Changes in anatomical structure of apple fruitlet pedicels preceding June drop

Abstract

The anatomical structure of pedicels of apple fruitlets was investigated. The fruitlets of cv. 'Mcintosh' and 'Bancroft' were collected on June 8th, 16th an 24th. The middle date coincided with the beginning of June drop. The pedicel structure of larger fruitlets which tended to be retained on the tree was compared with that of smaller fruitlets which tended to be shed of. In the pedicels of larger fruitlets, development of the xylem, especially secondary one, was more intensive. This difference increased in time. Lignification of cortex sclereids, phloem fibers, xylem parenchyma cells and pith cells was also more advanced. The differences in the amount of phloem tissue between both kinds of fruitlets were not large but usually significant. The mentioned differences especially in pedicel xylem development are considered to be partly responsible for the fact that smaller fruitlets loose gradually their ability to compete for nutrients. This finally leads to their starvation and shedding.