Pathogenicity of Fungi Isolated from Spoilt Sweet Oranges (Citrus sinensis) and from the Air in the Environment of the Orange Section of the Gamboru Market in Maiduguri, Nigeria

Abstract

Aim: Though Oranges are very important crops for man both economically and in terms of nutrition, they have a short life span due to poor handling during harvesting, transporting, and storage. The ubiquitous nature of fungi makes them ready contaminants for these oranges especially when their skin is broken. The aim of this study is to isolate, identify and determine the pathogenicity of fungi responsible for spoilage in sweet oranges and investigate the presence of fungi in the air of the environment where these oranges are sold. Place and Duration of Study: Department of Microbiology Faculty of Science University of Maiduguri between September and October 2020. Methodology: A total of 100 samples of ripe oranges with signs of spoilage (n=100) were collected randomly from 10 selling points in the Gamboru fruit market in Maiduguri, Borno state of Nigeria, and analyzed for fungal isolates using morphometric techniques. Two mycological media Potato Dextrose Agar and Malt Extract Agar (PDA and MEA) were used for isolation, by deploying direct plating method. Petri dishes containing prepared PDA and MEA were also exposed to the air in the shops for some minutes. Morphometric analysis was carried out to identify the fungal isolates using macroscopic and microscopic observed features. Pathogenicity tests were carried out to ascertain the ability of these isolates to cause spoilage. Results: The results of the morphometric characterization revealed the presence of seven (Aspergillus flavus, Aspergillus fumigatus, Aspergillus niger, and Penicillium oxalicum, Rhizopus oryzae, Cladiosporium sphaerospermum and Scopulariopsis brevicaulis) different fungi from the air and from the deteriorating oranges. Four of the isolates which were also positive for pathogenicity and observed to be responsible for causing spoilage in the oranges were also found to be the same as those isolated from the air, while three other organisms isolated from the air in the sales environment were not isolated from the spoilt oranges. Penicillium oxalicum was isolated from 41% of the oranges making it the most predominant organism causing spoilage in the oranges while Aspergillus fumigatus was isolated from only 10% of the samples. Conclusion: The findings of this study showed that fungal contaminants were responsible for the spoilage of oranges in this market and many of them were present in the air in the shops where these oranges were sold and stored leading to serious economic losses for both farmers and consumers.