Thesis (PhD(Agric))--University of Stellenbosch, 2000. / ENGLISH ABSTRACT: Little is understood regarding flowering in the genus Protea. The information
available on inflorescence initiation and development in the family Proteaceae was
reviewed and discussed. A number of experiments were conducted to investigate
inflorescence initiation and development, and their manipulation for commercial
production, in selected Protea cultivars, in the Western Cape, South Africa (33°S,
Protea species can be allocated into groups according to similar times of flower
initiation and of harvest. The stages occurring during flower initiation, and their
synchrony relative to shoot growth were investigated for three cultivars, viz. Protea
cv. Carnival (P. compacta x P. neriifolia), Protea cv. Lady Di (P. compacta x P.
magnifica) and Protea cv. Sylvia (P. eximia x P. susannae), when flower initiation
occurred on the spring growth flush.
For all three cultivars the spring flush was preformed and enclosed in the apical bud
before spring budbreak. During elongation of the spring flush the apical meristem
produced floral primordia which differentiated into involucral bracts. After
completion of the spring flush meristematic activity continued, to produce floral bracts
with florets in their axils. The three cultivars showed differences and similarities in
the time of budbreak, and the rates of shoot growth, appendage formation and flower
development. The presence of mature leaves on an over-wintering shoot is essential for
inflorescence initiation on the spring growth flush of 'Carnival'. Inflorescence
initiation in 'Carnival' started at spring budbreak, and production of involucral bracts
occurred concurrently with spring flush elongation. Shoots were defoliated at
different degrees of severity at intervals from pre- to post- spring budbreak. Total
defoliation applied earlier than 6-7 weeks before spring budbreak prevented flowering.
Defoliation closer to spring budbreak affected characteristics of the spring flush and
the inflorescence subtended by the spring flush. Effects were most marked following
total defoliation and diminished with less severe treatments imposed by partial
defoliation. Total defoliation applied before spring budbreak resulted in slower
inflorescence development and lead to later anthesis. Defoliation treatments applied
after completion of spring flush elongation had no effect on either vegetative or
reproductive spring growth.
The requirement for mature overwintering leaves to effect inflorescence initiation in
'Carnival' suggests that environmental factors, such as low temperature and daylength
may play an inductive role. Shoots were in the induced state and committed to
flowering 6-7 weeks before spring budbreak.
A change in source size and position subsequent to different severalties of defoliation
in 'Carnival' lead to reduced dry mass accumulation and altered partitioning. Mature
leaves on the overwintering shoot supported growth of the spring flush and the early
stages of inflorescence development. When these leaves were removed by total
defoliation dry mass accumulation in the spring flush was reduced. A hierarchy of priorities between competing sinks was revealed by defoliation during growth of the
spring flush and concomitant inflorescence development: formation of involucral
bracts> leaf growth> stem elongation. Dry mass accumulation of the inflorescence
subtended by the spring flush was supported by the spring flush leaves and was only
indirectly affected by defoliation. Treatments which resulted in the production of a
weaker spring flush lead to a reduction in dry mass accumulation of the inflorescence.
Different severalties of partial defoliation, whereby either upper or lower leaves were
removed from a shoot, indicated that the position of leaves relative to the active sink
is more important, with respect to source availability, than the number of leaves on the
shoot.
Mature overwintering leaves are essential in 'Lady Di' for shoots to achieve the
induced state for flowering; and are also crucial to the early stages of inflorescence
initiation. Defoliation applied before formation of involucral bracts was complete
prevented flowering. Defoliated shoots either remained vegetative or produced
inflorescences which aborted. Reserve carbohydrates in the stem and leaves of
overwintering shoots were low, and early growth and development of both the spring
flush and inflorescence were, therefore, supported by current photosynthates from the
overwintering leaves. Likewise, reserve carbohydrates available in the flowering
shoot were insufficient to account for the dry mass increase during the major portion
of growth of the spring flush and inflorescence. This rapid increase in dry mass
occurred after elongation of the spring flush was complete and was supported by
current photosynthates from the leaves of the spring flush. Defoliation treatments that did not prevent inflorescence initiation, had no effect on inflorescence development,
and flowering time of 'Lady Di' was not delayed by defoliation.
'Sylvia' has an open window for inflorescence initiation and can initiate flowers
throughout the year. Despite the 'open window' inflorescences are initiated more
readily on the spring flush, when it is subtended by one or more overwintering shoots.
This may be the expression of a facultative response to inductive conditions for which
'Carnival' and 'Lady Di' have an obligate requirement.
