Thesis (MScAgric)--Stellenbosch University, 2002. / ENGLISH ABSTRACT: Fruit size can be a problem in 'Clementine' mandarin and 'Valencia' orange in the Western
Cape region of South Africa. Small fruit is not only unacceptable to the consumer but is also
more difficult and expensive to harvest. Means of alleviating this problem is to manage the
crop load. Hand thinning trials were conducted to evaluate the effect of timing and severity
thereof in enhancing fruit size. The benefits of enhancing large fruit size was obtained by a
heavy-thinning (60% fruitlet removed) treatment, but the actual benefits were offset by a
reduction of total yield. Yield was reduced up to 30% when heavy thinning treatments were
applied. No effect on early or late treatments were obtained since the trial was conducted
rather late (4 to 6 weeks after the physiological fruit drop period) to obtain the desirable
results. However, better packouts are expected with thinning treatments since blemished fruit
are also removed.
The effect of multiple 2,4-dichlorophenoxy propionic acid (dichlorprop) sprays were also
evaluated on 'Nules Clemetine' mandarin. Comparing multiple sprays with a single spray, it
was observed that more than one spray was no better in improving fruit size. The use of
multiple dichlorprop sprays resulted in no additional yield reduction, while internal fruit
quality was also not affected. The best results were obtained with dichlorprop at 50 mg. L-1
•
The use of dichlorprop with different surfactants was evaluated in both 'Clementine'
mandarin and 'Valencia' orange. The fruit size was increased from 50 mg. L-1 up to 100 mg.
L-1
• Yield was usually not affected but, where reductions were experienced, yield of large
fruit (>55 mm) was not significantly affected. In the 'Valencia' orange trials, during the first
year, dichlorprop was sprayed relatively late (fruit diameter: 19 mm). No fruit size, yield and
internal fruit quality effects were observed. The following year, when early and late sprays (fruit diameter at spray time = 8 and 12 mm, respectively) were evaluated, it was observed
that late sprays had no effect on fruit size, whereas fruit size (48 fruit per carton) was
significantly increased by early sprays. This implies that the dichlorprop effect on fruit size
is during the early stages of fruit development, just after or during the late stage of the
physiological fruit drop period. Yield was drastically reduced by up to 35%, which affected
the actual kilograms of large fruit adversely in some treatments. Juice percentage was
inconsistent and tended to be reduced by dichlorprop application. Dichlorprop tended to
increase TSS slightly in year one and significantly so in year two, but did not affect the
TSS:TA ratio. The use of Orchex mineral oils as surfactant at 150 mL. 100 L-1 was effective
and seemingly allowed lower rates of dichlorprop to be used. Therefore, surfactants seemed
to show potential in enhancing dichlorprop efficiency to reduce the application cost.
The dichlorprop-sprayed fruit was used to measure carotenoid content of the rind during the
later stage of fruit development. Observations indicate that dichlorprop-sprayed fruit at 50
mg. L-1 obtained better carotenoid content in both 'Clementines' mandarin and 'Valencia'
orange. Also, fruit exposed to light had higher carotenoid levels as compared to fruit shaded
with brown paper bags. However, dichlorprop-sprayed fruit at 100 mg. L-1
, even though
exposed to light did not show significant differences with unsprayed in both shaded and
exposed conditions. Therefore, no consistent effect of dichlorprop was established on total
carotenoid content of the rind. / AFRIKAANSE OPSOMMING: Vruggrootte van 'Clementine' mandaryn en 'Valencia' lemoene kan 'n probleem wees in die
Wes Kaap area van Suid Afrika. Klein vrugte is nie net onaanvaarbaar vir die verbruiker nie,
maar is ook moeilik om te oes. Vrugdrag manipulasie is een manier om hierdie probleem te
beheer. Hand uitdunningsproewe is uitgevoer om die effek van tyd en graad van uitdunning
op vruggrootte te bepaal. Strawwe vruguitdunning (60% van vruggies verwyder) het groter
vrugte tot gevolg gehad maar het gelei tot 'n verlaagde opbrengs. Opbrengs is tot soveel as
30% verlaag met die strawwe vruguitdunning. Vroeë en laat behandelings het egter geen
effek gehad nie, aangesien die proewe te laat uitgevoer is (4 tot 6 weke na die fisiologiese
vrugvalperiode) om die gewenste effek te verkry. Beter uitpak word verwag na uitdunning,
aangesien vrugte met letsels ook verwyder word.
