Fungi associated with onion (Allium cepa L.) bulb rot and the impact of storage containers on the occurrence of the fungi in market centers, Tamale, Ghana

The onion bulb rot which is caused by a number of fungi pathogens is considered one of the most important factors leading to high postharvest loss in onions. Studies were conducted to determine the incidence of onion bulb rot, identify the associated fungi and evaluate the impact of storage containers on the incidence of the disease. Thirty (30) rotten onion bulbs var. ‘Bawku Red’ samples were collected from two markets in Tamale and studied in the Spanish laboratory, Faculty of Agriculture, University for Development Studies, Nyankpala. The results showed that the onion bulb rot was caused by five fungi species including Aspergillus niger, Aspergillus flavus, Penicillium sp., Rhizopus stolonifer and Fusarium oxysporum. A. niger had the highest percentage occurrence of 30.66% and 25.66% for the Tamale Central and Aboabo markets, respectively. The pathogenicity test conducted showed that A. niger and R. stolonifer were the most pathogenic species. Generally, black mould (A. niger), blue mould (Penicillium sp.), soft rot (R. stolonifer) and basal plate rot (F. oxysporum) were the commonest diseases associated with onion bulbs in the Tamale markets. The most encountered disease was black mould while the least was soft rot. The incidence of onion bulb rot was significantly (P < 0.05) higher in onions that were stored in sacks compared with those stored in baskets and pans. In order to reduce storage rot of onion bulbs, there is the need to encourage the use of pans and baskets for storing onion bulbs in the markets.