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Micropropagation is an important tool for the propagation for recalcitrant species, like Eucalyptus cloeziana. This is a first reported about a complete study of the E. cloeziana, it includes the vegetative rescue protocol of mature trees, its micropropagation up to the implementation of a mini-garden and clonal micro-garden and evaluation of adventitious rooting of their propagules. The in vitro rejuvenation of E. cloeziana genotypes (03, 05, 06, 13 and 15), over 21 successive subcultures, was evaluated by comparing minicutting and microcutting techniques and the efficiency of this biotechnological tool for cloning of the mature trees. The results provide evidence of the in vitro rejuvenation occurring in the mature E. cloeziana trees during micropropagation, leading to increases in the multiplication ratios of the microstumps of three genotypes (03, 05 and 15). The survival and callogenesis percentages of the mini and microcuttings of E. cloeziana were higher than 80% upon exiting of the greenhouse (30-days old) in the three cutting times. The results suggesting that factors beyond tissue maturity influence the adventitious rooting of the E. cloeziana because minicuttings and microcuttings of the 05 and 13 elite genotypes exhibited rooting percentages lower than 20%. These findings provided a theoretical basis for realizing the micropropagation of the epicormic shoots of the mature trees and, subsequently, its in vitro rejuvenation by axillary bud proliferation. [ABSTRACT FROM AUTHOR]

Acacia mearnsii De Wild. (Black wattle) is a forest species with great social and economical importance for the southern region of Brazil. This species has multifunctional characteristics, being cultivated to produce tannin, cellulose and energy. This research identified black wattle genotypes with competence for adventitious rooting for mini-cutting propagation. Single-bud mini-cuttings were treated with IBA at a concentration of 2000 mg L-1. After 30 days of cultivation in a humid chamber, the mini-cuttings were evaluated for percentages of survival, rooting, number of roots, average length of the three largest roots, and the number of mini-cuttings rooted per mini-stump. The identification of the best genotypes was performed with the Selegen REML/BLUP software. Selection between and within black wattle progenies can be performed based on the number of rooted mini-cuttings, making it possible to select genotypes with high competence for adventitious rooting while maintaining genetic variability for new selection cycles to develop clones for vegetative propagation by mini-cutting. [ABSTRACT FROM AUTHOR]

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Vegetative propagation with stem cuttings requires the origination of shoots and roots to form a complete plant. Factors involved in root generation have been researched, but little work has been done on pH. The research was conducted at the College of Postgraduates, Montecillo Campus, Texcoco, Mexico in 2021. In Ficus carica cuttings, the following were evaluated: pH values (4, 7, and 11) in solution with or without auxin, dilution (alcohol or NaOH) of indole butyric acid (IBA), concentration of alcohol to dissolve IBA (10, 15, and 20%), in the percentage of rooting, number of roots, length of the longest root, percentage of sprouted buds at 21 days, date of establishment and anatomical changes at 0, 3 and 6 days after the cutting. Meristematic cells and root primordia were found up to day 6. One hundred percent rooting was obtained in all treatments. pH was not shown to have an effect on the auxin solution, but it did influence the percentage of rooting assessed individually. The way auxin was diluted influenced the number of roots due to the concentration of alcohol used, lower concentration (10%) had a positive effect. [ABSTRACT FROM AUTHOR]

Acca sellowiana (Myrtaceae) is a multipurpose species with edible fruits and ornamental value, native to Uruguay and southern Brazil. Domestication of the species in Uruguay is incipient although in other countries, it is widely cultivated. It is an evergreen out-crossing shrub, pollinated by birds and bees. For this reason, it is necessary to develop vegetative propagation strategies such as stem cuttings to reproduce outstanding genotypes for conservation or breeding programs. Adventitious root (AR) formation in cuttings is regulated by environmental and endogenous factors. Among phytohormones, indole-butyric acid (IBA) is the most widely exogenous auxin used to improve rooting of cuttings. Most studies on AR formation at the molecular level use model species; however, the conservation of these mechanisms in non-model plants has been little studied, consequently the effects of different factors and their interactions in A. sellowiana are not well understood. The identification and expression analysis of genes known to be involved in the regulation of the process is an important step to elucidate the molecular mechanisms that regulate AR differentiation in A. sellowiana cuttings. In this study, we compared two genotypes with contrasting rooting ability, and we identified and characterized three genes that might regulate the onset of AR development in A. sellowiana: AsPIN1, AsTIR1 and AsSHR. Their expression analysis showed that in the difficult-to-root genotype, AsTIR1 increases strongly in response to exogenous IBA, shortly after induction treatment. Relative expression of AsPIN1 and AsSHR also increases 24 h later. The biological significance of this gene expression pattern is discussed. [ABSTRACT FROM AUTHOR]

Establishing vegetative propagation techniques to promote the rejuvenation/reinvigoration of genotypes is essential for the rescue of adult trees of the Eucalyptus genus used in species and provenance tests. The aim of this study was to evaluate the induction of epicormic buds and shoots in pruned branches and the in vitro establishment, multiplication, genetic fidelity, and elongation of three 44-year-old Eucalyptus pilularis selected plants. M1, M2 and M3 represent selected plants. M1 produced the highest number of epicormic buds, number of shoots, and with the lowest rate of tissue oxidation and non-reactive explants. In the establishment stage, M3 exhibited the lowest contamination percentage, number of shoots, and shoot length. The emission of shoots occurred only for M3, and it was the unique genotype subjected to the other stages (i.e. multiplication, elongation, and rooting). In the multiplication stage, the highest vigour and shoot length values of were found in the 15th subculture. Phenolic oxidation had its highest value in the 12th subculture, decreasing from the 13th. The highest value for number of shoots was found in the 11th subculture. No polymorphism was observed in the selected plant (M3) and the clonal plants obtained in the 15th subculture. For shoots elongation, the use of culture medium containing 0.10 mg L-1 BAP and 1.00 mg L-1 NAA provided the lowest means for oxidation, and the highest for vigour, number, and length of shoots. The emission of adventitious roots was observed, demonstrating that, through micropropagation, it was possible to induce the competence to root the material, even at an advanced ontogenetic age. [ABSTRACT FROM AUTHOR]

ABSTRACT The inoculation of seeds with associative and growth-promoting bacteria is a prosperous mechanism to achieve high germinability rates and production of well-developed plants, in addition to the aspects related to the rhizogenic process in the clonal propagation of superior genotypes. Consequently, the objective of this work was to isolate endophytic bacteria from Pinus caribaea var. hondurensis plant tissues and evaluate its potential as a promoter in seed germination and rooting of P. taeda mini-cuttings. Hence, endophytic bacteria were isolated from Pinus caribaea var. hondurensis micro-plants grown in vitro and phenotypically characterized. From this collection of formed endophytic isolates, in addition to two Azospirillum brasilense commercial strains, seed germination and rooting tests of Pinus taeda L. mini-cuttings were established. Bacterial inoculation promoted the germination rate, germination speed and vigor of the seedlings. A. brasilense and CNPF 316 promoted an increase in the percentage of rooted mini-cuttings, number and average length of roots. The isolates present characteristics of plant growth-promoting bacteria, as they enhance the development of plant physiological and morphological stages.

