Exogenous hormones supplementation improve adventitious root formation in woody plants

Characterization and genetic differences analysis in adventitious roots development of 38 Populus germplasm resources

To select poplar clones with excellent adventitious roots development (ARD) and deepen the understanding of its molecular mechanism, a comprehensive evaluation was conducted on 38 Populus germplasm resources with cuttings cultured in the greenhouse. Genetic differences between poplar clones with good ARD and with poor ARD were explored from the perspectives of genomics and transcriptomics. By cluster analysis of the seven adventitious roots (AR) traits, the materials were classified into three clusters, of which cluster I indicated excellent AR developmental capability and promising breeding potential, especially P.×canadensis 'Guariento', P. 'jingtong1', P. deltoides 'Zhongcheng5', P. deltoides 'Zhongcheng2'. At the genomic level, the cross-population composite likelihood ratio (XP-CLR) analysis identified 1944 positive selection regions related to ARD, and variation detection analysis identified 3426 specific SNPs and 687 specific Indels in the clones with good ARD, 3212 specific SNPs and 583 specific Indels in the clones with poor ARD, respectively. Through XP-CLR, variation detection, and weighted gene co-expression network analysis based on transcriptome data, eight major putative genes associated with poplar ARD were primary identified, and a co-expression network of eight genes was constructed, it was discovered that CSD1 and WRKY6 may be important in the ARD. Subsequently, we confirmed that SWEET17 had a non-synonymous mutation at the site of 928,404 in the clones with poor ARD, resulting in an alteration of the amino acid. After exploring phenotypic differences and the genetic variation of adventitious roots development in different poplar clones, this study provides valuable reference information for future poplar breeding and genetic improvement.

Optimization of Plant Growth Regulators for In Vitro Mass Propagation of a Disease-Free 'Shine Muscat' Grapevine Cultivar

This study addresses the propagation challenges faced by 'Shine Muscat', a newly introduced premium grapevine cultivar in South Korea, where multiple viral infections pose considerable economic loss. The primary objective was to establish a robust in vitro propagation method for producing disease-free grapes and to identify effective plant growth regulators to facilitate large-scale mass cultivation. After experimentation, 2.0 µM 6-benzyladenine (BA) exhibited superior shoot formation in the Murashige and Skoog medium compared with kinetin and thidiazuron. Conversely, α-naphthaleneacetic acid (NAA) hindered shoot growth and induced callus formation, while indole-3-butyric acid (IBA) and indole-3-acetic acid (IAA) demonstrated favorable root formation, with IBA showing better results overall. Furthermore, inter simple sequence repeat analysis confirmed the genetic stability of in vitro-cultivated seedlings using 2.0 μM BA and 1.0 μM IBA, validating the suitability of the developed propagation method for generating disease-free 'Shine Muscat' grapes. These findings offer promising prospects for commercial grape cultivation, ensuring a consistent supply of healthy grapes in the market.

Effect of Exogenous Plant Growth Regulators and Rejuvenation Measures on the Endogenous Hormone and Enzyme Activity Responses of Acer mono Maxim in Cuttage Rooting

The cuttage rooting method for Acer species is difficult to achieve a good efficacy as trees maintain good characteristics at the rejuvenation stage, thus improving the rooting of Acer species. The addition of exogenous hormones and rejuvenation can improve the rooting effect of cuttings; however, the specific regulatory mechanism is still unclear. Here, Acer mono Maxim rejuvenation and non-rejuvenation cuttings were used as test subjects, to investigate the effects of exogenous hormones on the activities of endogenous hormones and antioxidant enzymes in the rooting process of young cuttings. The results showed that exogenous growth-regulating substances significantly improved the rooting rate of A. mono. Exogenous hormones naphthylacetic acid (NAA) + indolebutyric acid (IBA) increased the initial levels of the endogenous hormones, indoleacetic acid (IAA) and abscisic acid (ABA), and the enzyme activities of peroxidase (POD) and polyphenol oxidase (PPO). Rejuvenation treatment prolonged the time of increase in ABA content and indoleacetic acid oxidase (IAAO) activity at the root primordium induction stage, while increasing trans-zeatin riboside (ZR) content and decreasing POD enzyme activity in cuttings. These results demonstrate that A. mono cuttings can achieve the purpose of improving the rooting rate by adding the exogenous hormone (NAA + IBA), which is closely related to the changes of endogenous hormone content and enzyme activity, and these changes of A. mono rejuvenation cuttings are different from non-rejuvenation cuttings.

Expression of CsSCL1 and Rooting Response in Chestnut Leaves Are Dependent on the Auxin Polar Transport and the Ontogenetic Origin of the Tissues

The mechanisms underlying the de novo regeneration of adventitious roots are still poorly understood, particularly in trees. We developed a system for studying adventitious rooting (AR) at physiological and molecular levels using leaves excised from chestnut microshoots of the same genotype but with two distinct ontogenetic origins that differ in rooting competence. Leaves were treated with auxin and N-1-naphthyl-phthalamic acid (NPA), an inhibitor of auxin polar transport (PAT). The physiological effects were investigated by recording rooting rates and the number and quality of the roots. Molecular responses were examined by localizing and monitoring the changes in the expression of CsSCL1, an auxin-inducible gene in juvenile and mature shoots during AR. The rooting response of leaves was ontogenetic-stage dependent and similar to that of the donor microshoots. Initiation of root primordia and root development were inhibited by application of NPA, although its effect depended on the timing of application. CsSCL1 was upregulated by auxin only in rooting-competent leaves during the novo root organogenesis, and the expression was reduced by NPA. The inhibitory effect on gene expression was detected during the reprograming of rooting competent cells towards root initials in response to auxin, indicating that PAT-mediated upregulation of CsSCL1 is required in the initial steps of AR in chestnut leaves. The localized expression of CsSCL1 in the quiescent center (QC) also suggests a role for this gene in the maintenance of meristematic competence and root radial patterning.

From the Wild to the Field: Documentation, Propagation, Pilot Cultivation, Fertilization, and Phytochemical Evaluation of the Neglected and Underutilized Amelanchier ovalis Medik. (Rosaceae)

The snowy Mespilus, or serviceberry (Amelanchier ovalis Medik., Rosaceae) represents a neglected and underutilized small fruit tree species with high nutritional value. In this work, we present the results of a long-term study facilitating the sustainable exploitation of A. ovalis as a new germplasm resource from the Greek flora. Ten wild-growing population samples of A. ovalis have been collected from natural habitats in northern Greece. Asexual propagation trials on these materials delivered successful propagation (83.3% rooting) on a selected genotype via leafy cuttings of young, primary, non-lignified soft wood with the application of the rooting hormone. The ex situ cultivation potential of the selected genotype has been evaluated under distinct fertilization regimes in a pilot field trial. Three-year results of this ongoing trial have shown that A. ovalis does not require external nutrient enhancement to be established during its early stages since plant growth rates between conventional fertilization and control plants were similar for the first two years and higher compared to organic fertilization. Conventional fertilization delivered higher fresh fruit production in the third year, with higher fruit number and fruit size compared to organic fertilization and control plants. The phytochemical potential of the cultivated genotype was assessed via the total phenolic content and radical scavenging activity of separate extracts from leaves, twigs, flowers, and young fruits, which revealed that individual plant organs have strong antioxidant activity despite their moderate total phenolic content. The multifaceted approach applied herein has provided novel data that may set the framework for further applied research toward the sustainable agronomic exploitation of Greek A. ovalis as a diversified superfood crop.