Application of Biotechnology to Davidsonia Species - an Australian Native Plum

Abstract

A survey conducted in south east Queensland (Qld.) and north eastern New South Wales (NSW) showed that Davidsonia species were highly popular as a bushfood in the study region. Wild harvests of many native fruits had been common to meet the demands for large number of products such as jams, sauces, conserves, vinegar, wines and liqueurs being developed for increasing number of local and overseas markets. Davidsonia jerseyana and D. johnsonii are listed as rare and endangered species. Small cultivations have gradually developed without much selection and breeding or horticultural research being done on these fruit species. Seed is the main method of propagation for tall D. pruriens with large hairy fruits and the shorter heavy fruiting D. jerseyana with smaller and less hairy fruits. However, cuttings or suckers of seedless D. johnsonii obtained from few wild populations have been used to establish small populations in polycultures. As demands for fruits and trees for ornamental purposes increased, the need for cultivation of selected genotypes and potential hybrids has become inevitable. Application of modern techniques in micropropagation, genetic studies and breeding of elite genotypes to establish plantations with high quality fruits and high yields would be greatly beneficial in meeting the supply and demand of a sustainable bushfood industry. Callus induction experiments using in vitro, glass house and field material (leaves) produced friable callus in all three species, but only D. pruriens and D. jerseyana produced organogenic shoots. Adventitious shoots could not be obtained from D. johnsonii. Despite using several cytokinin and auxin treatments, embryogenesis was not achieved in any of the three species. Regeneration and multiplication study of D. pruriens and D. jerseyana was ultimately focused towards organogenesis pathways. A combination of 1.0 μM BA and 1.0 μM GA3 in MS medium produced optimum shoot growth in D. pruriens. Juvenile and mature tissues were used because of difficulty in decontamination of mature explants with very hairy leaves, thick stems and apical buds especially for D. pruriens. A higher multiplication rate was achieved in D. jerseyana with optimum response on 0.01 μM 2iP and 0.01 μm GA3 in MS producing thin and tall shoots with multiple nodes. Exposure to higher GA3 concentration inhibited the root development in both species. Root induction was achieved by 32.2 μM IBA exposure for 8-9 days in D. pruriens before transfer onto rooting medium (½ strength MS macro and micronutrients containing 10 μM riboflavin). Best roots in D. jerseyana were produced after 2-3 days exposure to 32.2 μM IBA. Residual effects of exogenous cytokinin and GA3 adversely affected the rooting. The rooted shoots were transferred to seed germination substrate in pots and successfully hardened in the humidity cabinet for 3-4 weeks before transfer to green house.