Aflatoxin Biological Control

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Mycotoxins are substances produced by fungal moulds that contaminate various agricultural commodities either before, during or after harvest. They are a diverse group of substances numbering as many as 300. However, the five most important ones comprise ochratoxins, deoxynivalenol, zearalenone, fumonisins and aflatoxins.

While effects of mycotoxin contamination in food grains has been around since historical times, it is only during the 1960s following the discovery of aflatoxins that considerable attention was paid to mycotoxins. AATF equally recongnises this problem and hence the choice of working in the control of mycotoxins in cereal grains as one its priority problem areas.

Aflatoxins are produced by some species of fungi in the genus Aspergillus, the most notable being Aspergillus flavus and A. parasiticus. These fungi invade crops during maturation in the field and during storage contaminating them with aflatoxins. Maize is one of the most susceptible cereal crops to pre-harvest aflatoxin contamination particularly during periods of moisture stress and when insect damage is prevalent. Post-harvest contamination in maize also occurs when grains are stored in damp environments.

Consequently, dietary exposure to aflatoxin contaminated maize-based products has been associated with various human health-related conditions including the high incidence of liver cancer, growth retardation in children, reproduction impairment and the suppression of cell-mediated immune responses. In a number of cases, maize grains contaminated with aflatoxin-producing fungi have been implicated in incidences of food-poisoning commonly referred to as aflatoxicoses that claim many lives in a number of African countries.

Another food crop affected by mycotoxin contamination is peanuts. Peanuts are a valuable source of protein, fat, energy and minerals, and they generate cash income for many poor farmers, particularly women, in Sub-Saharan Africa. About 90 per cent of the peanuts produced in Africa primarily serve subsistence needs as a food source although significant quantities find their way to domestic and external markets. Aflatoxin accumulation in peanut seed has been found to reach 2000 ppb which if consumed can cause serious human health risks resulting in deaths. Apart from the health-related effects, aflatoxin contamination also results in rejection of potential marketable peanut products.

Indeed, exports of agricultural commodities particularly peanuts from Sub-Sahara African countries have declined by as much as 20% over the past two decades owing to rejection arising from non-compliance with the European Union (EU) market regulations on mycotoxins. This clearly poses a serious hurdle to international trade in this commodity.

Although the problem of aflatoxin contamination in peanuts was in the past addressed through several approaches including crop genetic improvement for resistance against fungal infection and regulatory restriction, only some partial degree of success in reducing aflatoxin contamination was realised.

Recently, a new approach has been developed for reducing pre-harvest aflatoxin contamination in peanuts based on applying competitive, non toxigenic strains of A. flavus and A. parasiticus to soils around developing crops in the field as a form of biological control. Use of these strains on peanuts in the United States reduced aflatoxin contamination on this crop by up to 98 per cent. Developed by United States Department of Agriculture-Agricultural Research Service (USDA-ARS), the technology referred to as Aflaguard has been licensed to a private company, CircleOne Global Inc, that has commercialised it in the USA and is now exploring potential markets in China, Latin America and Africa.

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