In the present study, the effects of different types of sugars and cultivation medium pH levels on the micropropagation of Krymsk 5® cherry rootstock were investigated. During the proliferation stage, the effects of four sugars (sucrose, fructose, glucose, and sorbitol) both separately and in two combinations were studied, along with the effects of pre-adjusted pH (4.5, 5.0, 5.2, 5.5, 5.8, 6.0, 6.2, or 6.5) on shoot proliferation parameters, growth medium's post-autoclaving and post-cultivation pH, and their relations. Similarly, during the rooting stage, the effects of four sugars (sucrose, glucose, fructose, or sorbitol) at three concentrations (1% w/v, 2% w/v, or 3% w/v) without any auxin inclusion were studied as well as the effects of two sugars (sucrose or fructose) at six pre-adjusted pH levels (4.8, 5.2, 5.8, 6.2, or 6.5), also in the absence of auxin, on rooting parameters. Explants cultivated in fructose-supplemented growth mediums exhibited superior proliferation performance, characterized by the highest values of shoots per explant, shoot length, and nodes per explant. Generally, the medium's pH decreased after autoclaving, and proliferation performance was favored by low pH values (either pre-adjusted or post-autoclaving). As far as rooting is concerned, fructose inclusion induced a higher rooting percentage (88%) compared to sucrose. The highest rooting was obtained in fructose-supplemented rooting mediums at concentrations of 2% or 3% w/v (95% rooting in both cases), in the absence of auxins. Post-autoclaving pH in fructose-supplemented rooting mediums was lower and buffered in low pH levels than in sucrose-supplemented ones, and the rooting of explants in all pH combinations with fructose exceeded 75%. In addition, rooting was negatively correlated with the post-autoclaving pH. These findings underscore the significance of both the sugar type and the post-autoclaving pH of the medium in both proliferation and rooting stages, highlighting their possible physiological, biochemical, or hormonal effects. Additionally, rooting without the use of auxin, but with the correct choice of sugar, emerges with both financial and environmental benefits, whereas fructose could be potentially used as a buffering agent. [ABSTRACT FROM AUTHOR]

ABSTRACT: Acacia mearnsii De Wild. (Black wattle) is a forest species with great social and economical importance for the southern region of Brazil. This species has multifunctional characteristics, being cultivated to produce tannin, cellulose and energy. This research identified black wattle genotypes with competence for adventitious rooting for mini-cutting propagation. Single-bud mini-cuttings were treated with IBA at a concentration of 2000 mg L-1. After 30 days of cultivation in a humid chamber, the mini-cuttings were evaluated for percentages of survival, rooting, number of roots, average length of the three largest roots, and the number of mini-cuttings rooted per mini-stump. The identification of the best genotypes was performed with the Selegen REML/BLUP software. Selection between and within black wattle progenies can be performed based on the number of rooted mini-cuttings, making it possible to select genotypes with high competence for adventitious rooting while maintaining genetic variability for new selection cycles to develop clones for vegetative propagation by mini-cutting.

Adventitious rooting is a process of postembryonic organogenesis strongly affected by endogenous and exogenous factors. Although adventitious rooting has been exploited in vegetative propagation programs for many plant species, it is a bottleneck for vegetative multiplication of difficult-to-root species, such as many woody species. The purpose of this research was to understand how N,N′-bis-(2,3-methylenedioxyphenyl)urea could exert its already reported adventitious rooting adjuvant activity, starting from the widely accepted knowledge that adventitious rooting is a hormonally tuned progressive process. Here, by using specific in vitro bioassays, histological analyses, molecular docking simulations and in vitro enzymatic bioassays, we have demonstrated that this urea derivative does not interfere with polar auxin transport; it inhibits cytokinin oxidase/dehydrogenase (CKX); and, possibly, it interacts with the apoplastic portion of the auxin receptor ABP1. As a consequence of this dual binding capacity, the lifespan of endogenous cytokinins could be locally increased and, at the same time, auxin signaling could be favored. This combination of effects could lead to a cell fate transition, which, in turn, could result in increased adventitious rooting. [ABSTRACT FROM AUTHOR]

Ontogenetic aging of tissues and the gradual decrease of adventitious rooting are known challenges for the clonal propagation of woody species, hampering clonal forestry programs. This study examined possible signatures of tissue rejuvenation/reinvigoration in different propagated materials of Eucalyptus microcorys by analyzing the total protein profile, peroxidase activity, macro- and micronutrient contents, and adventitious rooting of mini cuttings. The analyses were performed on E. microcorys shoots which were successfully obtained by seminal and grafting propagation, micropropagation with epicormic shoots, and indirect organogenesis. Among four mature trees used in the propagation, tissues from the one with the best propagation results were investigated for signs of tissue rejuvenation and/or reinvigoration. Five individuals from each technique were randomly selected and transferred to a semi-hydroponic "channel" system. After four weeks in the seedbed, the total protein, peroxidase activity, nutrient content and rooting of the mini cuttings were evaluated. SDS-PAGE enabled the differentiation of leaf samples obtained by grafting from the other propagation techniques, as revealed by two distinct bands. Materials obtained by micropropagation with epicormic shoots showed the highest peroxidase activity, while those obtained by seminal propagation and from the selected mature tree showed the lowest peroxidase activity. A portable X-ray fluorescence spectroscope (pXRF) identified adequate nutrient content in most of the nutrients tested in materials obtained by seminal and grafting propagation, and by indirect organogenesis. The analysis of adventitious rooting showed that the highest rooting percentage was observed in mini cuttings from seminal propagation (75%) followed by indirect organogenesis (35%). Based on principal component analysis, it was concluded that rooting of mini cuttings from both seminal propagation and indirect organogenesis was associated with phosphorous, sulphur, and potassium contents, which suggests a higher level of tissue rejuvenation/reinvigoration in these propagated plants. Further studies are recommended to search for other methods that present similarities with the responses to adventitious rooting in forest species and thus optimize the rescue and propagation of plants with distinct ontogenetic stages. [ABSTRACT FROM AUTHOR]

In the present study, the effects of different types of sugars and cultivation medium pH levels on the micropropagation of Krymsk 5® cherry rootstock were investigated. During the proliferation stage, the effects of four sugars (sucrose, fructose, glucose, and sorbitol) both separately and in two combinations were studied, along with the effects of pre-adjusted pH (4.5, 5.0, 5.2, 5.5, 5.8, 6.0, 6.2, or 6.5) on shoot proliferation parameters, growth medium’s post-autoclaving and post-cultivation pH, and their relations. Similarly, during the rooting stage, the effects of four sugars (sucrose, glucose, fructose, or sorbitol) at three concentrations (1% w/v, 2% w/v, or 3% w/v) without any auxin inclusion were studied as well as the effects of two sugars (sucrose or fructose) at six pre-adjusted pH levels (4.8, 5.2, 5.8, 6.2, or 6.5), also in the absence of auxin, on rooting parameters. Explants cultivated in fructose-supplemented growth mediums exhibited superior proliferation performance, characterized by the highest values of shoots per explant, shoot length, and nodes per explant. Generally, the medium’s pH decreased after autoclaving, and proliferation performance was favored by low pH values (either pre-adjusted or post-autoclaving). As far as rooting is concerned, fructose inclusion induced a higher rooting percentage (88%) compared to sucrose. The highest rooting was obtained in fructose-supplemented rooting mediums at concentrations of 2% or 3% w/v (95% rooting in both cases), in the absence of auxins. Post-autoclaving pH in fructose-supplemented rooting mediums was lower and buffered in low pH levels than in sucrose-supplemented ones, and the rooting of explants in all pH combinations with fructose exceeded 75%. In addition, rooting was negatively correlated with the post-autoclaving pH. These findings underscore the significance of both the sugar type and the post-autoclaving pH of the medium in both proliferation and rooting stages, highlighting their possible physiological, biochemical, or hormonal effects. Additionally, rooting without the use of auxin, but with the correct choice of sugar, emerges with both financial and environmental benefits, whereas fructose could be potentially used as a buffering agent.

