Effects Of Exogenous Methyl Jasmonate(MeJA) Induced Resistance To Blue Mold And Storage Preservation In Postharvest Pear Fruit

MeJA is used for the storage of postharvest fruit and disease resistance as natural elicitor.In this study,‘Cuiguan’pear fruit was fumigated with exogenous MeJA,the lesion diameter and induction effect of pear fruit blue mold were determined after inoculation with spore suspension(1.0 x 10~6 spores/m L)of Penicilliu expansum.Main pathogens of pear fruits during storage were isolated and identified.The mechanism of MeJA-induced resistance to blue mold of pear fruits was studied and the effect of MeJA on pear fruit during storage was analyzed.The results were shown as follow:1.Pathogens from postharvest’Cuiguan’pear(Pyrus pyrifolia cv.‘Cuiguan’)fruits were isolated and identified.Six pathogens were identified as Penicillium expansum,Botryosphaeria dothidea,Fusarium proliferatum,Alternaria gaisen,Trichothecium roseum,Monilinia fructicola based on the method of morphology,pathogenicity and molecular biology.2.Effects of MeJA on induced resistance of pear to blue mold rot:10-100μmol/L MeJA treatment had no direct inhibitory effect on P.expansum,both injection and fumigation could induce resistance of pear to blue mold,and the induction effects reached 12.38%and 15.60%,respectively.In the concentration range of 10-100μmol/L,MeJA improved the resistance of fruits to blue mold,the induction effect of MeJA on the resistance of pear fruit to blue mold was increased first and then decreased.And the best induction effect was 100μmol/L,which reached 14.59%.The induction effect was different with MeJA treatment and different inoculation order.MeJA fumigation treatment of pear fruit for 36 h before inoculation had the best induction effect reaching 16.14%,MeJA treatment and inoculation are performed simultaneously for 36 h,and the induction effect was 14.21%,the induction effect of the treatment of inoculated first and then treated with MeJA was only 4.19%.3.Physiological mechanism of MeJA-induced pear fruit resistance to blue mold rot:’Cuiguan’pear fruit was pretreated with 100μmol/L MeJA for 36 h,then inoculated with P.expansum,and then the changes of defensive enzymes in pear fruits were determined.Compared with control group and SHAM(Salicyhydroxamic acid,SHAM)treatment group,the activity of SOD(Superoxide Dismutase),CAT(Catalase),POD(Peroxidase),PPO(Polyphenol oxidase),GLU(β-1,3 glucanase)and CHI(Chitinase)of pear fruit treated with MeJA were significantly enhanced.At the same time,MeJA reduced the accumulation of malondialdehyde(MDA)content,but the total phenolic content was significantly promoted.4.Molecular mechanism of MeJA-induced pear fruit resistance to blue mold rot:RT-PCR was used to quantitatively analyze the gene expression of defense-related enzymes in pear fruits.The results showed that the expression levels of Pp CAT,Cu-Zn SOD,Pp POD and Pp PPO in pear fruit treated with MeJA was significantly higher than CK and SHAM group.The expression levels of Pp CHI and Pp GLU showed a trend of increasing first and then decreased with time increasing.The expression levels of MeJA treatment group were significantly higher than those of the control group 96 h later after inoculation,which were3.45 and 1.97 times that of the control group,respectively.5.The pear fruit was treated with MeJA by fumigation,and then the fruit quality changes during storage of 18 d and 42 d at(25±1)°C and(3±1)°C were measured.100μmol/L MeJA treatment increased the accumulation of total phenol content in pear fruits during room temperature storage,and it was significantly higher than the control group except 15 d,and the highest was 1.43 times of the control group,while the MDA content was 44.96%of the control group.It has no significant effect on decay rate,weight loss rate,Vc,total sugar content,TA content and hardness between MeJA treatment and control group.However,the MeJA treatment of 1000μmol/L improved the respiratory intensity of the fruit and reduced the hardness of the fruit.During cold storage,100μmol/L MeJA treatment significantly reduced the decay rate of fruit and improved the content of TSS and total sugar content,inhibited the increase of respiratory intensity,delayed the degradation of TA TSS and Vc and promoted the accumulation of total phenol content in pear fruits.In addition,MeJA treatment had no significant effect on fruit weight loss and hardness during cold storage.