Flower quality, in terms of ability to set fruits is often estimated by measuring the Effective Pollination Period or EPP.
The flowers formed in the spurs and on short terminal shoots of apple trees are initiated very soon after fruit set in the previous year.
- Approximately 3-4 weeks after petal fall the first floral primordia are visible under high power microscopy in the spurs.
- Providing these buds develop unhindered and differentiate into flowers, they should provide flowers of the highest quality (with long EPPs) in the subsequent spring.
In contrast, flowers forming on the current season’s extension shoots, known as axillary buds, are initiated later in the season, usually once the growth of the current season’s extension shoots begins to slow down in mid-late summer.
- These axillary buds are, on most varieties, poorer quality; they flower several days later than the flowers on spurs or short terminal shoots and they have shorter EPPs.
Flower bud quality is difficult to quantify but may be best described as the relative ability of the flower to set a fruit.
- However, it is now thought that flower quality may also influence the retention of the fruit after setting and its subsequent rate of growth.
- Flower buds of differing quality are very fully described in Abbott,1984.
- Other studies have suggested that a good correlation exists between the size of the flower cupula and eventual fruit size (Stosser et al.,1996).
Many environmental and tree management factors influence apple flower quality. The following factors are thought to be the most important influencing flower quality:
- Crop loading and flower and fruit thinning (including natural fruit drop).
- Tree health and nutrition.
- Tree pruning/training and flower bud position on the tree.
- Exposure of the sites of flower initiation to adequate light.
- Winter chilling and satisfying the dormancy requirements.
- Spring temperatures prior to bud burst.