Incidence, phylogeny and mycotoxigenic potentials of fungi isolated from rice in Niger State, Nigeria

The study reports on the natural occurrence of fungi in 21 samples of field (10), stored (6) and marketed (5) rice (Oryza sativa L.) collected from Niger State, Nigeria. Fungal isolates were primarily identified based on morphological characteristics, while representative isolates were characterized genetically. An evolutionary tree was constructed from the resulting sequences of the isolated fungi. The toxigenic potentials of some of the isolated fungi were also determined. A total of 357 fungal isolates of nine genera including Aspergillus, Fusarium, Sarocladium, Acremonium, Curvularia Botryosphaeria, Penicillium Alternaria and Ascomycota in decreasing order of predominance were identified. The most frequent fungal contaminants of the rice samples were A. flavus, A. fumigates, A. niger, A. parasiticus and F. proliferatum. All strains of A. flavus (aflatoxins B₁ and B₂), A. parasiticus (aflatoxins B₁, B₂, G₁ and G₂), A. ochraceus (ochratoxin A), F. proliferatum and F. verticillioides (fumonisins B₁ and B₂) tested, were excellent producers of their respective mycotoxins. Patulin was produced by A. terreus, whereas deoxynivalenol, zearalenone and T-2 toxin were produced by F. chlamydosporum and other Fusarium spp. The increased prevalence of toxigenic fungi in rice, a highly consumed food grain in Nigeria, poses serious health concerns to the general public. This study investigated the natural fungal occurrence of rice grown in Nigeria using polymerase chain reaction-based techniques as well as the toxigenic potentials of some of the identified fungi. The resultant fungal profile of rice, gene sequences of the fungi detected in the survey, which were deposited in the GenBank and the constructed evolutionary tree, will serve as reference data for the incidence of fungal species in rice and will help to evaluate the safety of Nigerian rice. It could be used in developing and predicting the degree of mycotoxin contamination in rice from Nigeria for effective mycotoxin control. The toxigenic fungi acquired from the work will be excellent microbial sources for production of mycotoxin standards namely aflatoxins BI, B₂, G₁ and G₂, ochratoxin A and fumonisin B₁ and B₂.