Influence of gelling agent and cytokinins on the control of hyperhydricity in Aloe polyphylla

Shoot regeneration and occurrence of hyperhydricity in Aloe polyphylla were greatly affected by the type of gelling agent. The use of gelrite resulted in a significantly lower multiplication and almost four times higher hyperhydricity (65%) compared to agar-solidified medium. Gelrite was further selected to evaluate if hyperhydricity can be overcome by altering the physical properties of the gel, as represented by increasing gelrite concentrations. Four concentrations of gelrite (0, 2.4, 6 and 16 g l(-1)) were tested in combination with zeatin, N-6-benzyladenine (BA) or thidiazuron (TDZ). Almost all explants grown in liquid media in the presence of cytokinins became hyperhydric and lost their ability to regenerate. The greatest shoot formation was obtained on media with 2.4 g l(-1) gelrite and 5 mu M zeatin or BA, however hyperhydricity was very high. Satisfactory reduction in hyperhydricity was achieved only at 16 g l(-1) gelrite, under which conditions the multiplication also decreased. The use of TDZ resulted in very low shoot regeneration and high hyperhydricity irrespective of the gelrite concentration.