Testing two chromosome doubling agents for in vitro tetraploid induction on ginger lilies, Hedychium gardnerianum Shepard ex Ker Gawl. and Hedychium coronarium J. Koenig

Polyploidization can be a way to produce new varieties in vegetatively propagated species where options on increasing genetic variability are limited compared with sexual reproduction. While there are hundreds of publications with in vitro methods in somatic doubling, it is cardinal to custom-test for a target species of interest on choosing specific reagents and optimizing conditions. This research was performed to provide a reference process for Zingiberaceae species of which the majority is reproduced with vegetative propagation. Ginger lilies, Hedychium gardnerianum Shepard ex Ker Gawl. and Hedychium coronarium J. Koenig, were employed to optimize chromosome doubling for tetraploid production as they are typically used by vegetative propagation. However, they have the popularity as ornamentals globally due to their horticultural aspects. Tetraploid induction was optimized by in vitro somatic chromosome doubling on H. coronarium and H. gardnerianum through callogenesis. The explant segments of young leaf blades or leaf sheaths were treated with different concentrations of either with colchicine or with oryzalin. The regenerated shoots from callus cultures were transferred to basal MS medium for 2mo to confirm somatic stability. The ploidy was assessed by flow cytometry, measuring the size and density of stomata, counting chromosomes, and chloroplasts in guard cells. The highest percentage of tetraploid regenerated plants was observed with 1250 µM colchicine treatment for Hedychium gardnerianum when compared to the other treatments tested, while no tetraploid plants were obtained from the oryzalin treatment. In H. coronarium , four mixoploid regenerated plants treated with 15 µM oryzalin were confirmed and no shoots were obtained from the colchicine treatment. The results indicated that the in vitro polyploid induction is optimized with the two Hedychium species, which could reference other Zingiberaceae species.