THE ROLE OF SUCROSE, AUXIN AND EXPLANT SOURCE ON INVITRO ROOTING OF SEEDLING EXPLANTS OF EUCALYPTUS-SIDEROXYLON

Explants (mainstem shoots or axillary shoots) excised from Eucalyptus sideroxylon seedlings were utilized for in vitro micropropagation studies. Modified half-strength Murashige and Skoog's (MS) medium supplemented with different levels of sucrose and auxin were tested to identify the optimal combination for rooting and plantlet formation. Explants from distal or proximal segments of the mainstem also were tested for rooting capacity and subsequent pattern of plantlet growth and performance. These studies demonstrated that 2-6% sucrose concentrations in the medium favored root development. However, 4 and 6% sucrose caused more callus formation and 8 and 10% levels of sucrose were detrimental to explant cultures. Adding 5 muM indolebutyric acid (IBA) to the rooting medium at any sucrose level in this study induced more callus than ce-naphthalene acetic acid (NAA). The average root number and frequency of callus formation per explant increased with increasing IBA concentrations (2.5- 1 0 muM). However, a rooting medium with a combination of 2.5 muM IBA and 2.5 muM NAA was most suitable for rooting and plantlet development. Explants from well-rooted donor plantlets exhibited a high rooting frequency and more well-developed root systems in subsequent subcultures.