The exploitation of polyploidy in sugar-beet breeding

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Abstract
SUMMARY Tetraploid lines were produced from colchicine treatments of European multigerm diploid material, and seeded in polycross plots. The same lines were crossed with European multigerm diploids to give anisoploid varieties, and also used as pollinators of American male-sterile diploids to yield monogerm and multigerm triploid varieties. Bigerm triploids were obtained from male-sterile hybrids heterozygous for the monogerm character, using European multigerm O-types in the grandparental generation. Double-cross monogerm triploids were obtained by crossing male-sterile diploids with non-equivalent O-types to provide male-sterile hybrids, and pollinating these with outbred tetraploids. Results from 35 root-yield trials showed that the sugar yields of the anisoploids and triploids were similar to those of contemporary commercial varieties, but that outbred tetraploids were slightly, and inbred tetraploids considerably, less productive. Changes induced in characters other than root weight by chromosome-doubling of diploid material were sometimes important, but not consistent in magnitude or direction. It is suggested that these changes result from selection and random drift rather than the ploidy change. A seed-yield trial demonstrated advantages of using hybrid seed-parents for triploid seed production. Problems of seed quality are discussed with particular reference to triploid varieties. It is concluded that the main importance of multigerm anisoploid varieties was in their combination of good sugar yield with near-monogerm fruit clusters at a time when commercial monogerm varieties were deficient in yield; the chief value of triploidy lay in its application to the short-term improvement of genetic monogerm varieties. The development of monogerm anisoploids is considered unlikely; but some advantages of deriving monogerm triploid varieties from tetraploid seed-parents are indicated, and it is suggested that these may become increasingly important in the future.