General Description

Tea Polyphenol (TP) demonstrates potent antifungal and antibacterial activities against a wide range of plant pathogens and postharvest diseases. Tea Polyphenol inhibits hyphal growth and spore germination in fungi, including rice blast disease-causing Pyricularia oryzae, and shows effectiveness against phytopathogenic bacteria like Erwinia and Pseudomonas. Mechanistically, Tea Polyphenol disrupts cell membranes, induces enzyme activities in plant defense, and perturbs bacterial membranes, leading to leakage and inhibition of biofilm formation. These actions highlight Tea Polyphenol as a natural and effective solution for controlling fungal and bacterial infections in agriculture, showcasing its diverse mechanisms of action in combating plant diseases.

Figure 1. Tea polyphenol

Antimicrobial Activities

Antifungal Activity

Tea Polyphenol exhibits remarkable antifungal activity against a variety of plant pathogenic fungi and postharvest disease microorganisms. In a study by Wang et al., different concentrations of TP were tested on fungi like Bipolaris maydis, Colletotrichum musae, and Fusarium oxysporum, showing significant inhibition of hyphal growth and spore germination in a concentration-dependent manner. Notably, Tea Polyphenol solutions at 10 mg/mL and 5 mg/mL demonstrated the highest inhibitive rates across various fungi. Additionally, Tea Polyphenol showed strong inhibitory effects on Pyricularia oryzae, the causative agent of rice blast disease, with complete growth inhibition at 10 mg/mL and 5 mg/mL concentrations. Further studies highlighted TP's effectiveness against eight plant pathogenic fungi species, including Colletotrichum horii and Phytophthora cryptogea, with notable inhibition against C. horii and P. cryptogea. Moreover, Tea Polyphenol displayed inhibitory effects against postharvest diseases in citrus fruits and grape fruits caused by Diplodia natalensis and Botrytis cinerea, respectively. In experiments, TP inhibited spore germination and mycelium growth effectively at varying concentrations. Furthermore, Tea Polyphenol exhibited promising results in controlling wheat stripe rust disease caused by Puccinia striiformis f. sp. tritici (Pst). In vitro and in vivo experiments demonstrated significant suppression of urediniospore germination and disease incidence, albeit requiring higher concentrations for optimal control due to limited systemic activity within plant tissues. Overall, the accumulating evidence underscores Tea Polyphenol's potent antifungal properties across a spectrum of plant pathogens and postharvest diseases. ¹

Antibacterial Activity

Tea Polyphenol has been shown to possess significant antibacterial activity against various phytopathogenic bacteria. Studies have demonstrated that Tea Polyphenol has inhibitory effects on bacterial infections, including strains of Erwinia, Pseudomonas, Clavibacter, Xanthomonas, and Agrobacterium, which commonly infect vegetables like lettuce, tomatoes, and onions. Research has shown that specific Tea Polyphenol compounds, such as EGC and EGCG, exhibit more potent inhibitory effects compared to EC and ECG, with minimum inhibitory concentrations mostly below 100 ppm. On the other hand, ECG has been found to be less effective, with MICs mostly exceeding 1000 ppm. Additionally, experiments conducted on tea extracts have also confirmed the antibacterial activity of Tea Polyphenol against phytopathogenic bacteria like Pseudomonas syringae in both in vitro and greenhouse trials. The inhibitory effect of tea extract was demonstrated through agar diffusion tests and viable cell counts, revealing significant growth inhibition of the pathogens. However, the effectiveness of tea extract varied depending on the bacterial strain and the method of application, as seen in tests where tea extract did not induce a hypersensitive reaction in bean leaves infected with Pseudomonas syringae strains. Overall, the antibacterial activity of Tea Polyphenol against phytopathogenic bacteria highlights its potential as a natural and effective solution for controlling bacterial infections in agriculture. ²

Mechanism

Tea Polyphenol exhibits antifungal and antibacterial activities through various mechanisms. In terms of antifungal activity, Tea Polyphenol induces changes in cell membranes, leading to altered membrane permeability, as evidenced by a study on rice blast fungus. The phenolic hydroxyl groups in Tea Polyphenol bind to the hydrophilic end of the lipid bilayer in the cell membrane, causing agglomeration of membrane lipids and subsequent destruction of the cell membrane. Additionally, Tea Polyphenol treatment induces the activities of several enzymes involved in plant defense against fungal infection, including phenylalanine ammonia-lyase, catalase, peroxidase, polyphenoloxidase, chitinase, and β-1, 3-glucanase. Regarding antibacterial activity, Tea Polyphenol perturbs bacterial membranes, resulting in leakage of intramembranous materials and aggregation of liposomes in organisms such as E. coli and S. aureus. Moreover, Tea Polyphenol inhibits biofilm formation in both commensal and pathogenic E. coli strains, reducing the expression of CsgD, a crucial activator of curli and cellulose biosynthesis. Furthermore, it is suggested that Tea Polyphenol, specifically EGCG, may directly bind to peptidoglycan, a major component of bacterial cell walls, leading to the degradation of the cell wall structure. Additionally, Tea Polyphenol is involved in the inhibition of toll-like receptor (TLR) signaling pathways, which are crucial for innate immune responses and pathogen recognition in bacteria. In summary, the mechanisms of Tea Polyphenol's antifungal and antibacterial activities involve perturbation of cell membranes, induction of enzyme activities, and direct interactions with key components of fungal and bacterial cell structures. ²

Reference

1. Liu HM, Guo JH, Liu P, et al. Inhibitory activity of tea polyphenol and Candida ernobii against Diplodia natalensis infections. J Appl Microbiol. 2010; 108(3): 1066-1072.

2. Khan N, Mukhtar H. Tea Polyphenols in Promotion of Human Health. Nutrients. 2018;11(1):39.