To investigate the molecular mechanism of the ADVENTITIOUS ROOTING RELATED OXYGENASE 1 (ARRO-1) gene in adventitious rooting of tree peony, the PsARRO-1 gene was isolated from Paeonia ostii. Subsequently, a yeast two-hybrid (Y2H) cDNA library using the split-ubiquitin yeast membrane system was constructed, the insert fragments lengths of pPR3-N membrane Y2H library were mainly concentrated between 500 and 3,000 bp, and the library capacity reached 1.3 × 107 CFUs, with an efficiency of recombinant of 100%, which met the requirements for subsequent screening of PsARRO-1-interacting proteins. Finally, 15 candidate PsARRO-1-interacting proteins were screened out by pBT3SUC-ARRO, among them potassium transporter 2, cytochrome b5 isoform E, and high mobility group B protein 3 (HMGB3) might be involved in the formation of roots. Both direct Y2H and bimolecular fluorescence complementation assays confirmed that PsARRO-1 interacted with PsHMGB3, which shared high identity with EgHMGB3 and MiHMGB3. The expression of PsHMGB3 was significantly up-regulated in the root outgrowth stage, and the overexpression of PsHMGB3 in Arabidopsis resulted in lengthened primary roots, more lateral roots. In short, the Y2H library provides a large number of useful resources for functional genomics research on roots of tree peony. [ABSTRACT FROM AUTHOR]

The occurrence of adventitious roots and somatic embryos is a crucial step in micropropagation that frequently limits the application of this technique in woody plants. Recent studies demonstrated that they can be negatively or positively regulated with γ-aminobutyric acid (GABA), which is a four-carbon non-proteinous amino acid that not only acts as a main inhibitory neurotransmitter in mammals. It has been reported that GABA affects plant growth and their response to stress although its mode of action is still unclear. This review dealt with the effects of GABA on adventitious root formation and growth as well as on somatic embryogenesis. Furthermore, we focused on discussing the interaction of GABA with phytohormones, such as auxin, ethylene, abscisic acid, and gibberellin, as well as with the carbon and nitrogen metabolism during adventitious root development. We suggested that research on GABA will contribute to the application of micropropagation in the recalcitrant fruit and forest species. [ABSTRACT FROM AUTHOR]

Maturation imposes several changes in plants, which are particularly drastic in the case of trees. In recalcitrant woody species, such as chestnut (Castanea sativa Mill.), one of the major maturation-related shifts is the loss of the ability to form adventitious roots in response to auxin treatment as the plant ages. To analyze the molecular mechanisms underlying this phenomenon, an in vitro model system of two different lines of microshoots derived from the same field-grown tree was established. While juvenile-like shoots root readily when treated with exogenous auxin, microshoots established from the crown of the tree rarely form roots. In the present study, a transcriptomic analysis was developed to compare the gene expression patterns in both types of shoots 24 h after hormone and wounding treatment, matching the induction phase of the process. Our results support the hypothesis that the inability of adult chestnut tissues to respond to the inductive treatment relies in a deep change of gene expression imposed by maturation that results in a significant transcriptome modification. Differences in phytohormone signaling seem to be the main cause for the recalcitrant behavior of mature shoots, with abscisic acid and ethylene negatively influencing the rooting ability of the chestnut plants. We have identified a set of related MADS-box genes whose expression is modified but not suppressed by the inductive treatment in mature shoots, suggesting a putative link of their activity with the rooting-recalcitrant behavior of this material. Overall, distinct maturation-derived auxin sensibility and homeostasis, and the related modifications in the balance with other phytohormones, seem to govern the outcome of the process in each type of shoots. [ABSTRACT FROM AUTHOR]

Selection of reference genes (RGs) for normalization of PCR-gene expression data includes two crucial steps: determination of the between-sample transcriptionally more stable genes, and subsequent choosing of the most suitable genes as internal controls. Both steps can be carried out through generally accepted strategies, each having different strengths and weaknesses. The present study proposes reinforcement of the normalization of gene expression data by integrating analytical revision at critical steps of those accepted procedures. In vitro olive adventitious rooting was used as an experimental system. Candidate RGs were ranked according to transcriptional stability according to several methods. An algorithm of one of these programs (GeNorm) was adapted to allow for partial automatization of RG selection for any strategy of transcriptional-gene stability ordering. In order to choose the more appropriate set of RGs, the achieved results were analytically revised, with special emphasis on biasing effects such as co-regulation. The obtained putative RG sets were also tested for cases restricted to fewer variables. The set formed by the genes H2B, OUB and ACT is valid for normalization in transcriptional studies on olive microshoot rooting when comparing treatments, time points and assays. Such internal reference is now available for wider expression studies on any target gene in similar biological systems. The overall methodology aims to constitute a guide for general application. [ABSTRACT FROM AUTHOR]

Improving clonal rootstock propagation of avocado has been a major industry/research challenge globally for many decades. Tissue culture has been a focus for clonal propagation with substantial advancements in recent years. In the process of tissue culture, avocado rootstocks display differences in rooting and acclimation capacity. Such differences may relate to the specific structural characteristics of the rootstock. This study aimed to investigate the structural difference during tissue culture in two rootstocks ‘Reed’ and ‘Velvick’, with differing rooting and acclimation capacity. Histological investigations were carried out of stem vasculature, leaves and roots of tissue cultured plantlets. Quantitative parameters; stomatal index, stomatal density, trichome density, vein-islet density and vein termination density were also analysed. Prominent fascicular cambium and fewer phloem fibres in stems positively correlated with rooting capacity. Acclimation success positively correlated to the presence of fully differentiated secondary xylem in root. Presence of smaller epidermal cells, high stomatal density and reduced vein termination density was associated with reduced acclimation success. These findings will support optimisation strategies for micropropagation of not only difficult-to-root and difficult-to-acclimate avocado rootstocks, but also, other woody perennials experiencing similar problems. [ABSTRACT FROM AUTHOR]

Background: Carbon monoxide (CO) has been reported to be participated in adventitious rooting. However, knowledge about the interrelationship between CO and phytohormones during rooting is obscure. The molecular mechanism of CO-induced rooting is currently unclear. Methods and results: The roles of CO in adventitious rooting in Cucumis sativus L. at the transcriptional level were investigated. The results show that 10 μM hematin (a CO donor) has a significant positive effect on adventitious rooting in cucumber. A total of 1792 differentially expressed genes (DEGs; 1103 up-regulated and 689 down-regulated) were identified in hematin treatment by RNA sequencing analysis. There were 37, 18 and 19 DEGs significantly enriched in plant hormone signal transduction, sucrose and starch metabolism, and phenylalanine metabolism, respectively. Both transcriptome and real-time quantitative PCR results showed that the expressions of AUX22D, IAA6, SAUR21, SAUR24, GH3.5, CYCD3-3, TIFY10a, TIFY10A and TIF9 promoted the accumulation of IAA, BR, JA and SA in plant hormone signal transduction. The up-regulation of HK3, TPPF, otsB, TPS7, TPS9 and the down-regulation of AGPS1, AGPS3 increased the content of starch and total sugar by mediating the activity of some critical enzymes, including HK, TPS, TPP and AGP. PER47, PER61, PER24, PER66, PER4 and CCR2 increased the lignin content. Conclusion: Our results suggest that CO could promote the accumulation of plant hormones, starch, sugar and lignin during adventitious rooting by regulating the expression of some related genes, including AUX22D, IAA6, SAUR21, SAUR24, GH3.5, CYCD3-3, TIFY10a, TIFY10A, TIF9 HK3, otsB, TPS7, TPS9, AGPS1, AGPS3, PER47, PER61, PER24, PER66, PER4, and CCR2. Thus, we provides an interesting candidate gene list for further studies on the molecular mechanisms of adventitious rooting. [ABSTRACT FROM AUTHOR]

