Thesis (PhD)--Stellenbosch University, 2002. / ENGLISH ABSTRACT: Various experiments were undertaken over a period of five years to investigate the feasibility of initiating a large-scale programme of controlled apple breeding and selection for the improvement of climatic adaptation, using budbreak number (NB) as a practical criterion of selection. NB is preferred to time of budbreak as sole criterion on the grounds that early budbreak is associated with low NB under local conditions. Variation within and between adult and juvenile seedling families was investigated and the genetic control of the traits involved was assessed, as well as direct and correlated responses to selection. In initial experiments different rating criteria for NB as measure of chilling requirement were tested in association with vegetative and reproductive budbreak time and flowering duration, viz, a classification index based on number and distribution of budbreak (pDS grade), an index where shoot length with increased budbreak was included in the index calculation (pDS index) and bud break number expressed as number per 100 cm of shoot length (NB index). Variance analysis (ANOVA and Variance component analyses) detected significant variation within seedling families for budbreak time and NB, but estimates of genetic components of variance between families were generally low. High genetic variance among seedlings within families is most likely due to the high level of heterozygosity in the parental cultivars as is characteristic of vegetatively propagated crops. Intra-class correlation coefficients for clones within and between families indicate moderate genetic determination for NB with broad sense heritabilities around 30 percent. Realized heritabilities calculated from response to two-way truncation selection were between 40 and 60 percent. For budbreak time (reproductive and vegetative), the broad sense heritability averaged around 75 and 69 percent, respectively, indicating a high degree of genetic determination. Significant response to selection for NB of one-year-old shoots of young seedlings and from seedlings grown into adult trees showed that pre-selection for increased budbreak successfully identified seedlings genetically inclined to more and better distribution of budbreak within a set time of 21 days after initial budbreak. Correlated responses indicated additional advantages of practical and horticultural value, viz, uniformity and position of bud break, and the number and length of side shoots. In general, it is concluded from responses to two-way selection that utilizable genetic variance in NB is present within seedling families and thus that selection may successfully be applied as an early screening method for increased budbreak in adult trees. The NB index of intact one-year-old shoots under prevailing sub-optimal winter conditions is therefore proposed as criterion of selection for improvement of climatic adaptation, and combined selection utilizing genetic variation between and within crosses as the selection method. / AFRIKAANSE OPSOMMING: Verskeie proewe is oor 'n periode van vyf jaar uitgevoer om die toepaslikheid van 'n grootskaalse appelteel- en seleksieprogram vir die verbetering van klimaatsaanpasbaarheid te ondersoek met 'aantal knopbreke' (NB) as praktiese seleksiekriterium. NB word verkies bo tyd van knopbreek op grond daarvan dat vroeë knopbreek onder plaaslike toestande met lae NB gepaard gaan. Variasie binne en tussen volwasse en jong saailingfamilies en die genetiese beheer van die betrokke eienskappe is ondersoek, asook direkte en gekoreleerde seleksieresponsie. In die aanvangs-eksperimente is verskillende kriteria vir die kwantifisering van aantal knopbreke getoets as potensiële maatstawwe van die inherente kouebehoefte in appelsaailinge. Die tyd van vegetatiewe en reproduktiewe knopbreek en blomperiode is ook getoets. Die volgende indekse is gebruik: 'n klassifikasie-indeks om die aantal en verspreiding van knopbreke te beskryf (pDS graad), 'n indeks waar die lootlengte, met verhoogde aantal knopbreke, ingesluit is in die berekening van die indekswaarde (PDS indeks), en knopbreke uitgedruk as die aantal per 100 cm lootlengte (NB indeks). Variansie analise (ANOVA en variansie komponent analise) het betekenisvolle variasie binne saailingfamilies aangetoon vir tyd van, en aantal knopbreke. Ramings van genetiese komponente van variansie tussen families was relatief klein. Hoë genetiese variansie tussen saailinge binne families is waarskynlik te wyte aan die hoë vlak van heterosigositeit in die ouergenotipes, wat kenmerkend is van gewasse wat vegetatief voortgeplant word. Intraklas korrelasie koëffisiënte vir klone tussen en binne families het gedui op 'n middelmatige oorerflikheid in die breë sin (ongeveer 30 persent) vir aantal knopbreke. Verhaalde oorerflikhede wat bereken is vanaf responsie op twee-rigting atknottingsseleksie was tussen 40 en 60 persent. Vir tyd van knopbreek (vegetatief en reproduktief) was die breësin oorerflikhede ongeveer 75 en 69 persent, onderskeidelik, wat aanduidend is van 'n hoë graad van genetiese bepaling. Betekenisvolle responsie op seleksie vir NB van jong saailinge en saailingbome wat volwassenheid bereik het toon dat pre-seleksie vir knopbreke saailinge kan identifiseer wat geneties meer knopbreke en 'n beter verspreiding van knoppe binne 'n periode van 21 dae na die eerste knopbreek lewer. Gekorreleerde responsie op seleksie toon 'n addisionele voordeel van praktiese en tuinboukundige belang, naamlik, meer en langer sylote. In opsomming kan dit gestel word dat responsie op twee-rigting seleksie bruikbare genetiese variasie vir NB binne saailingfamilies ontgin het en dat seleksie vir verhoogde aantal knopbreke suksesvol toegepas kan word. Die NB indeks op een-jaar-oue hout word dus voorgestel as seleksiekriterium vir verbetering van klimaatsaanpasbaarheid onder plaaslike sub-optimale wintertoestande, en gekombineerde seleksie "combined selection" wat genetiese variasie binne en tussen kruisings benut as seleksiemetode.

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.