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Adventitious root (AR) formation is the basis of vegetative propagation in rose, be it via stem cuttings or via stenting. During this process, wounding plays a pivotal role since cell reprogramming takes place at the tissue adjacent to the wound. We investigated the effects of wounding on AR formation on leafy single-node stem cuttings of the rose rootstock R. canina ‘Pfänder’ (codes R02-3 and R02-6) and the cut rose cultivar Rosa ‘Tan09283’ (Registration name ‘Beluga’). Laser wounding treatments were based on the assisted removal of tissue layers located in the bark. The positioning of wounding was studied based on two marking directions: along the cutting base (strip pattern) and around the cutting base (ring pattern). Additionally, the effects of external supply of indole-butyric acid (IBA 1 mg L-1) on rootingwere analyzed. Results showedthat inorder toremovespecific tissue layers, the calculation of the laser energy density (J cm-2) in terms of cutting diameter was necessary. Interestingly, the application of energy densities from 2.5 J cm-2 up to approximately 8.5 J cm-2 were sufficient to expose the tissue layers of epidermis up to regions of phloem. Regarding AR formation for R. canina ‘Pfänder’, characterized by a low rooting response, an increase in the rooting percentage was registered when the laser treatment eliminated the tissue up to phloem proximities. Analysis of the nodal position showed that bud location was a preferential place for AR formation independently of wounding treatment. In case of Rosa ‘Tan09283’, laser treatments did not reduce its high rooting capacity, but an apparent reduction in rooting quality due to an investment in tissue healing was observed when wounding reached deeper layers such as parenchyma and sclerenchyma. Results also showeda strongARformation directly fromwounded regions in case of Rosa ‘Tan09283’ specifically when the woundwas located below the axillary bud. In conclusion, wounding by assisted-elimination of layers by laser can induce positive effects on AR formation of single-node stemcuttings of the rose if energy applied is able to expose phloemproximities,a longitudinalorientation, and relative position to the axillary bud are considered.
One of the less explored aspects on adventitious rooting, despite being an essential requirement for cutting propagation is tissue excision. So far, studies on adventitious root formation in rose cuttings revealed that exposition of phloem proximities is necessary for a positive adventitious rooting response (Morales-Orellana et al., 2022). However, the optimal dimensions of laser wound patterns remains unknown. Establishing an appropriate area and perimeter of wounds together with optimal penetration depth would allow optimization of future root stimulation treatments based on wounds.
In this study was analyzed the effect of the wound geometry on the development of vascular tissue during the propagation phase of rose cuttings of Rosa canina 'Pfänder' in aeroponic conditions. Three laser patterns based on strips were marked on the base of the cutting keeping a constant tissue penetration: a wide single strip (10mm long and 1mm wide), a thin single strip (10mm long and 0.5mm wide) and two thin strips (10mm long and 0.5mm width each). The evaluation of stem sections showed how the development of phloem and xylem was significantly influenced by the pattern geometry. Interestingly, an accelerated xylogenesis during the first days of culture was a common characteristic directly at wounded regions. Through tissue quantification it was determined that a higher presence of xylem was associated with a wider wounded area, while an increase in phloem and less xylem was related to a reduction of area and an increase of wounded borders. The maximum rooting rate in wounded cuttings reached 49% from the pattern with two thin strips compared to the 10% for the control.
Although laser treatments have shown improvements in rooting, a detailed understanding of the effects of laser wounds during rooting has not been possible by traditional evaluation methods. In order to morphologically analyze the rooting development exposed to laser treatments, the construction of a hydroponic propagation system that included a monitoring equipment commanded by a microcontroller and programmed by the HALCON software has been carried out. By this system, timelapse videos registered the entire process of adventitious rooting. Results revealed how wounding influences the spatial positioning of adventitious roots depending on laser pattern and tissue removal.
The study of laser wounding in rose cuttings has helped to identify relevant aspects that wounded regions have to bring a positive effect on root stimulation. Nevertheless, a detailed understanding of the dynamic effects of laser wounds during rooting is not possible by traditional methods. To analyze the morphological development of rooting exposed to laser treatments, a hydroponic propagation chamber was constructed that included an internal monitoring system. Through this system, time-lapse videos recorded the entire adventitious rooting process. Results revealed how wounding influences spatial positioning of adventitious roots, depending on factors such as laser pattern, tissue removal, and the location of buds and leaves. A comparison of root distribution in terms of percentage, performed with both, the image analysis and the manual method, showed the same root growth trend with slight differences in the percentages obtained by both methods.
