National Agricultural Research Laboratories, P.O. Box 7065, Kampala, Uganda.
National Peanut Research Laboratories, P.O. Box 509, 1011 Forrester Drive, S.E, Dawson, GA, 39842, USA.
BMC Microbiol. 2020 Aug 14;20(1):252. doi: 10.1186/s12866-020-01924-2.
Groundnut pre- and post-harvest contamination is commonly caused by fungi from the Genus Aspergillus. Aspergillus flavus is the most important of these fungi. It belongs to section Flavi; a group consisting of aflatoxigenic (A. flavus, A. parasiticus and A. nomius) and non-aflatoxigenic (A. oryzae, A. sojae and A. tamarii) fungi. Aflatoxins are food-borne toxic secondary metabolites of Aspergillus species 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 of A. flavus in different groundnut growing agro-ecological zones of Uganda. This cross-sectional study was therefore conducted to fill this knowledge gap.
The overall pre- and post-harvest groundnut contamination rates with A. flavus were 30.0 and 39.2% respectively. Pre- and post-harvest groundnut contamination rates with A. flavus across 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 (χ = 2, p = 0.157) in overall pre- and post-harvest groundnut contamination rates with A. flavus and similarly no significant difference (χ = 6, p = 0.199) was observed in the pre- and post-harvest contamination of groundnut with A. flavus across the three AEZs. The LKB had the highest incidence of aflatoxin-producing Aspergillus isolates while WN had no single Aspergillus isolate with aflatoxin-producing potential. Aspergillus isolates from the pre-harvest groundnut samples had insignificantly higher incidence of aflatoxin production (χ = 2.667, p = 0.264) than those from the post-harvest groundnut samples. Overall, A. flavus isolates 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 among A. flavus populations 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 similar A. flavus isolates.
These findings provide evidence that genetic differentiation in A. flavus populations is independent of geographic distance. This information can be valuable in the development of a suitable biocontrol management strategy of aflatoxin-producing A. flavus.
花生的产前和产后污染通常是由曲霉属真菌引起的。黄曲霉是这些真菌中最重要的一种。它属于 Flavi 组；由产黄曲霉毒素（黄曲霉、寄生曲霉和 nomius 曲霉）和非产黄曲霉毒素（米曲霉、大豆曲霉和 tamarii 曲霉）真菌组成。黄曲霉毒素是与严重肝癌和儿童发育迟缓有关的曲霉属物种的食源毒性次生代谢物。尽管黄曲霉毒素中毒的公共卫生意义众所周知，但乌干达不同花生种植农业生态区黄曲霉的流行率、遗传多样性和种群结构的信息仍然很少。因此，进行了这项横断面研究以填补这一知识空白。
黄曲霉产前和产后污染花生的总体污染率分别为 30.0%和 39.2%。AEZs 中黄曲霉产前和产后污染花生的比率分别为：2.5%和 50.0%（西尼罗河）、55.0%和 35.0%（Kyoga 湖盆）和 32.5%和 32.5%（维多利亚湖盆地）。黄曲霉产前和产后污染花生的总体比率无显著差异（χ=2，p=0.157），三个 AEZs 之间黄曲霉产前和产后污染花生也无显著差异（χ=6，p=0.199）。LKB 有最高的产黄曲霉毒素曲霉分离株发生率，而 WN 没有单个产黄曲霉毒素的潜在曲霉分离株。产前花生样本中的曲霉分离株的产黄曲霉毒素发生率显著高于产后花生样本（χ=2.667，p=0.264）。总体而言，黄曲霉分离株在三个 AEZs 中表现出中度遗传多样性（92%，p=0.02），在个体 AEZs 中表现出低度遗传多样性（8%，p=0.05）。LKB 中黄曲霉种群之间存在弱正相关（r=0.1241，p=0.045），表明 LKB 种群中的遗传分化可能与地理距离有关。在整个研究区域（r=0.01，p=0.471）、LVB 耕作系统（r=0.0141，p=0.412）和 WN 耕作系统（r=0.02，p=0.478）中，遗传变异与地理位置之间存在非常弱的正相关。使用不带权配对组平均法（UPGMA）的层次聚类显示出两个主要的遗传相似黄曲霉分离株聚类。
这些发现提供了证据表明，黄曲霉种群的遗传分化与地理距离无关。这些信息可用于制定合适的黄曲霉毒素产黄曲霉生物防治管理策略。
