Thesis (MSc)--Stellenbosch University, 2002. / ENGLISH ABSTRACT: Successful export of South African fresh fruit requires fruit of a high quality. Variable
fruit quality within a consignment is detrimental to effective marketing of the product.
The light microclimate under which the fruit develops is one of the factors that affect
within-tree and between-tree variation in quality, maturity and yield. Light exposure
effects on fruit quality at harvest and after commercial storage and ripening periods, as
well as the physiological mechanisms of these responses to light exposure were studied.
Increased exposure to light resulted in the development of typical sun leaf characteristics,
with the associated increase in leaf nitrogen concentration and photosynthetic rates. Size
and mass of 'Laetitia' plums and 'Cripps' Pink' apples increased with increasing
exposure to light. Shade treatments were only started after the initial phase of cell
/
division was complete. Increased size of the fruit was likely due to the improved carbon
balance of the exposed foliage and fruit from the end of cell division until harvest. The
transpiration stream was higher in the more exposed foliage compared to the shaded parts
of the canopy. This was supported by increased transpiration rates and decreased midday
water potentials of exposed leaves. 'Songold' plums and 'Rosemarie' pears were also
investigated in the first season, but results were not conclusive.
Increased exposure to light was associated with advanced maturity of 'Laetitia' plums at
harvest. Shaded fruit were able to attain a similar level of maturity as exposed fruit
during storage and ripening periods. At harvest and after the storage and ripening
periods, exposed fruit had a higher total soluble solid (TSS) content and therefore an
improved eating quality. At harvest, blush colour of 'Laetitia' plums increased with
increased exposure to irradiance. Blush colour continued to develop during storage and
ripening, and after the ripening period it was evident that blush colour development was
associated with a dosage effect i.e. exposure to a cumulative level of irradiance gives the
fruit the potential to develop a certain amount of blush colour. Fruit exposed to more
than 70% photosynthetic photon flux density (PPFD) were .able to develop to a similar level of blush colour, whereas, fruit exposed to less than 50% PPFD were not able to
attain the same level of blush colour.
Increased exposure to light did not result in advanced maturity of 'Cripps' Pink' apples at
harvest, but it did lead to improved blush colour and increased TSS levels. Blush colour
of 'Rosemarie' pears was also dependent on exposure to light from four weeks before
harvest.
Exposed 'Laetitia' plums had a greater whole fruit content of Mn and B, but concentration
on a dry mass basis of P, K, and B decreased with increasing light. Exposed 'Cripps'
Pink' apples had increased whole fruit content of P, K, Ca, Mg, Mn, Fe, Cu and B, but
concentration on a dry mass basis of K and Na decreased with increasing light. Nutrient
content is often associated with the incidence of internal disorders of fruit after storage
and further investigation of this effect is necessary as internal disorders were virtually
absent in this study.
The termination of irrigation shortly before harvest in order to advance the maturity of all
the fruit to a similar level, and the subsequent strip harvest of the fruit on a single harvest
date, is a practice commonly used by South African plum producers to reduce cost and
ostensibly to improve fruit quality. The effect of this practice on 'Songold' plum quality
at harvest, after storage and after ripening was also studied.
Drip-irrigated plums and plums subjected to soil drying had a better eating quality and
were more marketable than micro-irrigated and non-droughted fruit. Following
commercial storage and ripening periods these fruit were firmer, had a higher TSS
content and were of a similar size and mass to micro-irrigated and non-droughted fruit.
The extended harvesting period, in contrast to a strip harvest, allowed the fruit that were
smaller and less mature at the beginning of the period to attain a greater size and
advanced maturity toward the end of the harvesting period. / AFRIKAANSE OPSOMMING: Suksesvolle uitvoer van Suid-Afrikaanse vars vrugte vereis volgehoue hoë gehalte.
Wisselvallige vruggehalte binne 'n besending is nadelig vir die effektiewe bemarking van
die produk. Die lig mikroklimaat waaronder die vrug ontwikkel is een van die faktore
wat variasie in gehalte, rypheidsstadium en opbrengs binne die boom en tussen bome
beïnvloed. Die effek van verhoogde ligblootstelling op vruggehalte by oes, na
kommersiële opberging en na die rypwordingsperiode, sowel as die fisiologiese
meganismes van die reaksie van verhoogde ligblootstelling is bestudeer.