The date of pruning affected flowering time of 'Sylvia' by influencing on which flush
inflorescence initiation occurred, and the harvest could be manipulated to fall within
the optimum marketing period for export to Europe. Flowers initiated on the spring
flush reach anthesis in January and February; on the first summer flush predominantly
in April and May; on the second summer flush in July and August; and on the autumn
flush in November and December. Thus, shoots harvested within the optimum
marketing period (September to February) initiated inflorescences on the autumn and
spring flushes. Due to the readiness of shoots to initiate inflorescences on the spring
flush many shoots harvested in January and February (following initiation in the
previous spring) were short and were rendered unmarketable. For commercial
production pruning in July is recommended. Long flowering stems will be harvested
in October to November of the following year. Since the vegetative and reproductive
cycles necessary to produce inflorescences on long stems span more than a year, a
biennial cropping system is recommended. / AFRIKAANSE OPSOMMING: Bloeiwyse-inisiasie en -ontwikkeling, en die manipulasie
daarvan, van geselekteerde cultivars van die genus Protea.
Min word verstaan van blomvorming in die genus Protea. Die beskikbare inligting
oor die bloeiwyse-inisiasie en -ontwikkeling in die familie Proteaceae is nagegaan en
bespreek. 'n Aantal eksperimente is uitgevoer waarin geselekteerde Protea cultivars
van die Wes-Kaap, Suid-Afrika (33°S, 19°0) se bloeiwyse-inisiasie en -ontwikkeling,
asook die manipulasie daarvan vir kommersiële produksie ondersoek is.
Protea spesies kan in groepe ingedeel word op grond van blominisiasietye en oestye
wat ooreenstem. Die verskillende stadiums van blominisiasie en hulle sinchronisering
relatieftot stingelgroei is ondersoek vir drie kultivars, naamlik Protea cv. Carnival (P.
compacta x P. neriifolia), Protea cv. Lady Di (P. compacta x P. magnifica) en Protea
cv. Sylvia (P. eximia x P. susannae) tydens blominisiasie op die lentegroeistuwing.
By al drie die kultivars was die lentegroeistuwing reeds gevorm en omsluit in die
apikale knop voor die lente-knopbreking. Gedurende die verlenging van die
lentegroeistuwing het die apikale meristeem blomprimordia, wat in bloeiwyseomwindselskutblare
gedifferensieer het, geproduseer. Na voltooiing van die
lentegroeistuwing, het meristematiese aktiwiteit voortgeduur en blomskutblare met
blommetjies in hulle oksels is gevorm. Die drie kultivars het verskille en
ooreenkomste vertoon tydens die periode van knopbreking, asook in die tempo van
stingelgroei, aanhangselformasie en blomontwikkeling. Die teenwoordigheid van volwasse blare op 'n oorwinteringstingel is noodsaaklik vit
bloeiwyse-inisiasie op die lentegroeistuwing van 'Carnival'. Bloeiwyse-inisiasie in
'Carnival' het met lente-knopbreking begin en die produksie van bloeiwyseomwindselblare
het gelyktydig met lentegroeistuwing verlenging plaasgevind.
Stingels is met tussenposes, van voor tot na die lente-knopbreking, en met
verskillende grade van felheid, ontblaar. Algehele ontblaring vroeër as 6-7 weke voor
die lente-knopbreking het blomvorming verhoed. Ontblaring nader aan die lenteknopbreking
het 'n invloed gehad op die eienskappe van die lentegroeistuwing asook
die bloeiwyse gedra deur die lentegroeistuwing. Die effek was die duidelikste sigbaar
by algehele ontblaring en het verminder namate die behandeling minder fel geword
het by gedeeltelike ontblaring. Algehele ontblaring wat voor die lente-knopbreking
gedoen is, het gelei tot stadiger bloeiwyse-ontwikkeling en later antese.
Ontblaringsbehandelings wat na die voltooiing van die lentegroeistuwing verlenging
toegepas is, het geen effek op die vegetatiewe of die reproduktiewe lentegroei gehad
me.
Die nodigheid van volwasse oorwinteringsblare vir bloeiwyse-inisiasie in 'Carnival'
dui daarop dat omgewingsfaktore soos lae temperature en daglengte 'n induktiewe rol
kan speel. Stingels was in die geïnduseerde toestand en verbind tot blomvorming 6-7
weke voor die lente-knopbreking.
'n Verandering in oorspronggrootte en -posisie as gevolg van verskille in die felheid
van ontblaring by 'Carnival', het gelei tot verminderde droë-massa-akkumulasie en veranderde verdeling. Volwasse blare op die oorwinteringstingel het die groei van die
lentegroeistuwing en die vroeë stadiums van bloeiwyse-ontwikkeling ondersteun. Toe
hierdie blare verwyder is in 'n algehele ontblaring, het die droë-massa-akkumulasie in
die lentegroeistuwing verminder. 'n Hiërargie van prioriteite tussen kompeterende
sinke is blootgelê tydens ontblaring gedurende die lentegroeistuwing en saamlopende
bloeiwyse-ontwikkeling: vorming van bloeiwyse-omwindselblare > blaargroei >
stamverlenging. Droë-massa-akkumulasie van die bloeiwyse onderspan deur die
lentegroeistuwing is ondersteun deur die blare van die lentegroeistuwing en is slegs
op 'n indirekte wyse deur ontblaring geaffekteer. Behandelings wat tot die produksie
van 'n swakker lentegroeistuwing gelei het, het tot 'n vermindering in die droë-massaakkumulasie
van die bloeiwyse gelei.
