PHYLOGENETIC DIVERSITY AND TOXIGENIC POTENTIAL OF FUSARIUM SPECIES IN WHEAT AND LEVELS OF DEOXYNIVALENOL AND FUMONISINS IN MARKET WHEAT PRODUCTS, KENYA

Abstract

ABSTRACT In Kenya, wheat is the second most consumed cereal grain after maize and provides nutrition for about 50% of the world's population. However, production of the grain often faces setbacks occasioned by fungal infections and the related chemical contaminants. Unrelenting fungal disease control system, sufficient wheat seed system and observation of food safety measures to curb deficiency and alleviate ill health associated with consumption of mycotoxin contaminated wheat products is essential. This study assessed farmers’ knowledge on fungal wheat diseases and, their practices in choices of wheat cultivars cropped in three ecological regions of Kenya. Prevalence and diversity of Fusarium species in the produce of farmer saved and certified seeds of wheat cultivars was also analyzed. In addition, the genetic ability of the isolated Fusarium spp. to produce mycotoxins was evaluated. Lastly, a survey to investigate occurances and levels of fumonisins and deoxynivalenol (DON) in selected market wheat products sampled in Narok town, Nakuru city and Nairobi, the capital city of Kenya was done. Two hundred and sixty wheat grain samples were collected from 123 farms in Narok, Uasin Gishu and Nakuru Counties between 2016 and 2017. Peptone Pentachloro-nitrobenze Agar was used for isolation of Fusarium spp. from the grains samples, while PDA, CLA and SNA media were used for cultural and morphological characterization. Fusarium species identity and diversity was determined using sequence analysis of the gene encoding translation elongation factor 1-alpha (tef1-alpha). The genetic ability of the Fusarium spp. to produce mycotoxins was determined using Tri13F/Tri13RDON and FUM1F/FUM1R primer pairs. ELISA Kit protocols were used for assessment of mycotoxin levels. ANOVA, the Tukey HSD test and microscopy were used for data analysis. Notably, barely 10% of wheat cultivars released into the Kenyan market were under cultivation in the targeted areas within the study period. In all the three regions, Njoro BWII wheat cultivar was the most preferred and the most frequently (48.8%) sampled wheat cultivar. Top on the list of agroeconomic factors that influenced the selection of wheat cultivars to plant were the weight of wheat grains at harvest and the resilience of wheat cultivars to wheat rust. Other than wheat rust, most farmers had limited knowledge about other fungal diseases while only 1.63% of them cited Fusarium head blight (FHB) as a problematic fungal disease in wheat production. Eight Fusarium spp. (Fusarium poae, F. verticillioides, F. equiseti, F. heterosporum, F. tricinctum, Fusarium sp. F. oxysporum, and F. culmorum) were identified. However, the species diversity in the study regions did not differ significantly. While certified commercial wheat seeds produced 33.75 percent of the recovered Fusarium spp., wheat grains from farmer-saved seeds produced 66.25%. Tri13DON gene was not detected in the isolated putative DON producers while FUM1 gene was detected in 60% of the isolated Fusarium species. Over 76% of the analyzed wheat grain samples had detectable levels of fumonisins. However, the highest level (9.6ppm) did not exceed the permissible levels of between 2000μg/kg and 4000μg/kg in whole grains according to EU guidelines. Over 75% of the sampled market wheat products contained levels of DON and fumonisins that were below the permissible maximum limits of 750μg/kg according to EU guidelines. Wheat flour contained the highest concentration of DON (5.6 μg/kg). The significant research finding is that a minimal percentage of wheat cultivars released into the market had been cultivated in the studied regions. Among other factors, farmers did not prioritize selection of cultivars based on their ecological growth requirements and they notably had minimal knowledge about other serious wheat fungal diseases such as FHB to the extend of referring to all diseases observed on the crop as wheat rust. Fusarium spp. with the ability to produce mycotoxins were prevalent in the wheat cultivars sampled in the three study areas. This calls for intensified integrated control measures of the pathogens across the three regions. Finally, the quantities of DON and fumonisin found in the wheat products from the market samples were within acceptable limits. Hence, this result highlights the safety of the products for human consumption. However, frequent surveys are recommended to ascertain consistency in the levels of the toxins within the recommended measures. More extension services are also needed to educate wheat farmers on all-important qualities of wheat cultivars released in the market. Lastly, enhancement of awareness on the prevalence of other dangerous fungal diseases such as FHB, it’s related health affecting mycotoxins and how farmers can participate in the control of such diseases.