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Geoffrey Roger Ashburner
Doctor of Philosophy (University of Melbourne, August 1994).
The genetic resources of coconut palms (Cocos nucifera L.) in the south Pacific region were characterised using fruit morphological and molecular characters (RAPD). It was concluded that there was continuous variation in fruit morphology and molecular characters throughout the region.
The south Pacific gene pool was considered to be composed of two groups, the first, a cline of populations from Papua New Guinea across the central Pacific to the south eastern Pacific, thought to represent the original gene pool of the Pacific. The second one was comprised of populations from the south western and south central Pacific and was thought to represent the original gene pool of the Pacific that has been affected by subsequent migration of domesticated types from elsewhere. The populations of Rennell Island, Marquesas Islands and Hawaii were members of this latter group but have diverged. The results of both the molecular and morphological characterisation were used to formulate a collection and conservation strategy for coconut germplasm in the region.
An average out-crossing rate of 68.7% was found in a coconut population in the Gazelle Peninsula of Papua New Guinea. The inflorescences of coconut palms appear to be unspecialised with regards to pollen vectors although wind pollination appears to be unlikely to occur to any great extent. The predominant pollen vectors for coconut palms in the Gazelle Peninsula appeared to be three species of bees, namely Homalictus cassiaefloris, H. dampieri, and H. latitarsis. The apparent flexibility of selfing and pollen vectors in the coconut palm may have contributed to its successful evolution as a colonising strand plant.
A method for the collection of coconut germplasm from remote locations with minimal facilities was devised and was based on an embryo culture technique and a simple pollen drying process using silica gel. It was possible to collect germplasm with 88% chance of the embryos germinating in an uncontaminated state. The collected embryos were grown as embryo cultures. It was concluded that the fastest growth of coconut embryo cultures results from germinating embryos in liquid media and then transferring them to solid media after germination.
It was possible to manipulate the growth rate of embryo cultures by changing the sucrose and NAA concentration of the basal medium. The pH of the basal medium fell rapidly over the first 14 days after sub-culture which was more rapid as the ammonium content of the basal medium increased.
There was a large variation of embryo culture growth rate due to the genotype of the embryos and genetic shift of collected germplasm may result. Acclimatisation of plantlets from embryo culture was difficult but the chances of survival increased with the size of the shoot. Leaves formed in culture do not have the ability to photosynthesise, which may be due to their abnormal anatomy. It was concluded that vigorous plantlets need to be produced in vitro so that they may quickly form normally functioning leaves out of culture.
The choice of the approach for conserving coconut germplasm depends upon the goals of the conservation program. It is proposed that in situ conservation should be through reserve collections to ensure genetic integrity and allow for continued evolution, while ex situ core collections should be established for ease of germplasm use in breeding programs.
The choice of germplasm to be included in the core collections depends on the goals of the program. Breeding core collections give preference to populations where the likelihood of conserving currently desirable traits is greatest, while conservation core collections have the greatest likelihood of conserving all genetic diversity. Composite core collections can meet the goals of the other two proposed approaches.
The number of individuals required to maintain maximum diversity in these collections varies with the population in question but a level of 37 appeared adequate for the most diverse populations measured. Methods used to import germplasm depend on the weighting given to potential risks to the germplasm and the importing country, but sea transportation is the most inexpensive option.
Any claims made by authors in the Australian New Crops Newsletter are presented by the Editors in good faith. Readers would be wise to critically examine the circumstances associated with any claims to determine the applicability of such claims to their specific set of circumstances. This material can be reproduced, with the provision that the source and the author (or editors, if applicable) are acknowledged and the use is for information or educational purposes. Contact with the original author is probably wise since the material may require updating or amendment if used in other publications. Material sourced from the Australian New Crops Newsletter cannot be used out of context or for commercial purposes not related to its original purpose in the newsletter
Contact: Dr Rob Fletcher, School of Land and Food, The University of Queensland Gatton College, 4345; Telephone: 07 5460 1311 or 07 5460 1301; Facsimile: 07 5460 1112; International facsimile: 61 7 5460 1112; Email:email@example.com
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originally created by:GK; latest update 6 June 1999 by: RF