Thesis (MScAgric)--University of Stellenbosch, 2005. / ENGLISH ABSTRACT: Quality of certain Leucospermum and Leucadendron cultivars after approximately 21
days shipping has been reported to be substandard due to ‘drying out’ of leaves and, in
the case of Leucadendrons, involucral leaves. The nature of the symptoms of this
‘drying out’ and the conditions under which they form, viz. long exposures to low
temperatures, has led us to hypothesize that these are symptoms of chilling injury (CI).
Chilling injury, as far as we are aware, has not been documented on Leucospermums or
Leucadendrons.
Typical CI symptomology is discussed and shown for Leucospermum ‘Gold Dust’, ‘High
Gold’ and ‘Succession’ and for Leucadendron ‘Chameleon’, ‘Laurel Yellow’ and ‘Safari
Sunset’. The nature of CI symptoms for Leucospermums and Leucadendrons was
generally membranous breakdown that manifested in some cases as a ‘water soaked’
appearance which, at a more advanced stage, was generally visible as ‘dried out’
patches on the leaves. In the case of the Leucadendrons CI was also visible on the
immature involucral leaves which are more sensitive to chilling conditions than mature
leaves. Dark discoloration of especially immature involucral leaves is also a symptom of
CI. As water uptake of shoots with chilling injury is hindered the styles of the
Leucospermums wilt. As can be expected, the lower the temperature below the
threshold temperature and the longer the exposure the more severe the symptoms.
CI was recorded on cut flower shoots of Leucospermum ‘Gold Dust’, ‘High Gold’,
‘Rigoletto’, ‘Succession’ and ‘Vlam’ after 21 and 24 days storage at 1ºC. After 24 days
storage the chilling injury was more severe than after 21 days storage in most cases.
Each cultivar was pulsed with 5 ml per stem of a 2% (w/v) sugar solution of either
lactulose, sucrose, glucose, fructose or mannose before storage. After storage, CI was
recorded on day 0, 3, 7 and 10 of the vase phase. Of the cultivars tested ‘Vlam’ and
especially ‘Rigoletto’ were more prone to chilling injury development. ‘High Gold’ and
‘Vlam’ shoots were pulsed with 0 (control), 1.5, 3 or 4% (w/v) solutions of either
mannose or fructose. The best control of CI for both cultivars was achieved with 1.5% (w/v) solution. Lower concentrations of mannose and fructose were tested on ‘High
Gold’ shoots, with a 1% (w/v) solution giving the best control for both. At high
concentrations signs of toxicity became evident directly after pulsing. ‘High Gold’ shoots
were pulsed with 1% (w/v) solutions of mannose and fructose and sugar analyses were
performed on shoots at different stages of storage and after 10 days in the vase. A slight
increase in mannose and fructose was detectable in the stems of the shoots directly
after pulsing but not in the leaves or the inflorescences. This is due to the low
concentrations being used. The levels of all the carbohydrates decreased during the 21
days storage and more so during the vase phase of the flowering shoots. The fact that
such low concentrations were effective in controlling chilling injury suggests that the
sugars may have an effect other than on the osmotic potential.
Cut ‘flower’ shoots of Leucadendron ‘Chameleon’, ‘Laurel Yellow’ and ‘Safari Sunset’
were stored for 14, 21 and 28 days, at 1º, 3º and 5ºC and CI development recorded
during the subsequent 10 day vase phase. ‘Laurel Yellow’ and ‘Safari Sunset’ showed
signs of chilling injury on the leaves after 28 days storage at 3ºC or lower and ‘Safari
Sunset’ stored for 21 days developed chilling injury during the vase phase. Immature
involucral leaves were more sensitive to chilling injury than leaves. CI increased with
longer exposure times and lower storage temperatures for all three cultivars evaluated.
