Prevalence of Aflatoxin Contamination in Maize and Groundnut in Ghana: Population Structure, Distribution, and Toxigenicity of the Causal Agents

Abstract

Aflatoxin contamination in maize and groundnut is perennial in Ghana with substantial health and economic burden on the population. The present study examined for the first time the prevalence of aflatoxin contamination in maize and groundnut in major producing regions across three agroecological zones (AEZs) in Ghana. Furthermore, the distribution and aflatoxin-producing potential of Aspergillus species associated with both crops were studied. Out of 509 samples (326 of maize and 183 of groundnut), 35% had detectable levels of aflatoxins. Over 15% of maize and 11% of groundnut samples exceeded the aflatoxin threshold limits set by the Ghana Standards Authority of 15 and 20 ppb, respectively. Mycoflora analyses revealed various species and morphotypes within the Aspergillus section Flavi. A total of 5,083 isolates were recovered from both crops. The L morphotype of Aspergillus flavus dominated communities with 93.3% of the population, followed by Aspergillus spp. with S morphotype (6%), A. tamarii (0.4%), and A. parasiticus (0.3%). Within the L morphotype, the proportion of toxigenic members was significantly (P < 0.05) higher than that of atoxigenic members across AEZs. Observed and potential aflatoxin concentrations indicate that on-field aflatoxin management strategies need to be implemented throughout Ghana. The recovered atoxigenic L morphotype fungi are genetic resources that can be employed as biocontrol agents to limit aflatoxin contamination of maize and groundnut in Ghana. Copyright © 2018 The Author(s). This is an open access article distributed under the CC BY 4.0 International license .

Fig. 1

Map of Ghana depicting agroecological zones and the seven regions where samples were collected. The Southern Guinea Savanna (SGS) zone has a semiarid climate, a unimodal rainfall pattern of up to 1,100 mm, and a growing period of 180 to 200 days. Poor soils low in organic matter with high levels of iron and susceptible to severe erosion are common in SGS. The Derived Savanna (DS) zone has a subhumid climate, an annual precipitation range of 1,000 to 1,500 mm, and a growing period of 180 to 270 days. Soils in DS are principally sandy loams to clay loams, and are mostly poorly drained. The Humid Forest (HF) zone is characterized by a bimodal rainfall pattern ranging from 1,500 to 2,200 mm and a growing period of 270 to 365 days. Soils in HF are generally loamy, porous, well drained, and have greater accumulation of organic matter in the topsoil in comparison with SGS and DS (MoFA 2011; Oppong-Anane 2006)

Fig. 2

Box plot showing the variation in quantities of aflatoxin B1 produced by isolates of Aspergillus flavus L morphotype, isolates with S morphotype, and A. parasiticus across three agroecological zones (AEZs) in Ghana. Boxes indicate the interquartile range of aflatoxin B₁ produced by each type of fungi within an AEZ. Solid lines and symbols inside boxes represent the median and means, respectively. Whisker bars indicate the 10th and 90th percentiles while points below or above whisker bars are outliers. DS = Derived Savanna; L morphotype = 2,020 isolates, S morphotype = 160 isolates, A. parasiticus = 13 isolates. HF = Humid Forest; L morphotype = 1,639 isolates, S morphotype = 86 isolates, A. parasiticus = 2 isolates. SGS = Southern Guinea Savanna; L morphotype = 1,077 isolates, S morphotype = 65 isolates.

Fig. 3

Distribution of toxigenic and atoxigenic A. flavus L morphotype fungi in maize and groundnut (Gnut) across three AEZs of Ghana. For each bar, vertical lines represent the standard error of the means.