Colchicine- and trifluralin-mediated polyploidization of Rosa multiflora Thunb. var. inermis and Rosa roxburghii f. normalis

Rosa multiflora Thunb. var. inermis and Rosa roxburghii f. normalis are two important diploid species for rose breeding. Interspecific crosses between diploid species and tetraploid rose cultivars result in triploids with generally decreased fertility. A most promising gene transfer strategy is the production of fertile tetraploid plants before mating with tetraploids. In our study, germinating seeds of R. multiflora and R. roxburghii were treated with colchicine, and cotyledon-stage seedlings of R. multiflora were treated with colchicine or trifluralin in order to obtain tetraploid plants. Also, various concentrations of antimitotic agents and different treatment durations were tested. The results showed the antimitotic agents affected the plant morphological characteristics (i.e. plant height, stem diameter) of R. multiflora and R. roxburghii. Twenty-three tetraploid plants were obtained from the germinating seed treatments (21 from R. multiflora and two from R. roxburghii), but no tetraploid plants were obtained from the seedling treatments. The highest rate of chromosome doubling (25.0%) was achieved when germinating seeds of R. multiflora were treated with 0.2% colchicine for 12 h. At the same time, marked morphological variation was observed and analyzed among tetraploid plants and their corresponding diploids of R. multiflora.