‘Chameleon’ was the most chilling tolerant of the cultivars up to 21 days. At 5ºC chilling
injury was low irrespective of cold storage duration but longer exposures to 1º and 3ºC
resulted in increased chilling injury development during the vase phase. All three
cultivars were pulsed with 5 ml per stem of a 1% (w/v) solution of lactulose, sucrose,
glucose, fructose or mannose and stored for 14, 21 and 28 days at 1ºC. The sugars
reduced chilling injury on the leaves for ‘Safari Sunset’ when stored for 28 days and, to a
lesser extent, in ‘Chameleon’. The sugars failed to reduce chilling injury of the involucral
leaves of ‘Chameleon’ and ‘Laurel Yellow’ whereas there was some control especially
after 28 days for ‘Safari Sunset’. In some cases the sugar pulse exacerbated chilling
injury. Chilling injury generally increased rapidly after storage during the first three days
in the vase and then at a lower rate for the next seven days. Leucadendron
‘Chameleon’, ‘Laurel Yellow’ and ‘Safari Sunset’ ‘cut flower’ shoots were pulsed with a 1% (w/v) glucose solution. Expressed on a dry weight basis, an increase in glucose
concentration was not detected. The reduction in chilling injury of leaves by a sugar
pulse is speculated, as for the Leucospermums, to be as a result of their presence in the
apoplast and not the symplast and that their presence there protects the membranes
against chilling conditions in some way. / AFRIKAANSE OPSOMMING: Die kwaliteit van sekere Leucospermum en Leucadendron kultivars na ongeveer 21 dae
verskeping is waargeneem as substandaard as gevolg van die uitdroog van blare en, in
die geval van Leucadendrons, die ‘involucral’ blare. Die aard van die simptome van
hierdie uitdroging en die toestande waaronder dit plaasvind nl. lang periodes van
blootstelling aan lae temperature, het ons tot die hipotese gebring dat hierdie simptome
van koueskade is. Sover as wat ons bewus is, is koueskade nog nie gedokumenteer op
Leucospermums of Leucadendrons nie.
Tipiese koueskade simptomologie word bespreek en gewys vir Leucospermum ‘Gold
Dust’, ‘High Gold’ en ‘Succession’ en vir Leucadendron ‘Chameleon’, ‘Laurel Yellow’ en
‘Safari Sunset’. Die koueskade simptome vir Leucospermums en Leucadendrons was
oor die algemeen membraan afbraak wat ‘n water deurdrenkte voorkoms tot gevolg
gehad het wat in ‘n meer gevorderde stadium sigbaar was as uitgedroogde kolle op die
blare. In die geval van Leucadendrons was koueskade ook sigbaar op die onvolwasse
‘involucral’ blare wat meer sensitief is vir koue toestande as volwasse blare. Donker
verkleuring van veral onvolwasse ‘involucral’ blare is ook ‘n simptoom van koueskade.
Aangesien wateropname van stele met koueskade verhinder word, verwelk die ‘styles’
van die Leucospermums. Soos verwag kan word hoe laer die temperature onder die
drempel temperatuur en hoe langer die blootstelling, hoe meer ernstig die simptome.
Koueskade is aangeteken op gesnyde blomstele van Leucospermum ‘Gold Dust’, ‘High
Gold’, ‘Rigoletto’, ‘Succession’ en ‘Vlam’ na 21 en 24 dae opberging by 1°C. Na 24 dae
opberging was die koueskade meer ernstig as na 21 dae opberging in meeste gevalle.
