Why Is Cross-Pollination Preferable to Self-Pollination?

Self-Pollination in Fruit and Flower Production

• Few types of fruit trees are considered “self-pollinating;” that is, pollinated with pollen from flowers on their own tree or from another tree of the identical variety. All sour cherries are self-pollinating, along with nectarines and peaches. Some varieties of European plums are self-pollinating, as well as all types of berries except blueberries. Please note that even though these types of fruits technically do not require another variety to pollinate them, they will all invariably produce a larger crop, year after year, when pollinated with pollen from a tree that is another variety.

Cross-Pollination in Fruit and Flower Production

• Cross-pollination occurs when pollen is transferred between flowers of two different species or varieties. The largest example of this is apple trees, which not only require pollination by another variety to set fruit, but many varieties of apple trees require specific apple varieties to ensure successful pollination. Other tree fruits, such as pears, sweet cherries and Japanese plums, also require pollination by a different variety for successful fruit production.

  This phenomenon is not limited to fruit trees. Many species of garden vegetables and ornamental flowers also produce larger crops when pollinated with another variety of their species. Pollinating varieties should be planted in close proximity to the desired variety to ensure that the bees and pollinating insects visit both varieties so cross-pollination occurs.

Self-Pollination in Plant Breeding

• Plant breeders routinely use self-pollination to develop hybrid varieties, or when trying improve a variety through natural selection. Known in the business as “selfing,” self-pollination of hybrids eventually will reveal which genes the parent plants possess, which can greatly aid the plant breeder in developing the desired traits in subsequent generations. Self-pollination also is used to keep certain hybrids “pure,” so the plants grown from seed comes “true to its parents.”

Cross-Pollination in Plant Breeding

• Cross-pollination using pollen from two distinct varieties is used in plant breeding to combine some or all characteristics of both parent plants, theoretically creating a superior variety. The plant breeder then grows the resulting seeds, observing the traits exhibited in the offspring. The offspring may be cross-pollinated with each other or with one of the parents, to further isolate the desired characteristics for the new variety, including fruit or flower size or color, flavor, disease resistance or hardiness. Perhaps the most well-known example of cross-pollination is the development of new rose varieties, obtained by cross-pollinating different rose varieties, while keeping careful records of the parents and origin of each. Many thousands of the resulting rose seeds are planted and cultivated, but only a small percentage of these hybrid crosses show the exceptional color, shape, size and vigor necessary to qualify it as a new rose variety in the marketplace.