Die effek van veelvuldige 2,4-dichlorofenoksie-propioonsuur (dichlorprop) spuite IS ook
geëvalueer op 'Nules Clementine' mandaryn. Daar is geen verskil gevind tussen enkel en
veelvuldige spuite in terme van vruggrootteverbetering nie. Die gebruik van veelvuldige
dichlorprop spuite het nie tot 'n verlaging in opbrengs gelei nie, en interne vrugkwaliteit is
ook nie beïnvloed me. Die beste resultate is verkry met die 50 mg. L-1 dichlorprop
behandeling.
Die gebruik van dichlorprop saam met verskillende benatters is op beide 'Clementine'
mandaryn en 'Valencia' lemoene geëvalueer. Vruggrootte het toegeneem vanaf 50 mg. L-1 tot
100 mg. L-1
• Opbrengs was net in sekere gevalle verlaag en dan sonder 'n betekenisvolle
verskil in groot-vrug produksie (>55 mm: Clementines). Tydens die eerste jaar van die
'Valencia' lemoen proef is die dichlorprop relatief laat gespuit (vrug deursneë: 19 mm). Daar
was geen effek op vruggrootte, opbrengs en interne vrugkwaliteit nie. Tydens evaluasie van vroeë en laat bespuitings die volgende jaar is waargeneem dat laat bespuitings geen effek op
vruggrootte gehad het nie, terwyl vruggrootte (48 vrugte per karton) betekenisvol verhoog is
deur die vroeë bespuitings (Vruggrootte voor bespuiting = 8 en 12 mm, onderskeidelik). Dit
impliseer dat dichlorprop se effek op vruggrootte gedurende die vroeë stadiums van
vrugontwikkeling is, net na of gedurende die laat stadiums van die fisiologiese
vrugvalperiode. Opbrengs is drasties verlaag deur dichlorprop, tot soveel as 35% wat die
kilogram groot vrugte negatief beïnvloed het in sommige behandelings. Sappersentasie was
nie konsekwent affekteer nie, maar is verlaag deur die dichlorprop bespuitings. Dichlorprop
het die TSS effens verhoog in beide jare, maar het geen effek gehad op die TSS:TA
verhouding nie. Die gebruik van Orchex minerale olie as benatter was effektief by 150 mL.
100 L-1
, en laat klaarblyklik die gebruik van dichlorprop by laer konsentrasies toe. Dus, kom
dit voor dat benatters die potensiaal het om die effektiwiteit van dichlorprop te verbeter wat
lei tot 'n verlaging in toedieningskoste.
Die dichlorprop gespuite vrugte is gebruik om karotenoïed-inhoud van die skil te meet tydens
die laat stadiums van vrugontwikkeling. Vrugte gespuit met dichlorprop teen 'n konsentrasie
van 50 mg. L-1 het 'n beter karotenoïed-inhoud in beide 'Clementine' mandaryn en 'Valencia'
lemoene tot gevolg gehad. Vrugte blootgestel aan lig het ook 'n hoër karatenoïedkonsentrasie
gehad as vrugte wat met bruin papiersakke bedek was. Dichlorprop bespuite
vrugte teen 100 mg. L-I, alhoewel blootgestel aan lig, het geen betekenisvolle verskil gehad
in vergelyking met onbespuite vrugte nie. Dus is daar geen konsekwente effek van
dichlorprop op karotenoïde inhoud van die skiI waargeneem nie.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/52699 |
| Date | 12 1900 |
| Creators | Mzini, Loyiso L. |
| Contributors | Rabe, E., Theron, K. I., 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 | 98 p. : ill. |
| Rights | Stellenbosch University |
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