The Fusarium head blight (FHB) species complex generates mycotoxins, leading to not only reductions in crop quality and yield but also posing significant health risks to both humans and livestock. Therefore, it is of great urgency to develop a green strategy to inhibit Fusarium mycotoxin production that can be applied in sprouted grains. Recent studies have shown that photosensitization, an emerging technology, effectively combats various microorganism and fungi through the interaction between photosensitizers (PS) and visible light in the presence of oxygen. The main limitation in this technology is the use of PS as they have weak antifungal activity in natural light, have low solubility, specificity, and high cost. This research seeks to understand the effectiveness of antifungal and mycotoxin inhibitory activity of natural PS (curcumin) in vitro and their antifungal mechanism of action. Initially, the water dispersible physically stable curcumin nanoemulsion was formed by preparing 3mM concentration of curcumin in 10 wt% propylene glycol, 10 wt% of Tween 80 and 80 wt% of water mixture. With regard to inhibition of spore germination of two chemotypes of Fusarium graminearum isolates (10-124-1 and 10-125-1), the concentration of curcumin nanoemulsions on 50% spore inhibition rates (EC50) were 2.32 mM/mL and 2.56 mM/mL, respectively. As revealed by scanning electron microscope (SEM), shrunken spores with rough and corrugated surfaces were observed in spores treated with curcumin nanoemulsions due to the massive loss of cytoplasm matrix in spores. Moreover, significant (p< 0.05) suppression on mycotoxin inhibition were achieved by treated with 3mM of curcumin nanoemulsion with light exposure. We further investigated the mechanism of action of curcumin nanoemulsion by studying Tri gene cluster (Tri3, Tri4, and Tri5) at genetic levels. Results indicated that the curcumin nanoemulsion significantly (p ˂0.05) up-regulated all the treatment samples than control (Tri3, Tri4, and Tri5) in isolate 10-124-1, whereas in isolate 10-125-1, all the Tri gene cluster in treatment conditions were down-regulated significantly (p ˂0.05) than control. Overall, this study established the potential application of natural PS as a safe preservative in grains.
ACKNOWLEDGEMENT AND DISCLAIMER
This material is based upon work supported by the U.S. Wheat and Barley Scab Initiative under Agreement No. 59-0206-2-131. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the authors and do not necessarily reflect the view of the U.S. Department of Agriculture