Overcoming Physiological Bottlenecks of Leaf Vitality and Root Development in Cuttings: A Systemic Perspective

Abstract

Each year, billions of ornamental young plants are produced worldwide from cuttings that are harvested from stock plants and planted to form adventitious roots. Depending on the plant genotype, the maturation of the cutting, and the particular environment, which is complex and often involves intermediate storage of cuttings under dark conditions and shipping between different climate regions, induced senescence or abscission of leaves and insufficient root development can impair the success of propagation and the quality of generated young plants. Recent findings on the molecular and physiological control of leaf vitality and adventitious root formation are integrated into a systemic perspective on improved physiologically-based control of cutting propagation. The homeostasis and signal transduction of the wound responsive plant hormones ethylene and jasmonic acid, of auxin, cytokinins and strigolactones, and the carbon-nitrogen source-sink balance in cuttings are considered as important processes that are both, highly responsive to environmental inputs and decisive for the development of cuttings. Important modules and bottlenecks of cutting function are identified. Critical environmental inputs at stock plant and cutting level are highlighted and physiological outputs that can be used as quality attributes to monitor the functional capacity of cuttings and as response parameters to optimize the cutting environment are discussed. Facing the great genetic diversity of ornamental crops, a physiologically targeted approach is proposed to define bottleneck-specific plant groups. Components from the field of machine learning may help to mathematically describe the complex environmental response of specific plant species.

Involvement of the auxin–cytokinin homeostasis in adventitious root formation of rose cuttings as affected by their nodal position in the stock plant

“…Formation of ARs in cuttings is highly dependent on diverse environmental factors at stock plant and cutting levels, the ontogenetic stage of the stock plant and the position of cuttings within the stock plant (Druege 2020 ). For positional effects the term ‘topophysis’ has been repeatedly used.…”

Identifying Molecular Chechkpoints for Adventitious Root Induction: Are We Ready to Fill the Gaps?

“…This signals the start of the initiation phase, when the new meristem is defined, and is followed by an expression phase that leads to AR emergence. The process can last days to weeks depending on the type of explant, the physiological, and developmental status of the mother plant and the environmental conditions ( Xu, 2018 ; Druege 2020 ). The signaling pathways set in motion during the induction phase start a chain of events that will determine the overall success and will be the main focus hereinafter.…”

“…In addition, local release of conjugated auxin by IAA-amino acid hydrolases (IAA-AAH), as described for petunia cuttings, can contribute to the increase of bioactive IAA ( Druege et al, 2019 ). Finally, as root-directed polar auxin transport (PAT) is interrupted, auxin from the shoot will accumulate at base of the cutting ( Druege, 2020 ; Jing et al, 2020 ).…”

“…Current knowledge of the basic biochemical, genetic, cellular, physiological, and environmental processes involved in de novo root organogenesis can provide clues to identify bottlenecks for vegetative propagation and introduce quantitative improvements ( Druege, 2020 ). However, woody species that show a sharp age-related decline in adventitious rooting capacity ( Abarca and Díaz-Sala, 2009 ; Pizarro and Díaz-Sala, 2019 ; Valladares et al, 2019 ) may need a qualitative approach to unlock signaling pathways that successfully elicit the formation of new root meristems in most herbaceous plants.…”

Model-based evaluation of management options in ornamental plant nurseries

“…The quality of ornamental plants strongly depends on shoot vitality, root number, and root function (Druege, 2020). The spectral signatures of 'Dead', 'Shoot Stress' and 'Root + Shoot Stress' show a minor reduction in the green peak compared to 'Healthy' and 'Temporary Shoot Stress' that can be related to the slightly browner shoot color observed for stressed shoots by naked-eye observation compared to the bright green shoot color for healthy shoots (e.g.…”