Evaluation of the synergistic antifungal effects of thymol and cinnamaldehyde combination and its mechanism of action against Rhizopus stolonifer in vitro and in vivo

Abstract

This study investigated the antifungal synergy between thymol and cinnamaldehyde (TH-CIN) to prevent and control post-harvest soft rot infections in papaya caused by R. stolonifer. In vitro, 11 combinations with different concentrations of TH-CIN were made to determine the highest antifungal effect against R. stolonifer. The results showed that ratio of (TH-CIN) was the optimal mixture, and the MIC reached 0.24 μL/mL. The MIC of the optimized mixture demonstrated an effective result against mycelia growth and germination of R. stolonifer spores. Moreover, it affected the content of protein, DNA, and cell membrane depending on the used dose. Electron microscopy results showed that the optimal TH-CIN mixture had a significant effect on the cell wall structure of R. stolonifer. For in vivo tests, papaya fruits treated with the MIC of the optimized mixture showed a decrease in weight loss, disease index, and disease severity. Treatment with 2MIC was able to preserve stored papaya for seven days, compared to untreated papaya, which was damaged after three days of storage. The improved shelf life and good protective action observed indicate that the TH-CIN combination could be a good option for post-harvest soft root disease control in papaya fruits.