l6o EIGSTI 



Valleau (1952) gives numerous important details about this achievement. 

 Mosaic resistance was obtained when chromosomes were substituted, viz., 

 glutinosa chromosomes exchanged for tabacum chromosomes that led to 

 mosaic resistance (Clausen, 1945). Tobacco breeders have access to mosaic- 

 resistant strains for the future development of new and better varieties. Such 

 genie transfer from one species to another is a considerable accomplishment. 

 Not only has its practical contribution meant much, but excellent theoretical 

 work has been done with Nicotiana (Smith, 1939). 



Three root crops may be improved by induced polyploidy: sugar beets 

 (Matsumura, 1953), radish (Nishiyama, 1952), and turnips (Josefsson, 

 1953). The triploid sugar beet has the capacity to produce more raw sugar 

 per acre, because the percentage of sugar per unit of beet remains proportional 

 to size of the root as it increases (Peto and Boyes, 1940), whereas the diploid 

 beet reduces yield of sugar per unit when the root approaches the largest 

 size possible. This basic difference between diploids and triploids means that 

 greater efficiency is in favor of triploids over diploids (Matsumura, 1953). 

 After many selections and careful plant breeding, better and new strains of 

 tetraploid sugar beets are now reported in Sweden. At first, the tetraploids 

 proved inferior, on an over-all basis, to the best diploids, but applied work 

 on improvement has brought new tetraploids with promise of superiority in 

 production of sugar. The tetraploid radish carries favorable disease resistance, 

 overcomes pithiness, and grows better under specific cold conditions than 

 the diploid. In Sweden a third root crop, the turnip, has been improved with 

 the use of tetraploid strains. Increases in the acreage of tetraploids have fol- 

 lowed the introduction of new and useful varieties of induced polyploids. 



Some new varieties of tetraploid rye have been introduced to agriculture 

 by Muntzing (1951) and others. Again, the first expectations for the "raw" 

 tetraploids were too high. Since then, selections have advanced new superior 

 polyploid strains. One tetraploid with wide adaptation for Europe and parts 

 of the U.S.A. is called Petkus tetraploid rye, first developed in Europe. The 

 advantages shown by the tetraploid rye must be balanced against certain 

 disadvantages before a superiority for tetraploids or diploids can be decided. 



Rye wheat hybrids made fertile by inducing polyploidy have been known 

 for many years. Certain advantages along with disadvantages attend these 

 polyploids, technically called the Triticales. The protein quality of the flour 

 shows superiority to rye flour. These hybrids develop on soil not suitable for 

 bread wheat. Inherent to new Triticales are the usual problems of low fertility, 

 lack of genotypical balance, and the need for suitable agronomic types attrac- 

 tive to farmers as well as millers of flour. 



Among the genus Triticum and related genera many induced polyploids 

 have been made (Sears, 1948). Much of this work contributes primarily to 

 an understanding of the origin of species and the mechanisms of evolution, 

 although practical breeding plans are greatly enlarged with induced amphi- 



