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The reproductive biology of Nerine (Amaryllidaceae)

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Brown, NR (1999) The reproductive biology of Nerine (Amaryllidaceae). PhD thesis, University of Tasmania.

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Abstract

The genus Nerine (Amaryllidaceae) native to Southern Africa, comprises bulbous
perennials with colourful, long-lasting blooms prized for cut-flower and bulb
production. Hybridisation programmes have been undertaken since the late 19th
century, breeding towards specific horticultural traits becoming more intensive in
recent years. This work represents the first major study of the reproductive biology
of Nerine, and provides a scientific basis for ongoing breeding work.
The inflorescence of Nerine is preformed within the bulb scales up to 32 months
prior to anthesis, with floral development occurring continuously during this period.
Sequential floret initiation occurs during the first growing season, followed by
differentiation of the floral organs in year two. Gametogenesis occurs in the final
months prior to anthesis, being asynchronous within an inflorescence. The lengthy
period of floral development renders the inflorescence susceptible to disturbance
over three growing seasons and two critical periods have been identified.
Environmental conditions also act on the inflorescence at the time of scape
emergence.
The fertilisation process from pollen germination to entry of the pollen tube into the
micropyle takes approximately three days. The onset, duration and period of
maximal pistil receptivity has been directly measured via seed set. However, this
period does not correlate with indirect measures of receptivity. The length of the
style at anthesis, relative to anther position, can be in one of three positions in
Nerine (below, level or exsert). In all cases, elongation of the style occurs postanthesis,
with maximal elongation occurring in the short-styled cultivars. These
short-style morphs have a greater rate of seed set from both open and selfpollinations.

The seeds of Nerine are fleshy and have no dormancy period. Following successful
fertilisation, a nuclear endosperm develops and the integumentary tissue increases.
At seed shed, a proembryo is present and the majority of embryo development
occurs during after-ripening. Embryo development is influenced by temperature,
with development and hence germination able to be suspended in some species by
storage at 4°C. There was evidence of parthenogenetic seed production.
A hybridisation programme, operating at intra- and inter-specific and inter-generic
levels, was initiated, with the fertility of seven species and 76 cultivars assessed.
This yielded seeds from 96 intra-specific, eleven inter-specific and eight intergeneric
crosses. In addition, self-compatibility has been established in five species
and 23 cultivars. Pre- and post-zygotic barriers have been identified in failed
crosses at all hybridisation levels, with a number of interventionist techniques being
tested to overcome these barriers. In vitro culture of fertilised ovules was found to
increase germination rates of hybrid seeds and protocols for in vitro pollination and
embryo rescue have been developed. In addition, a successful technique for
gynogenesis has been developed for use in N. flexuosa 'alba'. The hybridisation history of Nerine has resulted in the nomenclature of cultivars
being in a chaotic state. As a result of this project, 1291 Nerine hybrids have been
catalogued, with a collection of 95 Nerine cultivars described to allow assessment
for horticultural purposes. Morphological characters have been assessed for use in
cultivar identification schemes and for indicators of hybrid parentage. In addition a
preliminary RAPD analysis has indicated this will be a useful tool for establishing
relationships between cultivars and individual cultivar identification.

Item Type: Thesis (PhD)
Keywords: Bulbs (Plants), Amaryllidaceae, Amaryllidaceae
Copyright Holders: The Author
Copyright Information:

Copyright 1999 the Author - The University is continuing to endeavour to trace the copyright owner(s) and in the meantime this item has been reproduced here in good faith. We would be pleased to hear from the copyright owner(s).

Additional Information:

Thesis (Ph.D.)--University of Tasmania, 1999. Includes bibliographical references

Date Deposited: 25 Nov 2014 00:49
Last Modified: 20 Mar 2016 22:28
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