Thesis (MScAgric)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: Leaf blackening, a postharvest disorder which is characterized by a dark brown to black
discoloration, is found in most commercially important Protea cut flower species and cultivars. As
this disorder is known to increase with storage time, it is a major concern to the South African
industry as the use of sea freight is increasingly preferred due to lower transport costs and a more
favourable carbon footprint. The cause of leaf blackening has been strongly linked to a carbohydrate
stress exerted by the large inflorescence, thus requiring the utilization of sugar bound polyphenols in
the foliage, which when removed, can oxidize enzymatically or non-enzymatically.
A study where harvesting was done throughout the season as well as on selected days at
08:00, 12:00, 15:00 and 17:00, concluded that leaf blackening incidences in Protea cv. Sylvia stems
varies significantly throughout the season, between years and even with the harvest time of day.
Leaf blackening incidences increased from October onwards and remained high until February,
before decreasing to acceptably lower levels towards March to May. Carbohydrate- and phenolic
content together with water status of leaves at harvest was not able to accurately predict incidence
of the associated leaf blackening. However, irrespective of the season of harvesting, leaf blackening
was significantly lower when stems were harvested later in the day than compared to stems
harvested in the morning. Low sucrose and high water content at these harvest times was positively
correlated to high incidences of leaf blackening.
In a next study where uptake dynamics of glucose pulsing was investigated, Protea cv. Sylvia
was harvested at different times throughout the day, dehydrated to various levels and pulsed with
an increasing range of glucose concentrations. Pulsing solution uptake per stem was found to be
highly influenced by these factors, as dehydration of stems and a harvest time later during the day
both decreased stem water potential, which then increased pulse-solution uptake within a certain
time period. The daily harvest time influenced transpiration, whilst pulse-solution uptake decreased
with an increase in glucose pulse concentration.
When stems were pulsed pre-storage with an increasing range of glucose concentrations, not
only did pulses of between 4.7 – 13.7% glucose significantly delayed the incidence of leaf blackening,
but it also maintained a positive water balance longer in stems during vase life.
Ethanol or acetaldehyde vapour did not provide a viable alternative for reducing leaf
blackening incidence in Protea cv. Sylvia, although a synergistic effect was found when ethanol
vapour or pulsing was used in combination with glucose. A commercial verification trial disclosed
that Protea magnifica and Protea ‘Pink Ice’ reacted more beneficial to ethanol vapour than was
observed in ‘Sylvia’. This study confirms that carbohydrate availability within the Protea cut stem remains a key
factor in the control of leaf blackening. Factors which assist in maintaining high internal
carbohydrate levels, such as enhanced glucose pulse uptake or effective vase solution utilization will
contribute to providing an optimum control of leaf blackening during vase life following long-term
cold storage. / AFRIKAANSE OPSOMMING: Loofblaarverbruining is ‘n na-oes defek wat gekarakteriseer word deur ‘n donker bruin na
swart verkleuring wat voorkom in meeste kommersieël belangrike Protea snyblom spesies en
kultivars. Hierdie defek is bekend daarvoor dat dit toeneem met stoortyd, dus is dit ‘n groot
kommer vir die Suid-Afrikaanse industrie, met toenemende gebruik van seevrag as vervoer keuse
wat laer vervoer kostes en meer gunstige ‘koolstof voetspoor’ bevoordeel. Die oorsaak van
loofblaarverbruining word sterk gekoppel aan ‘n koolhidraat stres wat uitgeoefen word deur die
groot bloeiwyse op die loofblare, waar suiker-gebonde polifenoliese verbindings ensiematies of nieensiematies
geoksideer word met die verwydering van die suiker verbinding.
'n Studie waar geoes was regdeur die seisoen, sowel as op geselekteerde dae om 08:00, 12:00,
15:00 en 17:00, het bevind dat die voorkoms van loofblaarverbruining in stele van Protea kv. Sylvia
aansienlik geskil regdeur die seisoen, tussen jare en selfs met die oes tyd gedurende die dag. Die
voorkoms van loofblaarverbruining het toegeneem vanaf Oktober en het hoog gebly tot en met
Februarie, voordat dit gedaal het tot aanvaarbare laer vlakke teen Maart, tot en met Mei.
Koolhidraat-en fenoliese inhoud sowel as die water status van die blare by oes was onsuksesvol om
die voorkoms van die gepaardgaande loofblaarverbruining akkuraat te voorspel.
Loofblaarverbruining was egter aansienlik laer as stele geoes later in die dag teenoor stele geoes in
die oggend, ongeag die seisoen van oes. Lae sukrose en 'n hoë water inhoud geassosieer met
hierdie oes-tye was positief gekorreleerd met ‘n hoë voorkoms van loofblaarverbruining.
In 'n volgende studie waar die opname dinamika van glukose pulsing ondersoek was, is Protea
kv. Sylvia stele geoes op verskillende tye dwarsdeur die dag, gedehidreer tot verskillende vlakke en
met 'n toenemende reeks van glukose konsentrasies gepuls. Pulsoplossing opname per steel is sterk
beïnvloed deur hierdie faktore, aangesien dehidrasie van die stele asook stele geoes later gedurende
die dag die afname van steel waterpotensiaal veroorsaak het, terwyl die puls-oplossing opname
versnel het binne ‘n bepaalde tyd. Die tyd van oes beïnvloed ook transpirasie, terwyl vaas oplossing
opname afgeneem met 'n toename in glukose puls konsentrasie.
Wanneer ‘Sylvia’ stele gepuls was voor stoor met 'n reeks van toenemende glukose
konsentrasies, het nie net die puls van tussen 4.7 – 13.7% glukose aansienlik die voorkoms van
loofblaarverbruining vertraag nie, maar dit het ook ‘n positiewe water balans langer in stele
gedurende die vaas lewe behou.
Nie etanol of asetaldehied dampe is bevind as geskikte alternatief vir glukose pulsing om die
voorkoms van loofblaarverbruining in Protea kv. Sylvia te verlaag nie, alhoewel ‘n sinergistiese effek
waargeneem was wanneer etanol in kombinasie met glukose gebruik was. ‘n Kommersieële bevestigingstoetsing het bevind dat Protea magnifica en ‘Pink Ice’ meer voordeel uit ‘n ethanoldamp
behandeling kon trek teenoor ‘Sylvia’.
Hierdie studie het bevestig die belangrikheid van koolhidraat beskikbaarheid in die Protea
snyblom, vir beheer van loofblaarverbruining. Faktore wat die handhawing van hoë interne
koolhidrate vlakke, soos bevorderde glukose puls opname of effektiewe vaas oplossing benutting sal
bydra tot ‘n optimal beheer van loofblaarverbruining tydens vaas lewe na langtermyn koueopberging. / National Research Fund (NRF) for their financial support in 2009; Protea
Producers of South Africa (PPSA) and Productschap Tuinbouw (PT) as well as the Frank
Batchelor Will Trust Grant for the financial support.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/20396 |
| Date | 03 1900 |
| Creators | Windell, Nicole Elizabeth |
| Contributors | Hoffman, E. W., Jacobs, G., 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 |
| Format | 153 p. : ill. (some col.) |
| Rights | Stellenbosch University |
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