Wood properties and agronomic traits associated with fast growth and frost tolerance make Eucalyptus nitens a valuable forest alternative. However, the rapid age-related decline in the adventitious root (AR) formation (herein, meaning induction, initiation, and expression stages) limits its propagation. We analyzed transcriptomic profile variation in leaves and stem bases during AR induction of microcuttings to elucidate the molecular mechanisms involved in AR formation. In addition, we quantified expressions of candidate genes associated with recalcitrance. We delimited the ontogenic phases of root formation using histological techniques and Scarecrow and Short-Root expression quantification for RNA sequencing sample collection. We quantified the gene expressions associated with root meristem formation, auxin biosynthesis, perception, signaling, conjugation, and cytokinin signaling in shoots harvested from 2- to 36-month-old plants. After IBA treatment, 702 transcripts changed their expressions. Several were involved in hormone homeostasis and the signaling pathways that determine cell dedifferentiation, leading to root meristem formation. In part, the age-related decline in the rooting capacity is attributable to the increase in the ARR1 gene expression, which negatively affects auxin homeostasis. The analysis of the transcriptomic variation in the leaves and rooting zones provided profuse information: (1) To elucidate the auxin metabolism; (2) to understand the hormonal and signaling processes involved; (3) to collect data associated with their recalcitrance. [ABSTRACT FROM AUTHOR]

Clonal Eucalyptus propagation is essential for various industry sectors. It requires cuttings to successfully develop adventitious roots (ARs). Environmental conditions are influential on AR development and may be altered to modulate the productivity of hard-to-root clones. The current knowledge gap in research on the physiological patterns underlying commercial-scale propagation results hinders the design of novel strategies. This study aimed to identify patterns of variation in AR-relevant parameters in contrasting seasons and species with distinct rooting performances. E. dunnii and E. ×urograndis (hard- (hardR) and easy-to-root (easyR), respectively) mini-stumps were subjected to light modulation treatments and to mini-tunnel use (MT) for a year. The treatment impact on the branching and rooting rates was recorded. The carbohydrate content, AR-related gene expression, and mineral nutrition profiles of cuttings from the control (Ctrl) and treated mini-stumps were analyzed. Light treatments were often detrimental to overall productivity, while MTs had a positive effect during summer, when it altered the cutting leaf nutrient profiles. Species and seasonality played large roles in all the assessed parameters. E. ×urograndis was particularly susceptible to seasonality, and its overall superior performance correlated with changes in its gene expression profile from excision to AR formation. These patterns indicate fundamental differences between easyR and hardR clones that contribute to the design of data-driven management strategies aiming to enhance propagation protocols. [ABSTRACT FROM AUTHOR]

Breeding efforts within the Eucomis genus has resulted in the global availability of attractive cultivars with decorative leaves and inflorescences. A cultivar that is particularly valuable and attractive, but rarely cultivated due to its low propagation rate is 'Sparkling Burgundy'. In our research, we considered it advisable to check the possibility of intensifying the reproduction of the investigated cultivar by means of leaf cuttings. This study, conducted in the years 2016-2018, involved leaf cuttings collected from plants growing in an unheated polytunnel. The cuttings were soaked, watered or sprayed with 0.4% chitosan with a molecular weight of 7 000 or 10 000 g/mol. The control plants were not treated with chitosan. During the rooting period that followed, the cuttings were assessed for their chlorophyll a fluorescence and the intensity of their greenness, and for their root growth and bulb yield after five months. Chitosan applied during rooting improved some chlorophyll fluorescence parameters and the greenness index of the cuttings. Moreover, the compound with a molecular weight of 7 000 g/mol more efficiently increased the number and length of the roots and the number and weight of the adventitious bulbs than that with a molecular weight of 10 000 g/mol. Soaking the cuttings prior to rooting was more effective in terms of the number, length and weight of the produced roots and the number, diameter and weight of the daughter bulbs than watering or spraying.

Adventitious rooting is a process of postembryonic organogenesis strongly affected by endogenous and exogenous factors. Although adventitious rooting has been exploited in vegetative propagation programs for many plant species, it is a bottleneck for vegetative multiplication of difficult-to-root species, such as many woody species. The purpose of this research was to understand how N,N′-bis-(2,3-methylenedioxyphenyl)urea could exert its already reported adventitious rooting adjuvant activity, starting from the widely accepted knowledge that adventitious rooting is a hormonally tuned progressive process. Here, by using specific in vitro bioassays, histological analyses, molecular docking simulations and in vitro enzymatic bioassays, we have demonstrated that this urea derivative does not interfere with polar auxin transport; it inhibits cytokinin oxidase/dehydrogenase (CKX); and, possibly, it interacts with the apoplastic portion of the auxin receptor ABP1. As a consequence of this dual binding capacity, the lifespan of endogenous cytokinins could be locally increased and, at the same time, auxin signaling could be favored. This combination of effects could lead to a cell fate transition, which, in turn, could result in increased adventitious rooting.

In Brazil, nursery plum trees are traditionally produced by interspecific budding, where the rootstock is propagated by peach seeds often obtained from the waste of peach industrialization, which promotes heterogeneity among rootstocks. In addition, the conventional system of nursery plum tree production under field conditions requires approximately 18 months, from taking seeds to selling grafted trees. This research has aimed to assess the technical feasibility of adventitious root formation in the softwood cuttings of six cultivars of Prunus spp., as well as the budding of 'Irati' plum in the recently rooted softwood cuttings developed in a greenhouse, in order to reduce the time required to produce nursery plum trees with cloned rootstocks. Two tests were carried out in a greenhouse involving the rootstock propagation step (1) and the 'Irati' plum budding on the recently rooted cuttings (2). Under the experimental conditions adopted, we have concluded that it is technically feasible to propagate the cultivars of Prunus spp. under an intermittent mist system with 22 cm-long softwood cuttings. The cultivars 'Genovesa', 'Marianna 2624', and 'Myrobalan 29C' showed good propagation ability with high percentage of live rooted cuttings (>90%) and low mortality in acclimation (=5.0%). On the other hand, the budding of the 'Irati' plum by the chip budding method made in April in the original rootstock cutting showed low percentages of success (between 17.1% and 31.4%) and the beginning of scion growth was only observed at the end of winter. Considering the time necessary for the softwood cutting to root and the satisfactory growth of the scion for planting the nursery trees at the appropriate time (winter), we could not produce budded nursery trees of 'Irati' plum in less than 12 months, counting from the cuttings made. [ABSTRACT FROM AUTHOR]

Dalbergia nigra is an endangered species from the Brazilian Atlantic Rainforest, and in vitro propagation can be applied for its conservation. The aim of this study was to establish in vitro propagation and ex vitro rooting in D. nigra and evaluate the alterations in polyamines (PAs) and protein profiles during shoot development. The effects of MS and WPM culture media on in vitro germination were tested. For shoot induction, explants of apical and cotyledonary nodal segments from 45 day-old seedlings were inoculated in WPM culture medium supplemented with benzyladenine (BA; 0, 2.5 and 5 µM). Shoots obtained in vitro without and with 2.5 µM BA were rooted ex vitro with different concentrations (0, 100 and 500 µM) of indole-3-butyric acid (IBA). The seedlings grew best in WPM culture medium. Treatment with 2.5 µM BA significantly increased the shoot length by increasing free putrescine contents and the accumulation of proteins associated with shoot elongation, such as aspartate aminotransferase, elongation factor, calreticulin-3, and cell division cycle protein 48. Ex vitro rooting was obtained in all treatments, and the use of auxin was not necessary. The BA used for shoot multiplication significantly affected rooting, reducing the induction and number of roots but increasing their length. This study showed the relevance of cytokinin, PAs and proteomic profiles to in vitro shoot development, as well as the auxin and cytokinin balance to ex vitro rooting in D. nigra. Key message: BA significantly affected shoot multiplication and rooting and induced changes in PAs and proteomic profiles during micropropagation of Dalbergia nigra. [ABSTRACT FROM AUTHOR]

