Stellenbosch University. Faculty of AgriSciences. Dept. of Horticulture. / Thesis (PhD (Agric))--Stellenbosch University, 2006. / ENGLISH ABSTRACT: Market preferences for larger fruit have forced producers to adopt cultural practices that will
ensure bigger fruit even if this comes at the expense of reduced total yields. In order to obtain
acceptable fruit size there must be an adequate supply of photosynthetic carbon products
especially during the cell division stage of fruit growth. Competition between fruits and
between fruit and vegetative growth, as well as adverse climatic conditions, may limit the
carbon supply to the fruits at this critical period and thus limit the final fruit size. Growers are
showing renewed interest in the use of girdling or scoring in combination with the usual fruit
thinning program to achieve growth control and increase fruit size. A new and milder
chemical growth retardant, prohexadione-calcium (ProCa), is now also available for
vegetative growth control of apple trees. [n this study, the effects of, and potential interaction
between scoring, ProCa and fruit thinning were investigated, with respect to shoot and fruit
growth, yield and photosynthetic capacity, in 'Royal Gala" 'Fuji' and 'Cripps' Pink' apple
trees.
ProCa decreased final extension shoot length in all three cultivars. Extension shoots
were generally more sensitive than bourse shoots to scoring and ProCa. ProCa seems to be a
more effective way of controlling shoot growth than scoring, with 'Fuji' and 'Cripps' Pink'
being more sensitive than 'Royal Gala' to the application of ProCa. Scoring led to increased
fruit growth rates during the first 40 days after full bloom (DAFB), and culminated in better
fruit size at harvest. Scoring improved the total soluble solids concentration (TSS) of 'Fuji'
and 'Cripps' Pink' compared to control and ProCa treatments. ProCa inhibited shoot growth
effectively, but no evidence was found for improved carbon allocation to fruits and
reproductive buds.
Yield efficiencies of scored trees were significantly improved in all cultivars during
the second season, due to better reproductive bud development after the first year of scoring.
On 'Royal Gala' and 'Cripps' Pink', the efficiency of scoring to stimulate reproductive bud
development on old and new spurs declined after 4 weeks after full bloom (WAFB). In 'Fuji',
scoring later than I WAFB led to a decreasing positive response on old and new spurs. In
contrast, reproductive bud development on long shoots increased with later scoring (6 and 8
W AFB) on all cultivars. It seems that the most beneficial time of scoring is 2-4 W AFB, as early as possible during the cell division stage offruit growth, but not before natural drop has
occurred. The combination of early-season scoring and application of ProCa seems to hold
potential for increasing carbon allocation to the fruit and improving fruit size and quality
attributes.
Scoring early in the season reduced photosynthetic capacity, and this reduction in
carbon availability led to earlier cessation of shoot growth as well as shorter shoots. Later in
the season, reduced fruit numbers led to a decrease in photosynthesis. The optimum
temperature range for photosynthesis was found to adjust according to seasonal temperature
variations. The harvest-induced reduction in sink strength changed stomatal sensitivity to
higher temperature. Due to a reduced demand for carbohydrates by the plant, the maximum
rate of photosynthesis (Amax) was reduced post-harvest. Following this reduction in sink
strength and Am .. , stomata became more sensitive to high leaf temperatures, thus restricting
water loss. Pre-harvest there was a strong demand for carbohydrates, therefore stomata were
kept open at higher temperatures to ensure a high rate of C02 incorporation, but at a cost with
regard to water use efficiency. The sharp increase in dark respiration (Rd) in leaves and fruit
with an increase in temperature would mean that significant carbohydrate shortages could
occur in trees during source limited periods early in the season, especially under warm
weather conditions commonly experienced in the Western Cape region. / AFRIKAANSE OPSOMMING: Die effek van omgewings- en interne faktore op koolstofproduksie en -allokasie in
appelbome (Malus domestlca Borkh.).
