The Arctic Daisy, Chrysanthemum arcticum, Trifecta Is a Genetically Variable Polyploid Series

Area of Science:

• Plant genetics and evolutionary biology
• Understanding polyploidy in wild plant populations
• Genomic diversity and speciation studies

Background:

• Accurate ploidy determination is crucial for plant breeding, domestication, and understanding evolutionary history.
• The Chrysanthemum arcticum complex exhibits significant ploidy variation, with reported levels from diploid to octoploid.
• Previous studies indicate a wide range of ploidy levels within C. arcticum subspecies.

Purpose of the Study:

• To assess the ploidy levels of 225 genotypes from 46 wild populations of the Chrysanthemum arcticum complex.
• To investigate ploidy variation across mainland Alaska, Attu Island, and Hudson Bay.
• To utilize flow cytometry with a diploid reference (C. nankingense) for ploidy assessment.

Main Methods:

• Flow cytometry was employed to measure genome sizes (2C) of C. arcticum genotypes.
• Chrysanthemum nankingense (2n = 2x = 18) served as the diploid reference standard.
• Genotypes were collected from wild populations across Alaska and Canada.

Main Results:

• Genome sizes ranged from 5.27 to 20.69 pg (2C), indicating diploid to hexaploid levels.
• Triploids were the most frequent ploidy level (64%), persisting after reference standard correction.
• Ploidy levels showed no clear spatial, taxonomic, or latitudinal segregation, suggesting widespread distribution.
• High triploid incidence, self-compatibility, and fertility may indicate genetic instability or aneuploidy.
• Discrepancies between flow cytometry and reproductive compatibility suggest complex genomic interactions.
• Potential historical influences, such as WWII military activities, may contribute to genomic instability.

Conclusions:

• Accurate ploidy determination in the C. arcticum complex presents significant challenges.
• The high frequency of triploids and observed inconsistencies warrant further investigation.
• High-density SNP genotyping and chromosome imaging are recommended for resolving ploidy questions.
• Advanced methods are necessary to guide future breeding strategies for C. arcticum.