Root Surface Culturable Microflora Associated with Post Harvest Spoilage of Sweet Potato (Ipomoea batatas L.)

Abstract

The root surface microflora of sweet potato consists of a small group of fungi, i.e. Aspergillus nirger, A. awamori, Botryodiplodia theobroinae, Cochlobolus lunatus (Curvularia lunata), Fusarium oxysporum, F. pallidoroseum, Penicillium decumbens, Rhizopus oryzae and Ptichoderma sp., three yeast species i.e. Debaryomyces hansenii, Pichia anomala and Saccharomyces cerevisiae, and some bacteria. The fungal isolates i.e. B. theobromae, Fusarium spp. and R. oryzae were aggressively pathogenic on freshly harvested sweet potato tubers causing extensive rots while Cochliobolus lunatus (Curvularia lunata) was mildly pathogenic. Species of Aspergillus, Penicillium and Trichoderma were found as secondary invaders on tubers previously colonized by the mentioned species. The three yeast species and bacteria were not pathogenic at all for sweet potato. Removal of the rhizoplane microflora by surface sterilization using 1% sodium hypochlorite solution prevented fungal rot, thus extending the storage life of the tubers.