Effect of pre-storage UV-B treatment on disease resistance and health-beneficial properties of stored carrots

UV-B radiation (280-320 nm) is known to elicit multiple protective responses in plants, including antioxidant defense system and synthesis of phenolic compounds. The objective of this work was to investigate the potential of pre-storage treatment with UV-B light to enhance disease resistance and health-beneficial phyto-compounds in carrots. Fresh carrots (LSQUOSun255RSQUO) were treated with UV-B (0.0-14.0 kJ m^‑2) and stored at 4°C. The disease resistance of treated carrots was determined by challenge-inoculation with Botrytis cinerea. The titers of phyto-compounds of significance in disease resistance; the GC-MS secondary metabolite profiles; and the physiological and quality characteristics of treated carrots were monitored at regular intervals during six weeks of storage. The UV-B dose-disease resistance response relationship was bi-phasic, and the hormetic dose of UV-B for the induction of disease resistance was 7.0 kJ m^‑2, where the disease inhibition was about 70%. The disease resistance strongly related to the accumulation of phytoalexin 6-MM. UV-B treatment also greatly enhanced the accumulation of myristicin, with its titer increasing with increasing UV-B dose. However, the levels of polyacetylenes were not affected significantly by the treatment. Furthermore, the treatment enhanced the levels of phytochemicals, including phenylpropanoids, terpenoids, and iso-coumarins. The initial respiration rate and electrolyte leakage of treated carrots were higher immediately after the exposure to UV-B, which increased with increasing dose; but they gradually decreased to steady state levels comparable to the control. In addition, the weight loss and antioxidant capacity of the treated carrots were not affected significantly during storage. The results suggest a strong potential for pre-storage treatment with UV-B to preserve fresh carrots by controlling diseases, maintaining quality, and enhancing the levels of plant protective and health-beneficial phyto-compounds.