Research at Long Ashton showed that management of apple trees that results in excessive growth of bourse or extension shoots can reduce fruit set (Abbott, 1960).
- The reasons for this are probably primarily associated with competition between the shoots and the young fruitlets for assimilates and minerals, although hormones produced by the shoots may also play a role in this effect.
- Management practices, which reduce the vigour of shoot growth, generally result in improved fruitlet retention.
- Whilst initial bourse shoot growth may compete with fruitlets and cause fruitlet abscission, bourse shoots aid fruitlet growth later in the season, possibly by supplementing the supplies of available assimilates.
The effect of irrigation and water supply to the tree on fruit set and retention
Trees grown in droughty situations show significant reductions in shoot growth, leaf area and yields (Jones and Higgs, 1985; Jones et al., 1983; Lakso, 1983).
- However, experiments in Germany showed that the numbers of flowers formed per inflorescence (cluster) or the fruit set per linear branch length were not reduced (Sritharan and Lenz).
- The reduced yields must be mainly attributable to reductions in tree size or to reductions in fruit size.