Thesis (PhD)--Stellenbosch University, 2004. / ENGLISH ABSTRACT:Six experiments, five in the glasshouse and one in the field near Nelspruit, were
carried out to ascertain the effect of factors related to shoot die-back, and of water
treatments on the growth and physiological responses of Pterocarpus angolensis
seedlings. The study was undertaken to broaden the knowledge and understanding of
the phenomenon of shoot die-back in order to enhance our ability to regenerate the
species. The following experiments were carried out
(a) Assessment of biomass accumulation; anatomical characteristics of the shoot
apical meristem; foliar, stem and root concentration of micro- and macronutrients
associated with each phenophase,
(b) Effect of seedling age and seed source on the occurrence of shoot die-back
under field conditions;
(c) Water treatment effects on ChI. afluorescence traits of£'. angolensis seedlings
obtained by assessing the fluorescence yield of photosynthetic samples
subjected to dark- and light-adaptation;
(d) Genetic variation in shoot die-back and other traits of sixteen halfsib families
of £.. angolensis from Malawi, Namibia and Zambia grown over two die-back
seasons.
Experiments conducted revealed the following
1. Patterns of growth observed in phenophases are indicators of seasonal changes in
annual biomass allocation to the shoot and root. Phenophases such as leaf loss
and stem senescence, whether shoot die-back occurs completely or not, are
directly related to the decline in above-ground biomass and declined rate of
increase in root biomass respectively. Leaf flush, expansion and maturation result
in increased biomass accumulation whilst shoot die-back has a minimal downregulatory
effect on root biomass accumulation compared to the shoot. Shoot dieback
is not sudden, therefore from the first day of germination, seedlings
synchronise growth and development with the occurrence of shoot die-back.
2. Phenophasic concentration of foliar N, Ca and Mg, stem Fe and Cu and root
concentrations of P, K, Mg, Fe and B are associated with shoot die-back. Patterns
of mineral nutrient concentration obtained in foliage and roots but to a lesser
extent in the stem, may be related to nutrient remobilisation during shoot dieback.
Higher relative mineral nutrient changes during leaf yellowing and shoot
die-back may be an indication of the removal of significant volumes of mobile
nutrients from senescing tissues.
3. The volume of the shoot apex of E. angolensis remains constant during different
phenophases which points to seasonal uniformity in the size of the apical dome.
Changes in phenology associated with declined growth, or shoot die-back, is
revealed through declined cell number in the tunica which is a reflection of
declined mitotic activity.
4. Shoot die-back occurs in all seedlings from nursery stock planted under field
conditions and all seedlings of up to two years experience complete shoot dieback.
Shoot die-back takes place irrespective of seed source or the age of nursery
stock that is planted. Survival after the first shoot die-back is normally low. Water
treatments had no significant effect on the function of PSIJ reaction centres of P.
angolensis nursery seedlings. In the case of both dark- and light-adapted leaves,
water treatment had no significant effect on the measured Chi. a fluorescence
parameters or the calculated parameters (specific activities, phenomenological
fluxes, structure-function and performance indexes and drivingforces).
5. Water treatments affect the shape of ChI. a fluorescence transients of lightadapted
compared to that of dark-adapted photosynthetic samples of E.
angolensis. No significant water treatment effect was obtained for extracted and
technical Chi. afluorescence parameters, specific fluxes, quantum efficiencies and
phenomenological fluxes. Quantum yield, relative electron transport and quantum
yield limitation, de-excitation rate constants, structure-function, performance
indexes and driving forces were also not significantly different across water
treatments.6. Genetic variation was observed to exist among 16 halfsib families from Malawi,
Namibia and Zambia. High heritabilities were obtained for shoot die-back and
other traits, indicating that shoot die-back is genetically controlled. The trait is
passed from parents to offspring and it is highly probable that it occurs,
throughout its natural range, in all seedlings. Since shoot die-back is genetically
programmed, it remains crucial to the ability of a seedling to regenerate in the
following rainy season / AFRIKAANSE OPSOMMING:Ses eksperimente, vyf in die glashuis en een in die veld naby Nelspruit, is uitgevoer
om die effek van faktore wat verwant is aan die terugsterwing van lote op saailinge,
sowel as om die effek van waterstres op die groei en fisiologiese responsies van
Pterocarpus angolensis saailinge, te ondersoek. Die studie is ondemeem om die
kennis en begrip aangaande die regenerasie-dinamika van die spesies te verbeter. Die
volgende eksperimente is uitgevoer:
(a) Evaluering van die effek van jisiologiese veranderings op biomassa; blaar-,
stam- en wortelkonsentrasies van spoor- en makro-voedingselemente, en
anatomiese eienskappe van die apikale meristeem van die lote.
