Regulation Of Phenolic Compounds Based On Concentration Level In Fruit Peel Of Pingguoli Pear On Pre-penetration Process And Extracellular Degrading Enzymes Of Alternaria Alternata

Effects of chlorogenic acid,caffeic acid and catechin based on the level of exocarp of“Pingguoli” pear on growth(spore germination,length of germ tube,mycelial growth),infection structure differentiation(appressorium,infection hyphae)and activities of extracellular degrading enzymes of A.alternata,the causal agent of pear black rot,were studied through in vivo and in vitro test.The results showed as follows:1.The spore germination rate,the length of germ tube and mycelial growth of A.alternata were inhibited at different degrees with exogenous chlorogenic acid(1000~4000 ?g/g),caffeic acid(100~400 ?g/g)and catechin(500~2000 ?g/g)based on concentration level in fruit peel,and the effect was in concentration-dependent manner.Among them,4000 ?g/g chlorogenic acid,400 ?g/g caffeic acid and 2000 ?g/g catechin treatment showed the best effect,and the effect of catechin was relatively better than chlorogenic acid and caffeic acid.Black spot development was delayed after treatment with three kinds of phenolics in vivo test.2.The process of infection at the epidermal of pear and infect structure formation of A.alternata was significantly inhibited or delayed with exogenous chlorogenic acid,caffeic acid and catechin treatment,and the effect was in concentration-dependent manner,4000 ?g/g chlorogenic acid,400 ?g/g caffeic acid and 2000 ?g/g catechin completely inhibited appressorium and infection hypae formation of A.alternata,the effect of caffeic acid was relatively better than chlorogenic acid and catechin.In vitro the onion epidermal infection test further confirmed that the three phenolics could significantly inhibit the formation of appressorium and infection hypae of A.alternata,and the rate of the infect structure formation was obviously lower than that of the in vivo test.3.The three exogenous phenolics based on concentration level in fruit peel have different effects on the activity of extracellular degrading enzymes of A.alternata and the effect varied with in vitro and in vivo conditions,enzymes and phenolic species.In vitro,three phenolics treatments increased the activity of cutinase of A.alternata,whereas in vivo the cutinase activity was inhibited.The activity of PG of A.alternata was significantly inhibited with three exogenous phenolics in vitro and in vivo test,the PG activity was decreased by 72.3%?98.1% and 68.4%,respectively,compared with the control 4 days after treatment with 4000 ?g/g chlorogenic acid,400 ?g/g caffeic acid and 2000 ?g/g catechin in vitro test.Whether in vitro or in vivo,the three exogenous phenolics based on concentration level in fruit peel significantly inhibited the activity of PMG,PGTE,PMTE,Cx and ?-glucosidase of A.alternata.In summary,exogenous chlorogenic acid,caffeic acid and catechin based on concentration level in fruit peel could affect A.alternata infection by inhibiting or regulating infect structure differentiation and the activity of extracellular degrading enzymes.