10 



INDUCED POLYPLOIDY 



O.J. Eigsti 



More food and fiber are produced from polyploids than from the related 

 species that are diploid. This fact is well known to agriculturalists. Species 

 of the rank of polyploid are also distinguished by their mode of origin; that 

 is, polyploids may arise suddenly from parental diploids. Thus, in two botani- 

 cal fields, polyploidy attracts considerable attention: (1) in the area of crop 

 improvement (Levan, 1945), and (2) in the mechanisms of evolution (Steb- 

 bins, 1950). 



The present human population depends upon the greater increases in 

 annual production that come from the polyploids against the lesser quantity 

 that would be available if only diploids were under cultivation. Our daily 

 bread is made almost entirely from the flour obtained from hexaploid and 

 tetraploid species of Triticum (Sears, 1948). Cotton in largest supply is pro- 

 duced by the tetraploid rather than the diploid species. A long list of eco- 

 nomically important plants that are also polyploid could be prepared from 

 the many cases reported in the literature by Eigsti and Dustin (1955) and 

 Krythe and Wellensiek (1942). 



About one-half the species of flowering plants are polyploid (Stebbins, 

 1950). Among certain families, the proportion of polyploids to diploids is 

 higher than 50 per cent. Undoubtedly Darwin would have devoted an im- 

 portant chapter to the subject of polyploidy and origin of species had the 

 present information been available such as the investigations by Clausen, 

 Keck, and Hiesey (1945). During the last half century many excellent ex- 

 periments have confirmed the origin of polyploids from their parental diploids, 

 notably papers and books by Stebbins (1950), Beasley (1940), McFadden 

 and Sears (1945), Kihara and Lilienfeld (1948), and others. Usually the 

 diploids were suspected as parents for one or more reasons, and from these 

 cases interspecific sterile hybrids were made. Subsequently a doubling of the 

 chromosomes yielded the fertile polyploids, or equivalent species. Such syn- 

 thetic types as Frandsen (1947) made with Bras ska resemble the natural 



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