Verskille in die felheid van gedeeltelike ontblaring, waartydens óf die boonste óf die
onderste blare van 'n stingel verwyder is, het aangetoon dat die posisie van die blare
relatief tot die aktiewe sink belangriker is, met betrekking tot die beskikbaarheid van
die oorsprong, as die aantal blare op die stingel.
By 'Lady Di' is volwasse oorwinteringsblare noodsaaklik VIr stingels om die
geïnduseerde stadium van blomvorming te bereik en hulle is ook van die uiterste
belang in die vroeë stadiums van bloeiwyse-inisiasie. Waar ontblaring gedoen is
voordat die vorming van bloeiwyse-omwindsel voltooi was, het blomvorming nie
plaasgevind nie. Ontblaarde stingels het ófvegetatief gebly ófbloeiwyses geproduseer
wat geaborteer het. Reserwe-koolhidrate in die stam en blare van die
oorwinteringstingels was laag en die vroeë groei en ontwikkeling van beide die lentegroeistuwing en die bloeiwyse is dus deur die bestaande fotosintate van die
oorwinteringsblare onderhou. Net so was die reserwe-koolhidrate beskikbaar in die
blomdraende stingels nie voldoende om die toename in droë massa gedurende die
grootste deel van die groei van die lentegroeistuwing en die bloeiwyse te verklaar nie.
Hierdie vinnige toename in droë massa het plaasgevind nadat die verlenging van die
lentegroeistuwing voltooi was en is deur die bestaande fotosintate van die blare van
die lentegroeistuwing onderhou. Ontblaringsbehandelings wat nie bloeiwyse-inisiasie
verhoed het nie, het geen effek op bloeiwyse-ontwikkeling gehad nie en die blomtyd
van 'Lady Di' is nie deur ontblaring vertraag nie.
'Sylvia' beskik oor 'n oop venster vir bloeiwyse-inisiasie en kan regdeur die jaar
blomme inisieer. Ten spyte van die 'oop venster', word bloeiwyses tog meer geredelik
in die lentegroeistuwing geïnisieer, wanneer dit deur een of meer van die
oorwinteringstingels gedra word. Dit mag die uitdrukking wees van 'n fakultatiewe
respons op induktiewe toestande wat vir 'Carnival' en 'Lady Di' 'n verpligte vereiste is.
'Sylvia' se blomtyd is deur die snoeidatum geaffekteer omdat die snoeidatum 'n
invloed gehad het op die keuse van by watter groeistuwing bloeiwyse-inisiasie
plaasgevind het. Die oestyd kon gemanipuleer word om binne die optimum
bemarkingstydperk vir uitvoer na Europa te val. Blomme wat op die
lentegroeistuwing geïnisieer is, bereik antese in Januarie en Februarie; dié wat op die
eerste somergroeistuwing geïnisieer is, bereik antese hoofsaaklik in April en Mei; dié
wat op die tweede somergroeistuwing geïnisieer is, bereik antese in Julie en Augustus
en dié wat op die herfsgroeistuwing geïnisieer is, bereik antese in November en Desember. Stingels wat in die optimum bemarkingsperiode (September tot Februarie)
geoes is, het dus bloeiwyses op die herfs- en lente-groeistuwings geïnisieer. As gevolg
van die gereedheid van stingels om bloeiwyses op die lentegroeistuwings te inisieer,
was baie van die stingels wat in Januarie en Februarie geoes is, kort en kon nie
bemark word nie. Vir kommersiële doeleindes word snoei in Julie aanbeveel. Lang
blomdraende stingels sal in Oktober en November van die volgende jaar geoes word.
Aangesien die vegetatiewe en reproduktiewe siklusse wat nodig is om bloeiwyses met
lang stingels te produseer oor meer as fn jaar strek, word fn tweejaarlikse
oesinsamelingstelsel aanbeveel.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/51799 |
| Date | 03 1900 |
| Creators | Gerber, Audrey I. (Audrey Inga) |
| Contributors | Jacobs, G., Theron, K. I., Stellenbosch University. Faculty of AgriSciences. Dept. of Horticulture. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | 137 p. : ill. |
| Rights | Stellenbosch University |
Page generated in 0.0035 seconds