Exogenous Application of Iba Stimulated Adventitious Root Formation of Zanthoxylum Beecheyanum K. Koch Stem Cutting: Histo-Physiological and Phytohormonal Investigation

Abstract

Poor rooting characteristic of Chinese pepper (Zanthoxylum beecheyanum K. Koch) shrub is a restriction for its commercial production. This investigation was carried out to assess the effectiveness of the exogenous application of indole-3-butyric acid (IBA) on adventitious root (AR) formation and some morpho-physiological, biochemical, and histological alterations associated with rhizogenesis conditions. IBA at 1500 or 2000 mg kg-1, gave comparable effects for improving the performance of rooting architecture compared to the control treatment. The AR primordia of Z. beecheyanum originated from two distinct developmental pathways: (i) direct genesis from cells in the cambial zone and nearby tissues, and (ii) indirect genesis from cells in callus tissues. Rooting process involved four phases: (i) induction at 0-10 days after planting (DAP), (ii) initiation at 10-15 DAP, (iii) formation of the root primordia (Rp) at 15-20 DAP, and root extension at 20-30 DAP. In cuttings' inductive phase temporarily correlated with intensive cell divisions, high levels of endogenous indole-3-acetic acid (IAA) and gibberellins (GA3) were observable. However, IBA application led to a pronounced increase in soluble sugars and phenolic content. The initiation phase is accompanied by the first histological changes to meristemoid forms. This phase is also stimulated by the subsequent generation of low IAA and high GA3 contents. In the development of Rp and root extension phases, prominent Rp formation in the cambium and complete differentiation with vascular tissues continued with that of the stem cuttings.  In essence, the current study provides insights into the morphological, histo-physiological, and phytohormonal alterations in stem cuttings.

Keywords: Zanthoxylum beecheyanum K. Koch, indole-3-butyric acid, adventitious roots, histological structure, biochemical changes