Effect of trisodium phosphate treatment on black spot of apple fruit and the roles of anti-oxidative enzymes

Abstract Black spot caused by Alternaria alternata is an important postharvest disease of apple fruit. In this study, apple fruit (cv. Golden delicious) was used as the materials to study the effects of 0.25, 0.5, 1.0, 2.0 mg/mL trisodium phosphate (TSP) dipping treatment on lesion development of fruit inoculated with A. alternata . In vitro test was conducted to investigate the effect of TSP on mycelia growth of A. alternata . The optimal concentration of TSP was screened to assay its effect on the activity of anti-oxidative enzymes, the content of H 2 O 2 and phenylpropane metabolites in apple fruit. The results showed that the different concentrations of TSP significantly inhibited mycelia growth of A. alternata and indicated dose dependent. TSP treatment also inhibited lesion development of apple fruit inoculated with A. alternata . According these results, 0.5 mg/mL TSP was chose for the following study. The results also indicated that TSP treatment enhanced the activity of phenylalanine ammonialyase, peroxidase, catalase, ascorbate peroxidase, superoxide dismutase, glutathione reductase, increased H 2 O 2 accumulation and total phenolic compounds, flavonoids and lignin contents in apple fruit. All these results suggest that enhanced disease resistance in apple fruits by TSP against A. alternata is associated with increasing anti-oxidative enzymes activities and accumulation of phenylpropane metabolites.