Effect of UV-C on phytoalexin accumulation and resistance to Botrytis cinerea in stored carrots

The effect of UV-C (220–280 nm) on the accumulation of phytoalexin and resistance to Botrytis cinerea was studied in cold-stored carrots. Carrots were surface-wounded, treated with a range of UV doses and stored at 1 °C for 25 days in lots of 22 roots. The level of the phytoalexin, 6-methoxymellein, in each lot was then assayed in the peel of eight roots. Twelve of the remaining roots were subsequently inoculated with mycelial plugs to evaluate their level of disease resistance. The elicitation of 6-methoxymellcin by UV increased significantly the resistance of the roots to B. cinerea. The effect of UV in freshly harvested carrots was curvilinear, showing an optimum between 0.44 and 0.88 Merg/cm2. However, only a linear relationship was observed with aged (stored for 4 months at 1 °C) carrots for the same doses, suggesting a modification in the response to UV with age. Wounding was necessary for carrots kept at 1 °C to respond to UV treatment. Neither UV nor wounding alone caused any elicitation at this temperature. Since unwounded roots could respond to UV at 20 °C, it is hypothesized that the level of physiological activity of the roots determines their response to UV. An increase in the physiological activity by higher temperatures or wounding would allow the elicitation process to take place. Since UV irradiation can increase the level of disease resistance in treated tissues, this treatment has potential as an alternative method for the control of post-harvest diseases m carrots.