1995 Volume 60 Issue 1 Pages 53-61
A total of 391 accessions from 11 populations of Japanese Artemisia keiskeana were cytologically examined. Twenty-one percent of these accessions carried B chromosomes in addition to the regular diploid complement and 3.5% were triploids. The frequency of plant with B chromosomes ranged from 0% to 59% among 11 populations. B chromosomes were 1/2-1/5 in length as compared with the smallest autosome and were euchromatic in nature. They were ususally mitotically unstable and varied in number from zero to ten both within and between plants. This variation in number of B chromosomes within a plant may be caused by the non-disjunction and unequall segregation during mitotic anaphase. These B chromosomes seemed not to have any phenotypic consequences on plant. Neverthless B chromosomes have been found in 6 examined populations distantly isolated from each other and have occurred in large proportion of the individuals of three populations around the boundary of Okayama and Hiroshima Prefectures. The non-random spatial distribution of plants with or without B chromosome in these natural populations may, at least in part, be due to asexual reproduction. Triploids were found in 2 populations distantly isolated from each other. They are karyotypi-cally auto-triploids. They have occurred spontaneously and are maintained asexually in natual populations.
