Non-aflatoxigenic Aspergillus flavus to prevent aflatoxin contamination in crops: advantages and limitations

Abstract

Aspergillus flavus is a diverse assemblage of strains that include aflatoxin-producing and non-toxigenic strains with cosmopolitan distribution. The most promising strategy currently being used to reduce preharvest contamination of crops with aflatoxin is to introduce non-aflatoxin (biocontrol) A. flavus into the crop environment. Whether or not introduction of biocontrol strains into agricultural fields is enough to reduce aflatoxin contamination to levels required for acceptance of the contaminated food as fit for consumption is still unknown. There is no question that biocontrol strains are able to reduce the size of the populations of aflatoxin-producing strains but the available data suggests that at most only a four- to five-fold reduction in aflatoxin contamination is achieved. There are many challenges facing this strategy that are both short term and long term. First, the population biology of A. flavus is not well understood due in part to A. flavus’s diversity, its ability to form heterokaryotic reproductive forms, and its unknown ability to survive for prolonged periods after application. Second, biocontrol strains must be selected that are suitable for the environment, the type of crop, and the soil into which they will be introduced. Third, there is a need to guard against inadvertent introduction of A. flavus strains that could impose an additional burden on food safety and food quality, and fourth, with global warming and resultant changes in the soil nutrients and concomitant microbiome populations, the biocontrol strategy must be sufficiently flexible to adapt to such changes. Understanding genetic variation within strains of A. flavus is important for developing a robust biocontrol strategy and it is unlikely that a “one size fits all” strategy will work for preharvest aflatoxin reduction.

Biological control of aflatoxins in Africa: current status and potential challenges in the face of climate change

“…The long-term fate of atoxigenic VCGs after sporulation during the year of application has been questioned (Ehrlich, 2014). The atoxigenic VCGs composing a biocontrol product will sporulate and then move to other substrates, including the target crop but with time only a portion of the applied VCGs will remain in the treated field while other portions will disperse to other areas, will be outcompeted by fungi arriving from neighbouring areas, or will lose viability.…”

A review on the relation between soil and mycotoxins: Effect of aflatoxin on field, food and finance

“…Aspergillus flavus and A. parasiticus are the two most agriculturally important Aspergillus species; both include diverse groups of strains, some are toxigenic (toxin producing) and others are atoxigenic (Ehrlich, 2014;Nicholson, 2004). Aspergillus flavus is globally distributed and is known to proliferate in a wide range of environmental conditions (Hedayati, Pasqualotto, Warn, Bowyer, & Denning, 2007;Thathana, Murage, Abia, & Pillay, 2017).…”

Thanatin confers partial resistance against aflatoxigenic fungi in maize (Zea mays)

“…Conventional breeding strategies and agricultural practices such as irrigation and pest control can reduce aflatoxin levels (reviewed by Dorner 2008;Abbas et al 2012;Schmidt 2013;Ehrlich 2014) but it is clear that aflatoxin contamination cannot be solved entirely by individual treatments (Cary et al 2011). More recent molecular breeding strategies allow the targeted introduction of resistance traits into crops and have been used to develop aflatoxin-resistant maize lines (Brown et al 2009).…”