Studies on the control of diploid-like meiosis in polyploid taxa of Chrysanthemum. II. Octoploid Ch. ornatum Hemsley.

Abstract

1) In Ch. 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 5.1μm to 2.8μm and in arm ratio from 1.0 to 6.5. Five satellite chromosomes and seven small chromosomes with the extreme subterminal centromeres were well distinguishable. Karyomorphologically this strain is not an autooctoploid.2) One androgenetic polyhaploid with 2n=4x+1=37 was obtained by artificial ovary culture after hybridization with the diploid Ch. 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+1 I, 1 III+17 II and 18 II+1 I. A pentavalent association and a chromosome fragment were also observed rarely. The chromosomes derived from Ch. ornatum (Akune strain) paired homoeologously. The data of quadrivalent frequency conform to the theoretical Poisson expectation based on the random hypothesis.3) In Ch. 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 6.0μm to 3.2μm and in arm ratio from 1.0 to 4.6. Ten satellites chromosomes and five small chromosomes with extreme subterminal centromers were well distinguishable. Karyomorphologically this strain is not an autooctoploid.4) Three F1-hybrids with 2n=5x=45 between diploid Ch. boreale and Ch. ornatum (Yakushima Isl. 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 Ch. ornatum (Yakushima Isl. strain) paired homoeololgously.5) 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 two sites per chromosome. This restriction seems to be under the polygenic control which leads to the super-suppression in accompany with the increase of gene dosage. This system tends to act in a relatively more harmonious fasion in the even-numberd polyploid than in the odds.