Induction of Tetraploid Hibiscus moscheutos through Soaking of Seeds or Seedlings

Hibiscus moscheutos (2n=2x=38) is an herbaceous plant native to the eastern United States with a number of cultivars. Though possessing favorable characteristics of compact stature and large flowers in the midst of summer, they produce unsightly fruits which reduce late-season flowering. To improve ornamental characteristics and sterility, induction of tetraploid clones was attempted. Colchicine and oryzalin were used as mitotic inhibitors to induce tetraploid breeding lines that will be used to develop sterile triploids. Pre-scarified seeds and germinated seedlings of the cultivar ‘Luna Red’ were used. Seeds and seedlings were treated at three different concentrations of each doubling agent for three different periods of incubation. Following treatments, treated plants were thoroughly rinsed with water and were planted in a greenhouse. Survival data on seeds and seedlings were taken six weeks after treatment. Because less than 5% of the seeds survived treatments, the seed experiment was terminated. The ploidy level of seedlings was determined via flow cytometry. Overall, survival percentage in colchicine treatments was higher than in oryzalin treatments. The group of 0.025% colchicine for 12 hours was the most efficient at inducing tetraploids (survival 92.5%, tetraploid 22.5%). For the oryzalin treatment, incubation time (p=0.002), chemical rate (p<0.03) and the interaction (p<0.03) were significant for survival and tetraploid transformation. Treating seedlings in 100 uM oryzalin for 6 hours produced the highest survival rate and tetraploid transformation percentage (survival 57.5%, tetraploid 30%). Exposure to low concentrations of colchicine solution for a longer time or to a medium concentration of oryzalin for a short period were considered to be efficient in yielding a high number of tetraploids with a low rate of mortality. Diploid, mixaploid and tetraploid plants were also compared with respect to their ornamental characteristics: flower size, flower petal anthocyanin content, leaf stomata size and blooming period. While no difference was observed in flower size, stomatal size or blooming period, tetraploid plants were found to have higher content of anthocyanin in flower petals compared to diploid seedlings.