The reproductive biology of Nerine (Amaryllidaceae)
Creators: name: Brown, Natalie
Publisher: name: University Of Tasmania
Year: 2023

description: 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¬¨‚àûC. 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.