Thesis (MScAgric)--Stellenbosch University, 2002. / ENGLISH ABSTRACT: Internal breakdown (internal browning - IB and gel breakdown - GB), over maturity and
immaturity are the main factors adversely affecting the quality of exported South African plums.
Maturity problems occur when plums are strip harvested, i.e., all the fruit in a block or orchard are
harvested once, when the majority of the fruit are at optimum maturity. This results in both
ovennature and immature fruit being harvested and contributes to a high percentage of fruit being
rejected for export. In general, internal browning occurs when plums are exported under a single
10\,,, temperature regime and gel breakdown occurs when plums are exported under a dual
temperature regime. However, GB can also occur at harvest in fruit that are very ripe and may occur
at single low temperatures, where it would be masked by lB. While it is known that some cultivars,
like 'Angeleno', can withstand a single temperature regime, others cannot. To the best of our
knowledge, the reason for this difference is not understood.
Many factors affect the quality of plums, including light incidence in the canopy, mineral nutrition
and harvest maturity. Plums that were grown on high density training systems such as 'a V- or
spindle system yielded consistently high quality fruit with low incidences of gel breakdown. This
was in contrast to earlier findings where low-density training systems produced high levels of GB,
especially in the lower part of the tree canopy. Branches that were shaded with 80% shade netting
yielded fruit with high levels of GB, indicating that the main effect of improved canopy structure on
quality was improved light management.
A postharvest boron application on 'Songold' plums prior to storage had no effect on the incidence
of intemal breakdown in the fruit, but did damage the cuticle, resulting in severe shrivel. However,
internal conductivity and firmness measurements indicated that there was some effect of the boron
on cell membranes. A more thorough investigation of pre- and postharvest application of boron is
recommended in order to determine whether there could be a positive effect of boron in improving
fruit quality in plums.
Four cultivars of plums ('Pioneer', 'Sapphire', "Songold ' and 'Angeleno') were harvested
throughout, and extending beyond, the commercial harvesting period. In all cultivars, the drop in
firmness between harvests was not as great as expected and the later harvested fruit were of a similar, if not superior, quality as compared to the earlier harvested fruit. Later harvested plums
tended to have higher TSS and better colour development. Contrary to what was expected, later
harvested fruit did not have more internal disorders than earlier harvested fruit. This indicates the
importance of harvesting at optimum maturity. 'Angeleno' plums had no internal disorders, even
after five weeks of cold storage at a single low temperature.
'Pioneer' and 'Sapphire' plums were classified as climacteric and 'Songold' and 'Angeleno' were
classified as suppressed climacteric based on ethylene production. The climacteric plums respired
and produced ethylene at a higher rate than the suppressed climacteric plums. Climacteric plums
ripened faster during shelf life than suppressed climacteric plums. Furthermore, while climacteric
plums did not need a cold storage period prior to ripening, suppressed climacteric plums needed a
cold storage period in order to ripen normally. The longer the cold storage period prior to transfer to
higher temperatures, the faster the plums ripened and the higher the ethylene production at the
higher temperature. The suppressed climacteric genotype could possibly be incorporated into plum
breeding programs in order to extend the storage period and shelflife of new plum cultivars.
The long storage times required to ship plums from South Africa to the export markets has
necessitated research on postharvest physiology and quality of this fruit. The use of the climacteric
and suppressed climacteric system to classify fruit is expected to assist in understanding the
different physiological responses of the cultivars and assist in developing handling protocols.
Preharvest factors, particularly light and nutrition, also playa role in postharvest quality. / AFRIKAANSE OPSOMMING: Interne verval (interne verbruining en gelverval), oorrypheid en onryp vrugte, is die hoof faktore
wat die uitvoer van Suid Afrikaanse pruime negatief beïnvloed. Rypheidsprobleme ontstaan
wanneer pruime gestroop-oes word, met ander woorde, al die vrugte in 'n blok of boord word
geoes wanneer die meerderheid vrugte optimum rypheid bereik het. As gevolg hiervan word 'n
groot persentasie vrugte vir uitvoer afgekeur, omdat hulle te ryp of nie ryp genoeg is nie. Oor die
algemeen vind interne verbruining plaas wanneer vrugte onder 'n enkel lae temperatuur uitgevoer
word en gelvervel vind plaas wanneer vrugte onder 'n dubbele temperatuur regime vervoer word.
