Most animals have two sets of chromosomes, inherited from the mother and father respectively, and are known as "diploid". This is true of many plants too, including the majority of apple varieties. However several important apple varieties have three sets of chromosomes rather than two, and are known as triploids.
Triploid apple varieties have a couple of important characteristics which need to be considered when growing them:
- Their pollen is effectively sterile and cannot be used to pollinate other apple trees.
- They are usually not self-fertile, and therefore need another compatible apple variety nearby to pollinate them. (Some triploid varieties have a degree of partial self-fertility).
In short, if you are planting triploid varieties, it is best to to make sure you have the necessary pollinator trees nearby. You will need either one self-fertile apple variety (or crab-apple) or two other varieties which can cross-pollinate each other as well as the triploid variety.
Although the pollination requirements might be inconvenient, triploid varieties have several advantages which make them desirable for the home or community orchard:
- They usually produce vigorous trees, which can support large crops.
- The apples are often quite large.
- They usually display a good degree of natural disease resistance.
- They can often survive in difficult conditions.
It is perhaps no co-incidence that many well-known heritage apple varieties are triploids, because our ancestors would have found their large size and productivity very useful. Some of the best-known triploid varieties are:
- Ashmead's Kernel
- Belle de Boskoop
- Blenheim Orange
- Bramley's Seedling
- Crispin / Mutsu
- Ribston Pippin
- Newtown Pippin
- Roxbury Russet
- Zabergau Reinette