The control of di ploid like meiosis in poly ploid taxa of chrysanthemum 2. octo ploid chrysanthemum ornatum

Watanabe, K.

Cytologia 46(3): 499-514

1981


ISSN/ISBN: 0011-4545
Accession: 006620612

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Abstract
In C. ornatum (Akune strain) with 2n = 8x = 72 the following meiotic configurations were frequently observed; 2 IV + 32 II, 1 IV + 34 II, 36 II and 35 II + 2 I. Seventy-two chromosomes at mitotic metaphase varied in length from 5.1 to 2.8 .mu.m and in arm ratio from 1.0 to 6.5. Five satellite chromosomes and 7 small chromosomes with the extreme subterminal centromeres were distinguishable. Karyomorphologically this strain is not an autooctoploid. One androgenetic polyhaploid with 2n = 4x + 1 = 37 was obtained by artificial ovary culture after hybridization with the diploid C. makinoi. The following meiotic configurations were frequently observed: 1 IV + 1 III + 15 II, 1 IV + 1 III + 14 II + 2 I, 1 IV + 16 II + III + 17 II and 18 II + 1 I. A pentavalent association and a chromosome fragment were also observed rarely. The chromosomes derived from C. ornatum (Akune strain) paired homologously. The data of quadrivalent frequency conform to the theoretical Poisson expectation based on the random hypothesis. In C. ornatum (Yakushima Isl. strain) with 2n = 8x = 72, 36 II was the main meiotic configuration and 3 IV + 30 II, 2 IV + 32 II, 1 IV + 34 II and 35 II + 2 I were rarely observed. Seventy-two chromosomes, at mitotic metaphase, varied in length from 6.0 to 3.2 .mu.m and in arm ratio from 1.0 to 4.6. Ten satellite chromosomes and 5 small chromosomes with extreme subterminal centromers were distinguishable. Karyomorphologically this strain is not an autooctoploid. Three F1 hybrids with 2n = 5x = 45 between diploid C. boreale and C. ornatum (Yakushima strain) were obtained by ovary culture. The following meiotic configurations were frequently observed; 1 IV + 19 II + 3 I, 5 III + 12 II + 6 I, 2 III + 17 II + 5 I, 21 II + 3 I and 20 II + 5 I. The chromosomes derived from C. ornatum (Yakushima strain) paired homololgously. The genetic control system for the suppression of multivalent formation in octoploid, its polyhaploid and pentaploid F1 hybrid must be the restriction of pairing initiation at one of 2 sites/chromosome. This restriction seems to be under the polygenic control which leads to supersuppression with the increase of gene dosage. This system tends to act in a relatively more harmonious fashion in the even-numbered than in the odd-numbered polyploid.