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

Authors: AMOS, ACUR - National Agricultural Research Organization - Uganda; Arias De Ares, Renee; STEVEN, ODONGO - Makerere University; SAMUEL, TUHAISE - Makerere University; JOSEPH, SSEKANDI - Makerere University; DENNIS, MUHANGUZI - Makerere University; JOHN, ADRIKO - National Agricultural Research Organization - Uganda; STEPHEN, BUAH - National Agricultural Research Organization - Uganda; ANDREW, KIGGUNDU - National Agricultural Research Organization - Uganda

Submitted to: BMC Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/14/2020
Publication Date: 8/15/2020
Citation: Amos, A., Arias De Ares, R.S., Steven, O., Samuel, T., Joseph, S., Dennis, M., John, A., Stephen, B., Andrew, K. 2020. Genetic diversity of aflatoxin-producing Aspergillus flavus isolated from selected groundnut growing agro-ecological zones of Uganda.. BMC Microbiology. 20:252. https://doi.org/10.1186/s12866-020-01924-2.
DOI: https://doi.org/10.1186/s12866-020-01924-2

Interpretive Summary: Despite the health hazard of aflatoxin contamination by the fungus Aspergillus in agricultural produce, there is limited information about the extent of that contamination and about the potential genetic variability of the fungus invading groundnut in Uganda. This work was intended to generate information about different species and genotypes of Aspergillus invading groundnut in that country. Understanding the genetic diversity of these fungi can help develop more effective management practices.

Technical Abstract: Aspergillus is the main fungal genus causing pre- and post-harvest contamination of groundnuts. Aspergillus flavus belongs to section Flavi, a group consisting of both the aflatoxigenic species (A. flavus, A. parasiticus and A. nomius) and non-aflatoxigenic species (A. oryzae, A. sojae and A. tamarii). Aflatoxins are food-borne toxic secondary metabolites produced by Aspergillus species, causing hepatic carcinoma and stunting in children and are the most toxic carcinogenic mycotoxins ever identified. Despite the well-known public health problems associated with aflatoxicosis in Uganda, information about the genetic diversity of the main aflatoxin causing fungus, Aspergillus flavus in this country is still limited. A cross-sectional survey was therefore carried out in three main groundnut-growing agro-ecological zones (AEZs) of Uganda; West Nile farming system, Lake Kyoga basin mixed farming system and Lake Victoria basin farming system. This was to assess the genetic diversity of A. flavus and to establish the contamination rates of groundnuts with Aspergillus species at pre- and post-harvest stages. Out of the 213 A. flavus isolates identified in this study, 96 representative isolates were fingerprinted using 16 Insertion/deletion microsatellite markers. Data from fingerprinting were analyzed through Neighbor Joining while polymorphism was determined using Arlequin v 3.5. The pre- and post-harvest contamination rates were; 2.5 % and 50.0 % (West Nile farming system), 55.0 % and 35.0 % (Lake Kyoga basin mixed farming system) and 32.5 % and 32.5 % (Lake Victoria basin farming system) respectively. The Chi- square test showed no significant differences between pre- and post-harvest contamination rates among AEZs (p = 0.199). Only 67 out of 96 isolates showed polymorphism. Analysis of genetic diversity showed highest variation within populations than among populations. Two major clusters (aflatoxigenic isolates and the other non-aflatoxigenic isolates) were identified as colonizing groundnuts at pre- and post-harvest stages. These findings provide a preliminary insight on the existence of non-aflatoxigenic strains of A. flavus in Uganda. These strains are potential candidates for developing a reliable local Aspergillus bio-control agent.