Impact of simulated climate change conditions on Aspergillus flavus biocontrol effectiveness in peanut-based medium and peanut seeds

Peanut is a legume widespread in the world, but its high susceptibility to Aspergillus flavus infection poses a significant challenge due to the risk of aflatoxin contamination. It is predicted that changing climatic conditions will result in warmer, drier periods with elevated CO₂ levels, which promote the growth of A. flavus. The most effective pre-harvest mitigation strategy is the use of non-aflatoxigenic strains of biocontrol; however, future climatic conditions may influence the effectiveness of this practice. Thus, the objective of this study was to assess the impact of simulated climate change conditions on the efficacy of a non-aflatoxigenic A. flavus strain, the active agent of a biocontrol product, in reducing fungal growth and mycotoxin production. A range of temperature conditions (T = 25, 30, 35 °C), water activity (aw = 0.85, 0.90, 0.95) and CO2 concentration (400, 1000 ppm) were selected for investigation. The assay was conducted using three ratios of A. flavus spore suspensions (100 % aflatoxigenic, 100 % non-aflatoxigenic, 50/50 % aflatoxigenic:non-aflatoxigenic; 105 spores mL−1) inoculated in vitro on a peanut-based medium (PBM), and in situ on peanut seeds, and incubated for 10 days. Results of in vitro studies showed a significant influence of T and aw on fungal growth rates (μ), with a reduction when the aw decreased and T shifted from the fungus's optimum of 30 °C. The highest mycotoxin concentration was detected on PBM, with an aflatoxin B1 (AFB1) production by the aflatoxigenic strain in situ 50 % lower than in vitro. However, for all the treatments, the application of the biocontrol agent inhibited AFB1 production with a general reduction of 55 % in vitro and 71 % in situ, even though a significant increase in kojic acid production was observed. The effectiveness of the non-aflatoxigenic strain increased when T was raised up to 35 °C with higher AFB1 reductions both in vitro and in situ, of respectively 58 and 76 %. These observations provided the first evidence that climate change will not negatively influence the ability of the Italian A. flavus non-aflatoxigenic strain, which represents the biocontrol agent of the commercial product AF-X1, to reduce AFB1 contamination in peanuts.