Polyploid and Doubled Haploids Induction in Platycodon grandiflorum (Jacq.) A. DC. through Oryzalin Treatment-Mediated Chromosome Doubling

Through chromosome doubling in haploid regenerants derived from the microspore culture, doubled haploid (DH) homozygous lines were established within one to two generations.This process shortens the time required to produce homozygous plants compared to the time needed for conventional breeding methods, which require multiple generations of self-fertilization.In this study, we aimed to identify an optimal oryzalin concentration and duration of the treatment for chromosome doubling in Platycodon grandiflorum and develop a method for inducing DHs.Four different concentrations of oryzalin (12.5, 25, 50, and 100 mgL -1 ) were applied for one to three days (once a day) to the shoot apical meristem of P. grandiflorum plants.The polyploid induction rate reached its highest (27.78%) when 50 mgL -1 of oryzalin was applied for three days.The application of 50 mgL -1 oryzalin for three days to haploids obtained via shed-microspore culture induced chromosome doubling, with a ploidy analysis confirming successful DH induction in 238 of 564 plants.These plants were then evaluated for their morphological traits to identify superior lines, followed by seed harvesting.Thus, we established a technique for inducing polyploids and DHs in P. grandiflorum by means of an oryzalin treatment.This method can be applied to P. grandiflorum and other medicinal plants for DH induction, facilitating the rapid development of homozygous lines and considerably reducing the breeding time.