Production of medically valuable stilbenes and emodin in knotweed

•Five Fallopia clones were cultivated for 3 yr in the field.•Rhizomes and roots contain more stilbenes and emodin than shoots.•F. japonica produced most stilbenes per gram and hexaploid hybrids most biomass.•Knotweed yielded 0.7, 4, 6 and 0.6 kg/ha of resveratrol, resveratroloside, piceid and emodin, respectively.

Most people consider knotweeds to be dangerous, invasive weeds. These plants produce useful secondary metabolites, stilbenes and emodin. We conducted a 3-yr field experiment with two parental species Fallopia japonica and Fallopia sachalinensis, and three clones of their hybrid, F. × bohemica. Knotweed biomass and resveratrol, resveratroloside, piceid and emodin contents were assessed three times per year. Their biomasses (in descending order) are as follows: the two hexaploid hybrid clones, the octoploid hybrid clone, and the two parental clones. Although more energy is needed to harvest rhizomes and roots from knotweed, these produce more resveratrol, piceid and emodin than shoots. Out of the five clones tested, F. japonica contained the greatest amounts of resveratrol, resveratroloside, piceid and emodin, in its belowground biomass. The optimal harvest of rhizomes and roots from productive clones was in the autumn of the second year of cultivation.