IN VITRO STUDIES ON HELICONIA SPECIES

Abstract

Micropropagation of Heliconia psittacorum (varieties: Choconiana, Sassy, Andromeda and Golden Torch) and H. rostrata was successfully achieved. A protocol for shoot multiplication was developed by culture of terminal and axillary buds of rhizomes. Cultures were initiated on modified Murashige and Skoog (MS) medium containing 40 µM benzyladenine (BA), 150 ml/l coconut water, 30 g/l sucrose, and 2 g/l Gelrite. Shoot multiplication was achieved on the same medium without coconut water, and supplemented with 10 µM BA. Shoots were rooted on MS basal medium and transferred successfully to field conditions. High frequency plantlet regeneration was induced from callus derived from shoot tips and thin cross sections of in vitro cultures of H. psittacorum. Fine nodular regenerative callus was initiated in the dark on MS medium containing 0.5 g/l activated charcoal, 1.0 g/l casein hydrolysate and 80 µM 2,4-dichlorophenoxyacetic acid (2,4-D). Differentiation and maturation of protocorm-like bodies occurred when 2,4-D was withdrawn from the medium. The regenerative callus could be maintained on medium with 40 µM 2,4-D and subculturing at six week intervals. There was no appreciable loss in regeneration potential for over 18 months in these cultures. Various factors that have influenced regeneration in other plant tissues were investigated. These included media strength, abscisic acid, gibberellic acid, headspace gases and various carbohydrate sources. Regenerated plants were successfully transferred to field conditions. Measurements of the amounts of ethylene and carbon dioxide accumulating in the headspace of morphogenic and non-morphogenic callus indicated differences in the quantities and patterns of accumulation of these gases. Addition of ethylene inhibitors such as aminoethoxyvinylglycine (AVG), norbornadiene, salicylic acid and cobalt chloride or inhibitors of ethylene action such as silver nitrate did not affect the regeneration process in morphogenic callus. However, 1-aminocyclopropane-1-carbocylic acid (ACC), a precursor of ethylene biosynthesis, at 100 µM, appeared to reduce the regenerative potential of morphogenic callus. The growth of morphogenic callus was suppressed in sealed vessels but improved when ethylene and carbon dioxide were trapped and reduced in the presence of mercuric perchlorate and potassium hydroxide.