Abstract
The presence of more than two full chromosome sets, polyploidy, is an important component in plant evolution. However, knowledge of the frequency of polyploidization and which pathways contribute to polyploid formation and gene flow among cytotypes remains limited.
Flow cytometry and chromosome counts were used to determine genome size of Artemisia tridentata parents and offspring. Reduced-representation sequencing was used on the parents, offspring, and conspecific taxa to confirm genetic relationships among parents and offspring.
A polyploidization rate of 0.22% was determined from seedlings of diploid parents producing one triploid and one tetraploid. Genome-size estimates coupled with chromosome counts provide evidence for both one-step and two-step pathways in A. tridentata. A wild triploid produced viable offspring with varied aneuploidy (2n = 18 + 1 to 4n = 36 - 4) and genome sizes ranging from 11 pg to 18.2 pg.
Our results indicate that one- and two-step pathways to WGD can occur in A. tridentata. The two-step pathway could provide a mechanism for bidirectional gene flow via triploid bridge. These pathways could generate substantial genomic variation within the A. tridentata polyploid complex. Given the fecundity and WGD rates in this species, the generation of polyploid offspring from diploid progenitors can be relevant to environmental adaptation at generational timescales.