Aflatoxin contamination of maize and groundnut in Burundi: Distribution of contamination, identification of causal agents and potential biocontrol genotypes of Aspergillus flavus

Abstract

Aflatoxin contamination of the staples maize and groundnut is a concern for health and economic impacts across sub-Saharan Africa. The current study (i) determined aflatoxin levels in maize and groundnut collected at harvest in Burundi, (ii) characterized populations of Aspergillus section Flavi associated with the two crops, and (iii) assessed aflatoxin-producing potentials among the recovered fungi. A total of 120 groundnut and 380 maize samples were collected at harvest from eight and 16 provinces, respectively. Most of the groundnut (93%) and maize (87%) contained aflatoxin below the European Union threshold, 4 μg/kg. Morphological characterization of the recovered Aspergillus section Flavi fungi revealed that the L-morphotype of A. flavus was the predominant species. Aflatoxin production potentials of the L-morphotype isolates were evaluated in maize fermentations. Some isolates produced over 137,000 μg/kg aflatoxin B₁. Thus, despite the relatively low aflatoxin levels at harvest, the association of both crops with highly toxigenic fungi poses significant risk of post-harvest aflatoxin contamination and suggests measures to mitigate aflatoxin contamination in Burundi should be developed. Over 55% of the L-morphotype A. flavus did not produce aflatoxins. These atoxigenic L-morphotype fungi were characterized using molecular markers. Several atoxigenic genotypes were detected across the country and could be used as biocontrol agents. The results from the current study hold promise for developing aflatoxin management strategies centered on biocontrol for use in Burundi to reduce aflatoxin contamination throughout the value chain.

Keywords: Aspergillus section Flavi; atoxigenic; biocontrol; diversity; toxigenic.

Figure 1

Maize and groundnut sampling sites in Burundi provinces in March and July 2014.

Figure 2

Proportion of maize and groundnut samples contaminated with different aflatoxin concentration categories.

Figure 3

Population (colony forming units per gram) of Aspergillus section Flavi in maize (A) and groundnut (B) sampled from major provinces in Burundi. The letters attached to the bars represent statistical significance at 95% confidence level. Aspergillus population in maize was low in some provinces (Karuzi, Kayanza, Muramvya, Muyinga, Mwaro and Ngozo) and hence data for these provinces not plotted.

Figure 4

Proportion (%) of members of Aspergillus section Flavi recovered in maize (A) and groundnut (B) from major production provinces in Burundi.

Figure 5

Neighbor-Net tree of 376 unique non-aflatoxigenic haplotypes found in Burundi. Haplotypes seen only in maize are shaded red, those found only in groundnut are shaded blue, and those in both crops are shaded black.

Figure 6

Distribution across Burundi of the active ingredient atoxigenic Aspergillus flavus isolates composing the aflatoxin biocontrol product Aflasafe BU01 (A) and Aflasafe KE01 (B). Aflasafe KE01 was developed for use in Kenya but its active ingredients, apart from Burundi, have been detected in several other countries.