In crossing potato varieties, the anthers of the blooms to be fertilised have to be removed at an early stage so that the flowers do not self pollinate. Care must also be taken to prevent chance pollination by neighbouring plants.
Then the pollen from the male 'parent' is dusted onto the pistil. Following this, a muslin bag is tied over the cross-fertilised plant.
One difficulty is that the pollen may not be available at the time the flower is in bloom. Another is that the plant may not produce any "apples" even though it has been fertilized. Some varieties produce apples much less easily than others, and some produce none at all.
There are ways which can help to overcome this.
Taking off all the blooms except the one to be pollinated increases the likelihood of the plant producing fruit and seeds.
Another tactic is to pick away the growing tubers so that the plant expends more energy in producing seeds than tubers.
Even so, the potato breeder may pollinate 20 different blooms and consider himself lucky if he gets 'apples' on two of them.
When these are full-grown, they are gathered, and the seeds washed out. Each fruit may contain from 100 to 300 seed.
These are sown in fine compost in early Spring, and when they have sprouted they are planted out.
They will usually produce a few small tubers in the first year, and a very small number will produce large ones. There is a case on record of a seed from a potato apple producing six pounds of reasonable-sized tubers between March and October.
The tubers of the seedlings in the first year are generally quite variable in type and colour. Then the selection process begins, and has to be continued for several years until the ones selected are 'stable'. A lot of patience is required, because a seedling which looks promising in its first two or three years may still have to be discarded if it fails to live up to its early promise.
(Paraphrased by ND from "The Potato" by Grubb & Guilford, 1912).
ND / Diversity website
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