Effect Of Glycerol On Postharvest Brown Rot Of Peach Fruit

Peach fruit is popular due to its delicious taste and high nutritional value.However,peaches are susceptible to fungal infections during postharvest storage as they have soft tissues and thin peels.So brown rot,gray mold,and soft rot caused by fungi usually lead to huge losses,of which brown rot is the most severe disease after peaches harvest.At present,the control of postharvest fungal diseases of peach fruit largely depend on the use of chemical fungicides,but the excessive use of chemical fungicides has caused environmental pollution,harm to human health and the drug-resistance of pathogens.Therefore,it is necessary to explore safe,broad-spectrum,high-efficiency and simple methods for reducing postharvest disease of peach fruit.Glycerol,as a biodegradable sugar alcohol,is non-toxic,harmless,environmentally friendly and edible.It has high solubility in water,strong hygroscopicity and high safety.In recent years,studies have shown that glycerol is involved in the process of plant growth and disease resistance.In this study,the spraying method of glycerol to peach fruit was used,and theits fungal inhibition against Monilinia fracticula in vitro and inducing disease resistance of peach fruit in vivo were investigated,to explore the inhibitory mechanisms of glycerin on brown rot of peach fruit.The main findings are as follows:(1)Zhonghua Shou Tao was used as the test material.The different concentrations of glycerol and inoculation time after glycerol treatment were screened through the artificial inoculation test.It was found that 5%(v/v)concentration of glycerol had the best control effect on brown rot development.The disease onset of the fruit stored at 22 ? was delayed for 12 h.Even though at 96 h,the disease incidence rate was markedly lower than the control.Therfore,5%(v/v)concentration of glycerol was determined as the optimal concentration for use.The optimal inoculation time after treatment was 24 h.Therefore,it is recommended to use 5% to spray peach fruit in practice which can achieve good disease prevention effect.In addition,the results also indicate glycerol might induce disease resistance in peach fruit.(2)The fungal inhibition of glycerol against M.fracticula was investigated.The hyphae and spores of the fungus were treated with 1%?2%?3%?4%?5% and 6% glycerol,and then the diameter of the plaque and the germination rate of spores were measured.It was found that the each concentration of glycerol did not reduce the diameter of the plaque and the germination rate of the spores of the pathogen,indicating that glycerol did not directly inhibit or kill the M.fracticula.(3)Treatment with 5% glycerol can significantly increase the antioxidant-related enzymes activities of phenylalanine ammonia lyase(PAL),peroxidase(POD),superoxide dismutase(SOD)in peach fruit.But catalase(CAT)activity had not significantly difference compared to the control.Moreover,5% glycerol treatment reduced reactive oxygen species content of superoxide anion and hydrogen peroxide and improved antioxidant capacity of peach fruit.In addition,glycerol treatment reduced the level of Manual Data Automatic,consumption of soluble solids and acidity,slowed the decline of fruit firmness,delayed the softening of peach fruit,and reduced membrane lipid peroxidation.(4)The changes of chitinase(CHI)and ?-1,3-glucanase(GNS)activities were determined,as well as the relative genes expression of CHI,GNS,pathogenesis-related gene1(PR1),and pathogenesis related gene 1 non-expressor(NPR1).It was showed that 5%glycerol treatment could enhance the activities of CHI and GNS and genes expression of CHI,GNS,PR1 and NPR1.In addition,5% glycerol treatment also induced the increase of salicylic acid(SA).These results indicate that 5% glycerol treatment could enhance disease resistance by systemic acquired resistance(SAR)of peach fruit.(5)After treatment with 5% glycerol,the relative genes expression levels of two key enzymes related to Glycerol-3-phosphate(G3P)synthesis,glycerol kinase(GLI1)and glycerol triphosphatedehydrogenase(GPDH),were significantly increased,and the level of oleic acid decreased.In the initial stage after inoculation,the content of palmitic acid,stearic acid,linolenic acid and linoleic acid increased.5% concentration of glycerol could regulate the expression level of key enzyme genes of G3 P synthesis.G3 P is transformed into peach fruit and enter the plastids of peach fruit and then react with 18:1 to generate phospholipids,which can reduce the content of oleic acid(C18:1),thereby further triggering defense signals and enhancing disease resistance.