324 Colchicine 



cultivated types and ]Mo\ided material for selection. i^*^ Further search 

 for natural species useful in polyploidy is underway. Disease re- 

 sistance, flavor, quality, and size have been incorporated into hexa- 

 ploids. There were reportedly 24 breeding projects in the U.S.A. en- 

 gaged in various aspects of strawberry work. There are important 

 cytogenetical strains in polyploid series at hand in the Botany Depart- 

 ment at the University of Manchester, England.'^^ 



Including wild and cultivated varieties, chromosomal series from 

 2n = 14 to \2r} = 84 exist among the blackberries and raspberries. 

 Perhaps no other fruit can be correlated any more directly to poly- 

 ploidy than this one. The Nessberry, Logan, Boysen, along with 

 hundreds of forms of polyploid blackberries are in existence. Since 

 there are polyploids at hand, artificial doubling is not so necessary. 

 Where faster progress may be required, or the changing of sterile hy- 

 brids to fertile ones, colchicine serves as a useful tool.^^ 



Many cultivated cranberries are diploid, and in nature, tetraploid 

 as well as diploid species exist.^-' ^'^ Some sterile hexaploids have been 

 reported. By doubling the number of the cultivated diploid, a paren- 

 tal stock was made for crossing with the wild tetraploid. Selections 

 from all the important cultivated diploid varieties were doubled. 

 These types were selfed and hybridized. Such tyj^es have been grown 

 on large scale since their origin, and raw polyploids are being con- 

 verted into genotypically balanced types. 



Perhaps polyploidy as a direct mode for improvement in grapes 

 has advanced as far as any fruit crop of the United States. Here 

 naturally occurring sports, often chimeras, proved to be tetraploid. 

 They occurred in sufficient abundance, so that artificial doubling by 

 colchicine has not been necessary. Giant fruited sports from the vi- 

 nifera and bunch grapes are tetraploid. ^''"^ These studies have pro- 

 gressed to a stage where newly named tetrajjloid varieties now com- 

 bine important characters and are distributed as improved types. 



Named tetrajiloid varieties of summer radish were released in 

 Japan and tested widely enough to demonstrate a superiority for the 

 new polyploid. In vigor and growth the tetraploid exceeded the dip- 

 loid. Outstanding resistance to the common club root disease was 

 obtained with the tetraploid. The usual gigas features accompany 

 these autotetraploid radishes. ^^^ 



Polyploidy in water cress increased the succidence of leaves, which 

 feature made the tetraploid strains more desirable for salads. ^^ In- 

 creased content of vitamin C in the water cress, which is expected 

 in tetraploids, was an advantage over diploids. One disadvantage was 

 the slower-growing characters of tetraploids. Like the autotetraploid 

 rye, apparently a balance between the positive characters against the 

 negative ones is needed. When an immediate su])eriority in favor 



