The Effect of Different Portions of the Sunlight Spectrum on Ethylene Evolution in Peach (Prunus persica) Apices

Exposure of peach plants to the blue plus far-red (B/FR) portions of the sunlight spectrum caused a rapid rise in ethylene evolution from their apices. Two days were enough to produce a significant rise in ethylene evolution relative to blue without far-red or to neutral shade. Maximal level of ethylene evolution in the B/FR light, more than eight times that of the blue or the neutral shade, was reached after four days of exposure. A higher endogenous ethylene content was also found under B/FR relative to blue or to neutral shade conditions. The level of ethylene evolution from peach apices was correlated with their arrested growth as observed a few days later. Exposure of peach plants to dense leaf shade, under the canopy of a big avocado tree, enhanced ethylene evolution from their apices, relative to unfiltered sunlight and to neutral shade. It was suggested that the rise in ethylene evolution in both B/FR and leaf shade conditions resulted from a high far-red: red ratio. Ethylene was further suggested to act as a mediator of photomorphogenetic regulation of vegetative development in far-red-rich tree shade.