Regulation Of Phenolic Compounds Based On Concentration Level In Pear Fruit Peel On Growth And Pathogenicity Of Alternaria Alternata

Alternaria alternata,as the causal agent of black spot of postharvest pear fruit,can infect during fruit development and cause disease during storage.Previous studies showed that the latent infection rate of A.alternata was correlated with the content of phenols in pear peel.In order to further elucidate the regulation of pear peel phenols on A.alternata infection the effects of exogenous phenols(phenolic acids,flavonoids and simple phenols)based on pear peel content on the growth(colony diameter,biomass and cell membrane integrity)and pathogenicity(infection process,melanin and toxin production,black spot development)of A.alternata were studied using in vitro and in vivo.The results show that:1.The inhibitory effects of various phenols based on pear peel content on the growth of A.alternata varied.Phenolic acids including chlorogenic acid,caffeic acid,ferulic acid and p-coumaric acid significantly inhibited the mycelial growth and biomass accumulation of A.alternata and the control effects were a concentration-dependent manner.The inhibitory effect of catechin and epicatechin on the growth of A.alternata was lower,but arbutin had no effect on the growth of A.alternata.Correlation analysis showed that the growth of A.alternata was negatively correlated with phenolic acids and catechin content(P<0.01),but was not abviously correlation with epicatechin and arbutin.2.Seven phenols based on pear peel content damaged to the cell membrane of A.alternata at some extent.Among them,chlorogenic acid,caffeic acid,ferulic acid and p-coumaric acid significantly damaged the cell membrane of A.alternata,and the degree of damage increased with the increase of treatment concentration.The conductivity of A.alternata membrane was significantly increased by exogenous phenolic acids treatment and further promoted the leakage of intracellular nucleic acid,protein and soluble sugar.The two flavonoids also destroyed A.alternata cell membrane and increased its permeability,but the effect was lower than that of phenolic acids.However arbutin treatment had no significant effect on A.alternata cell membrane.3.Exogenous phenolic treatment delayed the formation of infection structure of A.alternata.Among them phenolic acids significantly delayed the spore germination and appressorium formation of A.alternata on hydrophobic surface,and no appressorium formation of A.alternata was observed on surface mounted with higher concentration phenolic acid.Catechin and epicatechin treatment also significantly delayed the formation of pathogen appressorium,but arbutin treatment had no significant effect.At the same time,phenolic treatment inhibited the elongation of A.alternata germination at some extent.Correlation analysis showed that the rate of appressorium formation was negatively correlated with phenolic acids and flavonoids(P<0.01),but was not correlated with arbutin.4.The 2 mg/m L exogenous phenols significantly decreased four non-host-specific toxin of A.alternata including alternariol(AOH),alternaria monomethyl ether(AME),altenuene(ALT)and tentoxin(Ten)production.At the same time,phenols treatment significantly promoted the melanin production of by A.alternata,and their stimulous effect varied with the type and concentration of phenols.Flavonoids had the strongest stimulating effect,followed by arbutin and phenolic acids.Correlation analysis showed that phenols were negatively correlated AOH,AME,ALT and Ten toxins synthesis by A.alternata(P<0.01),and positively correlated with A.alternata melanin production(P<0.01).Exogenous phenolic acids significantly inhibited the development of black spot in pear fruit wounding inoculated by A.alternata,among which ferulic acid and coumaric acid had the most obvious control effect.In conclusion,phenols in pear peel may regulate the pathogenicity of A.alternata through delaying the growth,infection structure formation and the pathogenic factors production.Among them,phenolic acids had the most obvious effect on the growth and pathogenicity of A.alternata.