Cross pollination is done in order to produce genetic variability and transgressive segregation. There are two steps in cross-pollination.
Emasculation involves the removal of the anthers so that the flower cannot self-pollinate. Emasculation is done the day before the flower opens, when the anthers are still immature and infertile. This stage is easily recognised because the petals are fully formed but still adhering to each other, so that the flower is closed. The petals must be gently separated with a needle (photo in preparation) and then each of the five anthers must be bent away from the pistil until it breaks off and falls to the ground (photo in preparation). The next day, an emasculated flower is wide open and is easily recognised by the absence of yellow anthers (photo in preparation). Each day, all the flowers that are ready should be emasculated, except those of the male parent (see next).
Cross-pollination involves the placing of pollen on the now receptive stigma of each emasculated flower. It is a good idea to use only one male parent, and a different male parent, each day in rotation, so that each parent is represented equally. The male parent flowers are wide open and are easily recognised by the presence of yellow anthers. One anther is picked with a pair of fine forceps (photo in preparation), and it is touched to the stigma of each of several emasculated flowers (photo in preparation). Make sure that the side with free pollen is used. A small dot of yellow pollen should be visible on the stigma. There are five anthers to each male parent flower and, with several flowers, this should provide adequate pollen for all the cross-pollinations to be done in one day.
Some potato cultivars are pollen-sterile, or even female sterile. If it is discovered that a male or female parent never forms fruits, its use must be discontinued. Famous cultivars that suffer sterility problems are Russet Burbank, Bintje and King Edward, and the use of these as parents should be avoided by amateur breeders.
Do not waste time labelling flowers, keeping detailed records, or keeping each batch of seed separate from all the others. All the true seed is going to be mixed, and sown as a single screening population.
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