In vitro experimental environments lacking or containing soil disparately affect competition experiments of Aspergillus flavus and co-occurring fungi in maize grains

ABSTRACT

In vitro experimental environments are used to study interactions between microorganisms, and to predict dynamics in natural ecosystems. This study highlights that experimental in vitro environments should be selected to match closely the natural environment of interest during in vitro studies to strengthen extrapolations about aflatoxin production by Aspergillus and competing organisms. Fungal competition and aflatoxin accumulation were studied in soil, cotton wool or tube (water-only) environments, for Aspergillus flavus competition with Penicillium purpurogenum, Fusarium oxysporum or Sarocladium zeae within maize grains. Inoculated grains were incubated in each environment at two temperature regimes (25 and 30°C). Competition experiments showed interaction between the main effects of aflatoxin accumulation and the environment at 25°C, but not so at 30°C. However, competition experiments showed fungal populations were always interacting with their environments. Fungal survival differed after the 72-h incubation in different experimental environments. Whereas all fungi incubated within the soil environment survived, in the cotton wool environment none of the competitors of A. flavus survived at 30°C. With aflatoxin accumulation, F. oxysporum was the only fungus able to interdict aflatoxin production at both temperatures. This occurred only in the soil environment and fumonisins accumulated instead. Smallholder farmers in developing countries face serious mycotoxin contamination of their grains, and soil is a natural reservoir for the associated fungal propagules, and a drying and storage surface for grains on these farms. Studying fungal dynamics in the soil environment and other environments in vitro can provide insights into aflatoxin accumulation post-harvest.

Graphical Abstract

KEYWORDS:

• Aspergillus
• Fusarium
• Penicillium
• Sarocladium
• aflatoxin
• competition
• soil
• in vitro

Acknowledgements

The authors wish to acknowledge the Nigerian and Australian governments for supporting the PhD scholarship of Titilayo Falade through nomination and funding for the Australia Awards scholarship respectively. The authors also thank Dr James Gethi, Kenya Agricultural and Livestock Research Organization, for the maize samples from which fungal isolates were retrieved.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the Department of Foreign Affairs and Trade, Australian Government (DFAT) funding of the Capacity and Action for Aflatoxin reduction in Eastern Africa (CAAREA) Project as part of the DFAT-Commonwealth Scientific and Industrial Research Organisation (CSIRO) Africa Food Security Initiative [grant number 57685]. There is no financial interest or benefit arising to DFAT from the direct applications of this research. The work was also supported by the Australian government through funding of the PhD scholarship of Titilayo Falade.