Mycological evaluation of spoilt onion bulbs sold in Lapai town

Abstract

Mycological investigation on spoilage fungi on apparently infected onion bulbs collected from Lapai, Niger state, Nigeria was conducted using both direct plating method and dilution of milled onion paste. Total of 15 onion bulbs (3 healthy bulbs and 12 bulbs showing symptoms of rotting and discolorations) were collected; four spoilt and one healthy bulb from each of three different locations: Lapai central market, Baddegi market and Onion Retail Outlet within Lapai town. The onion bulbs were found to be infected with eight species of fungi: Aspergillus niger, A. flavus, Fusarium spp, Mucor spp and Penicillium spp of which, A. niger and A. flavus were the most frequent isolated fungi. Penicillium spp was the least encountered fungus. The pH of the onion bulbs were also determined, Samples from Onion retail outlet within the town has a mean pH of 8.00 while the control has pH value of 5.83, samples from Baddegi Market has mean pH value of 6.66 and samples from Central Market had the lowest mean pH value of 5.37. Pathogenicity tests revealed that all the isolated fungi were pathogenic to healthy onion bulbs however, Fusarium spp and Mucor spp were the most pathogenic leading to rapid disintegration of infected bulbs within 4 days of inoculation. Contaminated onion bulbs should be sorted and eliminated to avoid re-infection while washing the onion bulbs with clean water prior to consumption should be strongly encouraged by appropriate authorities with the view to checking the spread of these fungi.