Dissertation (PhD (Agric))--University of Stellenbosch, 2003. / ENGLISH ABSTRACT: Leaf blackening is a particular problem limiting vase life and marketability of
Protea cut flowers. This research investigated suppression of Protea leaf blackening
with a specific focus on Protea cv. Sylvia (P. eximia x P. susannae) cut flowers.
Leaf blackening decreased significantly with decreasing storage temperatures m
'Sylvia' proteas and this was attributed to lower respiration rate and conservation of
carbohydrate. Low storage temperatures were beneficial in short term handling
procedures encountered during airfreight. However, use of low temperatures alone
during the longer sea freight period was unsatisfactory in either maintaining or
extending 'Sylvia' protea vase life. Cooling of 'Sylvia' proteas under vacuum
significantly suppressed leaf blackening and was of greater benefit than forced air
cooling.
Although removal of the uppermost leaves delayed leaf blackening in short term
storage no significant benefit was found for longer storage periods. Girdling directly
beneath the 'Sylvia' protea flowerhead significantly reduced leaf blackening and in
combination with low storage temperatures (O°C) enabled a significant extension in
both storage and vase life of 'Sylvia' proteas.
'Sylvia' proteas did not exhibit a climacteric respiration peak during 96 h storage
at O°C. Exposure to ethylene did not increase Protea leaf blackening or have a
detrimental effect on vase life of either proteas or pincushions evaluated.
No beneficial response to sucrose supplementation was found in 'Sylvia' proteas.
Analysis of the sugar content of both flowerhead and leaves indicated that glucose supplementation might be of benefit and was investigated. Holding solutions of 2.5 %
glucose significantly extended vase life due to a significant reduction in leaf
blackening. Vase life was terminated due to flowerhead collapse instead of leaf
blackening for the first time in 'Sylvia' protea cut flowers. Vase life was significantly
extended by 2:3% glucose pulse solutions and leaf blackening significantly suppressed
with increasing glucose pulse concentration. Solution uptake was facilitated by use of
high intensity PAR lights in the early morning and was attributed to increased stomata
opening and a consequent increase in both transpiration and glucose solution uptake.
The faster uptake of glucose solutions in shoots harvested in the afternoon was
attributed to higher shoot temperatures and consequent transpiration rate to those
harvested in the morning. There was a significant reduction in uptake time with
increasing pulse temperature, which enabled vacuum cooling to be performed earlier
further benefiting storage and vase life extension.
Enclosure of 'Sylvia' proteas in polyethylene (PE) lined cartons did suppress leaf
blackening in non-pulsed shoots. However, this had no practical significance on useful
vase life, which was terminated at this point due to excessive leaf blackening. Water
loss appears to have a minimal influence on 'Sylvia' protea leaf blackening.
Shading at four and three weeks prior to harvest coincided with a period of
significant flowerhead dry mass increase. It is thought that shading at this point,
concurrent with an increased carbohydrate demand by the developing flower head
resulted in a temporary limitation in carbohydrate supply resulting in the appearance of
preharvest leaf blackening. It would appear that proteas do not store large quantities of carbohydrate. Although accentuating winter light conditions by shading did result in a
decrease in carbohydrate content the fact that carbohydrate content was already low
precluded shading from having a significant impact on postharvest leaf blackening.
The finding that glucose was beneficial in extension of both storage and vase life
of 'Sylvia' proteas directed research into its use for other Protea and Leucospermum
cut flowers. Significant differences in the response to glucose supplementation were
found in both Protea and Leucospermum (pincushions). The significant difference in
sensitivity to glucose concentration in 'Pink Ice' proteas (phytotoxic at 2:4%) and
'Susara' proteas (no apparent toxicity), in conjunction with a lack of response in
'Cardinal' proteas, a hybrid from the same parents as 'Sylvia' indicates the need to
direct future research to individual cultivars. Glucose supplementation had no
beneficial effect on vase life of 'Scarlet Ribbon' and 'Tango' pincushions, whilst
significantly extending vase life of 'Cordi', 'Gold Dust', 'High Gold' and 'Succession'
pincushions. / AFRIKAANSE OPSOMMING: Blaarverswarting is 'n spesifieke probleem wat die vaasleeftyd en die
bemarkbaarheid van Protea snyblomme beperk. In hierdie navorsing is ondersoek
ingestel na die onderdrukking van Protea blaarverswarting met spesifieke fokus op die
snyblomme van die kv. Sylvia (P. eximia x P. susannae).
Die voorkoms van blaarverswarting by 'Sylvia' het merkbaar afgeneem tydens die
verlaging van bergingstemperature. Hierdie afname is toegeskryf aan 'n laer
respirasietempo en die behoud van koolhidrate. Lae bergingstemperature in die
korttermyn hantering van die produk tydens lugvrag was voordelig. Die gebruik van
lae temperature, slegs tydens die langer verskeepingsperiode, was egter onbevredigend
vir vaasleeftyd verlenging en onderhoud van 'Sylvia' protea. Die afkoeling van
'Sylvia' proteas onder vakuum het blaarverswarting in 'n groot mate onderdruk en het
beter resultate gelewer as geforseerde lugverkoeling.
