Thesis (MSc)--Stellenbosch University, 2003. / ENGLISH ABSTRACT: Apple (Malus x domestica Borkh.) is an important horticultural crop worldwide and in the Western
Cape. The income generated from apple and other deciduous fruit production amounts to
approximately 25% of the gross total value of horticultural production in the Western Cape.
Unfortunately diseases and pests adversely affect fruit production in this region.
Woolly apple aphids (Eriosoma lanigerum L. (Hausmann» have a significant effect on the apple
industry in the Western Cape. Damage caused is two-fold, occurring aerially and terrestrially. Insects
colonise the plants, feeding off the phloem sap. Aphid infestation around the root system results in
repeated infestation of the foliage as it serves as a reservoir of aphids. In extreme cases, the apple cores
are also infested, thus affecting the sale of apples. In 1962, Northern Spy was identified as a woolly
apple aphid resistant rootstock and has since then formed the basis for traditional rootstock breeding
programmes. The Er1 gene in Northern Spy confers resistance. According to one report, the natural
resistance of Northern Spy was overcome in South Africa in 1968, but this was not confirmed in an
independent study.
The main objectives of this study was to firstly identify molecular markers more closely linked to the
woolly apple aphid resistance gene, Er1, than existing markers, by applying AFLP technology to
selected seedlings, identified to be resistant by conventional phenotyping. If identified, these markers
can be incorporated into existing breeding programmes. Secondly, previously identified RAPD and
SCAR markers were tested to determine their applicability in local populations for use in breeding
programmes. Ultimately the segregation of the Er1 gene in South African populations can be
determined if tightly linked markers are identified.
Three families were derived from crosses of each of three resistant genotypes, namely Northern Spy,
Rootstock 5 and Russian Seedling and a susceptible cultivar, Braeburn. For the three successive years
of the study, each resistant genotype was allowed to cross-pollinate in isolation with the susceptible
parent. Two hand-pollinated families, Russian Seedling x Liberty and Russian Seedling x Northern
Spy, were also included in the study. The amplified fragment length polymorphism (AFLP) technique
was used in an attempt to identify markers in the resistant and susceptible seedlings. No markers were
identified using this technique. Known sequence characterised amplified regions (SCAR) and random amplified polymorphic DNA (RAPD) markers were used due to their suitability in marker-assisted
selection for woolly apple aphid resistance. Varying results were obtained with these markers and no
conclusive information was acquired with regard to the segregation of the Er] gene in any of these
rootstocks and crosses. This underlines the need for the development of markers that can readily be
applied in local breeding programmes. The identification and integration of such markers will greatly
benefit the local and world wide apple industries. / AFRIKAANSE OPSOMMING: Appels (Malus x domestica Borkh.) is wêreldwyd en in die Wes-Kaap 'n belangrike landbougewas.
Inkomste gegenereer deur appels en ander sagtevrugte vorm bykans 25% van die bruto inkomste uit
vrugte in die Wes-Kaap. Siektes en insekpeste verlaag egter die produksie van vrugte in hierdie streek.
Appelbloedluise (Eriosoma lanigerum L. (Hausmann» het 'n groot invloed op appelproduksie in die
Wes-Kaap. Skade word bogronds en ondergronds aangerig. Insekte koloniseer die plant en leef op
floeëmsap. Besmetting van die wortels lei tot herhaalde besmetting van bogrondse dele aangesien die
insekte aanteelop die wortels. In uiterste gevalle word die vrugte geaffekteer, wat vrug-verkope
beïnvloed. 'Northern Spy' is in 1962 geïdentifiseer as 'n onderstam met natuurlike weerstand teen
appelbloedluis en het vir lank die basis gevorm vir tradisionele telingsprogramme. Weerstand word
verleen deur die Erf geen. Volgens een verslag is die natuurlike weerstand van Northern Spy egter in
1968 in Suid-Afrika oorkom, maar dit is nog nie in 'n onafhanklike studie bevestig word nie.
Die hoof doelstellings van hierdie studie was om eerstens deur middel van die AFLP tegniek
molekulêre merkers te identifiseer wat nouer gekoppel is aan die appelbloedluis weerstandsgeen, En,
as bestaande merkers. Hierdie tegniek is toegepas op saailinge wat deur konvensionele fenotipering
geselekteer is. Indien merkers suksesvol geïdentifiseer is, kan dit in bestaande telingsprogramme
geïntegreer word. Tweedens is bestaande RAPD en SCAR merkers ook getoets om hul toepaslikheid
te bepaal vir gebruik in plaaslike teelprogramme. Oplaas sal die segregasie van die Erf geen in Suid-
Afrikaanse populasies ook deur middel van nou gekoppelde merkers bepaal kan word.
Kruisings van elk van die drie weerstandbiedende genotipes, naamlik 'Northern Spy', 'Rootstock 5' en
'Russian Seedling', en die vatbare kultivar, 'Braeburn' , het drie families daargestel. Elke
weerstandbiedende genotipe is toegelaat om in isolasie te kruisbestuif met die vatbare ouer. Twee
hand-bestuifde families, 'Russian Seedling' x 'Liberty' en 'Russian Seedling' x 'Northern Spy', is in 'n
latere stadium van die studie ingesluit. Die AFLP tegniek is gebruik vir die identifikasie van
polimorfiese merkers tussen vatbare en weerstandbiedende populasies. Geen merkers is egter
geïdentifiseer nie. Bestaande SCAR en RAPD merkers is vervolgens gebruik om te bepaal of hulle
geskik is vir gebruik in merker-bemiddelde seleksie vir appelbloedluis weerstand. Wisselende resultate
is verkry ten opsigte van amplifikasie, herhaalbaarheid van resultate was swak en geen onweerlegbare
bewyse oor die segregasie van die Erfgeen is bekom nie. Dit beklemtoon die noodsaaklikheid om merkers wat geredelik in plaaslike teelprogramme toegepas kan word, te ontwikkel. Die identifikasie
en integrasie van sulke merkers sal die plaaslike en wêreld-wye appel industrieë aansienlik bevoordeel.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/53454 |
| Date | 12 1900 |
| Creators | Christians, Gillian Eleanore |
| Contributors | Wamich, L., Stellenbosch University. Faculty of Science. Dept. of Microbiology. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | xiii, 132 p. : ill. |
| Rights | Stellenbosch University |
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