Shading and natural rooting biostimulator enhance potential for vegetative propagation of dogwood plants (Cornus alba L.) via stem cuttings

Auxins have been widely used to stimulate rhizogenesis in stem woody cuttings. Recently, more environmentally friendly biostimulators are reported to enhance rhizogenesis. Also, stock plants shading appears to be an easy and effective method to increase rooting of cuttings. The aim of the study was to examine the effect of shading and exogenous application of auxin or biostimulator AlgaminoPlant on rooting potential of two cultivars of dogwood (Cornus alba L.) and to detect anatomical modifications induced by shading that may be related to rooting ability. Stock plants were shaded with a nursery net reducing 50% of light for 6 weeks prior to cuttings' harvest while the control stock plants were grown under ambient light. Cuttings from shaded and non-shaded plants were treated with a commercial rooting powder (1% IBA), sprayed with water solution of IBA (200 mg·l− 1) or with biostimulator AlgaminoPlant (0.2% v/v), whereas the control cuttings were sprayed with water. The effects of treatments were evaluated after 8 weeks of rooting in a plastic tunnel. The two cultivars tested differed in natural as well as induced rooting potential, both in cuttings harvested from shaded stock plants and those grown under ambient light. Shading of stock plants significantly improved rooting abilities in comparison to control cuttings from plants grown under ambient light. Shading reduced diameters of stem and pith, with thinner layers of cortex, epidermis and collenchyma; vascular bundles and diameters of xylem vessels were also smaller. The thickness of leaf blades collected from shaded stock plants was lower due to thinner epidermal as well as spongy and palisade mesophyll layers. The best effects in rooting were obtained when shading was followed by the application of rooting inducers. The effects of synthetic auxin IBA and biostimulator AlgaminoPlant were similar; therefore, the latter is a viable option to reduce widespread use of rooting inducing chemicals based on synthetic auxins.