(b) Effek van saailingouderdom en saadbron op die voorkoms van lootterugsterwing
onder veldtoestande.
(c) Waterbehandelingseffekte op Chi. ajluorisensie eienskappe van ,e. angolensis
saailinge wat verkry is deur die jluorisensie te evalueer van fotosintesemonsters
wat aan donker- en lig-adaptasies onderwerp is.
(d) Genetiese variasie in loot-terugsterwing en ander groei-eienskappe van 16
halfsib families van ,e. angolensis vanaf Malawi, Namibia en Zambia wat
gekweek is oor twee terugsterj-seisoene.
Die eksperimente het die volgende aan die lig gebring:
1. Groeipatrone waargeneem gedurende die fenofases is indikatore van seisoenale
veranderings in jaarlikse biomassa allokasies aan die loot en die wortels.
Fenofases soos blaarverlies en lootafsterwing, ongeag of loot-terugsterwing
volledig is of nie, is direk verwant aan die afname in bogrondse biomassa en
afnemende tempo van toename in wortelbiomassa respektiewelik. Bottende blare,
vergroting en rypwording van blare lei tot toenemende biomassa akkumulasie
terwyl loot-terugsterwing 'n minimale afskalende effek op akkumulasie van
wortelbiomassa het in vergelyking met die van die loot. Loot-terugsterwing is nie
skielik, met ander woorde vanaf die eerste dag van ontkieming sinchroniseer
saailinge groei en ontwikkeling met die voorkoms van loot-terugsterwing.
2. Fenofase konsentrasies van en veranderings in blaar N en Ca en loot Fe, asook
veranderings in waargenome wortel N, K, Ca, Mn, Cu, Zn en B is sterk geassosieer
met loot-terugsterwing. Patrone van minerale
voedingselementkonsentrasies wat in blare en wortels, en in minder mate in die
loot, verkry is, mag direk verwant wees aan hermobilisering van
voedingselemente gedurende loot-terugsterwing. Hoe relatiewe minerale
voedingselementveranderings gedurende die vergeling van blare en lootterugsterwing
mag 'n indikasie wees van die verwydering van betekenisvoUe
hoeveelhede mobiele nutriente vanaf sterwende weefsel.
3. Die volume van die groeipunt van r. angolensis bly konstant gedurende
verskillende fenofases wat dui op seisoenale uniformiteit in die grootte van die
apikale koepel. Veranderings in fenologie ge-assosieer met afnemende groei, of
loot-terugsterwing, word gerejlekteer deur afnemende selgetaUe in die tunika wat
dui op afnemende mitotiese aktiwiteit.
4. VoUedige loot-terugsterwing kom voor in aUe saailinge vanaf die kwekery wat in
die veld geplant word tot op die ouderdom van twee iaar. Dit kom voor angeag
van saadbron of ouderdom van saailinge ten tye van planting. Oorlewing na
aanvanklike loot-terugsterwing is normaalweg laag.
5. Water behandelings het geen beduidende effek op die funksie van PSII
reaksiesentra van r. angolensis kewekery-saailinge gehad. Vir beide donker- en
lig-aangepaste blare is geen beduidende waterbehandelingseffek verkry vir
waargenome ChI. a jluoresensie parameters of die berekende parameters
(spes ifieke aktiwiteite, jenomenologiese jlukse, struktuur-funksie-indekse,
"perjormance-indekse oj" driving forces" ).
6. Genetiese variasie tussen 16 halfsibfamilies vanaf Malawi, Namibie en Zambie is
verkry vir loot-terugsterwing en ander groei-eienskappe. Dit dui op genetiese
beheer van terugsterwing en dat die eienskap oorerjbaar is, en waarskynlik in die
hele natuurlike verspreidingsgebied van die spesies in aUe saailinge voorkom.
Aangesien loot-terugsterwing gene ties geprogrammeer is, is dit noodsaaklik vir
die vermoe van die plant om in die volgende reenseisoen te regenereer.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/20431 |
| Date | 04 1900 |
| Creators | Mwitwa, Jacob Pacific |
| Contributors | Van Wyk, G., Stellenbosch University. Faculty of Agrisciences. Dept. of Forest and Wood Science., Jacobs, Ivan |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | 169, [32] p. : ill. |
| Rights | Stellenbosch University |
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