High-efficiency fungal pathogen intervention for seed protection: New utility of long-chain alkyl gallates as heat-sensitizing agents

Authors: Kim, Jong Heon; Chan, Kathleen - Kathy; Hart-Cooper, William; Palumbo, Jeffrey - Jeff; Orts, William

Submitted to: Frontiers in Fungal Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/13/2023
Publication Date: 7/28/2023
Citation: Kim, J., Chan, K.L., Hart-Cooper, W.M., Palumbo, J.D., Orts, W.J. 2023. High-efficiency fungal pathogen intervention for seed protection: New utility of long-chain alkyl gallates as heat-sensitizing agents. Frontiers in Fungal Biology. 4. Article 1172893. https://doi.org/10.3389/ffunb.2023.1172893.
DOI: https://doi.org/10.3389/ffunb.2023.1172893

Interpretive Summary: Chemical seed treatment is one of the crop protection strategies which enables healthy crop establishment in the fields through better seed preservation/germination and plant protection against food-contaminating microbes. Comparing to other protection strategies, seed treatment achieves a low-cost crop protection since the method requires a relatively low amount of active ingredients. Considering the limited efficacy of conventional seed sanitation methods, directly affecting food safety and food security, the development of safe, novel seed-treatment alternatives to the toxic chemical ingredients is highly needed. In 2020, the insufficient elimination of mycotoxin-producing fungi contaminating peanut seed surfaces in southeast United States resulted in elevated mycotoxin contamination. In this study, we investigated the mild heat (50 – 57.5 oC)-sensitizing capability of thirty-four compounds/derivatives, which are currently used as food additives (thus, repurposing) or antimicrobial agents, for the elimination of mycotoxigenic fungus A. flavus contaminated on the surfaces of crop seeds. We found the long-chain alkyl gallate octyl gallate (OG) was an effective heat-sensitizing agent for control of microbial contaminants, where OG and mild heat (57.5 oC) co-administration for 90 seconds achieved > 99.999% fungal death.

Technical Abstract: Control of food-contaminating fungi, especially pathogens that produce mycotoxins, is problematic since effective method for intervening fungal contamination on food crops is often limited. Generally Regarded As Safe (GRAS) chemicals, such as natural compounds or their structural derivatives, can be developed as antimicrobial agents for sustainable food/crop production. This investigation identified that long-chain alkyl gallates, i.e., octyl-, nonyl-, and decyl gallates (OG, NG, DG), can function as heat-sensitizing agents that effectively prevent fungal contamination. Out of twenty-eight candidate compounds and six conventional antifungal agents examined, the heat-sensitizing capacity was unique to the long-chain alkyl gallates, where OG exhibited the highest activity, followed by DG and NG. Since OG is a GRAS compound classified by the United States Food and Drug Administration (FDA), further in vitro antifungal studies were performed using OG. When OG and mild heat (57.5 oC) were co-administered for 90 seconds, the treatment achieved > 99.999% fungal death. Application of either treatment alone was significantly less effective at reducing fungal survival. Of note, co-application of OG (3 mM) and mild heat (50 oC) for 20 minutes completely prevented the survival of aflatoxigenic Aspergillus flavus contaminating crop seeds (Brassica rapa Pekinensis; Chinese cabbage hybrid), while seed germination rate was unaffected. Heat-sensitization was also determined in selected bacterial strains including Escherichia coli and Agrobacterium tumefaciens. Altogether, OG is an effective heat-sensitizing agent for control of microbial pathogens. OG-mediated heat sensitization will improve the efficacy of antimicrobial practices, hence achieving safe, rapid, and cost-effective pathogen control in agriculture/food industry settings.