The ultimate aim of this study was to establish a protocol for somatic hybridisation of mango(Mangifera indica L.) via protoplast isolation and fusion. This involved overcoming barriers to in vitroregeneration of mango from nucellar tissues enabling subsequent embryogenesis from putative somatichybrids. Somatic hybridization can then be used to create wide crosses in mango breeding programs andto study the inheritance of cytoplasmic versus genomic characters.Embryogenesis from cvs. Keow Savoey (60%), Kensington Pride (46%), Keitt (18%) and TommyAtkins (16%) was achieved using 4.5-9 μM 2,4-D in the culture medium. Callus induction occurredearlier in polyembryonic cvs. Kensington Pride and Keow Savoey produced than in monoembryoniccvs. Keitt and Tommy Atkins. Earlier callus induction was accompanied by a higher frequency ofembryo production.Cultivars produced 8.0-13.0g of proembryonic mass (PEM) after 3 subcultures in proliferation medium.Of the organics tested, proline increased PEM proliferation while yeast extract decreased the PEMproliferation rate in all cultivars. The effects of proline and yeast extract on PEM proliferation were notreplaced by other nutrient sources therefore they are assumed to be related to their role in response tostress rather than their nutritional properties.Inclusion of GA3 and 6-BAP in embryogenesis media accelerated the transition phase from globular toearly-heart shaped embryos. A combination of ABA and PCIB reduced secondary embryogenesis from75% to 13.3%. Secondary embryogenesis appeared to be the result of high endogenous auxin duringembryo development. The rate of embryo maturation and conversion to plantlets was increased from30% to 65.0% by inclusion of a low concentration (10 μM) of ABA in the culture medium for one week.Abnormal maturation was not related to a high level of endogenous auxin in maturation stage.A protoplast yield of 15.22×106 gfw-1 (~86% viability after 24 h) from PEM and 8.68×106 gfw-1 fromleaves from glasshouse-grown seedlings (~84% viability after 24h) were obtained for a polyembryoniccv. of Kensington Pride. Conditions optimized for protoplast isolation from Kensington Pride alsoproduced an adequate yield and viability of protoplasts from cvs. Keitt, Keow Savoey, Tommy Atkinsand Haden. Leaf protoplasts underwent cell division up to 40-cell colonies but failed to undergoembryogenesis whereas PEM protoplasts continued development to produce plantlets. Whenimmobilized in Ca-alginate beads, both PEM (FPE 2.85%) and leaf (FPE 2.12%) protoplasts gave betterresults compared to those in agarose beads, liquid or semisolid culture. Low protoplast mortality andbudding and high protoplast division were observed during the first two weeks of immobilized cultures.No differences in plating efficiency of leaf protoplasts was observed between the poly- andmonoembryonic cultivars studied but with PEM protoplasts, polyembryonic cultivars produced asignificantly higher plating efficiency than monoembryonic cultivars. This difference in the protoplastplating efficiency for PEM’s correlated with the rates of nucellar embryogenesis among the two groups.Somatic hybridization was achieved by PEG-mediated fusion between PEM protoplasts of cv.Kensington Pride and leaf protoplasts from Haden, Keitt or Tommy Atkins. Selection strategiesincluding hybrid vigour and medium enrichment resulted in 242 callus lines; 41 were shown to betetraploid by flow cytometry. RAF marker analyses using the genomic DNA of single embryos revealed4 somatic hybrid lines with Kensington Pride + Haden; the only combination that produced somatichybrids. No novel DNA bands were observed in the somatic hybrids thus there was no indication ofrecombination occurring.Overall, glasshouse-grown seedlings yielded sufficient viable protoplasts for future work but the leafprotoplasts proved non-regenerable. PEM protoplasts proved regenerable under specific conditions.However, the lack of regeneration from leaf protoplasts is an asset because they can be used as nonregeneratingparents to aid selection of somatic progeny from a target (regenerative) PEM parent.This thesis provides the first report of somatic hybridization in mango. It also presents a suite ofprotocols for each stage of the process and for mango cultivars not previously regenerated in vitro. Theprotoplast culture technology provides the basis for future application of DNA engineering techniquessuch as electroporation, microinjection, somatic hybridization and cybridization for mango plantimprovement. Future research should focus on evaluation of the somatic hybrids for chromosomearrangement, genome stability and the relative genomic contribution of the protoplast parents