Fruit firmness and ethylene biosynthesis in three cultivars of peach (Prunus persica L Batsch)

In the three freestone peach cultivars Springcrest, Redhaven, and Fayette, ethylene evolution was studied and related to fruit softening. Loss of firmness was accompanied by an increase in ethylene biosynthesis but great variability was observed within the selected fruit populations. By plotting data on a single-fruit basis, it appeared that the climacteric was a late event occurring when the fruit had already softened to about 10 to 20 N. The highest values of whole-fruit ethylene evolution at ripening were detected in 'Springcrest'. During the earliest phases of softening, whole-fruit ethylene production only rose slightly, whereas a marked increase of 1-aminocyclopropane-1-carboxylic acid (ACC) content, in vivo ACC oxidase activity and ethylene evolution was observed in isolated mesocarp disks, particularly in 'Springcrest' and '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.