Effects of Postharvest Oxalic Acid Treatments on Black Spot Disease and Phenylpropane Metabolism in Apricot Fruit
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Abstract:
The inhibitory effects of oxalic acid on postharvest black spot disease in apricot fruit were investigated by subjecting “Saimaiti” apricot fruit to pressure retarded osmosis using three different concentrations of oxalic acid (2, 4, and 6 mmol/L). Subsequently, the dried fruit were stored for 48 h at a temperature of (1±1.0) ℃ and a humidity of 90%~95%. Next, damaged fruit were inoculated with Alternaria alternata, and were stored under the same conditions described above. Indices related to phenylpropane metabolism, including spore germination rate and colony diameter, were regularly measured. The inoculation test results demonstrated that, on the 49th day, the incidence rate and lesion diameter of the 4 mmol/L oxalic acid-treated inoculated fruit were 16.94% and 19.44% lower, respectively, than those of the control group. Meanwhile, the activities of phenylalanine ammonia-lyase, 4-coumaric acid coenzyme-A-ligase, and cinnamate-4-hydroxylase in the 4 mmol/L oxalic acid-treated inoculated fruit were 1.06, 1.04, and 1.07 times, respectively, those of the control group. These results indicate that oxalic acid can effectively enhance the accumulation of total phenols, flavonoids, and lignin. Briefly, the in vitro experiments demonstrate that 4 mmol/L oxalic acid has considerable inhibitory effects on spore germination and mycelial growth of A. alternata. Thus, the application of oxalic acid treatments can enhance the resistance of apricot fruit to black spot diseases through the phenylpropane metabolic pathway.