1) In meiosis of
Ch. japonense (Saka strain) 2n=6x=54, 27 II was the main chromosome configuration and 1 IV+25 II and 26 II+2 I were rarely observed. Fifty-four chromosomes, at mitotic metaphase, varied in length from 8.4μm to 4.2μm and in arm ratio from 1.0 to 4.9. Ten satellite chromosomes and six small chromosomes with extreme subterminal centromeres were well distinguishable. Karyomorphologically this species is not an autohexaploid.
2) Eight F
1-hybrids between hexaploid
Ch. japonense (Saka strain) and diploid
Ch. boreale, with 2n=4x=36 and 2n=4x+1=37, were obtained. 2 IV+14 II, 1 IV+16 II and 18 II were the main meiotic configurations in the F
1-hybrid with 2n=4x=36. The quadrivalent frequencies conform to the Poisson distribution. The chromosomes derived from
Ch.japonense (Saka strain) paired both homoeologously and homologously with the
Ch. boreale chromosomes.
3) F
1-hybrids were partially fertile (0%-1.1% in interbreeding and 0.3%-5.9% in intrabreeding) and gave rise to triploid B
1-hybrids on backcrossing to diploid
Ch. boreale, and to tetraploid F
2-hybrids by intrabreeding.
4) In eight of the nine B
1-hybrids with 2n=3x=27 studied the average trivalent formation per PMC ranged from 4.66 to 5.55. The trivalent frequencies conform to the Poisson or binomial distribution. Further homoeologous chromosome associations were revealed in this generation. In the ninth B
1-hybrid, 9 II+9 I was the main chromosome configuration. This plant was indiscriminable morphologically from the others.
5) These B
1-hybrids with 2n=3x=27 were partially fertile (0%-0.2% in interbreeding and 0%-3.7% in intrabreeding) and gave rise to B
2-hybrids with 2n=24, 26, 27 and 36 on backcrossing to the diploid
Ch. boreale, and progenies with 2n=30, 32, 33, 34, 35 and 36 by intrabreeding. In B
2-hybrids with 2n=26, the following meiotic configurations were frequently observed; 7 III+2 II+1 I, 6 III+3 II+2 I, 5 III+4 II+3 I, 4 III+5 II+4 I and 3 III+6 II+5 I.
6) In seven F
2-hybrids with 2n=4x=36, the following meiotic configurations were frequently observed; 3 IV+12 II, 2 IV+14 II, 1 IV+16 II and 18 II. There is a significant difference in the frequency of quadrivalent and bivalent formation among F
2-hybrids; the maximum number of quadrivalents per PMC varied from four to two. Quadrivalent frequencies conform to the Poisson distribution. The rate of seed setting varied from 0% to 58.7% in F
2-hybrid intra-breedings. There was no correlation between the frequency of multivalent formation and the rate of seed setting.
7) Nineteen of the twenty F
3-hybrids studied had the chromosome number 2n=4x=36 and the twentieth had 2n=4x+1=37. In eleven F
3-hybrids with 2n=4x=36 the following meiotic configurations were frequently observed; 3 IV+12 II, 2 IV+ 14 II, 1 IV+16 II and 18 II. There was a significant difference in the frequency of quadrivalent and bivalent formation among F
3-hybrids; the maximum number of quadrivalents per PMC varied from eight to two. Quadrivalent frequencies conform to the Poisson distribution.
8) In
Ch. japonense (Nakamura strain) with 2n=6x=54, 27 II was the main meiotic configuration and 2 IV+23 II, 1 IV+25 II, 1 IV+24 II+2 I and 26 II+2 I were rarely observed. Fifty-four chromosomes, at mitotic metaphase, varied in length from 6.7μm to 3.8μm and in arm ratio from 1.0 to 4.4. Eight satellite chromosomes and six small chromosomes with extreme subterminal centromeres were well distinguishable. Karyomorphologically this species is not an autohexaploid.
9) Two F
1-hybrids with 2n=4x+1=37 between diploid
Ch. boreale and
Ch. japonense (Nakamura strain) were obtained by ovary culture.
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