Morphological effects at radicle level by direct contact of invasive Acacia dealbata Link

Seeds of Lactuca sativa L. (model plant) and Quillaja saponaria Mol. (native tree) were subjected to germination in direct contact with leaves, pods and seeds from invasive Acacia dealbata Link. (Fabaceae) to reveal whether morphological changes occur at radicle level. Bioassays were carried out with plant material deposited underneath A. dealbatás canopy under natural conditions at Mediterranean ecosystem in South America. Segments of radicle tip, cell elongation zone and root hair zone were analyzed under scanning electron microscopy. The three plant parts from A. dealbata inhibited the formation of root hairs and altered the rhizodermis (deformation and tissue destruction) of the two recipient species. In the case of Q. saponaria, an increase in thickness in the cell elongation zone was observed and internal tissues up to the vascular cylinder in the root hair zone were intensely damaged. The root cap and meristematic region suffered structural changes and damage resulting from the contact with leaves and pods. All morphological effects have been attributed to the impact caused at root level by potential allelochemicals released by different tested plant materials of A. dealbata. These results suggest that the morphological changes and damage produced by A. dealbata at the radicle level may pose a threat to the growth and survival of the recipient species.