Short-Term Changes in Cambial Growth and Endogenous IAA Concentrations in Relation to Phloem Girdling of Peach, Prunus persica (L.) Batsch

Abstract

For 2-3 days after all except one of the secondary limbs of a peach tree were girdled, all limbs (including the non-girdled limb) shrank. Shrinkage and subsequent growth was greatest in the zone immediately above the girdle whereas growth was least immediately below. After initial shrinkage the growth rate of the cambium, at specific positions in relation to the girdle, was more-or-less constant and consistent with the long-term effect of the girdle at each position. The concentration of indole-3-ylacetic acid (IAA) extracted from the bark immediately above the girdle first increased sharply but then decreased to the level in the non-girdled limb. On the other hand, beneath the girdle the IAA concentration decreased by 75% and remained low. Thus, immediately above the girdle IAA concentration in the bark increased while the limb shrank, and declined before the cambial growth rate increased. Beneath the girdle, however, the concentration of IAA was severely depleted while growth of the limb was inhibited. The possible implications of these observations in relation to control mechanisms of cambial growth are discussed.