PROMOTION OF RIPENING OF GEBHARD RED DANJOU PEARS BY TREATMENT WITH ETHYLENE

Pears (Pyrus communis L.,'d'Anjou'), 'Gebhard' red strain, harvested a t commercial maturity with flesh firmness (FF) of 64.5 N, did not ripe n normally at 20 degrees C even though the chilling requirement had be en met by storage at -1 degrees C. Treating fruit with 100 mu l l(-1) ethylene at 20 degrees C for 3 days, followed by 14 days of a simulate d transit period at -1 degrees C, induced normal ripening at 20 degree s C, with a climacteric-like rise in ethylene production, fruit soften ing, and reduction of extractable juice. Fruit did not ripen under the se conditions without the ethylene treatment. A 3 day treatment with 1 00 mu l l(-1) ethylene readily induced pulp tissue to convert 1-aminoc yclopropane-1-carboxylic acid (ACC) to ethylene, regardless of the len gth of chilling. Tissue conversion of ACC to ethylene was also induced by holding fruit at -1 degrees C for 2 months or longer. ACC synthase activity was induced only by ethylene treatment, and did not increase until the fruit had been transferred to 20 degrees C for 3 days. Prom otion of normal ripening in 'Gebhard' red 'd'Anjou' pears by ethylene treatment could be primarily attributed to the coordinate induction of ACC to ethylene conversion and ACC synthase, followed by increasing A CC synthase activity at 20 degrees C. (C) 1997 Elsevier Science B.V.