Factors affecting shoot proliferation and root initiation in organ cultures of the apple ‘Northern Spy’

Abstract

Factors affecting the establishment, proliferation and adventitious root initiation of ‘Northern Spy’ are described. Shoot-tips established best in Linsmaier and Skoog medium with 5 μM BAP and 1 μM IBA supplemented with 1 mM phloroglucinol, but after the fourth sub-culture, proliferation was similar in media without phloroglucinol. Shoot proliferation was influenced by cytokinin type and concentration, light level and ex-plant type. Of the cytokinins tested, BAP was superior to zeatin, kinetin and 2iP. Proliferation was better with 10 μM BAP than with 5 or 1 μM BAP, but at 10 μM shoots were dwarfed. Single nodes and basal mass expiants produced significantly more shoots than did shoot-tips. Shoot proliferation was maximum at photon flux densities of 75 μmolm −2s −1. Roots can be readily induced with IBA, but salt concentration and the physical support on which shoot-tips are grown influence both root initiation and growth. Half-strength salts and 1 μM IBA gave best root initiation. With agar, coarse sand, perlite and rotated liquid medium, 90–100% root initiation occurs, but root growth was poor in agar.