Synergistic effects of harpin and NaCl in determining soybean sprout quality under non-sterile conditions

Salinity induces antioxidant accumulation but always enhances disease susceptibility in plants. However, the effects of NaCl in regulating disease infection in soybean sprouts have not been well studied under conditions that are not strictly aseptic. Here, the effects of harpin and NaCl in controlling disease development and antioxidant accumulation were investigated in soybean sprouts under non-sterile conditions. After storage for 0 and 7 days, NaCl-enhanced disease severity was drastically suppressed by application of either harpin or salicylic acid (SA), relative to controls. Moreover, the decrease in SA content due to salinity was partially restored by harpin. Interestingly, the combined treatment with both NaCl and harpin drastically enhanced the accumulation of antioxidants (e.g., ascorbic acid and phenolics) and the total antioxidant ability (evaluated by Fe3+ reducing power) in soybean sprouts, compared with individual NaCl and harpin treatments. Compared with individual treatments, the synergistic effects of NaCl and harpin in eliciting phenylalanine ammonia-lyase and polyphenol oxidase activities were also examined in postharvest soybean sprouts. The results suggest that harpin drastically improved the quality of salt-treated soybean sprouts by reducing disease severity and elevating antioxidant accumulation during storage under non-sterile conditions.