Gelling Agent and Growth Regulator Effects on Shoot Vitrification of ‘Gala’ Apple in Vitro

Abstract

Shoot tips of ‘Gala’ apple (Malus domestica Borkh.) were grown on proliferation medium containing Murashige and Skoog salts, supplemented with 0.56 mm myo-inositol; 1.2 μm thiamine-HCl; 2.2 or 4.4 μm BA; 0.005, 0.05, or 0.5 μm IBA; and 1.3 μm GA3. The media were solidified with Gelrite at concentrations from 0.5 to 1.5 g·liter−1 plus agar (Sigma) from 0.5 to 4.0 g·liter−1. Vitrification was influenced both by gelling agent and BA concentration, whereas the IBA concentration had little effect. Increasing either agar or Gelrite concentration resulted in a decreasing percentage of vitrified explants. The higher BA level generally increased vitrification, but increasing the agar concentration tended to reduce the difference in effect of the 2 BA levels. Certain combinations of gelling agents produced no vitrification with no reduction in shoot proliferation, and with a clarity of the medium approaching that of Gelrite alone. Chemical names used: N-(phenylmethyl)-lH-purin-6-amine [benzyladenine (BA)]; lH-indole-3-butanoic acid (IBA); and gibberellic acid (GA3).