Micropropagation of two threatened Tasmanian species of Calocephalus (Asteraceae), with comments on phenotypic plasticity

Abstract

Micropropagation systems were developed for Calocephalus citreus Less. and C. lacteus Less., two threatened Tasmanian members of the Asteraceae. Disinfected cold-treated capitula were used to initiate regeneration. For C. citreus, initiation was achieved on Murashige and Skoog (MS) medium with 0.1 mg L^–1 or 0.5 mg L^–1 indoleacetic acid (IAA) and 1 mg L^–1 6-benzylaminopurine (BAP) in 5 weeks, while for C. lacteus initiation was achieved on MS with α-naphthaleneacetic acid (NAA) (0.1 mg L^–1) in 3 weeks and on MS without any plant growth regulator (PGR) in 6 weeks. Multiplication was achieved in both species on MS with various concentrations of IAA (0.01–0.5 mg L^–1) and BAP (0.1–1 mg L^–1). In C. citreus, shooting in all treatments did not differ significantly from PGR-free MS, while in C. lacteus PGR-free MS was one of the better treatments. Multiplication media also initiated root formation in C. lacteus, thereby facilitating immediate planting out. Optimal root induction in C. citreus was achieved by using MS with 1 g L^–1 activated charcoal. Clear morphological differences between in vitro and ex vitro plants of both species were observed. This phenotypic plasticity was more pronounced in C. lacteus than in C. citreus. As C. lacteus has a wider distribution than C. citreus and C. lacteus was more responsive during many stages of the micropropagation process, it may be possible to use the culture-induced phenotype to provide insights into the ecology of plant species.