Alhoewel die verwydering van die heel boonste blare blaarverswarting by
korttermynopberging vertraag het, het dit geen merkbare voordele vir langer
bergingsperiodes ingehou nie. Ringelering direk onder die blomkop van die 'Sylvia'
protea het blaarverswarting aansienlik verminder, en saam met lae bergingstemperature
(O°C) het dit 'n merkbare verlenging in beide die bergingstyd en die vaasleeftyd van
'Sylvia' proteas teweeggebring. 'Sylvia' proteas het geen klimakteriese respirasiekruin tydens 'n bergingsperiode
van 96 uur teen O°C getoon nie. Blootstelling aan etileen het nie die Protea
blaarverswarting laat toeneem of 'n nadelige effek op die vaasleeftyd van die proteas of
speldekussings wat geevalueer is, gehad nie.
Geen voordelige reaksie op sukrose-byvoeging is in 'Sylvia' proteas gevind nie.
'n Analise van die suikerinhoud van beide die blomkoppe en die blare het aangetoon
dat 'n glukose-byvoeging moontlik voordelig kon wees, en hierdie aspek is ondersoek.
Met stooroplossings van 2,5 % glukose is die vaasleeftyd aansienlik verleng omdat daar
'n merkbare afname in blaarverswarting was. Vir die eerste keer in die geval van die
'Sylvia' protea, het die vaasleeftyd van die snyblomrne tot 'n einde gekom omdat die
blornkoppe uitmekaar gebreek het en nie omdat blaarverswarting ingetree het nie. Die
vaasleeftyd is aansienlik verleng met ~ 3% glukose-pulsoplossings, en blaarverswarting
is merkbaar onderdruk met die verhoging van hierdie oplossings se
glukosekonsentrasie. Die opname van die oplossings is gefasiliteer deur hoe intensiteit
PAR (fotosinteties-aktiewe radiasie) ligte vroeg in die oggend, en is toegeskryf daaraan
dat meer huidmondjies oopgegaan het. Dit het gelei tot 'n toename in transpirasie en
'n toename in die opname van die glukose-oplossing. Die feit dat glukose-oplossings
vinniger opgeneem is deur lote wat in die middag geoes is, is toegeskryf daaraan dat
loottemperature dan hoer is as soggens en gevolglik lei tot 'n vinniger
transpirasietempo. Daar was 'n merkbare afname in die opnametyd wanneer die
temperatuur van die pulsoplossings verhoog is. Vakuumafkoeling kon dus vroeer
toegepas word, wat 'n verlenging in bergingstyd en vaasleeftyd tot gevolg gehad het. Verpakking van 'Sylvia' proteas in kartonne wat met poli-etileen uitgevoer is, het
blaarverswarting van lote wat nie aan pulsering onderwerp is nie, onderdruk. Hierdie
maatreel het egter geen praktiese waarde met betrekking tot vaasleeftyd nie; die
vaasleeftyd het tot 'n einde gekom as gevolg van omvangryke blaarverswarting. Dit
lyk asof waterverlies weinig invloed het op die blaarverswarting van' Sylvia' proteas.
Die vermoede bestaan dat lae koolhidraatvlakke proteas ontvanklik maak vir
blaarverswarting. Alhoewel die beklemtoning van winterligtoestande deur
beskaduwing gelei het tot 'n afname in koolhidraatinhoud, was hierdie inhoud reeds
laag en blaarverswarting na die oes is nie beinvloed nie. Beskaduwing tydens die vier
en drie weke voor oestyd het saamgeval met 'n tydperk van aansienlike toename in die
droe massa van die blomkop. Die vermoede bestaan dat beskaduwing tydens hierdie
fase, saam met die toename in die ontwikkelende blomkop se behoefte aan koolhidrate,
aanleiding gegee het tot 'n tydelike beperking in koolhidraatvoorraad wat die voorkoms
van blaarverswarting voor die oes tot gevolg gehad het.
Die bevinding dat glukose voordelig is vir die verlenging van beide die
bergingstyd en die vaasleeftyd van 'Sylvia' proteas het die navorsing gerig om ook
ondersoek in te stel na die gebruik daarvan vir ander Protea en Leucospermum
snyblomme. Merkbare veranderinge is gevind in die reaksie op glukosebyvoegings in
beide Protea en Leucospermum (speldekussings). Die opmerklike verskil in
sensitiwiteit vir glukosekonsentrasie in 'Pink Ice' proteas (fitotoksies by ~ 4%) en
'Susara' proteas (geen klaarblyklike toksisiteit), saam met 'n gebrek aan reaksie by
'Cardinal' proteas, 'n hibried van dieselfde ouers as 'Sylvia', dui aan dat verdere navorsing op individuele kultivars toegespits sal rnoet word. Glukosebyvoegings het
geen voordelige uitwerking op die vaasleeftyd van 'Scarlet Ribbon' en 'Tango'
speldekussings gehad nie, terwyl dit die vaasleeftyd van 'Cordi', 'Gold Dust', 'High
Gold' en 'Succession' speldekussingkultivars merkbaar verIeng het.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/49768 |
| Date | 04 1900 |
| Creators | Stephens, Iain Andrew |
| Contributors | Jacobs, G., Holcroft, D. M., Stellenbosch University. Faculty of AgriSciences. Dept. of Horticultural Science . |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | x, 144 p. : ill. |
| Rights | Stellenbosch University |
Page generated in 0.0036 seconds