To offer a viable alternative to seedling deployment of tea tree, clones will require the development of an efficient, robust, and vegetative propagation system for the large number of plants needed for plantations (i.e., typically 33,000 plants/ha). This study investigated the productivity of an intensive management system for tea tree stock plants and rooted cuttings grown in a subtropical environment (Lismore, NSW, Australia). Three stock plant densities (30, 100, and 200 plants/m2) were tested in coir and potting mix media (consisting of peat+perlite+vermiculite), with 11 settings of cuttings undertaken between April 2019 and March 2020. All stock plants in each media type survived 11 harvests and remained productive; however after 13 months, many plants in the coir media, appeared chlorotic and showed symptoms of iron deficiency. Rooting and cutting survival rates using the mini cutting technique were high, ranging from a maximum mean monthly setting value of 87.7% ± 4 at 84 days post-setting in potting mix, to a minimum of 80.4% ± 3.7 in coir. The most productive treatment was at high stock plant density in potting mix which had the potential to produce 13,440 plants/year/m2. Overall coir appeared less productive, but the pattern of difference among treatments was similar. For the highest system productivity, it is recommended to grow stock plants in potting mix at high densities and modulate temperatures to between 18 °C and 28 °C. Late spring and early summer were the best time for harvesting and setting tea tree mini cuttings in the subtropics. [ABSTRACT FROM AUTHOR]

Context: Increasing demand for therapeutic honey has driven establishment of Leptospermum nectar plantations. Methods for propagation involving synthetic seeds (artificially encapsulated miniature cuttings) may speed production of Leptospermum polygalifolium Salisb. and L. scoparium J.R.Forst. & G.Forst. Aims: The study aimed to determine how nutrient strength of the encapsulation solution and the presence of benzyladenine (BA) in the emergence medium affect shoot and root emergence from synthetic seeds of L. polygalifolium and L. scoparium. Methods: Nodes from in vitro shoots of three L. polygalifolium clones (P1, P6, P11) and two L. scoparium clones (S6, S12) were encapsulated in 3% sodium alginate with half- or full-strength Murashige and Skoog (MS) medium, and the synthetic seeds were placed on full-strength MS emergence medium containing 0 or 2.2 μM BA. Key results: Full-strength MS in the encapsulation solution was effective for shoot emergence of both species. BA increased the percentage of synthetic seeds with shoot emergence in clone P6 but decreased the percentage in clone S12. BA stimulated shoot emergence through callus in clones P1, P6, S6 and S12, and increased the number of shoots per emergent synthetic seed in clones S6 and S12. Surprisingly, the simple use of full-strength MS medium without hormones was highly effective for adventitious rooting, stimulating root emergence and plantlet formation in 26–57% of L. polygalifolium and 100% of L. scoparium synthetic seeds. Conclusions: These two Leptospermum species are highly amenable to propagation via synthetic seeds. A simple formulation of hormone-free, full-strength MS medium in the encapsulation solution and emergence medium provides high frequencies of plantlet conversion. Implications: Synthetic seeds have potential to assist in mass production of Leptospermum plants for nectar plantations to meet demand for therapeutic honey. This study developed synthetic-seed methods for Leptospermum polygalifolium and L. scoparium , which are sources of nectar for producing high-value therapeutic honey. Both species proved amenable to propagation via synthetic seed, using a simple formulation of hormone-free, full-strength Murashige and Skoog medium in the encapsulation solution and emergence medium. This method will facilitate mass-production of plants for establishing Leptospermum nectar plantations. [ABSTRACT FROM AUTHOR]

Copyright of Ciência Florestal (01039954) is the property of Ciencia Florestal and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Breeding efforts within the Eucomis genus has resulted in the global availability of attractive cultivars with decorative leaves and inflorescences. A cultivar that is particularly valuable and attractive, but rarely cultivated due to its low propagation rate is 'Sparkling Burgundy'. In our research, we considered it advisable to check the possibility of intensifying the reproduction of the investigated cultivar by means of leaf cuttings. This study, conducted in the years 2016-2018, involved leaf cuttings collected from plants growing in an unheated polytunnel. The cuttings were soaked, watered or sprayed with 0.4% chitosan with a molecular weight of 7 000 or 10 000 g/mol. The control plants were not treated with chitosan. During the rooting period that followed, the cuttings were assessed for their chlorophyll a fluorescence and the intensity of their greenness, and for their root growth and bulb yield after five months. Chitosan applied during rooting improved some chlorophyll fluorescence parameters and the greenness index of the cuttings. Moreover, the compound with a molecular weight of 7 000 g/mol more efficiently increased the number and length of the roots and the number and weight of the adventitious bulbs than that with a molecular weight of 10 000 g/mol. Soaking the cuttings prior to rooting was more effective in terms of the number, length and weight of the produced roots and the number, diameter and weight of the daughter bulbs than watering or spraying. [ABSTRACT FROM AUTHOR]

Establishing the optimal time for rooting permanence and evaluation of the rooting quality of eucalypt clones allows us to optimise the production process and increase the quality of the seedlings produced. This study aimed to determine the optimal time for rooting permanence and the rooting quality of three eucalypt clones. Minicuttings from the clones AEC 0144, GG100 and VM01 were propagated in a greenhouse and evaluated for six weeks. The percentages of callus- rooted, rooted and live minicuttings, the number of roots, root system length, and root dry mass were evaluated. The selected clones differed in the speed and rate of rooting, reflecting differences in the optimal time in the rooting house for the minicuttings. Clone VM01 presented the lowest rate and speed of rooting. We conclude that optimisation of the rooting process can be achieved using logistic model fitting and noting the intercept between the daily current increment and daily average increment curves of the rooting percentage, since the other variables are dependendent on this. [ABSTRACT FROM AUTHOR]

Apuleia leiocarpa is an environmentally and economically significant Atlantic Forest species threatened by ongoing exploitation. The vegetative propagation of the species could be a step forward to enable implantation of clonal seed orchards and multiplication of selected trees but remains unknown to date. This study assessed the mini-cutting technique for propagation of A. leiocarpa and determined the time required for rooting and viable mini-cutting type and sizes. The results show that it is possible to propagate A. leiocarpa with mini-cuttings derived from mini-stumps produced with seeds; the mini-stumps presented regrowth capacity and remained constantly productive for 1 year; 10-cm A. leiocarpa mini-cuttings should remain under misting conditions for at least 40 days, and the vegetative propagation of A. leiocarpa with intermediate 7- to 10-cm mini-cuttings resulted in more vigorous clonal seedlings than smaller mini-cuttings. [ABSTRACT FROM AUTHOR]

