The role of nodal roots in prostrate clonal herbs: ‘phalanx’ versus ‘guerrilla’

Abstract

The influence of nodal rooting on branching was studied in three evolutionarily and morphologically diverse species of prostrate clonal herbs: Tradescantia fluminensis (a monocotyledonous extreme 'phalanx' species), Calystegia silvatica (a dicotyledonous extreme 'guerrilla' species) and Trifolium repens (a dicotyledonous intermediate species). In all three, branch development from axillary buds is regulated by a positive signal produced by roots together with inhibitory influences from both pre-existing branches and shoot apical buds (apical dominance). Responses to nodal roots are cumulative and increased root activity leads to more vigorous bud outgrowth. In the absence of nodal roots, a single basal root system is unable to maintain continued extension growth of the shoot. We suggest that as individual nodal roots and stem internodes are both short-lived in these nodally-rooting clonal species, the plants' investment in them is minimal. Thus, in contrast to perennial species lacking nodal roots, individual root systems in prostrate clonal herbs are small and stems have little secondary thickening and development of long-distance transport tissues. Hence the decline in extension growth of the shoot in the absence of nodal roots could be linked to the weak development of long-distance transport tissues in their relatively thin horizontal stems and to resource sharing between primary stems and lateral branches (as suggested by the greater retardation of primary stem growth in the more profusely branched 'phalanx' species (Trifolium and Tradescantia) than in the weakly branched 'guerrilla' species, Calystegia). These findings are consistent with the view that the long-term persistence of genotypes of nodally-rooting prostrate species is dependent upon them encountering the moist conditions required to facilitate the continual development of new young nodal root systems.

<b>Rhizogenic behavior of black pepper cultivars to indole-3-butyric acid

“…In Dalbergia melanoxylon, cuttings treated with IBA presented a higher rooting percentage and a superior number and length of roots compared to untreated cuttings. (Table 1), and it can be inferred that this cultivar can be used as rootstock, considering the higher exploitation of its radicular system and its consequently greater effectiveness of water absorption and use of mineral substrates; this was observed in a paper by Veloso et al (2000), in which only the Guajarina cultivar responded to phosphorus application.…”

“…According to the authors, in the absence of nodal roots, the basal radicular system is unable to maintain the continuous growth of the sprout. According to Thomas and Hay (2008), stoloniferous plants present a physiologic link between the growth of nodal roots and the development of stem tissues.…”

“…In Brazil, black pepper, in addition to being a valuable spice, has shown other applications in research as a larvicide to fight Aedes aegypti (SIMAS et al, 2007;GRZYBOWSKI et al, 2012) and for the bactericide properties of the essential oil of its seeds (TRAJANO et al, 2009). …”

Rooting responses of black pepper (Piper nigrum cv. Bragantina) as affected by chemical, physical and microbiological properties of substrates and auxin

“…Nodal cuttings of Bambusa vulgaris had greater rooting percentages when exposed to IBA (8000 mg L -1 ) (Islam et al, 2011). In the absence of nodal roots, only the basal root system was able to maintain the continued growth of the bud (Thomas & Hay, 2010). The development of axillary buds was positively regulated by a signal from the roots (ex.…”

Incorporating clonal growth form clarifies the role of plant height in response to nitrogen addition

“…In this analysis, we focus on two simpliWed categories of clonal growth form distinguished by the distance between ramets of the same individual: clumpers with very short spacers (phalanx; sensu Lovett Doust 1981) and runners with longer spacers (guerilla). We recognize that many clonal species lie on a continuum between these two categories (e.g., Thomas and Hay 2010) and that many more categories of clonal growth can be used if appropriate morphological data are available (Klimenová and Klimen 2011). Unfortunately, this information is lacking for most North American species.…”