Thesis (MSc)--University of Stellenbosch, 2004. / ENGLISH ABSTRACT: Most South African peach and nectarine production areas lack in adequate
winter chilling. To address these issues, a conventional breeding programme
was started, to develop new and improved stone fruit cultivars with special
emphasis on climatic adaptation and pomological attributes. This study was
conducted to test the accuracy of the scientific method called the phenological
method of classification, currently used by the breeding programme to classify
the selections in the second phase of evaluation according to chilling
requirement.
During April 2000 and May 2001 and continuing until the next spring, 20 oneyear-
old shoots of 30 peach and nectarine selections were harvested
fortnightly from an evaluation orchard on Bien Donné Experiment Farm,
Simondium, Western Cape (34° S). All selections were previously
categorised as high (>800 Utah chilling units [CU]), medium (400-800 CU) or
_low «400 CU) chilling requirement based on phenologic observations.
According to the preliminary classification of the selections included in this
study, six selections were classified as high, three as medium and 21 as low
chilling requirement. Two replicate bundles of shoots of each selection were
prepared and forced at 25° C with continuous illumination until no further
changes in bud burst occurred for a period of five days after which the shoots
were then discarded. CU in the orchard were calculated according to the
Utah and Infruitec models. The hours below 12° C and 7° C were also
calculated. For each selection the number of days until 20% vegetative and
reproductive bud break was plotted over day of year, Utah CU, Infruitec CU,
hours below 12° C, and hours below 7° C, and expressed as a parabolic
function. Similarly, the inverse of the number of days until 20% bud break or
the rate of bud growth was also plotted against all the above variables. The
area under these parabolas was statistically analysed using the CANDISC
procedure of SAS Release 8.1. The groupings of the CANDISC procedure
were more or less consistent with the preliminary groupings obtained with the
phenoligical classification method. On 16 May 2000 and 15 May 2001, 100 one-year-old shoots of the same
peach and nectarine selections were harvested from the evaluation orchard
on Bien Donné Experiment Farm, covered in wet paper towelling and black
plastic bags and placed in a cold room kept at a temperature range between
4° C and 7° C. Two replicate bundles of 10 shoots of each selection were
prepared fortnightly and forced at 25° C with continuous illumination until no
further changes in bud burst occurred for a period of five days after which the
shoots were then discarded. CU accumulated in the cold room at each
transferral date was calculated according to the Utah model. For each
selection the number of days until 20% vegetative bud break was plotted over
Utah CU, and expressed as a parabolic function. Similarly, the inverse of the
number of days until 20% bud break or the rate of bud growth was also
plotted against the above variables. The area under these parabolas was
statistically analysed using the CANDISC procedure of SAS Release 8.1.
Once again, the groupings of the CANDISC procedure were more or less
consistent with the preliminary groupings obtained with the phenoligical
classification method.
Due to the nature of the scientific method used in this study, there is room for
a certain margin of experimental error to occur, which could account for the
misclassifications by the CANDISC procedure, when performed on the 2001
season's data. It can be concluded that the phenological method of
classifying the selections, as currently used in the breeding programme, is
consistent with the results of the scientific method described here. Therefore,
it is recommended that the phenological method be used in future to classify
the selections according to chilling requirement (CR), as this method is less
time consuming and less costly to perform.
Finally the outcome of the analysis of one season's data was used as
calibration data against which the other season's data was tested and the
consistency of the results, using one set of discriminant functions, was tested.
It can be concluded that a unique set of discriminant functions is necessary
for each winter season to accurately classify selections according to CR with
the CANDISC procedure. / AFRIKAANSE OPSOMMING: 'n Studie van dormansie en koue behoefte van perskes en nektariens
Gebrekkige winterkoue is 'n gegewe in die meeste Suid-Afrikaanse perske en
nektarien-produksie-streke. Om die gevolge hiervan aan te spreek, is 'n
konvensionele teelprogram tot stand gebring om verbeterde steenvrug
cultivars te ontwikkel met voortreflike pomologiese eienskappe en wat
aangepas is by die plaaslike klimaatstoestande. Hierdie studie is geloods om
die akkuraatheid van die wetenskaplike metode, genoem die fenologiese
klassifikasie metode, soos tans deur die teelprogram gebruik, waarvolgens
seleksies volgens kouebehoefte geklassifiseer word, te toets.
