The root-surface mycoflora of cassava were isolated from roots washed in serial changes of sterile distilled water and plated out on potato-dextrose agar. A small group of fungi which included Aspergillus niger, Botryodiplodia theobromae, Fusarium solani, Penicillium javanicum, Penicillium sp., and Trichoderma sp. were found to be consistently associated with the root surface. While the isolates, B. theobromae and F. solani were found to be aggressively pathogenic on freshly harvested cassava tubers causing extensive rot, A. niger was only mildly so.
The root-surface mycoflora, therefore, includes fungi which have been reported as the most important in postharvest deterioration of the tubers. The removal of the rhizoplane microflora by surface-sterilization using calcium hypochlorite or Clorox and subsequent incubation in loosely tied polyethylene bags extended the storage life of the tubers considerably.
The rapid deterioration of the tubers in storage has been attributed largely to vascular streaking (12) and microbial rotting (5, 10). The former abnormality has been considered to be physiological in nature (12) while the microorganisms involved in the later form of deterioration include Rhizopus sp, Lasiodiplodia theobromae, AspergilIus niger, A. flavus, Cylindrocarpon candidum and Trichoderma harzianum (5,10).
In contrast to the numerous work done on the microbial population of the rhizosphere (3,8,18,19) only a few comparable studies have been reported on the microbial population of the root surface. These include the studies on the rhizoplane floras of wheat, barley, red clover, soyabean and flax (15,16,17), dwarf bean, barley and cabbage (13) and species of Allium, viz, A. cepa (onion), A. porrum (leek) and A. sativum (garlic) ( 14). The commoner species reported on the root surfaces include species of Alternaria, Aspergillus, especially A. niger, Fusarium, Penicillium and a number of sterile mycelia.