Thesis (PhD (Agric))--University of Stellenbosch, 2003. / ENGLISH ABSTRACT: Downgrading of fruit due to insufficient red colour has limited the profitability of
lucrative blushed pear cultivars (Pyrus communis L.). In 'Rosemarie', poor fruit colour
has been ascribed to pre-harvest red colour loss during periods of high temperature.
The regulation of colour development in pears has not been studied and, in addition,
little is known about anthocyanin degradation in attached fruit.
Changes in colour were recorded and phenylalanine ammonia-lyase (PAL) and
UDPGalactose: flavonoid-3-0-glycosyltransferase (UFGT) activities assessed in
response to cold fronts and during fruit development in order to establish the
regulation of colour development in red and blushed pear cultivars. Best red colour
was generally attained a month or more before harvest whereafter red colour faded
towards harvest. Unlike in some other fruits, UFGT activity apparently did not limit
colour development whereas fading of red colour towards harvest might relate to
decreasing PAL activity. 'Rosemarie' colour fluctuated considerably, increasing with
cold fronts and decreasing during intermittent warmer periods, while red colour was
more stable in other cultivars. PAL and UFGT activities in 'Rosemarie' increased in
response to low temperatures, but were unaffected in 'Bon Rouge'. We concluded
that anthocyanin synthesis in 'Rosemarie' requires low temperatures while colour
development in 'Bon Rouge' and probably also other cultivars is primarily regulated
by endogenous factors.
Detached pome fruit were used to study temperature and light effects on anthocyanin
degradation and fruit colour and to assess the modifying effect of anthocyanin
concentration on colour loss. Anthocyanin degradation and red colour loss increased
linearly between 10°C and 30°C. Irradiation further increased the rate of degradation
and colour loss. The rate of colour loss depended on anthocyanin concentration,
being much faster in fruit with high compared to fruit with low pigment levels. This
was ascribed to the exponential relationship between anthocyanin concentration and
hue at high pigment levels and the linear relationship at lower pigment levels.
Anthocyanin degradation and pre-harvest red colour loss in 'Rosemarie' was
quantitatively confirmed and corresponded with a warm period during fruit
development. Based on these data, we attributed the susceptibility of 'Rosemarie' to pre-harvest colour loss to low anthocyanin concentrations in its peel that allow the
visualisation of net anthocyanin degradation at high temperatures.
Overhead evaporative cooling (EG) as measure to improve red colour in blushed
pears was evaluated. 'Rosemarie' fruit that received pulsed EG applications from two
weeks before harvest at air temperatures exceeding 28°G were redder than control
fruit at harvest. EG had no effect on 'Forelle' colour. Though EG could be used to
improve 'Rosemarie' fruit colour in warm production areas, its effect was relatively
small compared to colour change in response to temperature.
Lastly, we assessed the photoprotective function of anthocyanin in pear peel.
Photoinhibition was evident in exposed faces of pears under natural conditions. The
extent of photoinhibition increased with decreasing redness of peel and was
maintained after photoinhibitory treatment. Although anthocyanin was apparently able
to afford photoprotection at 40oG, we argued against this as a general function. There
were indications that photoprotection was associated, but not necessarily due to light
attenuation by anthocyanin. / AFRIKAANSE OPSOMMING: Afgradering van vrugte vanweë onvoldoende rooi kleur beperk die winsgewendheid
van blospeercultivars (Pyrus communis L.). In die geval van 'Rosemarie' word swak
kleur toegeskryf aan vooroes rooikleurverlies gedurende warm periodes. Die
regulering van kleurontwikkelling in pere is nog nie ondersoek nie terwyl min bekend
is oor antosianiendegradasie aan die boom.
