Seaweed Extracts as Substitutes of Synthetic Hormones for Rooting Promotion in Rose Cuttings

In the horticultural sector, the achievement of an efficient and eco-friendly sustainable production of plants is nowadays challenging. Indeed, in plant vegetative propagation of woody ornamentals, the substitution of chemical products used to promote rooting of cuttings with natural extracts would be a desirable goal. Thus, the aim of this work was to test the replacement of synthetic phytoregulators, such as auxins and brassinosteroids, with biostimulants, such as seaweed extracts, for the rooting promotion of rose cuttings. The rooting rate and biometric parameters of control cuttings treated with distilled water were compared with those of cuttings treated with synthetic hormones, i.e., auxins or 22(S),23(S)-homobrassinolide, or two commercial products based on low temperature seaweed extracts, i.e., Kelpak (R) and Phylgreen. Two scented hybrid tea rose cultivars were used to assess possible genotype-dependent effects, i.e., 'Michelangelo (R)' and 'Cosmos (R)'. Auxins confirmed their role in root growth enhancement in ornamental plant cuttings. Like these phytoregulators, Kelpak (R) improved the survival rate and root biometric parameters of both rose cuttings, highlighting its suitability for the replacement of synthetic products used for rooting promotion in rose propagation. Brassinosteroids showed a species-dependent effect, increasing the root biomass in 'Cosmos (R)' while it resulted as distilled water in 'Michelangelo (R)'. Phylgreen did not improve the rooting of both rose cuttings, highlighting the necessity of evaluating the applicability and methodology for this product before its use. In conclusions, our results highlighted the possibility to replace chemical products in rose cutting production.