INDUCED POLYPLOIDY l6l 



ploids that now carry certain desirable traits transferable to hexaploid wheat 

 from other genera. Induced polyploidy provides a key to wheat improvement. 



As soon as colchicine methods became known, certain interspecific hybrids 

 of cotton were treated by Beasley (1940) and other cotton geneticists with 

 this drug. It was proved conclusively that our present Upland tetraploid 

 cotton Gossypium hirsutum was indeed the composite of an Asiatic diploid 

 and an American diploid. Cytological and genetical investigations within the 

 genus Gossypium expanded at a fast pace with the rapidly introduced methods 

 for making polyploids. No group of economic plants offered greater promise 

 as a subject for polyploidy breeding. At the same time the problems confront- 

 ing these programs have been as complex as any group (Stephens, 1950). 

 Theoretical and practical work should be integrated as progress is made 

 with induced polyploidy and cotton. 



Larger and larger flowers are frequently desirable. When colchicine meth- 

 ods were perfected to make new polyploids, many projects were launched to 

 create large-flowered tetraploids. Success was not as outstanding as desired, 

 because features such as reduced seed germination, longer growing periods, 

 lack of uniformity, along with other disadvantages, tended to reduce the 

 advantages gained with polyploidy. 



Among ornamentals certain triploids are outstanding in comparison with 

 diploids. Triploid orchids have brought higher prices than diploids (Ka- 

 memoto, 1952). Mehlquist (1949) showed that polyploidy is a good pro- 

 cedure applied properly to specific flowers. The longer flowering period, 

 greater uniformity, increased vigor, and additional size are noteworthy. The 

 propagation becomes a problem since triploids are sterile. Tetraploid lilies 

 induced from diploid by Emsweller (1949) have been developed, with the 

 polyploids giving greater elegance, size, and beauty. Fruits of many kinds 

 come from polyploids (Darrow, 1950). Some of the best varieties of apples 

 are triploids, while others are special chimeral types (Dermen, 1952). These 

 problems represent the specific challenge to specialists. 



Other projects that consider forage crops (Levan, 1945), Brassica (Frand- 

 sen, 1947), Solanum, Mentha, the Gramineae, cucurbits, and numerous eco- 

 nomic types might have been more extensively reviewed. The bibliographies 

 by Eigsti and Dustin (1947, 1949) and their review (1955) should be con- 

 sulted. 



There is a rapid method for creating pure-breeding inbred lines by doubling 

 the chromosomal numbers of monoploids to give the plant breeder a wealth 

 of useful germ plasm. Specific maize-breeding projects include monoploid 

 techniques executed by qualified scientists, yielding valuable materials for 

 practical and theoretical consideration. 



Principles. Polyploidy as a breeding procedure. When many polyploids 

 became available among the numerous crops tested, probably our greatest 

 contribution came from the insight gained to general principles governing 



