IN VITRO STUDIES ON TWO TROPICAL TREE SPECIES - GENIPA AMERICANA L. AND LANSIUM DOMESTICUM CORR

Abstract

In vitro propagation of useful tree species is one of the important current topics to meet the needs of plantations, reforestation and biomass improvement. In the present study, successful methods for micropropagation were established for Genipa americana (Rubiaceae) and two varieties of Lansium domesticum - ‘Langsat’ and ‘Duku’ (Meliaceae) using various seedling explants. These are valuable tropical fruit tree species which are suitable for plantation development and reforestation. In Lansium domesticum, multiple shoot regeneration was also stimulated from nodal explants of mature trees. Plantlets obtained were successfully grown in the field. In Genipa americana, multiple shoots developed from shoot tip, nodal and cotyledonary node explants. Adventitious shoot proliferation was also induced from cotyledon, hypocotyl, leaf, internode and root as well as from callus. The highest number of plantlets were obtained from leaf and cotyledon explants. Shoot formation was achieved from hypocotyl and root segments even on medium without any growth regulators. In general, 5.0mg1-1 of BAP was optimal for enchancing shoot multiplication in all explants. Somatic embryogenesis was initiated from cotyledon and leaf explants with 2.0 mg1-1 of KIN and complete plantlets were successfully obtained from embryoids on basal medium. Callus and root formation were promoted with auxins (NAA, 2,4-D and IBA) both individually or in combination with cytokinins (BAP and KIN). High concentrations of auxins with low concentrations of cytokinins induced soft, translucent callus. Shoots did not develop from this callus. On the other hand, low levels of auxins with high levels of cytokinins stimulated growth of firm, green callus from which shoots developed. Regenerated shoots rooted readily in medium without growth regulators. In both varieties of Lansium domesticum, ‘Langsat’ and ‘Duku’, enhanced axillary branching was achieved from cotyledonary node explants with 0.5 mg1-1 of NAA and 2.0 or 5.0 mg1-1 of BAP. In addition, shoots were induced from nodal explants of seedlings as well as mature trees. Complete plantlets were also obtained from shoot tip cultures. Although callus formation was stimulated from leaf explants with 2,4-D and BAP and the callus could be maintained, caulogenesis was not achieved. Roots were induced directly from leaf explants with 0.1 or 1.0 mg1-1 of KIN and 5.0 mg1-1 of NAA in the dark. Regenerated shoots of both varieties rooted best in medium with 0.03% activated charcoal after an acute treatment with 20.0mg1-1 of IBA for 1 week. The vegetative and reproductive morphology and anatomy of the two main local commercial varieties of Lansium domesticum, ‘Langsat’ and ‘Duku’, were comparatively studied. Generally, the vegetative characters of the varieties are similar. However, the angle at which loop-forming branches of the secondary veins join the superadjacent veins is acute in ‘Duku’ leaves and obtuse in ‘Langsat’. Also stomatal configuration is anomo-staurocytic in ‘Langsat’ leaves and cyclo-staurocytic in ‘Duku’. In both ‘Langsat’ and ‘Duku’ flowers, although the stigmatic surfaces appeared receptive, pollen degeneration was observed. At anthesis, pollen had degenerated completely in both varieties and fruit is formed apomicatically. Fruits of the two varieties are distinctly different with ‘Langsat’ plans having small, oval fruits with thin pericarp and ‘Duku’ plants having large, round fruits with thick pericarp. The edible portion is the aril and in ‘Langsat’ the taste is sweet-sour whereas in ‘Duku’ the taste is sweet.