Vanaf April 2000 en Mei 2001 tot en met die daaropvolgende lente, is 20
eenjaar-oue lote van 30 perske en nektatrien seleksies twee weekliks in 'n
fase 2 evaluasie boord op Bien Donné Proefplaas, te Simondium in die Wes-
Kaap (34° S) versamel. AI die seleksies was vooraf op grond van fenologiese
waarnemings geklassifiseer in kategorieë van hoog (>800 Utah koue-eenhede
[CU]), medium (400-800 CU) of laag «400CU) ten op sigte van kouebehoefte.
Hiervolgens val ses van die seleksies wat in die studie ingesluit is
in die hoë-, drie in die medium- en 21 in die lae kategorie. Lote van elke
seleksie is voorberei en in twee herhalings gebondel, waarna dit geforseer is
teen 25° C met deurlopende beligting totdat geen verdere knopbreek vir 'n
periode van vyf dae voorgekom het nie, waarna die lote verwyder is. CU in
die boord is volgens die Utah en Infruitec modelle bereken. Die aantal uur
onder 12° C en onder 7° C is ook bereken. Die aantal dae wat dit elke
seleksie geneem het om 20% vegetatiewe en 20% reproduktiewe knopbreek
te bereik is bereken en geplot teenoor die dag van die jaar, Utah CU, Infruitec
CU, aantal uur onder 12° C en aantal uur onder 7° C en uitgedruk as 'n
paraboliese funksie. Die inverse van die aantal dae tot 20% knopbreek, of die
tempo van knopbreek, is op soortgelyke wyse geplot teenoor al bogenoemde
veranderlikes. Die oppervlakte onder die parabole is statisties ontleed met
behulp van die CANDISC prosedure van die SAS program (Vrystelling 8.1).
Die groeperings wat met die CANDISC prosedure verkry is het grootliks ooreengestem met die groeperings volgens die fenologiese klassifikasie
metode.
Op 16 Mei 2000 en 15 Mei 2001, is 100 eenjaar-oue lote van dieselfde perske
en nektarien seleksies in die evaluasie boord op Bien Donné versamel,
toegedraai in klam handdoekpapier, in swart plastiek sakke geplaas en in 'n
koelkamer geplaas waarvan die temperatuur konstant gehou is tussen die
grense van 4° C en T" C. Twee herhalings van 10 lote elk, van elke seleksie,
is twee weekliks voorberei en geforseer by 25° C met deurlopende beligting
totdat geen verdere knopbreek vir 'n periode van vyf dae plaasgevind het nie,
waarna die lote verwyder is. Op elke oordragdatum is die aantal CU, wat in
die koelkamer geakkumuleer het, volgens die Utah model bereken. Die
aantal dae wat dit elke seleksie geneem het om 20% vegetatiewe knopbreek
te bereik is bereken en geplot teenoor die Utah CU en uitgedruk as 'n
paraboliese funksie. Die inverse van die aantal dae tot 20% knopbreek , dus
die tempo van groei, is op soortgelyke wyse bererken en geplot teenoor
bogenoemde veranderlikes. Die oppervlak onder die paraboliese funksies is
statisties ontleed met behulp van die CANDISC procedure. Die groeperings
van die CANDISC prosedure het weereens grootliks ooreengestem met die
groeperings wat met die fenologiese metode van klassifikasie verkry is.
Weens die aard van die wetenskaplike metode wat tydens hierdie studie
gebruik is, kom daar 'n sekere mate van eksperimentele fout voor, wat
moontlik die misklassifikasies van die CANDISC prosedure kan verklaar,
wanneer dit op die 2001 seisoen se data uitgevoer word. Die gevolgtrekking
kan gemaak word dat die resultate van die fenologiese metode, soos dit tans
deur die teelprogram gebruik word, ooreenstem met die resultate wat deur die
wetenskaplike metode, wat hier beskryf word, verkry is. Dus word daar
aanbeveel dat die fenologiese metode in die toekoms gebruik word om die
seleksies te klassifiseer volgens koue behoefte (CR), aangesien hierdie
metode minder tyd in beslag neem en goedkoper is om uit te voer.
Laastens is die resultaat van die analise van een seisoen se data gebruik as
kalibrasiedata waarteen die data van die ander seisoen getoets is om so ooreenstemmendheid van die resultate te toets as slegs een stel diskriminant
funksies gebruik word. Die slotsom was dat 'n unieke stel
diskriminantfunksies nodig is vir elke winter seisoen om die seleksies
akkuraat met behulp van die CANDISC prosedure volgens koue-behoefte te
klassifiseer.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/49861 |
| Date | 12 1900 |
| Creators | Pieterse, Werner-Marcel |
| Contributors | Theron, K. I., Cook, N. C., 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 | 95 p. : ill. |
| Rights | Stellenbosch University |
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