Chapter Eighteen 

 HYBRIDIZING PLANTS 



The hybridizing of plants is a method of improving the 

 beauty or economic value of plants. The object of hybrid- 

 izing or crossing is to get certain selected desirable character- 

 istics of two strains or varieties into a single individual. In 

 certain cases a plant breeder may find a plant with a single 

 characteristic which he wants to substitute for an undesirable 

 character in an otherwise desirable plant. A common exam- 

 ple of this kind of breeding is the effort to develop resistance 

 to a certain disease common to a garden plant by crossing it 

 with a wild plant which is worthless except for its character- 

 istic resistance to this disease. For instance, rust resistance 

 has been taken from a wild species of snapdragon and intro- 

 duced into many varieties of cultivated snapdragon. Rust 

 resistance found in Khapli Emmer wheat was introduced 

 into common wheat. The tobacco mosaic virus disease is a 

 serious disease not only of tobacco but of tomato and many 

 other plants. In Nicotiana tabacum, the common Turkish 

 tobacco, the disease spreads throughout the plant and be- 

 comes very severe. In Nicotiana glutinosa, a related wild 

 species, the disease is localized in small spots or lesions. By 

 crossing the two species, and then by backcrossing the 

 progeny of this cross to the common tobacco many times, the 

 character for local lesions was introduced into a number of 

 commercial varieties of Turkish tobacco. Note that a char- 

 acter such as disease resistance from a wild plant can not 

 only be introduced into a cultivated plant, but into a par- 

 ticular variety of the cultivated plant. 



Hybridization of plants has become a very useful and 

 fascinating science. Governments, the world over, have 



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