Stimulation of adventitious root formation in rose cuttings through laser wounding

Abstract

Propagation by cuttings is based on the exploitation of plant plasticity, which enables the formation of adventitious roots for the survival of isolated plant parts. One strategy to enhance rooting by cuttings is related to presence of tissue manually wounded along the stem, though the physiological reasons for improved rooting remained unclear due to the lack of a reliable and reproducible wounding treatment. This article summarizes the effect of wounding by laser on single-leaf rose cuttings through the development of a tissuespecific wounding protocol. Rooting was highly influenced by tissue exposure and wound pattern dimensions. Results showed that sclerenchyma disruption triggers a root stimulatory effect, especially if applied on the axillary bud side of the cutting. The induction of new vascular tissue and cambium elongation were closely associated with rooting improvement, with a significant correlation between wound-induced phloem development and root formation. Regarding laser pattern, adventitious root formation was strongly correlated with increased wound perimeter compared to wound area. Biochemical analysis revealed that laser-treatments triggered changes in the stress response (jasmonic and abscisic acid) along with temporal increases of cytokinins (zeatin ribosides) and auxin-amino conjugates during the first days after treatment. Laser-wounded tissue became an additional sink, which modified the carbohydrate profile in the cutting base. In conclusion, a precise and proper laser wounding, in terms of dimension (perimeter/area), depth and position, plays a crucial role in stimulating root formation. Localized laser wounding thus offers potential to optimize cutting propagation without application of synthetic auxins