Genetic diversity of aflatoxin-producing Aspergillus flavus isolated from selected groundnut growing agro-ecological zones of Uganda

Résumé

Abstract Background Groundnut pre- and post-harvest contamination is commonly caused by fungi from the GenusAspergillus.Aspergillus flavusis the most important of these fungi. It belongs to sectionFlavi; a group consisting of aflatoxigenic (A. flavus,A. parasiticusandA. nomius) and non-aflatoxigenic (A. oryzae,A. sojaeandA. tamarii) fungi. Aflatoxins are food-borne toxic secondary metabolites ofAspergillusspecies associated with severe hepatic carcinoma and children stuntedness. Despite the well-known public health significance of aflatoxicosis, there is a paucity of information about the prevalence, genetic diversity and population structure ofA. flavusin different groundnut growing agro-ecological zones of Uganda. This cross-sectional study was therefore conducted to fill this knowledge gap. Results The overall pre- and post-harvest groundnut contamination rates withA. flavuswere 30.0 and 39.2% respectively. Pre- and post-harvest groundnut contamination rates withA. flavusacross AEZs were; 2.5 and 50.0%; (West Nile), 55.0 and 35.0% (Lake Kyoga Basin) and 32.5 and 32.5% (Lake Victoria Basin) respectively. There was no significant difference (χ2 = 2,p = 0.157) in overall pre- and post-harvest groundnut contamination rates withA. flavusand similarly no significant difference (χ2 = 6,p = 0.199) was observed in the pre- and post-harvest contamination of groundnut withA. flavusacross the three AEZs. The LKB had the highest incidence of aflatoxin-producingAspergillusisolates while WN had no singleAspergillusisolate with aflatoxin-producing potential.Aspergillusisolates from the pre-harvest groundnut samples had insignificantly higher incidence of aflatoxin production (χ2 = 2.667,p = 0.264) than those from the post-harvest groundnut samples. Overall,A. flavusisolates exhibited moderate level (92%,p = 0.02) of genetic diversity across the three AEZs and low level (8%,p = 0.05) of genetic diversity within the individual AEZs. There was a weak positive correlation (r = 0.1241,p = 0.045) between genetic distance and geographic distance amongA. flavuspopulations in the LKB, suggesting that genetic differentiation in the LKB population might be associated to geographic distance. A very weak positive correlation existed between genetic variation and geographic location in the entire study area (r = 0.01,p = 0.471), LVB farming system (r = 0.0141,p = 0.412) and WN farming system (r = 0.02,p = 0.478). Hierarchical clustering using the unweighted pair group method with arithmetic means (UPGMA) revealed two main clusters of genetically similarA. flavusisolates. Conclusions These findings provide evidence that genetic differentiation inA. flavuspopulations is independent of geographic distance. This information can be valuable in the development of a suitable biocontrol management strategy of aflatoxin-producingA. flavus.

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