Inhibitory Mechanism Of Ethyl Pyruvate On Postharvest Diseases Of Sweet Cherry

Sweet cherry?Prunus avium L.?are within the Rosaceae family and belong to the genus Prunus and subspecies Cerasus.The fruit contains rich bioactive components and extremely high levels of nutrients.It ranks among the fastest growing cultivated and consumed fruits in China.However,fresh sweet cherry fruits are highly susceptible to fungal spoilage,and the decay of sweet cherry fruit caused by fungal pathogens results in immeasurable economic losses all over the world.At present,there are lack of researches on sweet cherry fungal diseases at home and abroad,and the prevention and treatment strategies for diseases are still unclear.This research will study the kinds of postharvest pathogenic fungi and control methods of postharvest pathogenic fungi of sweet cherry fruits in Shanxi Province,and provide scientific basis and theoretical basis for preservation of sweet cherry during postharvest storage.The research mainly included three aspects.Firstly,sweet cherry fruit showing typical disease symptoms were collected during postharvest cold storage.Fungal pathogens isolate and purification were obtained by tissue isolation method and the pathogenicities of the pathogens were proved by in vivo.Fungal pathogens were identified by molecular method as well as morphological method to determine the biological classification.Secondly,the minimum inhibitory concentration and the minimum fungicidal concentration of ethyl pyruvate on fungal pathogens were determinated by the inhibition zone method.Then by using inhibition of mycelium growth method,variations of mycelium growth of pathogens were determinated under the different concentrations of ethyl pyruvate.Finally,the mechanisms of action of ethyl pyruvate against fungal pathogens were studied by measuring spore germination,mycelial growth,the integrities of the cell wall and plasma membrane,malondialdehyde?MDA?and intracellular reactive oxygen species?ROS?.The experimental results are as follows:1.The two strains fungal pathogens isolate from rotten sweet cherry fruit were identified: Penicillium oxalicum and Botrytis sp.,and the two strains fungal pathogens were inoculated to healthy cherry fruits for pathogenicity test.The results showed that Penicillium oxalicum and Botrytis sp.were the pathogens causing postharvest decay of sweet cherry in Shanxi Province.2.Ethyl pyruvate inhibited the mycelial growth of Penicillium oxalicum and Botrytis sp.,and reduced the germination rate of spores.The minimum inhibitory concentration of ethyl pyruvate on Penicillium oxalicum was 25 mg?L^-1,the minimum fungicidal concentration was 50 mg?L^-1;the minimum inhibitory concentration of ethyl pyruvate on Botrytis sp.was 25 mg?L^-1,and the minimum fungicidal concentration was 50 mg?L^-1.3.Ethyl pyruvate significantly reduced the disease incidence of blue mold and grey mold of sweet cherry fruit caused by Penicillium oxalicum and Botrytis sp.during postharvest storage.The experimental results showed that later,3,4,5 and 6 d after inoculation,in fruit inoculated with sterile water pretreated Penicillium oxalicum and Botrytis sp.for 6 h,the disease incidence were 80%,90%,100% and 100%;73%,77%,90% and 97% respectively.While the fruits inoculated with ethyl pyruvate pretreated Penicillium oxalicum and Botrytis sp.for 6 h still were not decayed.4.The effects of ethyl pyruvate on the spore germination and mycelial growth of Penicillium oxalicum and Botrytis sp.were investigated under different environmental conditions.The spores of Penicillium oxalicum and Botrytis sp.nearly did not germinate,regardless of the treatment used,at p H 2,and the spores of Penicillium oxalicum and Botrytis sp.were normally grown at p H above 3.5.Thus,p H should be considered as one of important parameters in the study of ethyl pyruvate as an antimicrobial agent for controlling postharvest disease of cherry fruit.5.The mechanisms of action of ethyl pyruvate against Penicillium oxalicum and Botrytis sp.were studied.The experimental results showed that the cell wall and cell membrane of the spores of Penicillium oxalicum and Botrytis sp.treated with 25 mg?L^-1 ethyl pyruvate were much more incomplete than controls.The results of transmission electron microscopy showed that the cellcytoplasm of Penicillium oxalicum and Botrytis sp.spores treated with sterile distilled water exhibited an organized,presenting complete organelles eg.,mitochondria and a central vacuole etc.In contrast,the cellcytoplasm of spores exhibited disorganized and the leakage of intracellular compounds treated with ethyl pyruvate,finally the cells became vacuolated.In the study,the ROS content in the spores of Penicillium oxalicum and Botrytis sp.treated with 25 mg?L^-1 ethyl pyruvate were significantly higher than that in the controls.Furthermore,the MDA content detected in ethyl pyruvate-treated Penicillium oxalicum and Botrytis sp.spores was higher than that in the controls.