Adventitious root formation (ARF) is the process by which roots arise from nonroot plant tissue (Bellini et al., 2014; Davis and Haissig, 2013). Effectively using ARF for plant propagation is a cornerstone of the ornamental horticulture industry as it allows for plants with preferred traits to be propagated asexually and thereafter perpetuated indefinitely. The process by which excised stem sections develop adventitious roots can be divided into two distinct stages; cells of the existing tissue must first dedifferentiate, and then these cells must redifferentiate into root cells (Hartmann et al., 1990).
Several elements, including N, P, B, Ca, Mg, Mn, and Zn, are necessary for ARF (Anderson, 1986; Blazich, 1988). Calcium is crucial to ARF because it is required for root primordia formation, cell expansion, and cell division (White and Broadley, 2003). Indole-3-acetic acid (IAA) is the primary hormone involved in ARF (Bellini et al., 2014; Verstraeten et al., 2014). Micronutrients, including B and Zn, are necessary for IAA metabolism (Jarvis et al., 1984; Kazan, 2013; Martín-Rejano et al., 2011). Root formation is stimulated by Fe availability (Giehl et al., 2012) and inhibited by S deficiency (Dan et al., 2007), and these effects are probably related to auxin activity (Kazan, 2013). There is some evidence that Cu can promote root formation and growth when applied at subtoxic concentrations, but the precise role of endogenous Cu in root formation is not known (Arnold et al., 1994; Chang and Lin, 2006; Dunn et al., 1997; Schwambach et al., 2005). Other macro- and micronutrients are required for subsequent growth and development after roots have formed (Bellini et al., 2014; Zhang and Forde, 2000).
Several studies have examined tissue nutrient concentrations of leafy stem cuttings (henceforth referred to as “cuttings”) during vegetative propagation in nutrient-free media. Good and Tukey (1967) showed that P was mobilized from older leaves to lower stems during the initial stages of ARF in Chrysanthemum morifolium (Ramat.). Nitrogen and K also became mobile after roots developed; N and P translocated from older leaves to expanding leaves and roots, whereas K moved from the older leaves to expanding leaves only. Calcium concentrations remained constant throughout the study. Blazich and Wright (1979) analyzed N, P, K, Ca, and Mg concentrations in the leaves, upper, and lower stems of box-leaved holly [Ilex crenata (Thunb.)]. Concentrations of all nutrients in the leaves, upper, and lower stems remained constant over a 27-d propagation period; no nutrient mobility was observed. In a later study, nutrient movement was characterized in box-leaved holly cuttings with and without auxin treatment under intermittent mist (Blazich et al., 1983). No nutrient mobilization occurred while the roots were forming. However, following root initiation and subsequent budbreak, N, P, K, Ca, and Mg were translocated from leaves to upper stems in untreated cuttings to support new shoot growth. In auxin-treated cuttings, N, P, and K were mobilized to the roots, probably to support enhanced root proliferation. Svenson and Davies (1995) analyzed several macro- and micronutrient concentrations in the leaves and basal stems of poinsettia stem cuttings during ARF. Before root development; Cu, Fe, and Mo accumulated in the basal stems, whereas concentrations of P, K, Ca, and Mg declined. After root initiation, B, Cu, Fe, Mg, Mn, Mo, and Zn concentrations increased in the basal stems. Foliar N, Fe, and Mo concentrations declined over the course of the study, suggesting that Fe and Mo may have been translocated from the leaves to lower stems.
This study was conducted to survey changes in nutrient concentrations in Hibiscus acetosella (Hiern.) Welw. ‘Panama Red’ (PP20121), a fast-rooting species, under standard commercial production conditions. Cuttings were harvested once every 3 d and divided into four sections for analysis: leaves, upper stems, lower stems, and roots (including callus). Tissue concentrations of 13 mineral elements (N, P, K, B, Ca, Cu, Fe, Mg, Mn, Mo, Ni, S, and Zn) were analyzed. Cuttings were stuck in a standard growing medium with starter fertilizer and kept under shade with intermittent mist to replicate industry practices.
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