Graduate Thesis Or Dissertation
 

Cytotaxonomic studies in the Artemisia ludoviciana polyploid complex of the Pacific Northwest

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  • The Artemisia ludoviciana polyploid complex is a highly polymorphic assembledge of eight taxa in the Pacific Northwest, with a chromosome base number of x=9. A cytogenetic analysis of this complex was carried out to determine the sources of its variation, the types of polyploidy present, and the genetic processes active in its evolution. Chromosome counts in the complex disclosed two diploid taxa, A. michauxiana and A. cavaticaulis, in addition to the previously counted diploids, A. suksdorfii and A. lindleyana. Results of meiotic analysis and artificial hybridization experiments strongly suggested the autoploid origin of the polyploid members of the complex. These results included the constancy of multivalent formation among the polyploids, the maximum number of multivalents formed in each taxon, the pairing relationships of the hexaploid and trisomic hexaploid A. douglasiana, the degree of homology between the included genomes of the artificial hybrids, and the presence of heteroploidy in at least five of the included taxa. The attributes of the complex that might have contributed to the origin and success of autoploidy were also examined. Observations indicate that the diploids produce a low but constant number of unreduced pollen grains. Introgression from the diploid to the tetraploid level, through tetraploid progeny, provides a source of variation for the newly formed autoploids. The complex has a broad physiological base. Mechanisms are present in the meiotic apparatus that could allow for an increase in fertility of autoploid individuals. The phylogenetic and taxonomic relationships among several of the taxa are discussed.
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