Inbreeding depression in diploid and autotetraploid sugarbeet,Beta vulgaris L.

Summary The effect of inbreeding on vegetative vigor, as measured by root yield, was evaluated in two diploid (2x) and equivalent autotetraploid (4x) sugarbeet strains, and one additional 2x and one 4x strain. Root yields of the 2x and 4x S₁ progenies each averaged 86.7% of their comparable open-pollinated progeny. Inbreeding depression of root yield was variable from strain to strain. The selfed 4x populations, when compared with their 2x equivalents, suffered more yield depression than was expected on the basis of the theoretic approach to homozygosity associated with selfing in autotetraploids. The inbreeding depression was partly attributed to (a) the approach to homozygosity, and (b) the fact that partially homozygous 4x S₁ individuals were probably unable to make compensating growth when located adjacent to a low vigor aneuploid plant. A major part of root yield depression remained unexplained. Sucrose content within strains and within ploidy levels was not significantly affected by one generation of selfing.Joint contribution of the Crops Research Division, Agricultural Research Service, US Department of Agriculture, the Colorado Agricultural Experiment Station, and the Beet Sugar Development Foundation. Published with the approval of the Director of the Colorado Agricultural Experiment Station as Scientific Series No. 1582.