Effects Of Methyl Jasmonate(MeJA) Induced Resistance To Soft Rot And Storage Preservation In Postharvest Kiwifruit

As a natural important disease resistance signal,methyl jasmonate(MeJA)is widely used in the diseases prevention and storage of postharvest fruit.In this study,’Jinkui’ kiwifruit was used as the test material and treated with methyl jasmonate(MeJA)fumigation,the disease index and induction effect of kiwifruit soft rot were determined after inoculation with Botryosphaeria dothidea,then the physiological and molecular mechanism of MeJA-induced resistance to soft rot of kiwifruit were analyzed,at the same time,the effect of MeJA on the storage of kiwifruit was explored.The main results are as follows:1.MeJA could significantly induce kiwifruit fruit resistance to postharvest soft rot,the inhibitory effect of MeJA on kiwifruit soft rot B.dothidea increased with concentration at the range of 0.001-10 mmol/L,but the optimal concentration was 0.10 mmol/L,and the induction effect was 26.01%.When the kiwifruit was fumigated with MeJA at 12-72 h before inoculation,the best induction effect was 26.85 % at 24 h.The effect of MeJA treatment and inoculation on the soft rot of kiwifruit was obvious.The induction effect of MeJA pretreatment for 24 h and then inoculation with soft rot was 22.00%,which was significantly higher than that of the first inoculation and then fumigation for 24 h,and the induction effect was 8.41%.Different concentrations of MeJA could increase the defense enzyme activities including peroxidase(POD),superoxide dismutase(SOD),catalase(CAT),polyphenol oxidase(PPO)and ascorbate peroxidase(APX)in kiwifruit inoculated with B.dothidea,thereby reduce the occurrence of soft rot,of which 0.1 mmol / L MeJA performed better.2.’Jinkui’ kiwifruit was pretreated with 0.1 mmol/L MeJA for 24 h,then inoculated with B.dothidea,and the diameter,induction effect of kiwifruit lesionsand dynamic changes of defensive enzymes in kiwifruit were determined.The results showed that after inoculation of B.dothidea,the diameter of MeJA lesions was significantly lower than that of the control and SHAM treatment groups,and the induction effect reached the highest 16.55% at 5 days after inoculation.At the same time,MeJA treatment significantly enhanced the activity of CAT,POD,SOD and PPO and the pathogenesis-related proteins chitinase(CHI)and β-1,3 glucanase(GLU),and promoted the accumulation of total phenolic content,but the accumulation of malondialdehyde(MDA)was significantly reduced.The MDA content of the control and SHAM groups was 1.43 and 1.88 times of that of the MeJA group respectively,which reduced the degree of membrane lipid peroxidation.These results suggest that MeJA-induced resistance to post-harvest soft rot of kiwifruit fruit may be related to its increased defense enzyme activity.3.The RT-PCR analysis of kiwifruit defense enzyme gene showed that the gene expression of AcPOD,AcSOD and AcAPX in MeJA treatment group were significantly higher than that of control and SHAM,but had no significant effect on AcCAT gene.The expression of AcCHI gene was up-regulated with the inoculation time,and the expression level in MeJA treatment fruits was significantly higher than that of the control and SHAM.At 7 days after inoculation,the AcCHI gene expression of MeJA treatment fruits was 1.69 and 1.60 times of that of the control and SHAM treatment groups respectively.AcGLU was expressed in both control and SHAM-treated fruits,but the expression level was significantly lower than that of MeJA treatment group,MeJA treatment promoted the expression levels of the AcCHI and AcGLU genes.This result further confirmed that the resistance of MeJA to B.dothidea was related to the initiation of the defense response in kiwifruit.4.The postharvest ’Jinkui’ kiwifruit was fumigated with MeJA,and the changes of fruit quality and antioxidant enzyme activities during storage at(0±1)°C and at room temperature(25±1)°C were measured.The results showed that compared with the control,MeJA fumigation treatment could significantly reduce the weight loss rate and rot rate of fruits in both storage conditions,among them,the rot rate and weight loss rate of kiwifruit treated by MeJA were decreased 26.09 % and 20.79% under room temperature storage,and the difference was significant.At the same time,MeJA treatment kept TSS at a high level,delayed the degradation rate of TA,inhibited the increase of respiratory intensity,promoted the accumulation of total phenolic content,reduced MDA content,effectively improved kiwifruit CAT,POD and SOD activities,in which the maximum CAT,POD and SOD activities were significantly higher than the control at 34.73%,30.09% and 2.70% respectively.In addition,MeJA had no significant effect on Vc,total sugar content and firmness in kiwifruit stored at both temperature.