The stimulation of adventitious root formation from laser-wounded rose cuttings in our previous study suggests that exposing the phloem proximities is one of the most relevant aspects for a positive effect on rooting response. But, the specific dimensions that wound patterns must fulfill to optimize rooting promotion remain unknown. This study analyzed the effect of wounded area and wound perimeter of laser marking patterns on the development of phloem, xylem, and callus using cross sections of single-leaf cuttings of Rosa canina ’Pf¨ ander’. Four distinct laser patterns were designed and marked along the cutting base. Among these, three patterns were based on longitudinal strips, while one pattern was characterized by small squares, resulting in two distinct wound area levels and four wound perimeter levels. Periodic evaluations of stem sections showed that the development of phloem and xylem was significantly influenced by the pattern’s geometry. Larger dimensions of xylem were associated with patterns of greater area and a smaller perimeter, while an increase in phloem was related to patterns of longer perimeter distributed in smaller areas. The maximum rooting success in wounded cuttings reached 44% in contrast to 9% observed in the control group in the absence of additional wounds. The development of vascular tissue was significantly correlated with adventitious rooting, with phloem being more closely linked with a Pearson coefficient of 0.92 compared to 0.30 for xylem. Additionally, a negative Pearson coefficient of 0.92 between the ratio area: perimeter and adventitious root formation showed that laser patterns with large wounded area with less borders led to a reduced rooting response. The results provide evidence of how wounded tissue contributes to the intrinsic development of adventitious roots and reveal the importance of proper wound dimensions.
The presence of wounds in addition to the excision-induced wounds after severance from the stock plants is known to positively influence adventitious root formation of woody plant cuttings. Previous morphological studies highlighted laser wounding as a technique allowing to precisely control the decisive ablation depth. However, the biochemical processes involved in the response of rooting to the additional wounding remained unexplored.MethodsThe present study analyzed changes in the plant hormone and carbohydrate profiles in response to laser treatments of rose leafy single-node stem cuttings (Rosa canina ‘Pfänder’). Concentrations of four groups of plant hormones and of carbohydrates were monitored in three different stem sections of the cutting base during the first eight days after excision of cuttings. In addition, histology was employed to investigate anatomical changes at the basal wound and the laser wounds at the start and the end of the experiment after 40 days.ResultsLaser ablation caused an increase of vascular tissue dimension directly in the laser wound, and increased the quantity and quality of rooting compared to control cuttings. A clear early local rise of jasmonic acid (JA) was detected directly in wounded areas after laser marking, as well as an increase in abscisic acid (ABA) that persisted for the subsequent days. Indole-3-acetic acid (IAA) levels were relatively high on day zero, but decreased thereafter. Interestingly, higher IAA levels were maintained in the stem section below the axillary bud compared with the opposite section. Laser-treated cuttings presented a clear increase in contents of IAA-amino acid conjugates (IAAGlu and IAAsp) and the oxidation product OxIAA. Differences in concentration of these IAA metabolites were related to the position of the laser wound relative to the axillary bud and leaf. Additionally, laser treatments caused gradually increased levels of the cytokinin N6-isopentenyladenine (iP) in laser-treated zones, and of zeatin riboside specifically when the laser wound was placed on the leaf-bud side. Additional laser wounding reduced starch and sucrose levels in all wounded sections at the end of the evaluation period, independently of the wounding location.DiscussionThe results of this study indicate that presence of additional injured tissue triggers a complex biochemical adjustment at the base of the cutting responsible of inducing vascular tissue growth and capable of generating a positive response to adventitious root formation.
The poster is a summary of recent work contributing to the field of fluorescence phenotyping in turfgrass studies. The F690/F730 index has been evaluated for its suitability in the field regarding the sensitivity of produced data against changes in sample object/device-proximity, excitation irradiances and photochemical states of the photosynthetic apparatus.