Research conducted at HRI-East Malling in the 1980s (Robbie et al., 1993) showed that training branches of the variety Cox’s Orange Pippin to the horizontal during August, produced flowers that gave better fruit set in the subsequent year than flowers on branches trained to the vertical.
- However, if branches trained to the vertical in August were subsequently trained to the horizontal in the following April, during flowering, then fruit set on these was also greatly improved.
- This indicates that the horizontal orientation is important not just to flower development but to the success of pollination/fertilisation itself.
- The failure of poor fruit set on vertically orientated shoots was not attributable to more vigorous shoot growth and competition between shoots and flowers for assimilates, minerals and water.
- Flowers on vertical shoots with all the competing shoot growth removed still set poorly.
- The studies also showed that the spurs and flowers on vertically and horizontally orientated branches did not differ in their mineral content or the ability of the primary leaves to acquire carbon and morphologically the flowers from the two branch types were similar.
- In a way that is not understood, training branches to the horizontal appeared to increase the proportion of healthy ovules in the flowers at anthesis (flower opening) and later.
- Increases in ovule fertility and associated increases in the Effective Pollination Periods (EPPs) of flowers from horizontally orientated flowers were evident, even in flowers on branches moved to the horizontal close to flowering time.