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.

Assessing the Genetic Diversity of Daylily Germplasm Using SSR Markers: Implications for Daylily Breeding

“…Examination of daylily ploidy showed the occurrence of triploids or pentaploids [53]. Such polyploids are induced by antimitotic agents [53] or by misinterpreting ploidy levels during registration [54]. This shows uncommon phenomena in plants of triploid existence and even the possibility of mating.…”

“…Examination of daylily ploidy showed the occurrence of triploids or pentaploids [53]. Such polyploids are induced by antimitotic agents [53] or by misinterpreting ploidy levels during registration [54].…”

Ploidy’s Role in Daylily Plant Resilience to Drought Stress Challenges

“…Tetraploid genotypes generally adapt better to water shortage conditions than diploid plants and exhibit larger stomata, higher chlorophyll content, and higher photosynthetic capacity, resulting in a competitive advantage under water-limited conditions [26][27][28]. A previous study with daylily polyploid induction by Misiukevičius and Stanys [29] showed that higher ploidy daylily plants had longer stomata.…”

Transcriptome Analysis of Diploid and Autotetraploid Hemerocallis Response to Drought Stress

“…Nearly 99 thousand daylily cultivars are registered by the American Hemerocallis Society [30]. Daylilies naturally occur only as diploids and triploids [31]. One of the common ways to make plants more resistant to biotic and abiotic stresses is whole genome duplication (WGD) [19,32,33].…”

“…One of the common ways to make plants more resistant to biotic and abiotic stresses is whole genome duplication (WGD) [19,32,33]. Tetraploid daylilies were artificially induced by using chemical antimitotic agents [34][35][36][37][38]. Currently, hybridizers focus on tetraploid daylily breeding programs with 69.8% of newly registered cultivars in the last five years being tetraploids [30].…”