Improvement of seed set and seed germination in apple

Summary

To improve seed set and seed germination in the apple cultivar Elstar, the influences of the number of pollinated stigmas per flower, the number of flowers per cluster and the pollinator were studied.

From 1 or 3 flowers per cluster 1, 3 or 5 stigmas were pollinated with pollen of the cultivars James Grieve, Cox’s Orange Pippin, Idared or Gloster. Fruits were harvested one week before or after the commercial picking date.

The seed set, expressed as the number of seeds per pollinated flower, increased with the number of pollinated stigmas on the flower. This increase, from 0.40 to 1.38, was caused by a higher fruit set after June drop and a higher number of seeds per fruit. The positive correlation between seed number per fruit and fruit set suggest that the sink strength of an individual fruit was influenced by seed number. Compared to 1 flower per cluster, seed set was slightly reduced when 3 flowers per cluster were left, due to a lower fruit set, although the seed number per fruit was somewhat higher. Since the pollinator has no clear effect on final fruit set, the influence of the pollinator on seed set was determined by the number of seeds per fruit, ranging on average from 2.0 to 3.2. Seed germination was lowest when Gloster was used as pollinator (58%) and highest in the case of Cox’s Orange Pippin (89%). For all pollinators seed germination was negatively correlated with seed number, probably due to competition between seeds in the fruit. A delayed picking time also reduced seed germination.