Verhoogde blootstelling aan lig lei tot die ontwikkeling van tipiese son-blaar
karaktertrekke, met die gepaardgaande verhoging in blaar stikstof konsentrasie en
fotosintetiese tempo. Grote en massa van 'Laetitia' pruime en 'Cripps' Pink' appels het
toegeneem met verhoogde blootstelling aan lig. Skadu behandelings is eers begin na die
einde van die periode van selverdeling. Toenemende grootte van die vrugte is as gevolg
van die verbeterde koolstofbalans van die blootgestelde blare en vrugte vanaffase II van
vruggroei tot oestyd. Die transpirasie stroom is geallokeer na die blootgestelde blare. Dit
word ondersteun deur die verhoogde transpirasie tempo en verminderde middag
waterpotensiaal van die blootgestelde blare. 'Songold' pruime en 'Rosemarie' pere is ook
bestudeer, maar die uitslae is nie so oortuigend nie.
Toenemende blootstelling aan lig is geassosieer met gevorderde rypheid van 'Laetitia' by
oes. Dit was moontlik vir skadu vrugte om dieselfde rypheidsvlak as blootgestelde
vrugte te bereik, tydens die opberging en rypwording periodes. Teen oestyd en na
opberging en rypwording, het blootgestelde vrugte 'n hoër suiker inhoud gehad en dus 'n
hoër eetgehalte. Teen oestyd, het die bioskleur van die pruime toegeneem met
toenemende blootstelling aan lig. Ontwikkeling van bloskleur het aangehou gedurende
opberging en rypwording, en na die die rypwordings periode was dit duidelik dat
bioskleur ontwikkeling met 'n dosis-effek geassosieer word, m.a.w. blootstelling aan 'n
sekere opgestapelde vlak van lig gee die vrug die potensiaal om 'n sekere hoeveelheid
bioskleur te ontwikkel. Vrugte wat meer as 70% ligblootstelling gekry het, het dieselfde bioskleur ontwikkel, maar vrugte wat minder as 50% ligblootstelling gekry het, het
minder bloskleur ontwikkel.
Toenemende blootstelling aan lig het nie gelei tot gevorderde rypheid van 'Cripps' Pink'
appels teen oestyd nie, maar dit het wel gelei tot verbeterde bioskleur en verhoogde
suiker inhoud. Bloskleur van 'Rosemarie' pere is afhanklik van blootstelling aan lig kort
voor oestyd.
Blootgestelde 'Laetitia' pruime het 'n verhoogde vrug inhoud van Mn en B met
verhoogde ligblootstelling gehad, maar die konsentrasie van P, K en B op 'n droë massa
basis het afgeneem met verhoogde ligblootstelling. Blootgestelde 'Cripps' Pink' appels
het 'n verhoogde vrug inhoud van P, K, Ca, Mg, Mn, Fe, Cu en B met verhoogde
ligblootstelling gehad, maar die konsentrasie van K en Na op 'n droë massa basis het
afgeneem met verhoogde ligblootstelling. Voedingstof inhoud is geassosieer met die
voorkoms van interne probleme in vrugte na opberging en verdere navorsing oor hierdie
effek is nodig.
Die terminering van besproeiing kort voor oestyd met die doelom die rypheid van al die
vrugte op dieselfde vlak te kry sowel as die gepaardgaande oes van al die vrugte op een
dag, is 'n algemene praktyke wat gebruik word deur Suid-Afrikaanse pruim produsente
om kostes te beperk en oënskynlik, om vruggehalte te verbeter. Die effek van hierdie
praktyke op 'Songold' pruim gehalte teen oestyd, na opberging en na rypwording is ook
bestudeer.
Drup-besproeide pruime en pruime wat blootgestel is aan grond uitdroging het 'n beter
eetgehalte en is meer bemarkbaar as mikro-besproeide en nie-droogte geïnduseerde
vrugte. Na kommersiële opberging en rypwording periodes het hierdie vrugte 'n hoër
fermheid en suiker inhoud gehad, en 'n gelyksoortige grootte en massa as mikrobesproeide
en nie-droogte geïnduseerde vrugte. Die verlengde oesperiode het die kleiner
en minder ryp vrugte aan die begin van die periode 'n kans gegee om toe te neem in
grootte en 'n gevorderde vlak van rypheid te bereik aan die einde van die oesperiode.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/53001 |
| Date | 12 1900 |
| Creators | Murray, Xavier John |
| Contributors | Wand, Stephanie l. E., Holcroft, D. M., Cook, N. C., Stellenbosch University. Faculty of AgriScience. Dept. of Horticulture. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | 191 pages : illustrations |
| Rights | Stellenbosch University |
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