Effects Of Penicillium Expansum And Trichothecium Roseum Infections On Ripening And Volatile Compounds Of Apple Fruits And Its Partial Mechanisms

Penicillium expansum and Trichothecium roseum are two important postharvest pathogens,which can cause blue mold and pink rot of temperate fruits.Both fungi not only cause severe decay of fruit,but also produce mycotoxin causing serious harm to human and animal health.In this study,‘Delicious',‘Ralls' and ‘Fuji' apple fruits were used as materials.Fruits were inoculated with P.expansum and T.roseum.The effects of inoculations were invesgated on respiration rate,ethylene production and membrane integrity of fruit.The changes of firmness and contents of total soluble solid(TSS)and titritable acid(TA)were evaluated.And the analysis of volatile compounds(VOCs)of infected fruit was focused on and its partical mechanisms were explored.The results showed as follow:1.'Delicious' fruits showed the biggest lesion diameter after inoculation,followed by the inoculated ‘Ralls' and ‘Fuji' fruits.Pathogen inoculation improved ethylene production and respiration rate of fruit,the maxmum change were found in the inouclated ‘Delicious',while the minimum one was the inoculated ‘Fuji'.Inoculation increased permeability of cell membrane,while the inoculated ‘Fuji' fruit showed thelowest.Moreover,inoculation significantly decreased firmness and contents of TSS and TA of fruits.Compared with the other two inoculated apple cultivars,the inoculated ‘Fuji' showed the highest firmness and contents of TSS and TA.2.P.expansum inoculation significantly changed release of VOCs of three apple cultivars.The contents and types of alcohols,aldehydes and esters of ‘Delicious' and ‘Fuji' weresignificantly increased by P.expansum inoculation,but had no significant effect on ‘Ralls'.According to VIP value of PLS-DA,the compounds with the highest VIP value of three apple cultivars were hexanoic acid,2-methylbutanoic acid and hexanal,respectively.Moreover,inoculation induced different cultivars releasing special VOCs.Ethyl benzeneacetate was only detectedin the inoculated fruits of three cultivars;Phenethyl acetate,methyl 2-methylbutanoate and 1-methoxy-3-methylbenzene were only detected in the inoculated ‘Delicious' and ‘Fuji' fruits;methyl 3-hydroxydodecanoate was only detected in the inoculated ‘Delicious' and ‘Ralls' fruits.3.P.expansumcaused higher lesion diameter of fruit than the T.roseum.Both fungi inoculations significantly increased ethylene production and respiration rate of frui,while P.expansum imporoved higher ethylene production and respiration rate of fruit than T.roseum.In addition,the two fungi significantly increased permeability of cell membrane and decreased firmness,contents of TSS and TA.Compared with the T.roseum inoculation,P.expansum inoculation improved higher permeability of cell membrane and lowed firmness,contents of TSS and TA.According to PLS-DA,different pathogen inculations induced different VOCs and special VOCs release of apple fruit.Moreover,1-octen-3-ol,which detedcted in the decay tissue of fruits,was the source of musty odor of fruit infected by both fungi.4.P.expansum and T.roseum inoculations significantly increased contents of straight-chain VOCs of ‘Delicious' fruit improved contents of straight-chain alcohols and aldehydes of fruit at early storage period(2d and 4d),and contents of straight-chain esters at later storage period(6d and 8d).Moreover,both fungi inoculations significantly increased contents of oleic acid,palmitic acid and stearic acid of fruis,and DBI values and enhanced activities of lipoxygenase,hydroperoxide lyase,alcohol dehydrogenase and alcohol acyltransferaseof fruit.Compared with the T.roseum,P.expansum inoculation improves a higher content of straight-chain VOCs and fatty acids,and a higher activity of LOX-related enzymes.5.P.expansum and T.roseum inoculations significantly increased release of branched-chain VOCs of ‘Delicious' fruit.Inoculations significantly enhanced contents of total amino acids,valine,leucine and isoleucine and activities of pyruvate decarboxylase and pyruvate dehydrogenase.P.expansum inoculation improves a higher content of branched-chain VOCs and aroma-related amino acids,and a higher activity of pyruvate decarboxylase and pyruvate dehydrogenase.To sum up,the different of lesion diameters of apple fruits infected by P.expansum and T.roseum were close related to the resistance of fruit cultivars and pathogenicity of fungi.Fungi inoculations promoted fruit ripening by increasing ethylene production and respiration rate,destroying permeability of cell membrane,and decreased firmness and contents of TSS and TA.In addition,both fungi infections changed the release of VOCs and induced production of special VOCs,which are closely related with fruit cultivars,pathogen species and infection stages.The releases of straight-chain VOCs are regulated by LOX pathway,while branched-chain VOCs are related with amino acid metabolism.