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Identification and the role of hybridisation in Pittosporum.

Godley (1985) proposed that species which have separate juvenile and adult forms may be derived from hybridisation, and proposed that the rare, heteroblastic species P. turneri is a putative hybrid. This study aims to identify whether Pittosporum turneri is derived from hybridisation between a divaricating shrub (P. divaricatum) and a non-divaricating tree (P. colensoi), and to improve resolution of relationships among very closely related species within the genus Pittosporum. A combined approach was used to test the origin of P. turneri. Phylogenetic analysis of the maternally inherited trnT-trnL region of chloroplast DNA was undertaken to compare with a phylogeny based on the biparentally inherited internal transcribed spacer of nuclear ribosomal DNA (ITS) for all New Zealand Pittosporum species. Additionally, inter simple sequence repeats (ISSR's) and allozymes were used in an attempt to identify hybridisation between P. colensoi and P. divaricatum. A morphological study was undertaken to determine whether P. turneri is morphologicaly intermediate to the putative parents. Cross-pollination between the putative parents of P. turneri was also undertaken in the wild between female flowers of P. divaricatum and male flowers of P. colensoi to investigate whether hybridisation between these co-existing species is possible. The trnT-trnL region resolved several clades within the New Zealand Pittosporum previously unresolved by the ITS region alone. P. turneri has the same trT-trnL sequence as P. divaricatum, implicating P. divaricatum as the maternal parent. The profile of ISSR bands in P. turneri, exhibit additivity of bands found in P. colensoi and P. divaricatum, supporting a hybrid origin of P. turneri. Morphological analyses also show that P. turneri is intermediate to P. divaricatum and P. colensoi. The cross-pollination experiment was unsuccessful and no seedlings germinated, although four seeds appeared viable. It is proposed that P. turneri has a hybrid origin, however this finding needs to be supported by further work.
Type of thesis
Carrodus, S. K. (2009). Identification and the role of hybridisation in Pittosporum. (Thesis). The University of Waikato, Hamilton, New Zealand. Retrieved from https://hdl.handle.net/10289/3593
The University of Waikato
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