Influence of fertilisers, host factors and storage conditions in relation to disease severity: a case study of black mould rot of onion

Abstract

Aspergillus niger was found to be the predominant pathogen associated with black mould rot of onion during storage. Market survey for the assessment of spoilage caused by the fungus recorded a loss of 2.9% to 12.09% during the period from June 1998 to February 1999. Application of higher doses of calcium in the form of gypsum (400 kg/ha) and lower dose of nitrogen in the form of urea (50 kg/ha) to the field and advancing the harvest of onion bulbs by fifteen days significantly reduced the spoilage of bulbs during storage. An inverse relationship existed between neck length of the bulbs and spoilage at storage. Bulb rotting was noticed when the storage temperature was between 30 °C and 40 °C and the relative humidity was above 80%. Further, A. niger infection caused reduction in pungency of onion bulbs which was more pronounced at grade 4 than grade 1. The culture filtrates of Aspergillus niger and Aspergillus flavus isolated from onion as well as the extracts from onion bulbs infected with the above fungi were free from aflatoxin contamination.