Tetraploid Robinia pseudoacacia L. is a difficult-to-root species, and is vegetatively propagated through stem cuttings. Limited information is available regarding the adventitious root (AR) formation of dark-pretreated micro-shoot cuttings. Moreover, the role of specific miRNAs and their targeted genes during dark-pretreated AR formation under in vitro conditions has never been revealed. The dark pretreatment has successfully promoted and stimulated adventitious rooting signaling-related genes in tissue-cultured stem cuttings with the application of auxin (0.2 mg L−1 IBA). Histological analysis was performed for AR formation at 0, 12, 36, 48, and 72 h after excision (HAE) of the cuttings. The first histological events were observed at 36 HAE in the dark-pretreated cuttings; however, no cellular activities were observed in the control cuttings. In addition, the present study aimed to uncover the role of differentially expressed (DE) microRNAs (miRNAs) and their targeted genes during adventitious root formation using the lower portion (1–1.5 cm) of tetraploid R. pseudoacacia L. micro-shoot cuttings. The samples were analyzed using Illumina high-throughput sequencing technology for the identification of miRNAs at the mentioned time points. Seven DE miRNA libraries were constructed and sequenced. The DE number of 81, 162, 153, 154, 41, 9, and 77 miRNAs were upregulated, whereas 67, 98, 84, 116, 19, 16, and 93 miRNAs were downregulated in the following comparisons of the libraries: 0-vs-12, 0-vs-36, 0-vs-48, 0-vs-72, 12-vs-36, 36-vs-48, and 48-vs-72, respectively. Furthermore, we depicted an association between ten miRNAs (novel-m0778-3p, miR6135e.2-5p, miR477-3p, miR4416c-5p, miR946d, miR398b, miR389a-3p, novel m0068-5p, novel-m0650-3p, and novel-m0560-3p) and important target genes (auxin response factor-3, gretchen hagen-9, scarecrow-like-1, squamosa promoter-binding protein-like-12, small auxin upregulated RNA-70, binding protein-9, vacuolar invertase-1, starch synthase-3, sucrose synthase-3, probable starch synthase-3, cell wall invertase-4, and trehalose phosphatase synthase-5), all of which play a role in plant hormone signaling and starch and sucrose metabolism pathways. The quantitative polymerase chain reaction (qRT-PCR) was used to validate the relative expression of these miRNAs and their targeted genes. These results provide novel insights and a foundation for further studies to elucidate the molecular factors and processes controlling AR formation in woody plants. [ABSTRACT FROM AUTHOR]

Cadmium (Cd) stress can cause system disorders in plants, affect the absorption of some nutrients. The roles and their relationship of salicylic acid (SA) and hydrogen peroxide (H2O2) in adventitious root formation (ARF) of cucumber (Cucumis sativus L.) under Cd stress were studied. The results showed that the exogenous SA and H2O2 in enhancing ARF in cucumber explants under Cd stress was concentration-dependent, with an optimal biological effect at 0.1 µM SA or 50 µM H2O2. Under Cd stress, SA-induced ARF was significantly reversed by H2O2 scavenger and inhibitor, indicating that endogenous H2O2 may be involved in SA-induced ARF under Cd stress. In addition, endogenous H2O2 levels were also promoted by SA in cucumber explants. The application of SA promoted pectin content and decreased pectin methylesterification degree under Cd stress. Moreover, we founded that SA and SA + H2O2 up-regulated the expression level of CsQUA and CsPME under Cd stress, respectively. However, the application of H2O2 scavenger and inhibitor could significantly reverse the effects of SA on the expression of the above genes. These results suggested that SA might play an important role in ARF in cucumber under Cd stress via enhancing endogenous H2O2 levels. [ABSTRACT FROM AUTHOR]

Investigation of the biochemical and molecular changes during rooting in woody species can reveal how specific molecules are involved in adventitious root (AR) induction. We investigated the effects of indole butyric acid (IBA) and inhibitors of polar auxin transport and auxin signaling on ex vitro rooting of micropropagated shoots of Cedrela fissilis and evaluated the proteomic profile and endogenous contents of indole acetic acid (IAA) during AR initiation. We observed that exogenous IBA was not necessary for ex vitro rooting, and root induction was significantly reduced by auxin signaling (p-chlorophenoxyisobutyric acid—PCIB) and polar auxin transport (triiodobenzoic acid—TIBA) inhibitors. The presence of meristematic cells and the formation of meristematic centers in the base of shoot cuttings at 3 days of rooting are necessary for AR formation. The accumulation of cell division- and auxin-related proteins and the presence of unique proteins related to cell wall modification in shoot cuttings at 3 days of rooting were associated with higher IAA contents and AR initiation. In addition, an accumulation of proteins related to dephosphorylation, glycolytic and tricarboxylic acid cycle pathways and a reduction in the accumulation of proteins from isoflavonoid metabolism were associated with the promotion of AR initiation. These results show the relevance of these proteins for AR initiation in this species. This is the first study showing the involvement of protein accumulation and endogenous IAA contents in adventitious rooting initiation in C. fissilis, an easily rooted endangered woody species from the Brazilian rainforest. Key message: Auxin contents and proteomic analyses during adventitious rooting of in vitro propagated Cedrela fissilis shoots. [ABSTRACT FROM AUTHOR]

The forestry sector has been able to sustainably satisfy the increasing global demand for forest products, thereby positively impacting the economy, while mitigating climate change. It is therefore necessary to continue developing technologies to support vegetative propagation activities that consider the diverse genetic resources and their optimal production environments. This study aimed to investigate the influence of mini-tunnel use in the clonal mini-garden (MG) and greenhouse (GH) environments on the survival and rooting of mini-cuttings of three Eucalyptus species and a Corymbia species under subtropical climate conditions across the four annual seasons. A factorial experimental scheme was adopted with two environments for stock plants [MG with mini-tunnel (MGWT) and without mini-tunnel (MGOT)], and two rooting environments [GH with mini tunnel (GHWT) and without mini-tunnel (GHOT)]. We found that the use of a mini-tunnel did not influence mini-cutting survival, and all species exhibited superior performance during cold seasons. Eucalyptus mini-cuttings had high rooting under average temperatures of 23.9 °C (GHWT), which occurred in autumn. Conversely, the rooting of Corymbia mini-cuttings was enhanced in winter, in environments with average temperatures of 19.55 °C (MGWT and GHWT). Mini-tunnels altered the clonal production microenvironment, thereby enhancing adventitious rooting. For Eucalyptus, their use is recommended in the GH in autumn and winter. For clonal production of Corymbia, mini-tunnel use is recommended in both the clonal MG and GH. [ABSTRACT FROM AUTHOR]

Abstract Background Propagation of cuttings is frequently used in various plant species, including blueberry, which shows special root characteristics that may hinder adventitious root (AR) formation. AR formation is influenced by various factors, and auxin is considered to play a central role; however, little is known of the related regulatory mechanisms. In this study, a comparative transcriptome analysis of green cuttings treated with or without indole-butyric acid (IBA) was performed via RNA_seq to identify candidate genes associated with IBA-induced AR formation. Results Rooting phenotypes, especially the rooting rate, were significantly promoted by exogenous auxin in the IBA application. Blueberry AR formation was an auxin-induced process, during which adventitious root primordium initiation (rpi) began at 14 days after cutting (DAC), root primordium (rp) was developed at 21 DAC, mature AR was observed at 28 DAC and finally outgrowth from the stem occurred at 35 DAC. Higher IAA levels and lower ABA and zeatin contents might facilitate AR formation and development. A time series transcriptome analysis identified 14,970 differentially expressed genes (DEGs) during AR formation, of which there were 7467 upregulated and 7503 downregulated genes. Of these, approximately 35 candidate DEGs involved in the auxin-induced pathway and AR formation were further identified, including 10 auxin respective genes (ARFs and SAURs), 13 transcription factors (LOB domain-containing protein (LBDs)), 6 auxin transporters (AUX22, LAX3/5 and PIN-like 6 (PIL6s)) and 6 rooting-associated genes (root meristem growth factor 9 (RGF9), lateral root primordium 1 (LRP1s), and dormancy-associated protein homologue 3 (DRMH3)). All these identified DEGs were highly upregulated in certain stages during AR formation, indicating their potential roles in blueberry AR formation. Conclusions The transcriptome profiling results indicated candidate genes or major regulatory factors that influence adventitious root formation in blueberry and provided a comprehensive understanding of the rooting mechanism underlying the auxin-induced AR formation from blueberry green cuttings.

