Occurrence of fumonisin producing fusarium species in maize and soil in Makueni County, Kenya
Kihara, Samson Njoroge
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Maize is an important cereal crop in Kenya contributing 3 % of Kenya’s Gross Domestic Product (GDP), 12 % of the agricultural GDP and 21 % of the total value of primary agricultural commodities. It is a staple food for majority of Kenyans. However its productivity has been on the decline due to fungal ear rot disease among other factors like rainfall, low soil fertility and arthropod pests. Fungal ear rot diseases of maize are caused by among other fungi, Fusarium and Aspergillus species which produce mycotoxin, like fumonisin that isassociated with oesophageal cancer in humans. This study aimed at identifying the Fusarium species causing ear rot of maize in Makueni County and establishing their toxigenicity. A total of 293 households from Nguumo, Malivani and Wote locations were randomly sampled,social economic background of the farmers established and maize and soil samples collected. Information on farmers’ perception on Fusarium ear rot, spoilt maize, farming, harvesting, threshing and stoage practices was gathered using structured questionnaire.Maize samples were taken from storage facilities and soil samples collected from maize fields.Fusarium species were isolated from maize kernels and soil and identified to species level using standard keys and molecular markers. Their potential to form fumonisins was also confirmed using Polymerase Chain Reaction (PCR). Fumonisin in maize kernels was quantified using Ezyme Linked Immunosorbent Assay (ELISA). The study found that most house holds were dominated by males as heads with an average age of between 31-40 years. However, most household heads had cautious perception of spoilt maize and decision making towards alleviation of occurrence of ear rot disease causing pathogens. Farmers mentioned color change, insect damage, mouldy, endosperm deterioration and rot, as indicators of maize spoilage. None seemed aware of latent infection due to poor handling or weather. Spoilt maize was mainly thrown away or fed to animals but most farmers were not aware of health implications of eating spoilt maize. About 52% of the farmers planted local maize varieties saved from previous harvest while 65% did not do crop rotation. Most maize samples were highly contaminated with Fusarium species with the most prevalent species beingF. verticillioides,24% of total isolates. Other fungi isolated included Aspergillus spp, Pennicilium spp, Alternalia spp and Tricoderma spp. Fusarium spp comprised 30% of all isolates from soil. Molecular tests confirmed 74 isolates to be F. verticillioides and four were F. proliferatum. Majority of the F.verticillioides and F proliferatum from maize and soil were found to have fumonisin producing gene. Nguumo location had 98% and 53% of F. verticillioides and F. proliferatum respectively being positive for fumonisin production. Sampled locations differed in concentration of fumonisin in maize kernels with Nguumo having the highest concentration of 22ppm and Malivani with least at 7.27 ppm. There was overall positive correlation(R = 0.0094) between kernels infectionwith Fusarium and the correspondingfumonisin content. This study revealed that most households had little awareness on the dangers emanating from spoilt maize hence did not follow good farming practices in production and storage leading to contamination of maize with fungi and fumonisins. The results also indicated wide spread occurrence of mycotoxigenericF. verticillioides and F. proliferatum. This means that there may be a risk of human exposure to fumonisins through the consumption of maize. Therefore there is urgent necessity of putting intervention measures to curb the long term health consequences in the mycotoxicosis among communities in Makueni County.