Distribution of indigenous strains of atoxigenic and toxigenic Aspergillus flavus and Aspergillus parasiticus in maize and peanuts agro-ecological zones of Kenya

Abstract

Background: Grains of important food and export crops in Africa are susceptible to contamination by toxin-producing moulds. Aflatoxins are mycotoxins associated with liver damage and cancer in humans and animals. These toxic substances are produced by fungi (such as Aspergillus flavus and Aspergillus parasiticus) in food and feed exposed to poor conditions during crop cultivation, storage or processing of harvest. The presence of aflatoxins in especially maize and peanuts in Kenya is of great concern. Recent developments in the application of atoxigenic strains of these fungi as biological control agents against toxigenic strains could be a solution to the problem. The objective of this study was to isolate, identify and characterize atoxigenic and toxigenic strains of A. flavus and A. parasiticus in Kenya, and investigate possible application of atoxigenic strains in control of aflatoxin levels in maize and peanuts. Fungal communities in soils of maize and peanut fields were examined to determine the distributions of aflatoxin-producing Aspergillus species and to identify endemic atoxigenic strains. 220 isolates belonging to A. flavus and A. parasiticus were collected randomly from soils of maize and peanuts fields in seven agro-ecological zones and characterized using morphological and physiological examination. Results:Aspergillus section Flavi was detected in all the 57 soil samples collected in Kenya. Members of Aspergillus section Flavi L strain was the most common (54 %), followed by S-strains (35 %). Among Aspergillus, A. flavus was the most predominant (63.2 %), followed by A. parasiticus (27.7 %), A. tamari (5.5 %) and A. nomius (2.7 %). The mean CFU of the Aspergillus colonies per gram of soil was highly variable among the districts, ranging from 3.0 × 10 3 to 1.72 × 10 6 (p < 0.05). The mean pH across the collection sites also varied according to the respective agroecological zones (pH 5.5-6.8) which is within the optimal pH requirement for the members of section Flavi. There was no significant variation in temperature across the sampling sites (p > 0.05). The results also showed that A. flavus was detected in all the zones examined.Conclusions: Each of the regions had atoxigenic strains of potential value which can be employed as biological control agents in the management of aflatoxicoses.

Distribution and genetic diversity amongAspergillus flavusisolates across three agro‐ecologies essential for maize cultivation in Ghana

“…which were present in few farms sampled, the fungi were found across all the agro-ecological zones; this indicates wide adaptation of the fungi across the contrasting environments, in agreement with a previous study in Nigeria (Atehnkeng et al, 2008). Although the fungi identified in the present study are all soilborne, they are very relevant to maize production because they can contaminate grains with spores carried by wind, rain or insects (Abbas et al, 2006;Cotty, 2006;Okun et al, 2015). Despite the ubiquitous nature of A. flavus and its presence in nearly all farms sampled, the soilborne saprophytes were absent in a few soils that had previously been cultivated with maize.…”

“…Because A. flavus requires decaying organic matter to grow and produce aflatoxin (Bruehl, 1987;Agrios, 1997;Schomberg & Steiner, 1997;Cookson et al, 1998;Perrone et al, 2014), there may have been too little organic matter in these fields to allow sporulation (typically when aflatoxin is produced). However, this observation contradicts the findings of Okun et al (2015) who detected various concentrations of aflatoxin B and G types in 27 out of 57 soil samples tested in Kenya for aflatoxin. It is unclear whether the fields from which the samples were taken were amended with organic matter or manure prior to the sampling, which could have boosted A. flavus growth and sporulation.…”

Aspergillusand aflatoxin in groundnut (Arachis hypogaeaL.) and groundnut cake in Eastern Ethiopia

“…Groundnuts that are used as raw materials for groundnut cakes or food products are prone to colonisation by Aspergillus species along the value chain and this leads to subsequent aflatoxin accumulation and exposure of consumers to health risks (Okun et al 2015). In eastern and lowland parts of Ethiopia, where the bulk of groundnut is produced (Kebede & Tana 2014), there is limited research work on specific aflatoxin contamination of groundnut and food products.…”

Aspergillus species from groundnuts (Arachis hypogaea) and mycotoxin production by toxigenic species

“…Seven isolates of A. flavus did not produce AFB1 and these isolates are considered as non-aflatoxigenic isolates. Occurence of non-aflatoxigenic isolates of A. flavus are common in groundnuts (Yin et al, 2009;Okun et al, 2015). In addition to groundnuts, non-aflatoxigenic A. flavus was also found in maize (Probst et al, 2011;Okun et al, 2015) and cotton seed (Cotty, 1997).…”