Cytogenetics of a synthesized allopentaploid (2n = 5x = 100) in the genus Glycine subgenus Glycine

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Abstract
The objectives of this study were to provide information on the origin, identification, meiosis, and breeding behavior of a synthesized allopentaploid (2n = 5x = 100) in the genus Glycine (Willd.) subgenus Glycine. The origin of the pentaploid plant was as follows: G. clandestina, 2n = 2x = 40, A1A1 × G. canescens, 2n = 2x = 40, AA (designated as H119), F1 (2n = 2x = 40, AA1) × G. tomentella (2n = 4x = 80, AxAxDD) → F1 (2n = 3x = 60, AAxD (assuming A-genome chromosomes from G. canescens were transmitted)) → 0.1% colchicine treatment → 2n = 6x = 120 (AAAxAxDD) × G. tomentella (2n = 4x = 80, AxAxDD) → BC1, 2n = 5x = 100 (AAxAxDD). Morphologically, the pentaploid plant very closely resembled the tetraploid G. tomentella, PI 441005. Compared with hexaploids, the pentaploid plant was less vigorous for several morphological traits. However, it was not possible to distinguish visually among 4x, 5x, and 6x plants. Intergenomic chromosome pairing was followed in hexaploid (A–A, Ax–Ax, D–D) and pentaploid (A, Ax–Ax, D–D) plants. Despite a close similarity between A and Ax genomes (A- and Ax-genome chromosomes pair normally in the absence of their homologues) meiotic stages were highly abnormal in the pentaploid, with univalents, laggards, and micronuclei, but the plant set normal pods and seeds. The pentaploid plant did not breed true, as chromosomes in the 14 examined plants of the progeny ranged from 2n = 86 to 97. Furthermore, progeny of a plant with 2n = 90 segregated for plants with 2n = 81–86. These results indicate that the preferential elimination of G. canescens (A genome) chromosomes is rapid and eventually AxAxDD genome chromosomes will prevail. Thus, pentaploids will stabilize at the tetraploid level.Key words: Glycine spp., allopolyploidy, chromosome pairing, genome.

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