Aspergillus flavus and aflatoxin levels in stored maize in Eastern Kenya and Antifungal activity of some plant extracts
Kiswii, Muange Theddeus
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Maize is the staple crop in Eastern Province of Kenya especially in Makueni, Kangundo, Kibwezi, Machakos and Kitui South Districts. It has been noted that the abiotic and biotic stresses associated with these Districts promote growth of toxigenic fungi that produce mycotoxins in maize in storage. The aflatoxin producing species of Aspergillus are a common phenomenon in maize contamination that has led to frequent outbreaks of aflatoxicoses in these regions. To address this problem, this study w as carried out between September 2007 and June 2008 to evaluate the incidences of A. flavus, determine the aflatoxin levels in stored maize from 5 Districts and evaluate the efficacy of 15 selected medicinal plants collected from Mwingi District. Four Aspergillus sp. that included A. flavus, A. niger, A. ochraceous and A. tamarii were isolated from maize collected from the 10 Divisions in the 5 Districts. Machakos (mean 58 80%), Kangundo (mean 58.4%), and Kitui South (mean 54.80%) Districts had significantly (P < 0.05) high incidences of total Aspergdlu.s sp. than Makuem (mean 45%) and Kibwezi (mean 24.20%). The incidences of A. flavus from the 5 Districts and the 10 Dix isions indicated a significant difference (P < 0.05). Kangundo District (mean 31.71%) liad the highest incidence of A. flavus while Machakos District (mean 12.92%) had the lowest. Among the 10 Divisions, high incidences of A. flavus were found in Matunguht (mean 33.18%), Kaiti (mean 32.6%) and Kangundo (mean 30.25%) Divisions. The love cst incidence was detected in Kathiani Division (mean 10.82%). Out of the 10 samples analyzed, 2 samples had > 50 ppb, 5 had > 20 ppb and the remaining 3 had < 20ppb of aflatoxin (AF) levels. The highest AF levels were recorded in samples from Kibwezi (60.35 ppb) and Kathiani (50 ppb) Divisions while the lowest was found in Kangundo (Oppb). I 'lie methanol leaf extracts of the 15 plants were evaluated for antifungal activity against A. flavus at different concentrations of 1000mg/ml, 750mg/ml and 400mg/ml rising Agar Well Diffusion Method. Plants found to have inhibition zones of more than 1Omm at 400mg/ml had their bark assayed for antifungal activity. Both the mcthanolic leaf and bark extracts of the fifteen plants assayed displayed concentration depended antifungal activities that were comparable to that of the reference drug Miconazolc at IOmg/ml. The leaf extracts showed better antimicrobial activities than the bark extracts. For the leaf extracts, Boscia coriacea (mean 17.40mm) had the highest zone of inhibition followed by Zanthoxvlem chalybeum (mean 17.20mm). For the bark extracts, Crown megalocarpus (mean 15.Omm) recorded significantly high antifungal activity while 77thonia diversfolia (mean 13.Omm) had the lowest at 400mg/ml. Both the leaf and bark extracts that were found to be effective were assayed for minimum inhibition concentrations (MIC) and minimum fungicidal concentrations (MFC) using broth (SDB) microdilution method. Senna stamea had the lowest MIC and MFC of 6.25mg/ml and 12.51ng/ml respectively. The preliminary phytochemical analysis of the effective plants revealed the presence of bioactive compounds that included tannins, saponins, flavonoids, terpenoids, cardiac glycosides and alkaloids. The results obtained from the study could be used as a viable management strategy against A. flavus.