Anatomical Characteristics and Resprouting Capacity of the Underground Organs of Bohemian knotweed (Polygonum ×bohemicum)

The hybrid Bohemian knotweed [Polygonum ×bohemicum (J. Chrtek & Chrtková) Zika & Jacobson [cuspidatum × sachalinense; syn. Reynoutria ×bohemica Chrtek & Chrtková ] is part of the worldwide problematic rhizomatous invasive plants which impact on (semi-)natural and agricultural systems. In this context, precise knowledge about the morpho-anatomy and the resprouting capacity of the underground organs is a key information for developing efficient eradication measures. In the present study, we aimed at (i) clarifying existing differences in the morpho-anatomical characteristics of rhizomes and roots, (ii) developing an easy-to-apply field identification method of the underground organs, and (iii) identifying the main morpho-anatomical features enhancing the rhizomes’ resprouting ability. To this purpose we collected the underground organs of two wild populations of P. × bohemica in Canton Ticino (southern Switzerland) and analyzed the morpho-anatomical differences between rhizomes and roots, using high-resolution microscope images and microtome sections. Collected material was then used for a resprouting capacity test after assessing rhizome characteristics such as weight, total diameter, pith diameter, pith brightness and pith color. Contrary to roots, rhizomes are characterized by a pith-tissue in the center and display nodes which peripheral dormant buds enable them to resprout. Resprouting ability of rhizomes was high (87.1% on average) and depends on the ontogenetic development stage of the organs (peak values of 97% for young and clear organs, 50% for old and dark ones). In conclusion, the smooth pith tissue of rhizomes represents a key discriminating feature between rhizomes and roots, whereas relating existing nodes to the corresponding rhizome pith color allows to assess the resprouting potential of a knotweed population.