Induction and analysis of polyploids in daylily (Hemerocallis L.) plants

Abstract

Daylily ( Hemerocallis L.) is a popular herbaceous perennial ornamental plant. The American Hemerocallis Society (AHS) currently has over 96,000 cultivars registered. Of these, half are tetraploids (4x), and the other half are diploids (2x). To enrich the breeding lines of tetraploid daylilies, colchicine is the most widely used. During the experiment, oryzalin (ORZ) and colchicine (CLC) were used for the polyploidisation of daylilies. Germinating seeds derived from diploid and tetraploid daylily cultivars as maternal plants were exposed to solutions of ORZ and CLC at different concentrations. Ploidy of seedlings was determined after six months by flow cytometry, and the obtained results were related to the size of the stomata. Chimerism of the young side shoots developing on treated plants was assessed three years after polyploidisation by checking the ploidy using a flow cytometer. It has been found that whole-genome duplication is not common in daylilies during polyploidisation of germinating seeds – triploids (3x), pentaploids (5x), hexaploids (6x), and heptaploids (7x) were obtained. The optimal concentration of CLC for induction higher ploidy was 125–250 µmol when exposed to seeds of the diploid maternal plant (DMP) and 250–500 µmol when exposed to the tetraploid maternal plant (TMP) one. In the case of ORZ, optimal treatments were 10 µmol for germinating DMP seeds and 40 µmol for TMP seeds, respectively. Stomata size can preliminarily determine daylily ploidy. A flow cytometry should be used for a more accurate determination of ploidy. Individuals treated with antimitotic agents are prone to chimerism. The most extensive ploidy variation observed in individuals with uneven ploidy is usually in the direction of even ploidy. Therefore, the ploidy of clones used for breeding should be checked regularly.