BRANCH ORIENTATION AS A FACTOR DETERMINING FRUIT-SET IN APPLE-TREES

Shoot growth, flower production and fruit set were examined in branche s of Cox's Orange Pippin trained to either the horizontal or vertical axis. Branches orientated to the horizontal in August during flower bu d development showed a decline in shoot extension growth and an increa se in fruit set in the following year. This increase in fruit set was also evident in branches which had been trained to a vertical position in August and then re-orientated to the horizontal in the following A pril during flowering. A decline in fruit set was equally obvious when the reverse treatment was undertaken. The failure of vertical branche s, without their shoot tips, to show an increase in fruit set would su ggest that shoot extension and flower production were not antagonistic . Studies of flower and cluster leaf development showed that branch or ientation had no influence on their mineral content, or the ability of cluster leaves to acquire carbon. Morphologically, the flowers from d ifferent branch orientations were similar. The underlying cause of enh anced fruit set on horizontal branches appeared to be due to an increa se in the proportion of healthy ovules at anthesis and later. Increase s in female fertility and length of effective pollination period were evident even in branches orientated from the horizontal to the vertica l at a time (April) close to flowering.