Antifungal Activity Of Tea Extract Against Rhizopus Nigricans On Harveted Peaches And The Mechanism

Peaches are typical climacteric fruit. They are highly susceptible to pathogens and rapidly decay after postharvest. This paper systematically studied the in vitro antifungal activity of tea extracts against Rhizopus nigricans, Botrytis cinerea, Penicillium expansum and antifungal mechanism. The results were as follows:1. The antifungal activity of tea extracts against pathogens in vitro was determined by mycelial growth assay. The results showed that tea extract A inhibited the mycelial growth of pathogens in a dose-dependent manner, and it could cause mycelial death. The activity was significantly increased when the concentration was higher. R. nigricans turned out to be most sensitive one (EC50=2.91 mg/mL), and the antifungal activity is relatively poor on B. cinerea and P. expansum, their EC50 were 4.96 mg/mL and 10.42 mg/mL, respectively. Tea extract B also has apparent inhibiton to the mycelial growth of pathogens, and could cause mycelial death. The activity was significantly increased when the applied concentration was higher, their EC50 of tea extract B to three kinds of pathogens were 2.16 mg/mL,1.67 mg/mL and 1.09 mg/mL, respectively.2. The interactive measurement experiment showed that when tea extract A was combined with tea extract B at the ratio of 70:30, they exhibited synergistic antifungal interactions with the highest synergistic ratios (SR) value of 1.85, and the EC50 was 1.43 mg/mL, smaller than others.3. The antifungal mechanisms of tea extracts against R. nigricans were studied. The result showed that the treatment of both tea extract A and B could increase the conductivity of culture medium of R, nigricans, enhance the leakage of soluble protein> soluble sugar and metal ions such as K+、Na+、Mg2+ as well as Ca2+, induce the activity of chitinase and β-1,3-glucanase, cause the accumulation of superoxide anion radicals, hydroxyl radicals, hydrogen peroxide and MDA in mycelium; then, these led to the degradation of mycelial cell wall, the enhancement of membrane permeability and cellular senescence, which caused mycelial cell death. The result also showed that the combination of tea extracts significantly increased the conductivity of culture medium, the protoplasm leakage, the related enzyme activity as well as the accumulation of related free radical and MDA in mycelium, thus enhancing the antifungal activity, compared to tea extract A and B individually. These results suggested that the antifungal mechanism might be to increase the degradation of mycelial cell wall as well as the permeability of cell membrane and induce cellular senescence.