Influence of Agar Concentration on in Vitro Shoot Proliferation of Malus sp. ‘Almey’ and Pyrus communis ‘Seckel’1

Shoot tips of ‘Almey’ crabapple [ Malus baccata (L.) Borkh. × M. pumila var. niedzwetzkyana (Dieck) Schneid.] and ‘Secke!’ pear ( Pyrus communis L.) were cultured on Murashige and Skoog medium supplemented with 2 mg/liter 6-benzylamino purine and agar levels ranging from 0 to 1.2%. The greatest shoot proliferation and shoot growth in ‘Almey’ occurred on medium containing 0.3% agar. Higher agar concentrations decreased both shoot proliferation and shoot growth. Increasing agar concentrations resulted in decreased shoot growth in ‘Seckel’, but shoot proliferation was significantly greater at concentrations of 0.6% and higher as compared to 0.3% or lower. Autoclaving caused an acidification of the medium. The addition of agar reduced media acidification. This pH variation does not explain the effect of agar on shoot proliferation and growth.