Beach Strawberry Fragaria chiloensis|
|Virginia Strawberry Fragaria virginiana Image: Walter Siegmund|
Crosses often occur between plants classified as distinct species. Many hybrids are sterile, but many others are merely of reduced fertility and can, in fact, produce offspring. The level of fertility seen in the hybrids varies both with the cross in question and, for a given type of cross, from one individual hybrid to another. Some crosses produce hybrids apparently just as fertile as their parents.
Typically, hybrids combine the traits of their parents. Often, too, a given trait in a hybrid, say flower color, will be intermediate (for example, the hybrid's flowers might be orange, whereas the flowers of one of its parents are red and those of the other, yellow). Sometimes, however, a new trait not seen in either of its parents will arise in a hybrid.
Plant breeders commonly start with variable plant hybrids and then apply selection to produce new crops, trees, and flowers with desirable properties. Soliman (1992: 199) says no other factor has had a greater impact on agricultural production.
New breeds produced by hybridization vary widely in the proportion of their genetic composition (Carver and Taliaferro 1992). Some varieties so produced are very close to one parent, but have only one or a few traits from the other (natural processes of this sort are sometimes called introgression). At the other end of the spectrum are breeds that derive their traits in equal number from both parents. In the former case, one can think of the new hybrid as a slightly altered version of one of the parents, in the latter as a distinct, new composite.
A complete list of all the new crops derived from the production of plant hybrids, followed by selection, would be both tedious and beyond the scope of this article, but the reader is referred to a summary paper on this topic by Kalloo (1992). An inventory of the cultivated flowers derived from hybridization would probably be even more lengthy. Here we will mention a only one example of the many new breeds of plants derived from hybridization: The modern commercial strawberry is derived from hybridization of the Virginia strawberry (Fragaria virginiana) and the beach strawberry (F. chiloensis), both of which are shown at right. But if you want to read in detail about hybrid plants, click on this link.
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