ABSTRACT

Mycological investigations of the array of fungal pathogens associated with postharvest rots of fruits (Persea americana, Annona muricata, Citrus sinensis, Carica papaya and Lycopersicon esculentum) in Akwa Ibom State, and the potentiality of aqueous and ethanolic leaf extracts of Heinsia crinita, Lasienthera africanum, Gongronema latifolium and Piper guineense as bio-control/preservatives on the fresh fruits were conducted using standard mycological techniques. The phenotypic and genotypic identifications of the fungal pathogens isolated from fruit samples were carried out using standard cultural, morphological and molecular methods respectively. The pathogenicity, mycotoxins production of the isolates, antifungal efficacies of the extracts on mycelial radial growth and spore germination, qualitative phytochemistry and Fourier Transformation Infrared Spectroscopy (FT-IR) of the extracts were determined using standard mycological, agar well/diffusion, Chemical and Atomic Absorption Spectroscopy (AAS) techniques. The phylogenic relationships among the fungal species were also constructed. Fourteen fungal genera identified were Talaromyces, Lasiodiplodia, Trichoderma, Pichia, Penicillium, Mucor, Moniliella, Geotrichum, Candida, Aspergillus, Rhizopus, Absidia, Fusarium and Purpureocillium. The pathogenicity tests revealed that the fungal isolates were able to cause rots at varying degrees. The most rapid rots were caused by R. oligosporous, P. kudriavzevii and A. niger within 24 hours, while A. aculeatus and M. suaveolens were slower in initiating rots (5th day). These fungal isolates produced mycotoxins in different range of concentrations. The highest concentration of ochratoxin was produced by A. niger (10.5ppb) and the lowest was by A. parasiticus (0.1ppb). The highest concentration of aflatoxin was seen in A. nomius (15.6ppb) and the lowest inA. aculeatus and A. carbonarius(0.3 ppb). Phytochemical screening of the extracts revealed the presence of alkaloids, tannins, saponins, cardiac glycosides in varied concentrations. The FT-IR analysis of the extracts revealed groups of carboxylic acids, amines, esters, ketones, and aromatics with absorption bands ranging from 534.3 to 3416cm-1 . The extracts exhibited inhibitory effects on the fungal radial mycelial growth and spore germination with ethanolic extracts of G. latifolium being the most potent and aqueous extracts of H. crinita being the least effective (inhibiton zones of 21.0mm and 8.0mm respectively). The regression values (R2 ) of the plant extracts concentration/inhibitory zones ranged from 0.75 to 1.0. The extracts at the 750mg/ml concentrations were able to preserve the fresh fruits up to 14 days. The dendrogram showed great similarities among the fungal isolates, with T. koningiopsis being related to P. lilacinum and P. kudriavzevii closely related to G. candidum. This study establishes the array of mycotoxigenic fungi associated with post-harvest fruit rots and efficacies of these plant extracts as biocontrol of fruit spoilage organisms due to the bio-active secondary metabolites and chemical functional groups present in the plant extracts.