Hypobaric treatment stimulates defence-related enzymes in strawberry

Abstract

Strawberry fruit are very prone to fungal decay. Postharvest hypobaric treatment is a potential new technique to delay fungal decay in strawberries. Hypobaric treated (50kPa, 4h) strawberries had reduced rot incidence from natural infection during subsequent storage for 4 days at 20°C and after subsequent inoculation with Botrytis cinerea or Rhizopus stolonifer spores. Biochemical analysis of strawberries suggested that activities of defence-related enzymes were increased with the hypobaric treatment; phenylalanine ammonia-lyase (PAL, EC: 4.3.1.24) and chitinase (EC: 3.2.1.14) peaked 12h after treatment, while peroxidase (POD, EC: 1.11.1.7) increased immediately. Polyphenol oxidase (PPO, EC: 1.10.3.1) activity remained unaffected during subsequent storage for 48h at 20°C. In addition, the effect of low oxygen treatment (10% at 101kPa, 4h) was investigated to determine if the lower partial pressure of oxygen generated during hypobaric treatment contributed to the observed effect. However the low oxygen treatment did not influence rot development, suggesting that the treatment effects were pressure rather than oxygen related. The results suggest that hypobaric treatment causes reduced decay incidence due to stimulation of defence-related enzymes. Studies of defence-related genes are required to further explore the induced resistance mechanisms of hypobaric treatments.