📖 ABSTRACT/OVERVIEW
Atoxigenic Aspergillus flavus strains that outcompete toxigenic populations in soil and on grain surfaces represent the most promising biological strategy for pre-harvest aflatoxin reduction. However, the molecular basis regulating aflatoxin biosynthesis in Nigerian A. flavus strains, and the genomic determinants distinguishing atoxigenic from toxigenic strains in local populations, remain uncharacterised. This doctoral research conducts a functional genomics investigation of aflatoxin biosynthesis regulation in Nigerian A. flavus strains with the goal of identifying genomic targets for rational development of improved atoxigenic biocontrol strains adapted to Nigerian agroecological conditions. The research encompasses: comparative whole-genome sequencing of 50 toxigenic and 30 atoxigenic A. flavus strains isolated from groundnut, maize, and sorghum farms across Nigeria's groundnut belt; differential expression analysis of the aflatoxin biosynthesis gene cluster using RNA-seq under simulated drought and temperature stress conditions; CRISPR-Cas9 deletion of candidate regulatory genes including aflR, aflS, veA, and laeA orthologues to determine their contribution to biosynthesis activation; and competitive fitness assays in soil and on host grain surfaces under contrasting temperature and moisture conditions. An original theoretical contribution concerns the development of a transcriptional regulatory network model for aflatoxin induction under tropical stress conditions. Practical outputs include a genomically characterised panel of elite atoxigenic biocontrol candidates ready for field evaluation, filling a critical gap in the Nigerian aflatoxin biocontrol development pipeline. Keywords: Aspergillus flavus, aflatoxin biosynthesis, functional genomics, atoxigenic biocontrol, Nigeria.
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