Elimination of toxin producing fungi by competitive exclusion: the case of biocontrol in the maize production chain in Zambia

We investigate fungi naturally adapted to maize under different rainfall patterns, using Zambia as the model. We then investigate the prospects for use of such fungi to control the fungi that produce AF and FB. The control of one fungus by another is termed ‘Biocontrol.’ 

Background

Maize is a widely consumed cereal in sub-Saharan Africa, Latin America and Asian countries, providing essential calories for both human and livestock. Unfortunately, maize is often contaminated with an array of fungi. Common members of fungi contaminating pre-harvest maize are known to be Fusarium, Aspergillus, Penicillium. Some of the fungi within these three genera produce harmful chemicals termed mycotoxins. Aflatoxins (AF) and Fumonisin (FB) are important mycotoxins in maize. Other than a negative effect on human health and livestock productivity, contamination of grain with mycotoxins results in revenue loss due to regulation of the mycotoxins in trade. 

To mitigate the negative effects of mycotoxins, several approaches are employed such as Good Agricultural Practices which include the drying the grain at harvest to avoid fungal growth, the sorting out of damaged grain at harvest, the controlling of pests in field and storage, etc. However, this does not completely prevent the contamination. The use of Biocontrol is a promising tool to counter the AF (as well as FB) challenge. This can help avert contamination both in the field and during storage. 

Project description

This project investigates the contamination of maize with fungi, aflatoxin (AF) and fumonisin (FB) with respect to abiotic and biotic stimuli. The exploration is in the context of the current status of biological control of Aspergillus and Fusarium in maize for the combat of their human- and livestock-harmful mycotoxins AF and FB, respectively. Biological control (Biocontrol) of Aspergillus and Fusarium, premised on competitive exclusion, is known to be currently deployed for the control of AF and FBs in cereals such as maize and wheat. Certain fungi may be more specialised to a particular crop, and may competitively exclude other fungi under given abiotic (eg rainfall and temperature) and biotic (interaction between different fungi) conditions. 

A number of aspects have a link to biocontrol. This study does not directly explore biocontrol of Aspergillus and Fusarium, but identifies some of the specific aspects that would augment current knowledge on fungal contamination dynamics in maize for the success of current Biocontrol strategies. Firstly, the study investigates the structure of the spectrum of fungi (mycobiome structure) naturally contaminating maize; and how niche partitioning on maize as a result of abiotic stimulus (rainfall) shapes the fungal abundances (mycobiome composition) and subsequently FB and AF due to Fusarium and Aspergillus, respectively. It further looks at three more aspects namely: the natural infection of Aspergillus section Flavi (Flavi); the Flavi diversity and its influence on AF contamination levels in pre-harvest maize. These two aspects provide a better understanding of the community diversity of Flavi contaminating maize for biocontrol intelligence. Third aspect is the effect of antioxidant as an abiotic factor on toxigenic and atoxigenic Flavi fitness and AF levels. It is envisaged that increasing the oxidative capacity of seed would indirectly positively affect the proportion of Flavi that do not produce AF compared to those that produce AF. Further, this would also reduce the chances of spikes in levels of AFs in the seed at pre-harvest or during storage. 

Publication

• Prevalence of Aflatoxin- and Fumonisin-Producing Fungi Associated with Cereal Crops Grown in Zimbabwe and Their Associated Risks in a Climate Change Scenario