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Meiotic Behavior of a Disomic Nematode-Resistant Sugarbeet¹

A disomic (2n = 18) sugarbeet (Beta vulgaris L.), selection 51501, resistant to cyst nematode (Heterodera schachtii Schm.), was recovered from the progenies of resistant alien addition lines. Meiosis of this plant was not normal and gave univalents, laggards, fragments, bridges, unequal chromosome distribution, restitution nuclei, and "carry-over" Al bridges. Two heterozygous paracentric inversions were evident. These aberrations were not necessarily related to the nematode resistance. Nuclear restitution occurred in either the first or second division, or both; consequently, diploid and tetraploid gametophytes were produced. More than 25% of the pollen aborted. The preliminary findings showed that nematode resistance was transmitted to the progenies through the pollen and ovules at an equally low rate (13%). A multiple gene hypothesis of three complementary dominant genes was proposed to interpret the phenomenon of the low frequency transmission of nematode resistance.

Key Words: Beta vulgaris L. • Heterodera schachtii Schm. • Cytogenetics • Paracentric inversion • Interspecific crosses • Complementary genes

² Research geneticist, SEA, USDA, P. O. Box 5098, Salinas, CA 93915.

Received for publication October 13, 1977.