STUDIES ON IN VITRO PROPAGATION AND ORGANOGENESIS IN GARCINIA MANGOSTANA L. AND DURIO ZIBETHINUS MURR

Abstract

In vitro propagation methods for two economically important tropical fruit trees, Garcinia mangostana (mangosteen) and Durio zibethinus (durian), are described in this thesis. In mangosteen, shoot proliferation was induced in leaf, cotyledon and stem explants from seedlings and leaf explants from mature trees. For cotyledon segments, the best response was in agitated liquid cultures with BAP. Such cultures were maintained for more than 3 years without loss of regenerative potential. Shoot tip and modal segments produced multiple shoots in medium containing 2 mg 1 -1 BAP while 2-5 mg 1 -1 BAP was optimum for internodal segments. Changing the orientation of the explants affected shoot proliferation. Root segments gave few buds. Direct shoot bud formation was obtained from red leaf segments of 1-3-year old seedlings and 16-year old mature mangosteen trees cultured on WPM with BAP. The frequency of shoot bud formation decreased when the leaves turned red to green in both seedlings and mature trees. The number of buds produced was higher in red leaves from seedlings compared to those from mature trees. Young green leaves from seedlings and mature trees only produced callus. Secondary shoot buds also developed on leaves of cultured epiphyllous shoots from both seedlings and mature trees. Detached leaves from in vitro shoots were highly regenerative. Shoots were also multiplied by enhanced axillary and adventitious bud formation. Shoots were rooted with IBA treatment. Plantlets were acclimatised and established in soil. Nodes from seedlings, grafted plants and mature trees of durian produced axillary shoots on medum with 0-5mg 1 -1 BAP. Multiple adventitious shoot buds developed on internodal segments of seedlings cultured on medium with 2 mg 1 -1 BAP. Hypocotyl segments produced direct multiple adventitious shoots when cultured on medium with 2-5 mg 1-1 BAP. In vitro shoots showed defoliation, vitrification and necrosis. A low percentage of shoots from seedling nodes rooted in vitro giving rise to plantlets. A repetitive somatic embryogenesis system was established using immature zygotic embryos of durian in a 2-stage initiation phase. Proliferation and development of somatic embryos were influenced by the concentration of cytokinin, physical state of the medium and light condition. ABA, at 0.02-4.0 mg 1 -1, was very effective in regulating embryo development and morphology. A few somatic embryos germinated into plantlets. The development of in vitro and in vivo embryos was similar. Through cytological studies, pollen developmental stages were correlated to flower bud sizes of durian cultivar D2. Durian anthers did not require cold pre-treatment. More anthers from buds measuring 20mm in length survived and produced good callus in float cultures containing 9% sucrose, 100 mg 1-1 ascorbic acid, 0.1mg 1-1 K and 1.0 mg 1-1 2,4-D in continuous dark condition. Mangosteen and durian explants did not respond to several strains of Agrobacterium tumefaciens and A. rhizogenes, using direct inoculation and co-cultivation methods.