Mode of action of hot-water dip in reducing decay of lemon fruit

A hot-water dip for 2 min at 52-53 degreesC prevented decay for at least on e week in lemon fruit inoculated with Penicillium digitatum. The mode of ac tion of hot water in reducing decay wa's investigated by studying the effec ts of this treatment on the pathogen and on the resistance mechanisms of th e fruit. The hot-water dip had a transient inhibitory effect on the pathoge n, arresting its growth for 24-48 h. During this lag period, the combined e ffects of the pathogen and the hot-water dip induced the build up of resist ance in the peel. Lignin production in the inoculated sites began within 24 h after inoculation or wounding. When inoculation was followed by the hot- water dip, lignin accumulation continued for a week. Inoculated lemons that were not dipped in hat water rotted completely within 3 days after inocula tion and their lignin content did not rise or even decreased. The scoparone concentration in the inoculated sites of hot dipped fruit started to rise 24 h after treatment and reached a level sufficient to inhibit the pathogen within 2 days after treatment. Parallel to scoparone accumulation, scopole tin was detected in inoculated and heat-treated lemons. Without the pathoge n challenge or wounding, heat treatment by itself was not able to induce an y of the above-mentioned defensive effects. Our data do not support the inv olvement of ethanol-extractable aldehydes, associated in the literature wit h wound gum, or of citral in decay inhibition in hot-water dipped lemons.