PREVALENCE AND DETERMINTION OF FUNGAL PATHOGENS AND AFLATOXINS ASSOCIATED WITH COWPEA (VIGNA UNGUICULATA L. WALP) SEEDS OBTAINED FROM COMMERCIAL FARMERS IN SOUTH WEST, NIGERIA.

Abstract

A study was conducted to identify fungal pathogens associated with Cowpea (Vigna unguiculata (L.) Walp) seeds obtained from southern western states of Nigeria, characterize the fungi pathogens suing Polymerase Chain Reaction (PCR), and identify the aflatoxins associated with the fungi pathogens. Three hundred seed samples of cowpea were collected from twenty (20) local governments across five states in the south west of Nigeria namely Oyo, Osun, Ondo, Ekiti and Ogun.

The seed samples were sterilised before plated on Potato Dextrose Agar (PDA) in order to isolate and identify the fungi pathogens present. The identification was done morphologically, and using molecular method. For the molecular method, ITS Universal Fungi primer was used for the PCR analysis to amplify the extracted DNA. This was followed by gene sequencing using Genetic Analyzer 3130x1 sequencer from Applied Biosystems. Aspergillus flavus isolated from these seed samples were screened for aflatoxin production using High-performance liquid chromatography (HPLC) techniques.

A total of twenty-four fungi belonging to 14 fungal genera and 24 species were detected from seeds of cowpea. These were Aspergillus flavus, Aspergillus fumigatus, Aspergillus niger, Aspergillus temarii, Botryodiplodia theobromae, Cladosporium cladosporioides, Cladosporium cladosporioides, Corynespora cassiicola,, Curvularia lunata, Fusarium equiseti, Fusarium oxysporum, Fusarium solani, Fusarium verticilioides, Lasicodiplodia theobromae, Macrophomina phaseolina, Penicillium oxalicum, Penicillium chyrosogenum, Pseudomonas syringae pv phaseolicola, Rhizopus stolonifera, Rhizotonia solani, Rhizopus oligosporus, Septoria vignae, Xanthomonas vignicola, Xanthomonas axonopodis. Result shows that Aspergillus niger, Aspergillus flavus and Botryodiplodia theobromae were the most common with respective values, 7.77, 7.61 and 6.59%. Ondo state had the highest level of disease incidence of 76.61%. The size of the amplicon ITS1/ITS4 fragment ranges from 345 to 740bp. Aflatoxins B1 and B2 were detected in 298 of the tested samples across the states with Ado Ekiti from Ekiti states recording the highest aflatoxin load of when compared among the states. The study concluded that the level of fungi infestation across the states is high resulting in high occurrence of aflatoxin BI and B2 in the states.