The Variable Effect of Polyploidization on the Phenotype in Escallonia

Abstract

To induce new variation within the Escallonia genus, chromosome doubling was performed in E. rubra, E. rosea, and E. illinita, three important species within this genus of mainly evergreen woody ornamental species. Obtained tetraploids and diploid controls were analyzed for rooting capacity, leaf and flower characteristics, and plant architecture using image analysis and cold tolerance. In the present study, a breeders' collection of 23 accessions was characterized cytogenetically and described morphologically. All analyzed species and cultivars were diploid (2n = 2x = 24), with exception of E. pendula, a tetraploid. Today, breeding in Escallonia is limited to lucky finds in seedling populations and few efforts in interspecific hybridization. Three selected Escallonia species underwent an in vitro chromosome doubling with both oryzalin and trifluralin applied as either a continuous or shock treatment. The treatments successfully induced polyploids in all three species. Image analysis revealed that tetraploid E. rosea had decreased shoot length (from 3.8 to 1.3 cm), higher circularity and more dense growth habit compared to diploids. No significant changes in cold tolerance were seen. Tetraploid E. illinita did not differ in shoot length, but an increased outgrowth of axillary buds on the main axis led to denser plants. For tetraploid E. rubra, an increase in plant height (from 4.9 to 5.5 cm) was observed together with a large decrease in circularity and density due to a more polar outgrowth of branches on the main axis. E. rubra tetraploids bore larger flowers than diploids and had an increased cold tolerance (from −7.7 to −11.8°C). Leaf width and area of tetraploids increased for both E. illinita and E. rubra, while a decrease was seen in E. rosea genotypes. For all three species, the rooting capacity of the tetraploids did not differ from the diploids. We conclude that the effect of polyploidization on Escallonia was highly variable and species dependent.

Synthetic Polyploidy in Grafted Crops

“…Regarding biomass production, there is no consensus about ploidy effects on plant growth, since some species may present similar (Niu et al, 2016) or lower (Hennig et al, 2015;Denaeghel et al, 2018) organ size or biomass associated to polyploidy. Independently of plant height, polyploid plants often develop higher biomass that results in thicker tissues and organs and alter plant architecture when compared to the 2x.…”

“…These effects can be highly variable between species or even among individuals within the same species. For instance, Denaeghel et al (2018) reported increased cold tolerance in autotetraploid Escallonia rubra (Ruiz and Pav. ) Pers.…”

Induction of Synthetic Polyploids and Assessment of Genomic Stability in Lippia alba

“…Although many studies provide polyploidization protocols (Rêgo et al, 2011;Gomes et al, 2014;Tavan et al, 2015;Widoretno, 2016;Salma et al, 2017;Denaeghe et al, 2018), they generally demonstrate that the optimal procedures are rather species specific. The development of a proper method for polyploidization requires the conduction of several tests to obtain the most suitable combination of antimitotic agent, concentration, exposure time, type of explants, exposure method, and the regeneration mode employed (Allum et al, 2007;Dhooghe et al, 2011;Yang et al, 2014;Sattler et al, 2016).…”

Artificial Chromosome Doubling in Allotetraploid Calendula officinalis

“…Tetraploids are often bigger than triploids, which are in turn bigger than diploids. But it is also possible that tetraploids have a more compact growth habit as compared to diploids, as shown in Escallonia (Denaeghel et al, 2018). Higher ploidy levels are often marked by stunted growth as was shown in A. thaliana (Corneillie et al, 2019).…”

“…However, the very low number of octaploids makes it difficult to make general conclusions. Other studies have shown that the optimal antimitotic agent and concentration is strongly genotype-dependent (Dhooghe et al, 2010), such as in parsley (Nasirvand et al, 2018), Onobrychis elata (Avci et al, 2019), and Escallonia (Denaeghel et al, 2018), among many others. Unfortunately most of the octaploid plants detected at 3 weeks after transplant reverted to tetraploid status after 9 weeks.…”