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Study of intergeneric hybridization in Hippeastrum


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Jirakiattikul, Yaowapha 1999 , 'Study of intergeneric hybridization in Hippeastrum', PhD thesis, University of Tasmania.

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Hippeastrum is a bulbous genus within the family Amaryllidaceae which is of
horticultural importance as a cut flower and potted plant crop. The colour range
available in commercial hybrids is dominated by white and red. The commercial
potential of Hippeastrum as a floriculture crop is significant, but production of the cut
flowers is limited to warm climatic regions or glasshouse production in temperate
regions. Improved cold tolerance, along with extended colour range and flower
fragrance, are key breeding objectives for Hippeastrum hybrids. One breeding
strategy which may facilitate the introduction of these characteristics is intergeneric
crossing. This strategy has recently been used successfully in other important bulbous
genera including Lilium, and has some potential for Hippeastrum breeding as a number
of intergeneric hybrids within family Amaryllidaceae have been reported previously.
This study therefore aimed to develop methods for intergeneric hybridization of
Hippeastrum based on detailed investigation of flowering physiology, reproductive
biology and in vitro plant growth techniques.
Rapid development of the flower bud and at least two new growth units was
observed in bulbs which flowered following planting whereas none or only one
growth unit was initiated in bulbs which produced only vegetative growth. A decrease
in dry weight suggested that the stored reserves from the bulb were utilized during the
flowering process. Starch and fructans were found to be the major storage
carbohydrates in H. hybridum bulbs and fructans appeared to be involved in scape
elongation and floret growth. The transport carbohydrate sucrose was found in lower
concentrations in non-flowering bulbs than in flowering bulbs, implying a lower rate
of carbon mobilization in non-flowering bulbs. ' 4C-sucrose translocation studies
showed that under glasshouse conditions sucrose originating from the outermost scale
tended to be partitioned towards the roots and the emerging flower bud, in contrast to
carbon originating from the youngest expanded leaf which was directed predominantly
towards the inflorescence. Carbohydrate partitioning from the bulb scales to the
emerging flower bud was increased by repotting, a treatment shown to stimulate
flower emergence.
Pollen viability of H. hybridum, Brunsvigia orientalis and Amaryllis
belladonna was high from 0-6, 0-2 and 0-2 days after anthesis respectively. Long
term storage of pollen was necessary to overcome lack of synchronisation in flowering for controlled crosses and the results for this study showed that pollen of these three
plant genera can be stored for at least 1 year at 2°C, -18°C or -80°C. Pollen viability of
H. hybridum decreased rapidly after 64 weeks storage at 2°C but remained high after
104 weeks storage at -18°C and -80°C. The period of maximum receptivity of H.
hybridum, B. orientalis and A. belladonna stigmas was two days after anthesis. Slow
growth rate of pollen tubes were recorded in all intergeneric crosses with H.
hybridum, suggesting a pre-fertilization incompatibility barrier based on rate of pollen
tube growth in the style. Despite this barrier, pollen tubes were detected in the base of
H. hybridum styles following crosses with A. belladonna and swelling of ovaries was
observed in these crosses. The cross-pollinated pods, however, often died 10-18 days
after pollination, suggesting that a post-fertilization bather was present.
Ovule and ovary culture were used to overcome the post-fertilization
incompatibility in the crosses H. hybridum x A. belladonna and H. hybridum x B.
orientalis. Excised ovules or ovaries were cultured on MS medium supplemented with
60 g/L sucrose. Small bulblets were obtained from the cross H. hybridum x A.
belladonna using ovule and ovary culture. Cut-style pollination, heat treatment of the
style prior to pollination and in vitro pollination were used in an attempt to overcome
the pre-fertilization barrier in the style. Application of cut-style pollination and heat
treatment had no effect on pollen tube growth rate in H. hybridum styles. Small
bulblets, however, were obtained from the crosses H. hybridum x B. orientalis, and
H. hybridum x A. belladonna using in vitro pollination combined with ovule culture.
The hybridity of these bulblets was confirmed using isozyme electrophoresis. The
techniques developed in this study thus provide the basis for the incorporation of
desirable traits from other genera of family Amaryllidaceae into H. hybridum.

Item Type: Thesis - PhD
Authors/Creators:Jirakiattikul, Yaowapha
Keywords: Plant hybridization, Hippeastrum
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

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