Cytogenetic and Molecular Studies of Actinidia Genomes

by Yan, Guijun

Abstract (Summary)
Restricted Item. Print thesis available in the University of Auckland Library or available through Inter-Library Loan. Actinidia deliciosa (kiwifruit), a dioecious vine native to China, is a key component of the New Zealand horticultural industry and is becoming increasingly important worldwide. Present kiwifruit breeding programs are concentrating on breeding new or novel cultivars different from ‘Hayward’, the only widely cultivated female cultivar. To speed this development, a better understanding of evolutionary relationships in the genus is needed. This thesis discusses a series of cytogenetic, molecular cytogenetic and molecular studies on Actinidia genomes. Ploidy levels of 192 plants were determined by chromosome counts. A number of new polyploids was found. The most important of these are the fifteen accessions of tetraploid A. chinensis, which had previously been thought to be a diploid species. Chromosome numbers are reported for the first time for six taxa, including the first report of naturally occurring octoploids, in A. arguta var. purpurea. Intraspecific ploidy variation was found to be common. Metaphase I observations on tetraploid A. chinensis revealed predominantly bivalent formation, but up to 7 quadrivalents were observed in three different accessions. Univalents and bivalents were observed in one A. chinensis (2x) x A. eriantha (2x) hybrid, and trivalents, bivalents and univalents were observed in an artificially produced triploid A. chinensis. These results suggested that the constituent genomes of diploid and tetraploid A. chinensis are homologous, whereas those of diploid A. chinensis and A. eriantha showed a lesser degree of homology. In situ hybridization, in conjunction with dot-blotting, with several genomic probes suggested that A. deliciosa, diploid and tetraploid A. chinensis and tetraploid A. chrysantha showed considerable genome homology. However, a repeat sequence cloned from A. deliciosa, pKIWI516, divided these plants into two groups, one group (A. deliciosa, some tetraploid A. chinensis accessions (4x+) and A. chrysantha) was positive to the repeat, whereas the other group (diploid and some other tetraploid (4x-) A. chinensis accessions and eight other Actinidia taxa) was negative. In situ hybridization with this repeat sequence revealed that there were six hybridization sites on six different chromosomes of both 4x+ A. chinensis and hexaploid A. deliciosa. Meiotic observation and progeny analysis of controlled crosses demonstrated that functioning unreduced gametes are produced by both male and female plants. First division restitution appears to be the major mode of unreduced gamete production. The finding of functioning unreduced gametes in Actinidia could account for the high frequency of polyploid plants in the genus, the multiple origins of tetraploid A. chinensis, and can also explain the evolution of a simple XY sex determination system that may function at both diploid and polyploid levels. Phylogenetic relationships between hexaploid A. deliciosa (DA), diploid A. chinensis (2x) and the two types of tetraploid A. chinensis (4x+, 4x) were investigated using chloroplast DNA RFLP analysis. The resulting data generated a phylogenetic tree which split the four into two groups, 4x- with DA and 4x+ with 2x. In an intraspecific cross between the two types of tetraploid A. chinensis, chloroplast DNA inheritance was maternal. This result contrasts with a previous report that chloroplast DNA inheritance in the genus is paternal. The results of these studies are discussed in relation to evolutionary pathways and patterns in the genus and also to the present kiwifruit breeding programs. Some of the results obtained in this thesis have already resulted in changes to the aims and methods being used in the New Zealand kiwifruit breeding program.
Bibliographical Information:


School:The University of Auckland / Te Whare Wananga o Tamaki Makaurau

School Location:New Zealand

Source Type:Master's Thesis



Date of Publication:01/01/1996

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