Chitosan versus plant growth regulators: a comparative analysis of their effects on in vitro development of Serapias vomeracea (Burm.f.) Briq.

Abstract

This study aimed to compare the in vitro effects of chitosan oligomers and polymer with commonly-used plant growth regulators (PGRs) on seed germination, protocorm formation, and organ development in Serapias vomeracea. The effects of N-acetylated (10%) chitosan oligomer mixture (CHI-OM) with a degree of polymerization (DP) between 2 and 15 (5, 10, 15, and 20 mg L−1) and chitosan polymer (CHI-P) with a DP of 70 were compared with commonly-used cytokinins [6-benzylaminopurine (BAP) and kinetin (KIN)], auxins [indole-3-acetic acid (IAA) and indole-3-butyric acid (IBA)], and jasmonic acid (JAS) at 0.25, 0.5, 1.0, and 2.0 mg L−1. The medium supplemented with CHI-P at 5 mg L−1 gave the highest seed germination rate, whereas JAS and CHI-OM triggered protocorm formation better than the all treatments tested. The JAS and IAA treatments resulted in intense browning of the roots. The CHI-P treatments at high concentrations and JAS treatments at moderate concentrations increased mean shoot length while the medium containing KIN at 0.5 mg L−1 induced root elongation significantly. The root elongation-inhibitory effect of chitosan was observed at the higher concentrations of CHI-OM, but the media containing 10 mg L−1 CHI-OM and 15 mg L−1 CHI-P triggered adventitious rooting. However, the highest tuberization success was found after 10 mg L−1 CHI-OM and 0.5 mg L−1 JAS treatments. Tuber development was achieved in the media supplemented with BAP and CHI-OM. This study suggested that well-characterized chitosan could be used as an alternative to JAS and BAP in orchid cultures. Well-characterized chitosans at the right concentration induce similar effects with jasmonic acid and 6-benzylaminopurine in orchid cultures.