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    Exploration of Limonium interspecific breeding possibility : a thesis presented in partial fulfilment of the requirement for the degree of Master of Science in Plant Science at Massey University, Palmerston North, New Zealand
    (Massey University, 1995) Zhang, Celia
    Interspecific crossability was investigated in the genus Limonium (Plumbaginaceae). Six Limonium species were chosen for this study, five of which are dimorphic and L.perigrinum which is monomorphic. Ovary, ovule and embryo development was investigated, as were in vitro pollen germination and pollen tube growth. Unilateral incompatibility was observed in 8 interspecific combinations. A high frequency of interspecific crossability was observed between L.perezii X L.sinuatum and L.sinense X L.aureum. Pollen tubes were frequently observed penetrating the ovules in these crosses. Pollen tube growth that terminated in the styles or was restricted to the stigmas was found in some Limonium interspecific crosses. Abnormalities of pollen tube growth in the interspecific crosses included heavy callose deposits at the tips of pollen tubes; pollen tube branching and pollen tube growing in the wrong direction. Embryo, ovule and ovary development was studied with L.perezii plants following conspecific pollination. Three distinct groupings of florets can be recognised at the basis of their post-pollination growth and development. Twenty-six percent of conspecific pollinated florets showed no ovary and ovule growth. No embryo was found in this group. In eleven percent of florets, ovaries and ovules grew up to Day 12 after pollination and then shrivelled. No embryo was ever found in this group. Sixty-three percent florets produced embryos following conspecific pollination and developed normally. The viability of Limonium pollen was assessed with Alexander's stain and fluorochromatic reaction (FCR) stain. Optimal conditions for in vitro L.perezii pollen germination and tube growth were established. Poly-ethylene glycol and filter paper supports were of particular significance. In vitro pollen germination rate of about 40% was achieved. Plant growth regulators (IAA, GA 3 and ethylene), some minerals (manganese sulphate, copper sulphate) and prehydration treatment were used in experiments to improve pollen germination and tube growth. None of these factors, however, had positive effect on either pollen germination or tube growth. It was found that while L.perezii pollen tube growth tolerates a wide range of temperature, there is an optimum between 20°C-25°C.
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    The physiology and control of crown bud formation and development in gentians : a thesis presented in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Plant Physiology at Massey University, Palmerston North, New Zealand
    (Massey University, 2012) Samarakoon, Uttara Chandani
    The spread in time to flower harvest maturity and an inability to produce an adequate number of crown buds during crop establishment, were perceived as problems by commercial growers of gentians for cut flowers. By identifying and investigating plant and environment related factors that influence growth and development, the current thesis aimed to investigate both the causes of these problems and identify potential solutions. Crown buds which appeared during the previous growth cycle were the source of floral shoot production and, in both true seedlings and clonally propagated plants, these buds typically originated on the transition zone between shoots and roots. When formed on the transition zone the first and, as a consequence, apical bud of the crown bud cluster, originated adventitiously. The individual crown buds which subsequently initiated within the cluster developed as axillary buds from that apical bud. As evident from the appearance of two to five times more crown buds and shoots, and crown bud clusters, the naturally occurring short photoperiodic regime promoted the crown bud formation process, compared to a long photoperiodic regime. With the application of Ethephon, or Ethephon followed by either Thidiazuron or Paclobutrazol, it was possible to achieve a similar increase in the number of crown buds under the long photoperiodic regime. In contrast to the strong photoperiodic response, exposure to the cooler temperatures experienced outside did not influence the crown bud formation process. Once formed, crown buds were under different types and degrees of dormancy (i.e. endo, para or eco). Dependent on both the developmental stage of plants and the hierarchical position of buds within a crown bud cluster, shoot emergence and subsequent development to flowering varied in the quantity, quality of shoots, and timing in response to dormancy breaking treatments (chilling, gibberellic acid (GA3), or clipping), Hence when applied prior to shoot emergence, application of chilling to plants of the cultivar ‘Diva’ resulted in an eight-fold increase in the number of floral shoots, along with a 83 day reduction in the spread in time to harvest maturity. The requirement of chilling could be substituted by GA3. In contrast, when applied following the start of shoot emergence, only application of GA3 was effective in increasing shoot emergence and narrowing the spread in time to harvest maturity.Within a bud cluster, a positive relationship between duration to harvest maturity and a negative relationship with floral shoot length was evident with hierarchical position of the crown bud from proximal to the distal end. This influence of hierarchical position was most evident following application of chilling or GA3, potentially explaining up to 28 days spread in duration to harvest maturity in ‘Diva’. While the aforementioned factors related to shoot emergence, development and hierarchical position contribute to the sources of variability within a plant or an individual cluster, both the sources and extent of variation in time to harvest maturity, varied within cultivars, with wider spread in time to harvest maturity in ‘Starlet’ (41 days) than ‘Diva’ (35 days) and ‘Spotlight’ (29 days). The present study has increased the understanding of factors contributing to growth and development of gentians as an ornamental crop. Treatments have been developed to allow manipulation of the formation of crown buds, subsequent emergence and compactness of flowering duration.