips were collected from various parts of Benin and Cameroon. Affected pieces of the stems, roots, and chips were cut out, surface sterilized, and cultured on water agar amended with 4% (vol/vol) lactic acid. Pieces were incubated for 1 week. For the purposes of identification, mycelia were subcultured on carnation leaf agar medium. More than 36% of the total fungi isolated from the samples were Fusarium spp. Fifty-five percent of the Fusarium were isolated from rotted roots and crowns of both young and old plants, and 45% from chips. More than 44% of the Fusarium isolates obtained from the chips, and 19% of isolates from the rotted crowns and roots, were F. moniliforme J. Sheld. To complete Koch's postulates, stem pieces of four cassava cultivars (Agriculture, Tchukunochi, TMS 30572, and Ben 86052), were disinfested in hot water (52°C, 5 min), transplanted in sterilized sand, and maintained in a greenhouse (natural light, 28 to 30°C). Two weeks after transplanting, stems were wound inoculated (epidermal scalpel slice) just below the soil line. A 0.5-ml aliquot of mycelial suspension of F. moniliforme was applied onto each wound, and the sand covered back on the stem. For each cultivar, control plants were similarly wounded but treated with sterile distilled water. Six to 10 days after inoculation, all plants inoculated with F. moniliforme showed variable degrees of wilting (0 to 80% of foliage) and necrosis (2.9- to 6.2-cm-long lesions) of the stem base. Control plants remained symptom-free. Necrotic stem and root pieces from artificially inoculated plants were plated on potato dextrose agar, and consistently yielded F. moniliforme. This is the first report of F. moniliforme pathogenic on cassava.