Effects Of SA, ASM, INA And Citric Acid On Postharvest Disease Resistance And Quality Of Yali Pear Fruit

In this study, control of postharvest diseases of Yali pear (Pyrus bretschneideri Rehd.) fruit by various treatments with salicylic acid (SA) and acibenzolar-S-methyl (ASM) sprays during fruit growth and development, or with postharvest infiltration or dipping of SA, ASM, 2,6-dichloroisonicotinic acid (INA) and citric acid were investigated, and effects of these treatments on storage characteristics, quality and physiological metabolisms of pears were also evaluated during storage at 20℃, 85-95% RH. Mechanisms of these treatments involved in enhancement of fruit resistance against postharvest diseases and improvement of fruit quality were further studied. Results from our studies will provide theoretical and practical information on how to effectively reduce postharvest decay and improve storage quality of Yali pear fruit, and provide alternatives to traditional applications of chemical fungicides on horticultural crops.Sprays with 2.5 mM SA or 75 mg/L ASM during fruit growth could effectively reduce natural decay or inoculated disease incidence and significantly (P<0.05) inhibit disease development of blue mould in fruit inoculated Penicillium expansum after harvest. Additional, postharvest Alternaria rot, caused by Alternaria alternata, was inhibited in pears by ASM sprays. Fruit decay, inoculated diseases of blue mould and Alternaria rot were effectively inhibited by postharvest treatments with 5 mM SA, 0.5 mM ASM and INA, respectively. And, postharvest ASM and INA treatments also inhibited ring rot in fruit caused by Physalospora piricola Nose. Treatments of SA and ASM sprays during fruit development, or postharvest ASM and INA infiltration effectively delayed appearance of brown heart and occurrence of dry and black stem of the fruit. However, combination of SA or ASM sprays with bagging during fruit development have further improved fruit quality of pears in storage. Postharvest dipping with 2% citric acid also significantly inhibited natural decay and inoculated blue mould in fruit, reduced the degree of superficial brown and delayed senescence of Yali pear fruit during storage.Results from biochemical determinations showed that an enhanced resistance system was established in Yali pear fruit sprayed with SA or ASM during growth and development. Activities of defense enzymes including peroxidase (POD), phenylalanine ammonia-lyase (PAL), chitinase (GHT) and β-1,3-glucanase (GLU) significantly increased, and activities of antioxidant enzymes such as catalase (CAT) and ascorbic peroxidase (APX) decreased but glutathion reductase (GR) activity increased, and H2O2 accumulated in young Yali pears sprayed with SA or ASM. Furthermore, activities of PAL, CHT and GLU in mature pears from trees sprayed with SA or ASM were still higher than those of control after harvest. Activity of CAT decreased, wherase that of superoxide dismutase (SOD) increased in SA- or ASM-sprayed pears during storage.Postharvest SA treatment stimulated activities of POD, CHT and GLU in pear fruit during storage. Activities of PAL and CHT increased, and total phenolic compounds and flavonoids accumulated in the fruit treated with ASM or INA after harvest. CAT Activity decreased but SODactivity increased in fruit with SA dipping or INA infiltration after harvest. However, activites of both enzymes increased in fruit with ASM infiltration. H2O2 content increased in the early stage of storage but decreased subsequently in fruit with postharvest SA, ASM or INA treatment. Production of malondialdehyde (MDA) was markedly reduced and lipid peroxidation was inhibited in fruit by ASM or INA infiltration. Postharvest 2% citric acid treatment enhanced activities of POD, PAL, CAT and SOD, whereas inhibited activity of polyphenoloxidase (PPO), and reduced contents of superoxide radical (O2-). H2O2 and MDA in pears during storage.During the infection, activities of POD, PAL and CHT further increased, and H2O2, MDA, total phenolic compounds and flavonoids further accumulated in ASM- or INA-treated fruit after challenge-inoculation with P. expansum. CAT activity...