Effects of zeatin and gibberellic acid on regeneration and in vitro flowering of Phlox paniculata L.

Headnote

Received: 13 September 2015 /Accepted: 12 June 2017 /Published: 20 June 2017

Abstract: The present work reports on the regeneration and in vitro flowering of Phlox paniculata L. Different explants (leaves, petioles and stems) were cultured on Murashige and Skoog (MS) solid medium supplemented with different concentrations and combinations of α-napthaleneacetic acid (NAA) and 6-benzylaminopurine (BAP). Among the explants studied, leaves were found to be the most responsive and had the highest regeneration frequency (100%) when they were cultured in the presence of 8.0 µM NAA and 6.6 µM BAP. However, the regenerated plantlets did not produce any flower buds in successive subcultures. In vitro flowering was only induced after 4 weeks of culturing from shoot tip segments which were maintained on MS solid medium supplemented with zeatin (2.2-11.2 µM) or gibberellic acid (GA₃,1.4-7.2 µM). In the present study treatment with 11.2 µM zeatin showed the highest frequency of in vitro flowering (67.8 ±3.2%), whereas 5.6 µM GA₃ gave a lower percentage (48.8±9.3%). Although the flowers generated in vitro were sterile, our study would provide an important step towards future investigation on the essential factors in in vitro flowering in P. paniculata and to elucidate other developmental, physiological and environmental stimuli, which are required for promoting or inhibiting the transition of a vegetative state to a flowering state in this species.

Keywords: Phlox paniculata L., in vitro flowering, zeatin, gibberellic acid, micropropagation

INTRODUCTION

Phlox paniculata L. is an important flowering plant that belongs to Polemoniaceae [1]. P. paniculata L. is a perennial ornamental plant, bears dense terminal clusters of flowers in pink, crimson and mauve, is commonly grown as borders, and is also suitable for window boxes and tubs [2-4]. The species produces sterile seeds [1, 2], and even though the traditional method of propagation is by root cuttings, the roots are often damaged by red ants and sometimes by soil-born fungi. Therefore, in vitro culture is an effective technique for obtaining large-scale clonal propagation of P. paniculata. Schnabelrauch and Sink [5] studied the clonal propagation of P. paniculata through axillary bud culture. Later, shoot regeneration was induced from adult leaf segments cultured by Declerck and Korban [6]. These studies revealed the potential for inducing multiple shoots in in vitro cultures...