Gel verval kan egter in baie ryp vrugte by oes voorkom en mag by enkel lae temperature voorkom
.waar dit deur interne verbruining gemaskeer sal word. Kultivars soos 'Angeleno' kan onder enkel
lae temperatuur uitgevoer word sonder interne probleme, terwyl ander pruimkultivars me so
uitgevoer kan word nie. So ver ons weet, word die rede hiervoor nie goed verstaan nie.
Daar is baie faktore wat die kwaliteit van pruime beïnvloed, onder meer lighuishouding, minerale
voeding en die rypheid waarby die pruime geoes word. Pruime wat in hoë-digtheid sisteme soos 'n
V- of "spindle" groei het goeie kwaliteit vrugte met 'n lae persentasie gelverval gelewer. Dit is in
teenstelling met vroeër bevindinge, waar vrugte van lae digtheid boorde hoë persentasies geverval
gelewer het, veral in die onderste gedeeltes van die boom. Takke wat met 80% skadunet bedek is
het hoër persentasies gelverval as die kontrole gelewer, wat aandui dat die hoof effek van die
verbeterde boom struktuur op kwaliteit, verbeterde lighuishouding was.
'n Na-oes aanwending van boor op 'Songold' pruime het geen effek op die voorkoms van gelverval
gehad nie, maar het die kutikula beskadig en tot hoë persentasies verrimpeling gelei. Fermheid en
inteme weerstand lesings het egter getoon dat daar wel 'n effek van die boor op die selmembrane en
selwande was. 'n Meer omvattende ondersoek van voor- en na-oes aanwending van boor word
aanbeveel om vas te stelof daar wel 'n positiewe effek van boor in die verbetering van pruim
kwaliteit is.
Vier pruim kultivars, ('Pioneer', 'Sapphire', 'Songold' en 'Angeleno'), is gedurende, sowel as later
as die kommersiële oesperiode geoes. In al die kultivars was die afname in fermheid kleiner as wat
verwag is, en vrugte wat later geoes is het dieselfde, en soms beter, kwaliteit as die vrugte wat vroeër geoes is gehad. Pruime wat later geoes is het beter kleur en gewoonlik hoër suikers gehad. In
teenstelling met wat verwag is, het pruime wat later geoes is nie meer interne verval gehad as die
pruime wat vroeër geoes is nie. Dit dui die belangrikheid van optimale oesrypheid aan. 'Angeleno'
het geen interne verval gehad nie, selfs na vyfweke opberging by -0.5°C.
'Pioneer' en 'Sapphire' pruirne is as klimakteries en 'Songold' en 'Angeleno' as onderdrukte
klimakteries geklassifiseer, gebaseer op etileen produksie. Die klimakteriese pruime het teen 'n hoër
tempo gerespireer en etileen geproduseer as die onderdrukte klimakteriese pruime. Gedurende
raklewe het klimakteriese vrugte vinniger as onderdrukte klimakteriese vrugte ryp geword. Verder,
terwyl klimakteriese pruime nie opbgerging by 'n lae temperatuur nodig gehad het nie, het
onderdrukte klimakteriese vrugte welopberging by 'n lae temperatuur nodig gehad om normaal ryp
te word. Hoe langer die koel opbergingsperiode was, hoe vinniger het die pruime ryp geword by
raklewe en hoe hoër was hulle etileen produksie. Die onderdrukte klimakteriese genotipe kan
moontlik in teelprogramme geïnkorporeer word om kultivars met verlengde opbergings- en raklewe
te teel.
Die lang vervoer tye wat benodig word om Suid Afrikaanse pruime by die uitvoer markte te kry het
dit nodig gemaak om navorsing oor die na-oes fisiologie en kwaliteit van pruime te doen. Die
klassifisering van pruime as klimakteries of onderdrukte klimakteries kan ons in staat stelom die
verskillende fisiologiese reaksies van die kultivars te verstaan en om hanterings prosedures te
ontwikkel. Voor-oes faktore, veral lighuishouding en mineraalvoecling speelook 'n rol in na-oes
kwaliteit van pruime.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/53037 |
| Date | 04 1900 |
| Creators | Kruger, Liezl |
| Contributors | Holcroft, D. M., Cook, N. C., Stellenbosch University. Faculty of AgriSciences. Dept. of Horticultural Sciences. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | 97 p. : ill. |
| Rights | Stellenbosch University |
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