Karyotypes and chromosome association in aneuploid varieties of Japanese garden iris, Iris ensata Thunb

Summary

Karyotypes, chromosome association and pollen fertility of aneuploid varieties (2n=25), ‘Ochibagoromo’, ‘Matsusakatsukasa’ and ‘Isehomare’ in Iris ensata were analysed and compared with those of eu-diploid varieties (2n=24), ‘Shishinden’, ‘Kachô’ and ‘Asahimaru’. The somatic chromosome complement of the aneuploid varieties consisted of 11 pairs and 3 singles of chromosomes and that of the eu-diploid varieties 12 pairs of chromosomes. The singles of chromosomes in the aneuploid varieties had similarity with one another and with a pair of chromosomes in the eu-diploid varieties. The high frequency of normal association was present in the eu-diploid varieties, and this indicated that 12 pairs of chromosomes had full homology between each other. In contrast, the mean chromosome association per cell in an aneuploid variety ‘Ochibagoromo’ was 4.615_I+10.067_II+0.077_III+0.005_IV, indicating that the chromosome complement of this variety consisted of 11 pairs and 3 singles and that these singles had partial homology among them. The eu-diploid varieties exhibited high pollen fertility due to their regularity of chromosome association; the aneuploid varieties considerably lower fertility, i.e. 28.2% for ‘Ochibagoromo’, 31.8% for ‘Isehomare’ and 43.8% for ‘Matsusakatsukasa’. The primary cause for the low fertility of these varieties seemes to be the partial homology among 3 single chromosomes. Finally, the origin and the development of the aneuploid varieties were discussed.