Genetic characterisation of Macadamia with DNA markers

Peace, Cameron Paul (2005). Genetic characterisation of Macadamia with DNA markers PhD Thesis, School of Molecular and Microbial Sciences, The University of Queensland.

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Author Peace, Cameron Paul
Thesis Title Genetic characterisation of Macadamia with DNA markers
School, Centre or Institute School of Molecular and Microbial Sciences
Institution The University of Queensland
Publication date 2005
Thesis type PhD Thesis
Supervisor Dr B. Carroll
Dr Vasanthe Vithanage
Dr Colin Turnbull
Total pages 259
Collection year 2005
Language eng
Subjects L
270200 Genetics
620207 Tree nuts
Formatted abstract

Macadamia Is a subtropical nut crop and the first Australian native to become a major commercial food crop. Two morphological types occur in cultivation, which are regarded as separate species {Macadamia integrifolia and M. tetraphylla). Two additional Macadamia species that are closely related produce nuts unsuitable for consumption and are not cultivated. These four species form the southern clade of macadamia, and are able to hybridise. The species are threatened in their natural state, reduced to fragmented remnants of rainforest in south-east Queensland and north-east New South Wales. The preferred type in the worid macadamia industry is M. integrifolia, though agronomic species differences are unclear. Some cultivars were classified as hybrids. Species distinction had relied on morphology, but the system was flawed as it used overlapping features and was complicated by the presence of hybrids. The crop was first domesticated only 150 years ago, with just a handful of generations separating modern cultivars from their wild progenitors. Very little is known about which native populations were originally selected, and pedigree information is severely limited. Hundreds of cultivars and selections exist, with morphology unable to distinguish each. Genetic relationships amongst cultivars are poorly understood. There is much potential for genetic improvement of macadamia, and a recognised need to conserve available diversity. However, baseline information on species differences, the genetic organisation of natural and cultivated germplasm, and the genetic basis of cultivar performance are required. 

Such gaps in our knowledge may be filled by the application of new DNA marker technologies. In this project, DNA marker systems were developed and evaluated for their use in various genetic analyses of macadamia. The recent marker system, RAF (Randomly Amplified DNA Fingerprinting), was included, and from this, a new marker type was developed for macadamia. RAMiFi (Randomly Amplified Microsatellite Fingerprinting) is very informative and versatile, suitable for a wide range of applications. 

Macadamia was characterised with the markers at four hierarchical levels: species, population (wild and cultivated), individual, and chromosome. Numerous cultivars and selections, a wild germplasm collection, related species, and progeny populations were surveyed. At the species level, confirmation of species identity, calculation of the species compositions for any tree, and the extent of species natural distributions and hybrid zones were addressed. At the population level, the structure of genetic diversity across wild populations was analysed. Compositions, natural origins, and relationships between cultivated germplasm groups were determined. At the individual level, several cases of cultivar identity were resolved, and parentage for some elite lines was deduced or verified. At the chromosome level, genetic linkage mapping was performed. 


Key findings included the confirmation that the four southern clade species of macadamia represent distinct taxa. Natural hybrid zones were identified where the species ranges come into contact, including never-before reported natural hybridisation between M. integrifolia and the non-cultivated species M. ternifolia. Most cultivars/selections were found to be M. integrifolia x M. tetraphylla hybrids, often with only a small portion of one of the species that is undetectable in the field. Trees selected in Hawaii were usually pure M. integrifolia. One cultivar was identified as containing M. ternifolia DNA, highlighting the potential for incorporating diverse germplasm into breeding programs. Wild macadamia germplasm was highly differentiated between regions and populations, warranting the development of a racial classification system. Most cultivated M. integrifolia individuals appear derived from the northernmost part of that species' natural range, which also coincided with the regions of least diversity. Species composition and natural origins were the dominant factors determining cultivated germplasm organisation, with selection origin playing a lesser role. Some important cases of confusion over cultivar identity and parentage were resolved. The first genetic map of macadamia, and the first for a member of the Proteaceae family, was constructed. The foundations were laid for marker-assisted selection in this crop. 

The results obtained from genetic characterisation of macadamia with DNA markers have major implications for crop improvement and the conservation and management of remaining genetic resources. 

Keyword Macadamia nut -- Genetics.
Additional Notes THere are some pages are not in right order.

Document type: Thesis
Collection: UQ Theses (RHD) - UQ staff and students only
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Created: Fri, 24 Aug 2007, 18:44:37 EST