Comparison of seven colchicine-induced tetraploid clones with their original diploid clones in purple coneflower (Echinacea purpurea L.)

Seven clones of colchicine-induced tetraploid purple coneflower (Echinacea purpurea L.) plants were grown on a farm for comparison with their corresponding original diploid plants. In the first year of cultivation, the plant height, number of capitula, and inflorescence (branched flower stalk) were significantly reduced in all of the tetraploid plants, while the length-to-width leaf ratio, pollen size, and root thickness were significantly increased. Although the tetraploid plants had larger seeds, most of the seeds of tetraploid plants were not fully filled and the naked seeds (i.e., seeds observed without the outer seed coat) were noticeably smaller than those of the diploid plants. In the second year of cultivation, the phenological stages were markedly delayed in the tetraploid plants; the number of capitula increased much more in tetraploid plants than in diploid plants. Among the seven tetraploid clones, two yielded significantly higher plant biomass and higher cichoric acid content per gram dry weight as well as per plant. The results of the present experiments indicate that some effects of tetraploidization of diploid E. purpurea are genotype-dependent, suggesting that the tetraploidization of more genotypes of the diploid is needed to breed better tetraploid varieties.