Adventitious root formation – from the laboratory to the greenhouse

Unlike most animals, plants have the ability to regenerate new organs which is not part of their original developmental program. This ability underlies the phenomenon of adventitious root formation in which non-root cells change their fate and coordinately form a functional root. The precise signals required for the successful formation of an adventitious root are not entirely clear and probably consist of a repertoire of signals that differ from plant to plant. Thus, mature/ juvenile, woody/herbaceous, and phenolic and aromatic compound-rich /poor plants are probably using a slightly different repertoire of signaling molecules to create the rooting permissive conditions. In some cases, there is a huge clone-to-clone difference in rooting capability which probably results from genetic heterogeneity within individuals of the same species. Accordingly, rooting conditions should be adjusted to meet the requirements of each situation, especially in the case of rooting-recalcitrant ones. Thus, obtaining adventitious root formation from various plants might require precise and individualized protocols. Rooting efficiency is strongly affected by several parameters: (1) the physiological status and well-being of the mother plant – season, age, proper nutrition, shading or etiolation, and pruning regime are very important; (2) the cutting itself – herbaceous or woody, apical or subapical, dormant or growing, the thickness and length of the stem and the number of leaves all play a role; (3) the rooting conditions – bedding composition, temperature of the rooting table and air inside the greenhouse, humidity, and light intensity; (4) the auxin treatment – concentration, type of auxin (IBA or other synthetic auxins), mode of application (submergence of the cutting base or foliar spray), and length of the treatment. Adventitious roots can also be induced under tissueculture conditions, or in hydroponic systems, where conditions can be tightly controlled throughout the process. The molecular mechanisms underlying adventitious root formation, or the barriers that block adventitious root formation in recalcitrant plants, are slowly being revealed, by the scientific community, but much has yet to be discovered. The current special issue, dedicated to adventitious root formation, provides an overview of recent findings and insights. Adventitious root formation – from the laboratory to the greenhouse