In vitro shoot multiplication of Macadamia tetraphylla L. Johnson

Abstract

SummaryMacadamia, Macadamia tetraphylla L. Johnson, is a highly valued nut tree grown in tropical and sub-tropical parts of Australia and USA. A protocol for rapid in vitro shoot multiplication of macadamia using single node segments from two year old grafted plants and four month old seedling plants is described. Cultures were established by placing node segments on half strength of MS medium. Of the six levels of 6-benzylaminopurine tested, 2 mg l­1 BA produced the highest percentage bud break, mean shoot numbers per explant and shoot length. Levels above 2 mg l­1 BA in the medium produced stunted and vitreous shoots. Combining 2 mg l­1 BA with varying levels of gibberellic acid (0.0, 0.125, 0.25, 0.5, 0.8, and 1.0 mg l­1) in the medium further improved bud break, shoot numbers and shoot length significantly from explants of both types of plants. Highest shoot numbers and shoot length were achieved in the medium containing 1 mg l­1 GA3+2mgl­1 BA. A 12-fold shoot multiplication was achieved in a culture period of 12 weeks. This study demonstrates that macadamia nodes are amenable to produce high quality multiple shoots in vitro and hence are suitable material for clonal multiplication and genetic transformation studies.