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Production and Reproductive Behavior of Monoploid Sugarbeet¹

The rarity of sugarbeet (Beta vulgaris L.) monoploids has limited the usefulness of monoploids sugarbeet breeding. This study was conducted to evaluate the production and cytogenetical behavior of monoploid sugarbeets. The rate of occurrence of monoploids in three sugarbeet lines was 0.017%. Meiotic pairing in the monoploids indicated the presence of three or more duplications that involved at least six of the nine chromosomes in the basic genome. Chromosomes of monoploid sugarbeet usually were condense and seldom congregated at metaphase plates. Chromatid bridges and a centric fragments occurred in > 2% of microsporocytes. Only those gametes that developed from restitution nuclei and contained a complete set of sugarbeet chromosomes did not abort. Seed setting was rare, and not every monoploid sugarbeet produce viable seed. Sugarbeet monoploids gave rise to monoploid progeny through pollination with diploids at a rate of 1.49%, which was > 80 times higher than that from pollinating diploids. The progeny plants also contained 18 , 19, 27, 36, and 18/36 chromosomes when monoploids were pollinated with diploids. A great majority (92.3%) of these progenies were diploids. The 19-chromosome (trisomic) progeny was the only aneuploidy class recovered. It may not be possible to establish monosomic series of sugarbeet genotypes through conventiona pollination techniques because unbalance gametes (without an intact genome) do not survive. Although the monoploids exhibited morphologic dailvergence from diploid parents, the monoploid progeny resembled their respective maternal monoploids. This is the first reports howing the feasibility of recovering monoploid sugarbeet from monoploids.

Key Words: Haploids • Meiosis • Restitution nuclei • Parthenogenesis • Breeding • Beta vulgaris L.

² Research geneticist, USDA-ARS.

Received for publication August 11, 1986.