Polyphasic characterization reveals the first evidence of an atypical AFG1-dominant toxigenic profile of Aspergillus section Flavi in Uganda's cassava value chain

Abstract Understanding the diversity and toxigenic potential of Aspergillus section Flavi in cassava remains limited in sub-Saharan Africa despite increasing aflatoxin contamination. This study investigated fungal diversity across Uganda's cassava value chain using a polyphasic approach integrating morphology, chemotype profiling, ITS and calmodulin sequencing, and LC-MS/MS. A total of 288 samples comprising soil, fresh tubers, dried chips, and cassava flour were collected from eight major cassava-producing districts. Aspergillus was the predominant fungal genus (mean 4.82 × 10⁵ CFU/g; P = 0.007), while Aspergillus section Flavi exhibited the highest abundance among Aspergillus sections (1.48 × 10⁵ CFU/g; P = 0.021). Of 162 isolates screened, 77 (47.5%) were aflatoxigenic, with soil harbouring the greatest proportion of toxigenic isolates (22/27; 81%), identifying soil as the principal environmental reservoir of contamination. Polyphasic characterization of 52 representative isolates identified five species: Aspergillus flavus (64%), A. parasiticus (25%), A. novoparasiticus (8%), A. minisclerotigenes (1.9%), and A. tamarii (1.9%). Unexpectedly, AFG₁ rather than AFB₁ was the predominant aflatoxin produced by the isolates, with a significantly higher mean concentration (229.1 ± 21 µg/kg; range 0.68–1571.7 µg/kg; P = 0.0039) than AFB₁ (213.9 ± 3.3 µg/kg), indicating an atypical toxigenic profile of the Aspergillus section Flavi population associated with cassava production in Uganda. This is the first report of G-type aflatoxin predominance in Ugandan cassava-associated Aspergillus populations. The findings identify soil as a critical intervention point and demonstrate that reliance on AFB₁ alone may underestimate aflatoxin risk in cassava production systems.