2018 ASHS Annual Conference

The genus Vernonia Schreb., commonly known as ironweeds, comprises ≈ 1000 species worldwide and are widely known for their pharmaceutical qualities. Several species also have desirable ornamental characteristics. Many ornamental varieties are often difficult or slow to propagate through conventional methods such as stem cuttings or divisions. The development of micropropagation systems may facilitate faster propagation and the release of new varieties. In vitro regeneration studies on Vernonia have focused on medicinal species such as Vernonia cinerea. However little work has been done to develop in vitro propagation systems for ornamental species. Therefore, the objective of this study was to develop an efficient micropropagation system for a novel ornamental Vernonia hybrid and to examine the effects of selected media and cytokins on shoot proliferation. Multiplication was evaluated by culturing on either MS, WPM, DKW, Q&L or B5 basal salts. DKW produced the highest number of shoots (3.5 plants per explant), longest shoots (66 mm), and the highest multiplication rate (3.8 fold). A second study evaluated the effects of cytokinins BAP, 2iP, meta-Topolin and TDZ at concentrations of 0, 1.25. 2.5, 5.0 or 10.0 µM. Explants cultured on media containing 2.5 µM TDZ produced the highest number of shoots (12.7 shoots per explant) and the highest multiplication rate (15.6 fold), while explants cultured on media containing meta-Topolin produced the longest shoots (86 mm). To test the long-term effects of TDZ, explants were maintained for 4 subculture cycles on 1.25, 2.5, 5.0 and 10.0 µM. At 1.25 and 2.5 µM TDZ, shoot regeneration increased to 27 fold during the second subculture period and remained high. For higher concentrations of TDZ, shoot multiplication rate and quality declined with increasing subcultures. Shoots from 1.25 and 2.5 µM formed roots in vitro and were successfully transferred ex vitro through 4 sub culture cycles.