The occurrence of adventitious roots and somatic embryos is a crucial step in micropropagation that frequently limits the application of this technique in woody plants. Recent studies demonstrated that they can be negatively or positively regulated with γ-aminobutyric acid (GABA), which is a four-carbon non-proteinous amino acid that not only acts as a main inhibitory neurotransmitter in mammals. It has been reported that GABA affects plant growth and their response to stress although its mode of action is still unclear. This review dealt with the effects of GABA on adventitious root formation and growth as well as on somatic embryogenesis. Furthermore, we focused on discussing the interaction of GABA with phytohormones, such as auxin, ethylene, abscisic acid, and gibberellin, as well as with the carbon and nitrogen metabolism during adventitious root development. We suggested that research on GABA will contribute to the application of micropropagation in the recalcitrant fruit and forest species.

Maturation imposes several changes in plants, which are particularly drastic in the case of trees. In recalcitrant woody species, such as chestnut (Castanea sativa Mill.), one of the major maturation-related shifts is the loss of the ability to form adventitious roots in response to auxin treatment as the plant ages. To analyze the molecular mechanisms underlying this phenomenon, an in vitro model system of two different lines of microshoots derived from the same field-grown tree was established. While juvenile-like shoots root readily when treated with exogenous auxin, microshoots established from the crown of the tree rarely form roots. In the present study, a transcriptomic analysis was developed to compare the gene expression patterns in both types of shoots 24 h after hormone and wounding treatment, matching the induction phase of the process. Our results support the hypothesis that the inability of adult chestnut tissues to respond to the inductive treatment relies in a deep change of gene expression imposed by maturation that results in a significant transcriptome modification. Differences in phytohormone signaling seem to be the main cause for the recalcitrant behavior of mature shoots, with abscisic acid and ethylene negatively influencing the rooting ability of the chestnut plants. We have identified a set of related MADS-box genes whose expression is modified but not suppressed by the inductive treatment in mature shoots, suggesting a putative link of their activity with the rooting-recalcitrant behavior of this material. Overall, distinct maturation-derived auxin sensibility and homeostasis, and the related modifications in the balance with other phytohormones, seem to govern the outcome of the process in each type of shoots.

Selection of reference genes (RGs) for normalization of PCR-gene expression data includes two crucial steps: determination of the between-sample transcriptionally more stable genes, and subsequent choosing of the most suitable genes as internal controls. Both steps can be carried out through generally accepted strategies, each having different strengths and weaknesses. The present study proposes reinforcement of the normalization of gene expression data by integrating analytical revision at critical steps of those accepted procedures. In vitro olive adventitious rooting was used as an experimental system. Candidate RGs were ranked according to transcriptional stability according to several methods. An algorithm of one of these programs (GeNorm) was adapted to allow for partial automatization of RG selection for any strategy of transcriptional-gene stability ordering. In order to choose the more appropriate set of RGs, the achieved results were analytically revised, with special emphasis on biasing effects such as co-regulation. The obtained putative RG sets were also tested for cases restricted to fewer variables. The set formed by the genes H2B, OUB and ACT is valid for normalization in transcriptional studies on olive microshoot rooting when comparing treatments, time points and assays. Such internal reference is now available for wider expression studies on any target gene in similar biological systems. The overall methodology aims to constitute a guide for general application.

Chlorogenic acid (CGA) and rutin in various concentrations and application times were examined over a period of three years to determine their effectiveness in adventitious rooting on the leafy cuttings of an easy to root olive cultivar, 'Arbequina' and a recalcitrant one 'Kalamata'. Exogenous application of phenolics and the season the cuttings were collected affected significantly the rooting potential of both cultivars. The rooting efficiency of 'Arbequina' treated with IBA alone was 51% in summer and 90% in autumn. Among the phenolics, in 'Arbequina', the highest rooting was recorded after the application of 0.1 mM CGA for 30 min reaching 88% in summer (37% increase) and 100% in autumn (10% increase). In 'Kalamata', IBA was almost ineffective in both seasons, as was also the case for the applied phenolics in summer. The greatest overall rooting, for 'Kalamata' (25%) occurred in autumn, when the cuttings' bases were immersed with 0.1 mM CGA for 30 min, corresponding nearly to 830% increase in the rooting performance compared to control. Carbohydrate concentration was also assessed in 'Kalamata' cuttings to examine the influence of CGA in adventitious rooting. It was found that glucose and starch concentration increased during rhizogenesis, whereas the other soluble sugars, except for fructose, exhibited high concentrations at day 1 and 7. The ratio of hexoses/starch, sucrose/starch and sucrose/hexoses exhibited lower values in CGA treated cuttings compared to control. Thus, CGA enhanced rooting performance in both olive cultivars, possibly through a modification of carbohydrate's ratios, strengthening therefore their role in rhizogenesis. [ABSTRACT FROM AUTHOR]

Clonal Eucalyptus propagation is essential for various industry sectors. It requires cuttings to successfully develop adventitious roots (ARs). Environmental conditions are influential on AR development and may be altered to modulate the productivity of hard-to-root clones. The current knowledge gap in research on the physiological patterns underlying commercial-scale propagation results hinders the design of novel strategies. This study aimed to identify patterns of variation in AR-relevant parameters in contrasting seasons and species with distinct rooting performances. E. dunnii and E. ×urograndis (hard- (hardR) and easy-to-root (easyR), respectively) mini-stumps were subjected to light modulation treatments and to mini-tunnel use (MT) for a year. The treatment impact on the branching and rooting rates was recorded. The carbohydrate content, AR-related gene expression, and mineral nutrition profiles of cuttings from the control (Ctrl) and treated mini-stumps were analyzed. Light treatments were often detrimental to overall productivity, while MTs had a positive effect during summer, when it altered the cutting leaf nutrient profiles. Species and seasonality played large roles in all the assessed parameters. E. ×urograndis was particularly susceptible to seasonality, and its overall superior performance correlated with changes in its gene expression profile from excision to AR formation. These patterns indicate fundamental differences between easyR and hardR clones that contribute to the design of data-driven management strategies aiming to enhance propagation protocols.

Wood properties and agronomic traits associated with fast growth and frost tolerance make Eucalyptus nitens a valuable forest alternative. However, the rapid age-related decline in the adventitious root (AR) formation (herein, meaning induction, initiation, and expression stages) limits its propagation. We analyzed transcriptomic profile variation in leaves and stem bases during AR induction of microcuttings to elucidate the molecular mechanisms involved in AR formation. In addition, we quantified expressions of candidate genes associated with recalcitrance. We delimited the ontogenic phases of root formation using histological techniques and Scarecrow and Short-Root expression quantification for RNA sequencing sample collection. We quantified the gene expressions associated with root meristem formation, auxin biosynthesis, perception, signaling, conjugation, and cytokinin signaling in shoots harvested from 2- to 36-month-old plants. After IBA treatment, 702 transcripts changed their expressions. Several were involved in hormone homeostasis and the signaling pathways that determine cell dedifferentiation, leading to root meristem formation. In part, the age-related decline in the rooting capacity is attributable to the increase in the ARR1 gene expression, which negatively affects auxin homeostasis. The analysis of the transcriptomic variation in the leaves and rooting zones provided profuse information: (1) To elucidate the auxin metabolism; (2) to understand the hormonal and signaling processes involved; (3) to collect data associated with their recalcitrance.

