INDUCTION OF 6-METHOXYMELLEIN AND RESISTANCE TO STORAGE PATHOGENS IN CARROT SLICES BY UV-C

Biotic (beta-glucan, fructosan and polygalacturonic acid fragments) and abiotic agents (ultraviolet-C radiation, gamma radiation and heat) were screened for their potential to elicit the accumulation of the phytoalexin 6-methoxymellein in carrot slices. Ultraviolet radiation was the only elicitor found effective, with an optimum dose of 2.20 x 10(5) erg cm-2. At 20-degrees-C, the maximum level was reached in 72 hours and thereafter degradation was apparent. At lower temperatures (1-degrees or 4-degrees-C), 6-methoxymellein accumulation was slower but reached higher levels which remained stable for up to 35 days after induction. Ultraviolet-treated slices which were stored at 1-degrees or 4-degrees-C for two weeks to allow 6-methoxymellein accumulation were significantly more resistant to infection when challenged with Botrytis cinerea or Sclerotinia sclerotiorum. Slices inoculated immediately after ultraviolet treatment did not show any resistance. The data showed that concentrations of 6-methoxymellein above 30 mug g-1 of tissue were inhibitory to B. cinerea, with maximum inhibition observed around 60 mug g-1. Thus ultraviolet treatment could have potential to enhance the resistance of carrots to storage pathogens.