FRUIT FIRMNESS AND ETHYLENE BIOSYNTHESIS IN 3 CULTIVARS OF PEACH (PRUNUS-PERSICA L BATSCH)

In the three freestone peach cultivars Springcrest, Redhaven, and Faye tte, ethylene evolution was studied and related to fruit softening. Lo ss of firmness was accompanied by an increase in ethylene biosynthesis but great variability was observed within the selected fruit populati ons. By plotting data on a single-fruit basis, it appeared that the cl imacteric was a late event occurring when the fruit had already soften ed to about 10 to 20 N. The highest values of whole-fruit ethylene evo lution at ripening were detected in 'Springcrest'. During the earliest phases of softening, whole-fruit ethylene production only rose slight ly, whereas a marked increase of 1-aminocyclopropane-1-carboxylic acid (ACC) content, in vivo ACC oxidase activity and ethylene evolution wa s observed in isolated mesocarp disks, particularly in 'Springcrest' a nd 'Redhaven'. In the three cultivars, a gradient between epicarp and mesocarp tissue has been detected in terms of ethylene physiology, the former being characterized by a lower ACC concentration but a higher efficiency in converting ACC to ethylene.