Thesis (MScAgric)--University of Stellenbosch, 2004. / ENGLISH ABSTRACT: The exomorphology and size of Leucadendron pollen was examined using a scanning
electron and light microscope respectively. Pollen was found to have a consistent
triangular shape with three apertures. Pollen grain size however, show difference
between species, sections and subsections on Leucadendron. Pollen of all species
examined had a woven appearance like the intertwined threads of a fabric with
orbicules present on the surface of L. chamelaea, L. elimense subsp. elimense and L.
galpinii. Pollen viability was successfully assessed using a solidified agar medium
containing 2g agar and 109 sucrose. Pollen germination for all species was found to
be above 55% viability. A diallellayout of crosses has demonstrated conclusively
that fecundity differs when crossing between species of the genus Leucadendron.
Artificial hand pollination was applied successfully on Leucadendron and showed
repeatedly that seed set following intraspecific crosses between the male and female
inflorescence of the same species gave the same high rate of seed set as found in
nature. However, seed numbers declined sharply when crossing between species of
the section 'Leucadendron'. Seed set following crosses between species of different
sections or sub-sections was the lowest and in most cross combinations there was no
seed harvested or no seed germination. The diallellayout was useful in identifying
incompatible species and for locating possible incompatibility barriers to interspecific
seed development. The morphology of the stigma was examined with a scanning
electron microscope. Stigma appearance of all species had a consistent round to oval
shape, except for L. rubrum, which had an elongated shape. Stigma surfaces of all
species were densely covered with a large number of unicellular papilar cells on the
swollen base. The aniline blue staining technique, together with the fluorescent
microscope technique was used to follow the growth of the pollen tube following compatible and incompatible cross combinations. Pollen on the stigmas of
compatible and incompatible species examined showed signs of germination. Pollen
tubes grew between the papilla cells in all directions and only the most vigorous ones
reached the upper part of the style. From the upper region of the style, yellow green
tubes grew cohesively in the middle of the style towards the ovule. In compatible
combinations a not more than 4 tubes reached the ovule region, but was difficult to
observe when they entered the micropyle for fertilization. In incompatible species a
large number of abnormalities occurred beyond the upper region of the style. / AFRIKAANSE OPSOMMING: Die morfologie en grootte van Leucadendron stuifmeel is deur middel van 'n
skandeerelektron - en ligmikroskoop bestudeer. Baie klein verskille in stuifmeel
morfologie het voorgekom. Diverse verskille in stuifmeelgrootte het wel voorgekom
tussen spesies, groepe en subgroepe van Leucadendron. Stuifmeelvorm was
deurgaans driehoekig en die oppervlakte van die stuifmeelkorrel het die voorkoms
van geweefde vesels gehad. Klein, bolvormige struktuurtjies was teen verskillende
digthede oor die stuifmeeloppervlak van L. chamelaea, L. elimense subsp. elimense en
L. galpinii versprei. Stuifmeelkiemkragtigheid is bepaal deur dit op soliede agar
medium te ontkiem en was deurgaans bo 55% kiemkragtig. Onderlings dialleliese
kruisings van Leucadendron spesies het variasie in saad set getoon. Handbestuiwing
is suksesvol uitgevoer en saadset in intraspesie kruisings hoog en soortgelyk aan
natuurlike bestuiwing. Saadset en saad ontwikkeling het drasties verswak toe verder
vewante spesies as ouers gebruik. As gevolg van hulondeurdringbare saadhuid is
neutagtige sade gewoonlik moeiliker ontkiembaar. Die diallel uitleg was ook nuttig
om verenigbare en onverenigbare kruisingskombinasies te identifiseer en om
onverenigbaarheidskanse op te spoor. 'n Skandeerelektronmiskoop is gebruik om die
morfologie van die stigma te bestudeer. Stigmas was deurgaans rond tot ovaalvormig,
behalwe die van L. rubrum wat 'n verlengde voorkoms gehad het. Die stigma bestaan
uit 'n groot aantal eensellige papilla, wat dig teen mekaar gepak is op 'n geswolle
basis. Aniline-blou fluoresserende kleurstof en 'n fluoressensie mikroskoop is
gebruik om die pad van die stuifmeelbuis in verenigbare en onverenigbare
kruisingskombinasies in Leucadendron te volg. Stuifmeelontkieming het in alle
kruisingskombinasies geskied. Stuifmeelbuise het in alle rigtings tussen die papilla gegroei en slegs die mees kiemkragtige stuifmeelbuise het die boonste deel van die
styl bereik. In die styl het die buise dig teen mekaar gegroei en was dit moeilik
telbaar. 'n Maksimum van vier buise het die vrugbeginsel bereik, maar dit was
moeilik om verder te volg nadat hulle die poortjie bereik het. In onverenigbare
kruisingskombinasies het stuifmeelbuise abnormale groeipatrone in die boonste
gedeelte van die styl getoon.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/50110 |
| Date | 12 1900 |
| Creators | Rhode, Adele |
| Contributors | Louw, J. H., Venecourt, G. M. (nee Littlejohn), Stellenbosch University. Faculty of AgriSciences. Dept. of Genetics. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | 135 p. : ill. |
| Rights | Stellenbosch University |
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