Control of hyperhydricity in Eucalyptus axillary shoot cultures grown in liquid medium

Shoots of four clones of two Eucalyptushybrids were successfully grown in a liquid medium containing modified MS basal salts supplemented with 0.01 mg l ^–1 (0.04 M) BAP and various concentrations of a proprietary anti-hyperhydricity agent (sold commercially as anti-vitrification agent EM2). Shoots of a single clone were also grown using the same medium but with the anti-hyperhydricity agent replaced with various concentrations of a commercially available gelling agent containing pectin (M-Gel) or a polysaccharide extract (iota-carrageenan) from seaweed. A range of supplements applied to the media were effective in reducing the hyperhydricity of shoots. The addition of EM2 and M-Gel led to a significant decrease in hyperhydricty, without showing any significant detrimental effect on the numbers of shoots produced for three of the four genotypes tested. At a concentration of 5 g l^–1, for either compound, the percentage rooting and percentage survival of shoots, both in vitro and ex vitro, either equalled or exceeded those of untreated shoots. Addition of iota-carrageenan, although beneficial in reducing hyperhydricity and improving percentage rooting in vitro, was detrimental to shoot production and acclimatisation ex vitro. Common factors of these agents' contributions to their anti-hyperhydric properties are discussed.