Bee honey improved the performance of indole-3-butyric acid on promoting adventitious roots formation of Cupressus macrocarpa L. var. Goldcrest: Morpho-biochemical and histoanatomical investigation

Abstract

The effective role of different auxins on adventitious roots (Ars) formation of stem cuttings relies on several factors including type of auxins, concentrations and the intermixing materials. In this study, bee honey (BH) was evaluated as a cofactor for maximizing the promoting effect of indole-3-butyric acid (IBA) for better survival of propagated hard-to-root ornamental plants. To improve Ars morphogenesis of Cupressus macrocarpa L. var. Goldcrest, a greenhouse experiment was conducted to evaluate the efficacy of exogenous application of IBA intermixed with BH in comparison with talcum powder (TP) on morphological, biochemical, histoanatomical, and ultrastructural responses. Results indicated that 500 mg kg-1 IBA intermixed with BH (T5) was the superior treatment for improving rooting percentage and root growth measurements. Exogenous application of T5 led to maximize activities of polyphenol oxidase and catalase enzymes as well as total phenols content; however, it caused a sharp decline in peroxidase enzyme activity as compared with untreated cuttings. Additionally, this treatment decreased amounts of gibberellin, benzyl adenine, kinetin and abscisic acid, while the endogenous content of indole-3-acetic acid increased. Histoanatomical observations of stem cuttings treated with T5 showed four prominent phases for adventitious root formation including: induction, initiation of meristemoids, root primordial formation and Ar elongation at 0–6th, 6-12th, 12-18th and 18-30th day after planting (dap). The Ar primordia evolved via two different developmental pathways: (i) indirect genesis (i.e., callus tissues) and (ii) direct genesis (e.g., cells in the inner bark, medullary rays and surrounding tissues). The time-course histoanatomical data of this study provide insights regarding the potential utilization of IBA intermixed with BH to improve Ar formation of several hard-to-root ornamentals.