Elke kultivar het 5ml per steel van ‘n 2% (g/v) suiker oplossing van laktolose, sucrose,
glucose, fruktose of mannose voor opberging opgeneem. Na opberging is koueskade
aangeteken op dag 0, 3, 7 en 10. Van die kultivars wat getoets is, was ‘Vlam’ en veral
‘Rigoletto’ meer geneig tot koueskade ontwikkeling. ‘High Gold’ en ‘Vlam’ stele is
geplaas in oplossings van 0 (kontrole), 1.5, 3 of 4 % (g/v) oplossings van mannose of fruktose. Die beste beheer van koueskade vir beide kultivars is deur die 1.5 (g/v)
oplossing behaal. Laer konsentrasies van mannose en fruktose is getoets op ‘High Gold’
stele met ‘n 1% (g/v) mannose oplossing wat die beste beheer gegee het. Met hoë
konsentrasies het tekens van toksisiteit sigbaar geword direk na opneem van die
oplossing. ‘High Gold’ stele is geplaas in 1% (g/v) oplossings van mannose of fruktose
en suiker analises is uitgevoer op stele by verskillende stadiums van opberging en na 10
dae in die vaas. ‘n Effense toename in mannose en fruktose is waargeneem in die stele
van die blomme direk na opname van die oplossing, maar nie in die blare of die blomme
nie. Dit is as gevolg van die lae konsentrasies wat gebruik is. Die vlakke van al die
koolhidrate het afgeneem gedurende die 21 dae opberging en nog meer so gedurende
die vaas periode van die blommende stele. Die feit dat sulke lae konsentrasies effektief
is in die beheer van koueskade dui daarop dat die suikers ‘n effek het anders as op die
osmotiese potensiaal.
Snyblomme van Leucadendron ‘Chameleon’, ‘Laurel Yellow’ en ‘Safari Sunset’ is
opgeberg vir 14, 21 en 28 dae, by 1º, 3º en 5°C en koueskade ontwikkeling is
aangeteken gedurende die opvolgende 10 dae vaas periode. ‘Laurel Yellow’ en ‘Safari
Sunset’ het tekens gewys van koueskade op die blare na 28 dae opberging by 3°C of
laer en ‘Safari Sunset’ opgeberg vir 21 dae het koueskade ontwikkel gedurende die
vaas periode. Onvolwasse ‘involucral’ blare was meer sensitief vir koueskade as die
blare. Koueskade het toegeneem met langer blootstellingstye en laer opbergins
temperature vir al drie kultivars geëvalueer. ‘Chameleon’ was die mees
koueverdraagsaam van die drie kultivars tot op 21 dae. By 5°C was laag ongeag van die
koue opberging tydperk, maar langer blootstellings aan 1º en 3°C het gelei tot toename
in koueskade ontwikkeling gedurende die vaas periode. Al drie kultivars is voorsien met
5ml per steel van ‘n 1% (g/v) oplossing van lactulose, sucrose, glucose, fruktose of
mannose en opgeberg vir 14, 21 en 28 dae by 1°C. Die suikers het koueskade
verminder op die blare van ‘Safari Sunset’ wanneer opgeberg vir 28 dae en, tot ‘n
mindere mate, in ‘Chameleon’. Die suikers het egter nie koueskade verminder van die
‘involucral’ blare van ‘Chameleon’ en ‘Laurel Yellow’ nie, waar daar egter wel in ‘n mate
beheer was veral na 28 dae vir ‘Safari Sunset’. In sommige gevalle het die voorsiening van suiker die koueskade vererger. Koueskade het oor die algemeen vinnig toegeneem
na opberging gedurende die eerste drie dae in die vaas en dan teen ‘n laer tempo vir die
volgende sewe dae. Leucadendron ‘Chameleon’, ‘Laurel Yellow’ en ‘Safari Sunset’
snyblom stele is voorsien van ‘n 1% (g/v) glukose oplossing. Uitgedruk op ‘n droëmassa
basis is ‘n toename in glukose konsentrasie nie waargeneem nie. Die afname in koueskade
van blare deur die voorsiening van ‘n suiker oplossing is gespekuleer vir die
Leucospermums, om ‘n resultaat te wees van hulle teenwoordigheid in die apoplas en
nie die simplas nie, en dat die teenwoordigheid daar die membrane op ‘n manier
beskerm teen koue toestande.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/21453 |
| Date | 12 1900 |
| Creators | Graham, Shelly |
| Contributors | 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 |
| Type | Thesis |
| Format | x, 100 leaves :i ll. |
| Rights | Stellenbosch University |
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