ISHS Acta Horticulturae 602: VI International Protea Research Symposium
PRELIMINARY RESULTS OF THE STUDY OF THE SEXUAL REPRODUCTION BIOLOGY OF LEUCADENDRON |
| Authors: | A. Robyn, G.M. Littlejohn |
| Keywords: | hybridization, pollen viability, pollen tube growth, seed set, stigmatic groove |
| Abstract:
Over the years controlled interspecific crosses of Leucadendron species have produced hybrid cultivars that have outperformed both parental species. However, as with other cut flower producing genera of the Proteaceae, hybrid seed production is reduced when hybridizing between distantly related species. Unlike other Proteaceae genera, we have little practical knowledge about the sexual reproduction system of this dioecious genus. Our investigations therefore touch many aspects such as pollen and stigma appearance, stigma receptivity, and most importantly, the pattern of growth of the pollen tube after pollination with pollen from different sources. Scanning electron microscopy observations of the stigmatic surface of different species shows an abundance of unicellular papillae embedded on the base of the style with no distinct stigmatic groove. The only difference detected is the stigma shape of different species. Stigmatic surfaces show cytochemically detectable esterase activity and seem to be receptive immediately after anthesis. Applying aniline blue fluorescence, the path of many pollen tubes down the style was successfully followed to the base of the style seven days after pollination with self-pollen from the male cone of the same species. Pollen of distantly related species develops short pollen tubes that penetrate between papillae and can only be observed up to the base of the papillae layer. | |
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