Morphological Variations in Buddleia Induced by Gamma Ray Irradiation

Abstract

Buddleia species is commonly used as a perennial for landscaping as a result of its heavy flowers and long bloom period. However, this species has a few concerns such as lack of flower color, excessive growth, and an invasive nature. Attempts to improve Buddleia using conventional breeding methods have resulted in limited success. In this study, mutagenesis by gamma ray irradiation was used to induce genetic variations. In vitro shoot tips of two Buddleia cultivars, B. davidii ‘Potters Purple’ and Buddleia ‘Lochinch’, were exposed to 0 to 150 Gy gamma rays and then recovered in Murashige and Skoog (MS) medium supplemented with 2.5 μM benzyladenine (BA). Shoots that recovered from the gamma ray treatment were rooted in half-strength MS medium with 0.5 μM naphthalene acetic acid (NAA) and grown in the greenhouse. The growth of shoot tips was inhibited after they were exposed to gamma rays. An average of 50.8% of shoots treated with 50 Gy gamma rays were recovered, whereas only 9.7% and 6.5% of shoots recovered when exposed to 100 and 150 Gy gamma rays, respectively. After transfer to the greenhouse, a few plants showed reduced growth with some dying before they reached the flowering stage. Various variations including characteristics of leaves (shape, size, hairs), stems (shape, internode length, branching), flowers (color, size, and structure), and plant stature were observed. This research demonstrates that in vitro mutation induction using gamma ray irradiation could be a useful protocol to develop new cultivars or genetic materials for further breeding of Buddleia or other related species.