PHYTOTOXIC RESPONSE OF LEMONS TO HOT WATER

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  • 1 U.S. Dept. Agric, 2021 S. Peach Ave., Fresno, CA 93727

Hot water immersion of citrus fruit is a potential postharvest quarantine treatment for insect disinfestation. Little is known about fruit injury in the temp. ranges/exposure times required to control surface insects. We immersed lemons in water at 25, 50, 52.5 or 55C for 5, 7.5 or 10 min. Fruits were held overnight at 20, 25 or 30C before hot water immersion. Fruits were stored at 10C for 4 wk after treatment. We compared (1) fresh-picked late-season (July-Aug.) coastal “silver” maturity lemons with (2) fresh-picked ripe but green-colored early/mid-season (Oct.) desert lemons and (3) similar desert lemons commercially degreened 7 days with ethylene to attain desirable yellow color prior to heat treatment. Heat injury symptoms were small-large light-dark brown necrotic lesions or discoloration which developed on peel surface within 2-3 wk after treatment. Order of sensitivity to heat was: most sensitive = coastal silver (≥ 90% of fruit injured at 55C/10 min) > degreened desert > green (≥ 34% of fruit injured at 55C/10 min) desert lemons. Up to 50C/5 min could be used on coastal and 52.5C/5 min on desert lemons without appreciable injury. There were no differences between fruit cured overnight at 20, 25 or 30C before heat treatments.

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