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 COQ 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 degrees 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 (mu), with a reduction when the aw decreased and T shifted from the fungus's optimum of 30 degrees 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 degrees 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.