Nearly all apple cultivars have two parents – just like humans! Apples have a genetic system that generally prohibits self-fertilization. This self-incompatibility system is a way of insuring that each apple seed will be a hybrid between the maternal (seed) parent and a paternal (pollen) parent. The self-incompatibilty system is also the reason why two or more cultivars must be planted in an orchard to achieve fruit production through insect-vectored movement of pollen from one cultivar to the other.
The parentage of many apple cultivars is unknown, perhaps because they are very old and any record of their origin is lost or perhaps because they were simply found in nature – a seedling that grew in an orchard or forest or along a fencerow. Cultivars with this kind of origin are called chance seedlings, basically a good seedling that was identified by chance. Most cultivars from the early 1900s are chance seedlings. Examples of chance seedlings include McIntosh, Delicious, Golden Delicious and Granny Smith
With the rise of plant breeding and rediscovery of Mendel’s basic genetics research in the early 20th century, the purposeful breeding of apples became more common. In apple breeding, the breeder will isolate (by covering with a paper or mesh bag) and sometimes emasculate (remove the stamens) the flowers on the female tree to insure that they are not self-pollinated or cross-pollinated by insects carrying unwanted pollen. The breeder will then hand pollinate those flowers using pollen collected from a tree of the paternal parent. The parentage of the seedling will be recorded by the breeder, such as 'Redstart' x 'Pippin'. As a convention in plant breeding the maternal parent (in this case 'Redstart') is listed first and paternal parent ('Pippin') is listed second. Examples of purposely bred cultivars include Gala ('Kidd's Orange' x 'Golden Delicious'). 'Macoun' ('McIntosh' x 'Jersey Black') and 'Fuji' ('Ralls Janet' x 'Delicious')
Sometimes, despite the best practices of breeders, the parentage of a cultivar may be found to be incorrect. This may be due to any number of factors such as stray pollen during pollination, a mix up seeds during handling at harvest, or a mixup of seedling trees at planting, among others. Recently available DNA fingerprinting techniques can now allow breeders to check and confirm the parentage of a cultivar.
James Luby, University of Minnesota