To offer a viable alternative to seedling deployment of tea tree, clones will require the development of an efficient, robust, and vegetative propagation system for the large number of plants needed for plantations (i.e., typically 33,000 plants/ha). This study investigated the productivity of an intensive management system for tea tree stock plants and rooted cuttings grown in a subtropical environment (Lismore, NSW, Australia). Three stock plant densities (30, 100, and 200 plants/m2) were tested in coir and potting mix media (consisting of peat+perlite+vermiculite), with 11 settings of cuttings undertaken between April 2019 and March 2020. All stock plants in each media type survived 11 harvests and remained productive; however after 13 months, many plants in the coir media, appeared chlorotic and showed symptoms of iron deficiency. Rooting and cutting survival rates using the mini cutting technique were high, ranging from a maximum mean monthly setting value of 87.7% ± 4 at 84 days post-setting in potting mix, to a minimum of 80.4% ± 3.7 in coir. The most productive treatment was at high stock plant density in potting mix which had the potential to produce 13,440 plants/year/m2. Overall coir appeared less productive, but the pattern of difference among treatments was similar. For the highest system productivity, it is recommended to grow stock plants in potting mix at high densities and modulate temperatures to between 18 °C and 28 °C. Late spring and early summer were the best time for harvesting and setting tea tree mini cuttings in the subtropics.

Microplants of Eucalyptus microcorys were produced through indirect organogenesis, and the interaction of plant growth regulators (PGRs) (TDZ-thidiazuron and NAA-α-naphthalene acetic acid), juvenile tissues (cotyledon and hypocotyl) and different types of polylactic acid (PLA) microvessels on plant production were evaluated. Cotyledon-derived callus induction increased by 30–60% in all tested combinations of TDZ and NAA concentrations compared the absence of PGRs. Hypocotyl-derived callus induction was improved in most tested combinations of TDZ and NAA concentrations. Moreover, 100% callus induction from both tissues was achieved with TDZ (1, 2 and 3 mg L−1) + NAA (0 mg L−1). Bud induction from cotyledon tissues was improved with TDZ (1 and 3 mg L−1) + NAA (0 mg L−1) and from hypocotyl with TDZ (1 and 2 mg L−1) + NAA (0 mg L−1). Shoot elongation from cotyledon tissues was not improved from any combination of PGRs, whereas TDZ (1 mg L−1) + NAA (0 mg L−1), TDZ (1 mg L−1) + NAA (4 mg L−1), TDZ (2 mg L−1) + NAA (4 mg L−1) and TDZ (3 mg L−1) + NAA (2 mg L−1) improved shoot elongation from hypocotyl tissues. Adventitious rooting and acclimatization of microcuttings ranged from 40 to 70% in three of the tested microvessels. The acclimatized microcuttings had low genetic variability. Successful production of E. microcorys microplants was achieved in this study using hypocotyl tissue and cultivated a culture medium supplemented with TDZ and NAA, using PLA-based microvessels. [ABSTRACT FROM AUTHOR]

Copyright of Ciência Florestal (01039954) is the property of Ciencia Florestal and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Brazilian Journal of Biology is the property of Instituto Internacional de Ecologia and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In commercial plantations, mass propagation and deployment of identified and tested clones has potential economic benefits. However, the major challenge is the adventitious rooting ability of high yielding genotypes. In Eucalyptus, large-scale plantations of hybrid clones with enhanced productivity are well documented. However, the understanding of genetic architecture of adventitious rooting traits in this genus is limited. The present study was conducted to decipher the genetic control of this quantitative trait in a bi-parental pedigree of E. tereticornis × E. camaldulensis. The selected parental clones used for controlled hybridization were divergent for their adventitious rooting capacity from stem cuttings. The juvenile shoots of parents and hybrids were coppiced and two-node stem cuttings were harvested and treated with 4000 mg L−1 Indole-3-butyric acid. Phenotypic variation in adventitious rooting traits was documented after 40 days of root induction in parents and 68 hybrids across two settings (March 2015 and April 2015). Significant difference in rooting percentage and number of roots was recorded between the settings. The study revealed a positive correlation between root length and rooting percentage. Broad sense heritability coefficient was the highest for rooting percentage and the predicted genetic advance was maximum for root volume (60.77%). Transgressive inheritance pattern was recorded for all rooting traits and several hybrids registered higher rooting percentage, enhanced root area and volume when compared to parents. These out-performing hybrid clones with superior root system will have potential resource use efficiency and can be deployed in arid and semi-arid zones to enhance productivity. [ABSTRACT FROM AUTHOR]

Demand for therapeutic honey is driving establishment of Leptospermum plantations. This study developed micropropagation methods for two species – Leptospermum polygalifolium Salisb. and L. scoparium J.R.Forst. & G. Forst. The study determined how shoot proliferation and adventitious rooting were influenced by the original explant position on the seedling and the concentration of benzyladenine (BA) in the proliferation medium. Hormone-free node culture was highly effective for both species. Nodal explants often formed roots in the absence of BA and developed elongated axillary shoots. Median shoot numbers of 584 and 659 were formed in 31–32 weeks from a single L. polygalifolium or L. scoparium seed, respectively. A low BA dose was effective for callogenesis and shoot proliferation of L. polygalifolium, but not L. scoparium. The median number of shoots produced from a single L. polygalifolium seed was 630 using 2.22-mM BA. This dose induced extremely high shoot numbers in some clones because explants often produced extensive callus and multiple short shoots. Shoots formed adventitious roots without indole-3-butyric acid and plantlets were acclimatised to nursery conditions. The original explant position did not influence shoot proliferation or adventitious rooting. Leptospermum polygalifolium and L. scoparium proved amenable to micropropagation, facilitating rapid establishment of nectar plantations. [ABSTRACT FROM AUTHOR]

Sweetgale (Myrica gale), rhodora (Rhododendron canadense), and catberry (Ilex mucronata) are shrubs of eastern North America that may have potential for broader use in horticultural landscapes. Because information on their vegetative propagation is scarce, we conducted experiments over 2 years to evaluate the effects of cutting collection date, wounding, substrate composition, and the concentration of applied potassium salt of indole-3-butyric acid (K-IBA) on rooting of each species. In 2015, we collected cuttings of each species on three dates to obtain both softwood and semihardwood cuttings. Cuttings were unwounded or wounded with a razor blade, and treated by dipping into water containing K-IBA at concentrations ranging from 0 to 15,000 mg·L−1, after which they were inserted into a substrate of 3:1 perlite:peat (by volume) and placed under intermittent mist. In 2016, semihardwood cuttings of each species were all wounded, treated with K-IBA from 0 to 15,000 mg·L−1, and inserted into substrates of 100%, 75%, or 50% perlite, with the remaining volume occupied by peat. In both years, the greatest percentage of sweetgale cuttings rooted when no K-IBA was applied. K-IBA application also reduced root ratings, root dry weights, and root lengths of sweetgale. For rhodora and catberry, maximal responses for all measures of rooting occurred when 5000 to 15,000 mg·L−1 K-IBA was applied. We recommend that growers use no exogenous auxin to propagate sweetgale, and 5000 to 10,000 mg·L−1 K-IBA to propagate rhodora and catberry. Cuttings of all three species can be collected from softwood or semihardwood shoots. Finally, sweetgale can be rooted in perlite alone, whereas rhodora and catberry required the addition of peatmoss for satisfactory root development.