Identification of tetraploid mutants of Platycodon grandiflorus by colchicine induction

Platycodon grandiflorus is an important medicinal plant in China and its root has been used as medicine or food for centuries. Polyploidy may increase the amounts of functional compounds in vegetative organs for medicinal plants. So polyploid manipulation for medicinal plants is an effective approach of germplasrn development. This research focused on tetraploid induction of P grandiflorus by modified colchicine method. The diploid seedlings were induced under three treatments (24h, 48h and 72h) to test the best treatment time. Morphology and cytology identifications between obtained mutants and diploid controls were also conducted. The seedling growth and development of all mutants was more stunted than controls. According to preliminary morphological characteristics, mutant rates in different treatment times were statistically estimated and the highest mutant rate was 50% under the treatment of 72h. The chromosome number of most mutants was 36 (2n=4x), while the chromosome number of diploid. controls was 18 (2n=2x) by cytology observation of root tip cells. Chimeras and octoploids were also identified from obtained mutants. By microscope observation of low leaf epidermis, there were significant differences for stoma area between tetraploid mutants and diploid controls. As a result, tetraploid mutants of P grandiflorus were successfully obtained by modified colchicine method and their desirable traits would be further evaluated to incorporate into next breeding and pharmacy production program.