Mark voorkeur vir groter vrugte forseer produsente om tegnieke te gebruik wat groter vrugte
sal verseker selfs al beteken dit verlaagde totale opbrengste. Om aanvaarbare vruggrootte te
bereik moet daar voldoende voorsiening van fotosinteties geproduseerde koolstofprodukte
aan die vrug wees, veral gedurende die selverdelingstadium van vruggroei. Kompetisie tussen
vrugte, en tussen vrugte en vegetatiewe groei sal die voorsiening van koolstof gedurende die
kritieke stadium aan die vrug beperk en so vruggroote benadeel. Daar is dus hernude
belangstelling in die gebruik van ringelering in kombinasie met die gewone vrug
uitdunprogramme om groei te beheer en vruggrootte te verbeter. 'n Nuwe, sagter chemiese
groeireguleerder, proheksadioon-kalsium (ProCa) is ook nou beskikbaar vir groeibeheer op
appelbome. In hierdie studie is die effekte van, en moontlike interaksie tussen ringelering,
ProCa en vruguitdunning ondersoek ten opsigte van loot- en vruggroei en opbrengs, sowel as
die effekte op gaswisseling op 'Royal Gala', 'Fuji' en 'Cripps' Pink' appelbome.
ProCa veroorsaak korter lote in aJ drie kultivars. Verlengingslote is meer sensitief as
beurslote vir ringelering en ProCa. ProCa is effektiewer as ringelering om lootgroei te beheer,
en 'Fuji' en 'Cripps' Pink' is sensitiewer as 'Royal Gala'. Ringelering lei tot verbeterde
vruggroeitempos gedurende die eerste 40 dae na volblom en verbeterde vruggrootte by oes.
Ringelering verbeter die totale oplosbare vastestotkonsentrasie (TOVS) van 'Fuji' en
'Cripps' Pink' in vergelyking met kontrole- en ProCa-behandelings, onderskeideHk. ProCa
inhibeer lootgroei effektief, maar geen bewyse van verbeterde koolstomllokasie na vrugte en
reproduktiewe knoppe is gevind nie.
Opbrengseffektiwiteit van geringeleerde borne verhoog gedurende die tweede seisoen
van ringelering weens beter reproduktiewe knopontwikkeling. Ringelering later as 4 weke na
volblom (WNVB) is minder effektief om reproduktiewe knopontwikkeling op ou en nuwe
spore in 'Royal Gala' en 'Cripps' Pink' te stimuleer. Die positiewe effek van ringelering op
reproduktiewe knoppe op 'Fuji' verminder sodra dit later as I WNVB gedoen word. Op
langlote het 'n laat ringelering (6 en 8 WNVB) die beste effek op reproduktiewe
knopontwikkeling. Die mees voordelige tyd om te ringeIeer was 2-4 WNVB, so vroeg as
moontlik gedurende die selverdelingstadium van vruggroei, maar nie voor natuurlike vrugval voltooi is nie. Die kombinasie van vroei! ringelering en die toediening van ProCa het
potensiaal om koolstofallokasie na die vrug te verbeter, met die gepaardgaande verbetering in
vruggrootte en -kwaliteit.
RingeJering vroeg in die seisoen inhibeer fotosintese en hierdie verlaging in koolstof
beskikbaarheid het tot gevolg dat lootgroei vroei!r gestaak word. Later in die seisoen
veroorsaak verlaagde vruggetalle 'n afname in fotosintese. Die optimum temperatuur vir
fotosintese verander na gelang van heersende lugtemperature. Die oes-geinduseerde verlaging
in sinksterkte verander stomatale sensitiwiteit vir hoo temperature. Weens 'n verJaagde
aanvraag vir koolhidrate deur die plant word fotosintese verlaag na-oes. Weens die verlaging
is stomata sensitiewer vir hoer temperature en beperk dus waterverlies. V oor oes is daar 'n
hoo aanvraag na koolhidrate dus word stomata oop gehou selfs by hoe temperature ten koste
van watergebruiksdoeltreffendheid. Die skerp styging in donker respirasie in blare en vrugte
met 'n verhoging in temperature sal beteken dat koolhidraat-tekorte kan ontstaan in bome
gedurende die bron-beperkte periodes vroeg in die seisoen, veral onder warm toestande 500S
wat algemeen ervaar word in die Wes Kaap.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/49198 |
| Date | 04 1900 |
| Creators | Pretorius, Jeremia Jesaja Bierman |
| Contributors | Midgley, S. J. E., Theron, K. l., 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 | ix, 181 leaves : ill. |
| Rights | Stellenbosch University |
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