Molecular characterization of Actinidia deliciosa: interspecific and intraspecific relationships
Abstract (Summary)Restricted Item. Print thesis available in the University of Auckland Library or available through Inter-Library Loan. Kiwifruit (Actinidia deliciosa var. deliciosa) is a species particularly important to the New Zealand economy yet little is known of the genetics or origins of it's hexaploid genome. The aim of this thesis was to investigate interspecific and intraspecific relationships of kiwifruit and in particular to determine whether the kiwifruit genome had arisen primarily via an autopolyploid or allopolyploid mechanism. Phylogenetic relationships between A. deliciosa and three of its closest relatives within the same section of the genus Actinidia were investigated using restriction fragment length polymorphism and the data used to generate a phylogenetic tree depicting this relationship. The four species were differentiated into two pairings, A. chinensis with A. deliciosa and A. eriantha with A. latifolia. The results support the known close taxonomic relationship between diploid A. chinensis and hexaploid A. deliciosa and suggest A. chinensis is a likely progenitor of A. deliciosa. It is unlikely that either of the other two diploid species is a possible progenitor. A close relationship was noted between A. eriantha and A. latifolia and was somewhat unexpected since there was no prior indication that they were particularly closely related to each other. Six members of a family of moderately repetitive DNA sequences from kiwifruit were cloned and characterized. The repeat family is comprised of elements with a unit length of 463 base pairs. The elements are highly methylated, occur in tandem arrays of up to 50 kb in length, and constitute about 0.5% of the kiwifruit genome. Individual elements diverge in nucleotide sequence by up to 5%, suggesting that the repeat sequence is evolving rapidly. Homologous sequences were found in A. deliciosa var. chlorocarpa. The repeat sequence was not found under low stringency hybridization conditions in the diploid A. chinensis, nor was it detected in eight other Actinidia species. However, homologous repeats were detected in a distantly related tetraploid species, A. chrysantha. The results provide the first molecular evidence to suggest that kiwifruit may be an allopolyploid with more than one constituent genome. Preliminary studies using minisatellite probes to differentiate between cultivars of A. deliciosa were encouraging but not conclusive. Human minisatellite sequences or those from M13 did not identify 'fingerprint' patterns in DNAs from A. deliciosa cultivars. Restriction analysis of four minisatellite containing sequences isolated from a kiwifruit genomic library showed that each was different, indicating that minisatellite arrays are dispersed throughout the genome. Results obtained with one of these sequences suggested that DNA fingerprinting of Actinidia cultivars will be possible, but may require optimization of the hybridization conditions, or the isolation of alternative probes.
School Location:New Zealand
Source Type:Master's Thesis
Date of Publication:01/01/1990