Micropropagation of Spigelia marilandica L.

Abstract

Commercial micropropagation of Spigelia marilandica (Loganiaceae) requires the development of proliferation and rooting protocols for in vitro-generated microcuttings. Seedling microshoot explants formed the most axillary shoots when cultured on half-strength Murashige and Skoog basal medium supplemented with 11 or 22 μM benzyladenine. Monthly serial subculture of shoot cultures for 6 mo had no impact on the mean total number of axillary shoots formed. Microshoot explants with shoot tips formed more axillary shoots compared to single nodes, and microshoot explants with basal nodes formed more axillary shoots compared to microshoot explants without basal nodes. Microcuttings were rooted ex vitro. Microcuttings, 1–2 versus 2–5 cm in length, rooted equally well whether placed in Redi-Earth, sand, or vermiculite. After potting, plants from short and long microcuttings grew equally well based on leaf number and stem height; however, plants grown in the sun had more leaves and were taller than plants under 50% shade (6 versus 3.1 cm in height, respectively). Microcuttings dipped in indolebutyric acid, 500 or 1000 ppm, had more roots with longer mean total root lengths compared to control microcuttings. Microcuttings grown under mist for 4 wk survived better than those under mist for 6 wk. Neither microcutting age (6, 8, 12, 16, or >20 wk post-subculture) nor cold storage (8, 12, or 16 wk post-subculture; 6°C for 7 wk) affected the percent of shoots with roots (100%), mean root number, or mean total root length. Field-grown in vitro-derived plants (60% survival) had more stems and more leaves compared to field-grown seedlings of comparable age (90% survival). Micropropagation of S. marilandica on a commercial scale has practicality based on the ease with which microshoot explants formed axillary shoots in vitro and microcuttings rooted ex vitro.