Om die regulering van kleurontwikkelling in rooi- en blospeercultivars vas te stel, is
veranderinge in kleur en in die aktiwiteit van fenielalanien ammonia-liase (FAL) en
UDPGalaktose: flavonoied-3-o-glikosieltransferase (UFGT) gemeet gedurende
vrugontwikkelling en in reaksie op koue fronte. Pere was op hul rooiste 'n maand of
langer voor oes. Hierna het rooi kleur afgeneem tot met oes. Anders as in sommige
ander vrugsoorte het UFGT aktiwiteit nie kleurontwikkeling beperk nie. Die afname in
rooi kleur tot met oes mag egter verband hou met 'n gelyktydige afname in FAL
aktiwiteit. 'Rosemarie' kleur het aansienlik gefluktueer in reaksie op temperatuur.
Rooi kleur het toegeneem met koue fronte en afgeneem in die warmer periodes
tussen fronte. Rooi kleur was meer stabiel en klaarblyklik minder afhanlik van lae
temperature in ander peercultivars. Die noodsaaklikheid van lae temperature vir
kleurontwikkelling in 'Rosemarie' is bevestig deur 'n toename in ensiemaktiwiteit in
reaksie op koue fronte. Lae temperature het geen effek gehad op ensiemaktiwiteit in
'Bon Rouge' nie.
Appels en pere is gebruik om die effek van temperatuur en lig op
antosianiendegradasie en vrugkleur te ondersoek. Die modifiserende effek van
antosianienkonsentrasie op kleurverlies is ook ondersoek. Antosianiendegradasie en
rooi kleurverlies het lineêr toegeneem tussen 10° en 30°C. Beligting het degradasie
en kleurverlies verder versnel. Die tempo van kleurverlies was afhanklik van
antosianienkonsentrasie. Kleurverlies was aansienlik vinniger in vrugte met hoë
pigmentvlakke, in vergelyking met vrugte met lae pigmentvlakke vanweë die
eksponensiële verwantskap tussen antosianienkonsentrasie en
kleurskakeringswaardes (hue values) by hoë pigmentvlakke en die lineêre
verwantskap by lae pigmentvlakke. Antosianiendegradasie en vooroes
rooikleurverlies in 'Rosemarie' is kwantitatief bevestig en het saamgeval met 'n warm periode tydens vrugontwikkelling. Gebaseer op hierdie data is die gevoeligheid van
'Rosemarie' vir vooroes rooikleurverlies toegeskryf aan lae antosianienkonsentrasies
wat die sigbaarheid van netto antosianiendegradasie by hoë temperature verhoog.
Die gebruik van oorhoofse evaporatiewe verkoeling (EG) om rooi kleur van blospere
te verbeter is ge-evalueer. 'Rosemarie' vrugte wat evaporatief verkoel is bo 28°G
vanaf twee weke voor oes, was rooier as kontrole vrugte by oes. 'Forelle' kleur het
nie gereageer op EG nie. Die effek van EG op vrugkleur was relatief klein in
vergelyking met die effek van temperatuur. AI kan EG 'Rosemarie' kleur verbeter in
warm produksiestreke sou dit meer effektief wees om 'Rosemarie' se verbouing te
beperk tot koeler klimaatstreke.
Laastens is die vermoë van antosianien om peerskil teen fotoinhibisie te beskerm
ondersoek. Fotoinhibisie was aanwesig in vrugskil wat direk blootgestel was aan
sonlig in die boord. Die omvang van fotoinhibisie het toegeneem met 'n afname in
rooi pigmentasie van vrugskil. Die verband tussen skilkleur en fotoinhibisie was
steeds aanwesig na blootstelling aan ligstres by 10° en 400G. Ons het egter
geredeneer teen 'n algemene funksie vir antosianien in fotobeskerming by hoë
temperature. Verder was daar aanduidings dat, alhoewel geassossieer met rooi
skilkleur, beskerming teen ligstres nie noodwendig te wyte was aan antosianien nie.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/53569 |
| Date | 03 1900 |
| Creators | Steyn, Willem J. (Willem Jacobus) |
| Contributors | Jacobs, G., Wand, S. J. E., Holcroft, D. M., Stellenbosch University. Faculty of AgriSciences. Dept. of Horticulture. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | 175 p. : ill. |
| Rights | Stellenbosch University |
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