Induction of tetraploids in Escallonia spp

Escallonia is a genus of flowering shrubs, native to South-America. As for most woody ornamentals, current breeding efforts in Escallonia are low. In an attempt to enlarge the assortment and to introgress winter hardiness and a more compact growth habit, we performed in vitro polyploidization on Escallonia species. We collected 25 species and characterized their genome size, chromosome number, and leaf and flower parameters. Measured genome sizes of the collection varied between 1.01 and 1.31 pg/2C. In vitro polyploidization on E. rubra and E. rosea was more efficient when using oryzalin and trifluralin compared to colchicine. We obtained up to 56.7% E. rubra tetraploids using trifluralin (1 μM for 6 weeks) and 33.3% E. rosea tetraploids using oryzalin (150 μM for 3 days), compared to colchicine which only yielded 16.7% E. rubra (1000 μM for 3 days) and 3.3% E. rosea (2000 μM for 3 days) tetraploids. Short (2, 3 and 4 days) and chronic (6, 8 and 10 weeks) treatments on E. rubra displayed a higher polyploidization efficiency for trifluralin (28%) compared to oryzalin (18%). Ploidy doubled plantlets and diploid controls were acclimatized in the greenhouse for further morphological evaluation. The most efficient treatment was chosen to polyploidize other Escallonia species.