Characterization of Fusarium species on maize (Zea mays) and determination of their mycotoxins in Eastern province of Kenya

Abstract

Maize (Zea mays L.) is an important staple and mycotoxin susceptible food crop in Kenya. Fusarium and Aspergillus species are major fungal genera associated with maize infestation and mycotoxin contamination. Fusarium species cause stalk and ear rot of maize reducing yields and produce fumonisins. Fumonisin toxins are produced by several closely related species of Fusarium that can grow within maize tissues without causing visible symptoms of disease. Consumption of fumonisins has been shown to cause leucoencephalomalacia in horses, pulmonary edema in swine, experimental liver and kidney cancer in rodents, and has been epidemiologically associated with esophageal cancer in humans. The objectives of this study were to isolate Fusarium species from maize collected in selected farmers fields in Eastern province of Kenya, to identify the Fusarium species isolated using morphological and molecular characters, and to extract and quantify fumonisin mycotoxin produced by the fungi. Maize samples were collected from selected farmer in Aflatoxin ‘hot’ zones of Eastern province of Kenya. Samples were collected from Kitui and Kibwezi districts in May to June 2008. Fusarium species were isolated and identified using morphological characteristics at the Mycology Laboratory, Kenya Medical Research Institute. Fumonisin quantification was done using ELISA (RIDASCREEN® ELISA test kit (Art. No.: R3401) at Bora Biotech, Nairobi. Maize kernels were also analyzed for damage.Results of kernel damage showed Makueni district had the highest percentage of damaged kernels (10.95 ± 0.78), compared to Kitui districts (6.62 ± 0.57). Fusarium species isolated in kernels with highest degree of damage also had the highest colony count (CFU).Colony forming Units (CFU) counts indicated that apart from Aspergillus a common contaminant in maize, Fusarium species infestation was also high. The most common speciesbeing F. verticilloids isolated at (39.9 %) in the two districts. Other isolated Fusarium species included, F. proliferatum (15.1 %), F. solani (9.0 %), F. anthophilium (9.0 %), F. oxysporium (15.1 %), and F. lateritium 12.1 %). In general, the most isolated species were of the section Liseola. Fumonisin contamination in the two districts was high (mean 1.04 mg / kg). Makueni district had the highest mean fumonisin compared to Kitui district (1.17 ± 0.08 mg / kg and 0.91 ± 0.133 mg / kg, respectively). High fumonisin concentrations were seen in sample plates where the isolated species is a high fumonisin producer. The mean fumonisin concentration however varied significantly (p < 0.05) in the two locations and between Fusarium species isolated per isolated sample plates. Correlation studies indicated a significant correlation between damaged kernels (%) and Fusarium species count (CFU) (R2 = 0.348) (p < 0.05). In addition, there was a significant correlation between damaged kernels (%) and fumonisin levels (R2 = 0.279). Similarly, significant correlation was observed between fumonisin levels and Fusarium Colony count (CFU) (R2 = 0.015), though it was not strong. In an attempt to characterize Fusarium species using primers obtained from the ITS gene region of some Fusarium species, no amplification fragments were observed in any of the PCR assays. This may have been attributed to the lack of specificity of the selected primers to the targeted DNA regions in the Fusarium genomes. These findings indicates a wide spread infection and contamination of maize by Fusarium species and fumonisins. This study demonstrates a high level of Fusarium and fumonisin exposure in the high risk population necessitating urgent intervention measures to curb the long term health consequences in the population