According to Dutch research (Visser and Verhaegh, 1980), the application of compatible pollen twice with a one to two day interval between applications, could stimulate the activity of the pollen applied on the second occasion.
- This was thought to be due to some action by the first applied pollen, thereafter called the ‘pioneer pollen’.
- This phenomenon has been used in attempts by plant breeders to overcome self-incompatibility by applying compatible pollen from another variety first, followed by self pollen one to two days later (Visser et al., 1983).
Research conducted in Russia many years ago showed that whilst self pollen generally grew poorly on apples, its addition to pollen from another compatible variety on the stigma, actually helped fruit set and the number of seeds in the fruits (Nesterov, 1956).
In further work conducted in the Netherlands (Visser and Oost, 1982), combinations of self-incompatible pollen with viable but sterile (irradiated) compatible pollen were shown to be effective in overcoming self-incompatibility and this phenomenon came to be known as the ‘Mentor Pollen’ effect.
However, more recent studies in Switzerland (Kellerhals and Wirthner-Christenet, 1996) have shown that double pollination of Gala or Elstar, first with self pollen and secondly with compatible pollen one day later, inhibited the growth of the compatible pollen.
- It is possible that the contribution of self pollen to fruit set in apple is greater than previously thought.
- If combined with warm weather conditions and some cross compatible pollen, the self pollen may play a significant contribution to fruit set and seed numbers in some situations.