Mechanism Of Regulating On Anthracnose Of Tea Plants And Leaf Senescence By Selenium And Melatonin

Tea anthracnose is caused by the infestation of Colletotrichum sp.,a fungus of thedeuteromycota,which is a fungal disease commonly occurring in the major tea-producing regions of China and can cause massive defoliation of tea trees resulting in reduced yield and quality of tea leaves.The strength of the physiological activity of tea leaves will directly affect the formation and accumulation of their own photosynthetic products,which in turn affects the yield and quality of tea leaves.Therefore,there is an important theoretical basis and practical application prospect to study the regulatory mechanism of disease resistance and senescence in tea tree leaves.In this paper,"Shuchazao"was used as the experimental material,and the effects of exogenous selenium（Se）and melatonin（MT）on the control of anthracnose and leaf senescence,as well as the effects of Se and MT on the level of antioxidant enzymes and pathogenicity-related proteins in regulating the interaction between tea tress and pathogens were investigated by using two methods:needle prick inoculation and treatment solution immersion.The main findings are as follows:1.Treatment with 25 mg/L Se and 150μmol/L MT followed by 24 h interval inoculation with the pathogenic bacteria resulted in significantly smaller spot diameters in the treated group than in the control group after 7 d.Their spot expansion was reduced by 68.3%and 69.4%,respectively.The results of the plate inhibition experiments on anthracnose pathogens by different concentrations of Se and MT showed that both Se and MT at different concentrations had no significant inhibitory effects on the growth of anthracnose pathogens.Se and MT were found to decrease carboxymethyl cellulase（Cx）,β-glucosidase,and polymethylgalacturonase（PMG）enzyme activities through Se and MT experiments on cell wall degrading enzymes of anthracnose.2.Treatment with 25 mg/L Se and 150μmol/L MT followed by tea anthracnose inoculation significantly increased catalase（CAT）,superoxide dismutase（SOD）,peroxidase（POD）and phenylalanine aminolase（PAL）activities and enhanced antioxidant enzyme system activity in tea leaves.Se and MT treatments promoted the synthesis of soluble proteins in the leaves,increased chlorophyll content,and reduced malondialdehyde（MDA）accumulation at a later stage.Se and MT treatments increased the expression of disease-resistance-related genes such as ALD1,NPR1,TGA3,TGA2 and PR1 on the salicylic acid signaling pathway in leaves,which suggested that exogenous Se and MT enhanced tea tree resistance to tea anthracnose by consistently increasing the activity of defense enzymes and expression of disease resistance genes in the leaves.3.Treatment with 25 mg/L Se and 150μmol/L MT increased the content of tea polyphenols,free amino acids and caffeine in tea tree leaves.Se and MT treatment groups increased the leaf Se contents and their contents were 1.36,2.57and 1.71 times higher than that of the control group,respectively.Among them,the most significant difference in selenium content was observed when Se was treated alone.4.Se and MT treatments slowed down the degradation damage of chlorophyll in isolated leaves of tea tress.Treatment with 25 mg/L Se and 50μmol/L MT slowed down the accumulation of MDA content,reduced chlorophyll content,SOD activity,soluble protein content and H₂O₂ content during senescence in isolated leaves,and also reduced the rate of O₂^-production,the indicates that selenium and melatonin can reduce the degree of lipid peroxidation in isolated tea leaves and reduce the degree of damage to chloroplast ultrastructure,thus delaying the aging of tea leaves.