Isolation and identification of pathogen causes brown spot disease on yam tubers (Pachyrizus erosus) in Indonesia

Abstract

Yam (Pachyrhizus erosus) is a tuber that is widely used in industry. Controlling the condition of yam tubers during storage is very important to maintain the quality of the industrial product. This study aimed to isolate and identify pathogen in storage that causes brown spots on yam tubers. This research was conducted based on the main principles of the Koch postulate, i.e. isolation, inoculation, re-isolation and identification. The disease was characterized with brown spots with thin mycelium on the surface of the spots. Macroscopically, the hyphae of pathogens formed were white, cotton-like on the media. Microscopically, the hypha were insulated, branched, hyaline, and forming conidia (microconidia). The conidia were oval, one or two cells, and hyaline. Based on the identification, the fungus found in the yam tuber storage was Fusarium sp., a weak pathogen that can only infect yam tubers after a wound. Fusarium infection in yam tubers in this recent study is the first report of the disease in yam tubers that causes brown spots. The results of this study can be one of the bases in determining the level of brown spot discoloration control in yam during storage.