Inheritance of Cell-Division Rate in Roots of Sugarbeet 1

Differentiation in sugarbeet (Beta vulgaris L.) roots is completed in the first 4 to 5 weeks of growth. From then on, growth is by simultaneous cell division and cell expansion. Selection for root yield may exert selection pressure on either cell-division rate or cell expansion or both. The degree of selection pressure applied to either of these two cellular parameters depends on their respective inheritance behavior and the breeding and selection methods used. This study was initiated to determine the inheritance of cell-division rate (cell number). Cell-division rate was based on the number of cells across the radius of a cross section of 20- to 28-day-old plants. Heterosis was determined in progeny of six males crossed to line L29, two-by-five females ✕ males crosses and a five-parent diallel. Genotypic variance estimates were made in a three-by-three female ✕ males cross and the five-parent diallel. Cell number showed significant heterosis in all but two hybrids tested. Both general and specific combining ability effects were significant for cell number, with specific combining ability showing the greatest significance. Estimates of nonadditive genetic variance accounted for between 75 and 95% of the total genetic variance. It is concluded that cell-division rate (cell number) is conditioned largely by nonadditive type genes and that beet root heterosis is due primarily to increases in cell number rather than cell size. Breeding and selection methods that capitalize on nonadditive genetic variation will, therefore, increase sugarbeet root yield by increasing cell-division rate.