Thesis (MScAgric)--University of Stellenbosch, 2002. / ENGLISH ABSTRACT: In order to study the dormancy of apple buds in conditions of inadequate chilling a number of trails were done during 2000 and 2001. Year-old, unbranched shoots of 'Royal Gala', 'Braeburn', 'Cripps' Pink' and 'Granny Smith' apple were harvested randomly from bearing commercial orchards in the Koue Bokkeveld [33°S, 945m, ca.1300 Utah model chili units (CU)) and Elgin (34 "S, 305m, ca.750CU) regions of the Western Cape, South Africa, respectively. Shoots were chilled at 5-rC. Two replicate bundles were removed from the cold room, prepared and forced at 25°C with continuous illumination until budburst had occurred on at least 25% of the shoots per bundle. The change in the rate of budburst over time was calculated for each orchard and to this response; either a linear or a quadratic function was fitted. Poorly correlated variables were selected that best describe these functions. Using these variables, the orchards were separated into cluster groupings that represented a dormancy pattern. The first split separated the lower chilling requirement cultivars from the higher cultivars. The second and third split separated the orchards according to area differences. The clusters representing the warmer area orchards initially entered deeper into dormancy before exiting. The clusters for the colder area immediately had an increased budburst rate. This data confirm that the chilling requirement includes a period of dormancy induction. An important genotype and environment interaction, other than cold unit accumulation, was observed that could be responsible for terminating bud dormancy. Terminal apple buds from 'Royal Gala' Braeburn', 'Cripps' Pink' and 'Granny Smith' apples were cut from orchards in the Koue Bokkeveld and Elgin regions of the Western Cape, South Africa. Buds were harvested every two weeks during the dormant period. The buds were cut in half and leaf scales removed before the water potential were measured. Fresh and dry weights of the buds were also determined. The data presented confirms the changes in availability of free water in dormant buds and that it could be measured in this way. A definite influence of temperature was illustrated. The water potential from buds in a cold production area (Koue Bokkeveld) behaved more "normally" - water is in a bound form during most of the winter and change to an available form later in winter - whereas buds from a warmer production area did not change much in water potential or content. In the trial, two-year-old proleptic-branched shoots, ca. 500mm long, were selected from a 'Royal Gala' orchard in the Koue Bokkeveld region in the Western Cape, South Africa. During the dormancy period of 2000, shoots received two cold treatments; chilling in a cold room at 5-7°C and the natural chilling received in the field. In 2001, the trail was repeated, but only with the field chilling. The shoots received five dormant pruning treatments: control (not pruned), pruning back to the fourth lateral (heading) before or after chilling; and removal of the 2nd and 3rd laterals (thinning) before or after chilling. After pruning and chilling treatments, the shoots were removed from the orchard or cold room every two weeks and forced in a growth chamber. The rate of bud burst (1/days to 50% bud burst) was calculated for the terminal buds of the lateral shoots. Laterals were categorisation according to position: the terminal extension shoot, the 4th lateral, and all other laterals were pooled. Removing distal tissue by pruning (heading more than thinning) promoted bud burst on laterals. Pruning before chilling was more effective than after chilling. The correlative phenomena that inhibit bud burst on proximal shoots within two-yearold branches were manipulated by pruning. The branching response of one-year-old unbranched shoots, 0.5m long, from 'Royal Gala' and 'Cripps' Pink' apple and 'Rosemary' pear were studied after physical manipulation treatments. Shoots for treatment a to d were re-orientated from either a horizontal or vertical position or left in the original position as control, treatment e to h involved the same re-orientation of shoots and were headed. The amount of growth (in mm) from each node was recorded as well as the position from the terminal bud. The 'Cripps' Pink' had a definite shift in the acrotonic branching pattern (for headed and unheaded), towards a more basitonic response. The reduced effect on 'Royal Gala' and 'Rosemary' suggest a difference in genotype response to the treatments as well as time of treatment. / AFRIKAANSE OPSOMMING: Ter wille van die navorsing oor die invloed van gebrekige koue op dormansie van apple knoppe en die gepaardgaande probleme is 'n reeks proewe gedoen gedurende 2000 en 2001. Jaar oue onvertakte lote van 'Royal Gala', 'Braeburn' , 'Cripps' Pink' en 'Granny Smith' appels is ewekansig geoes vanaf komersieële boorde in die Koue Bokkeveld [33°S, 945m, ca.1300 Utah koue eenhede (CU)] en Elgin (34°S, 305m, ca.750CU) omgewings van die Wes Kaap , Suid Afrika. Die lote is daarna verkoel gehou by 5- 7°C. Lote is elke twee weke vanuit die koue kamer geneem en geforseer met 25°C en deurlopend belig. Die aantal knoppe wat groenpunt bereik het is genoteer totdat 25% van die lote begin bot. Die verandering oor tyd vir elke boord is bereken en 'n liniëre of kwadratiese funksie is daarop gepas. Swak gekorreleerde waardes is gekies wat die funksies die beste beskryf. D.m.v hierdie die waardes is die boorde in groepe ingedeel wat 'n dormansie patroon verteenwoordig. Na die eerste vedeeling is die hoë en lae koue behoefte kultivars geskei. In opvolgende verdelings is die boorde verder in die twee areas geskei met elk 'n spesifieke dormansie patroon. Die groepe wat die warmer area se boorde bevat het aanvanklik dieper in dormansie in beweeg voor dit 'n styging in groei potensiaal getoon het. Die groepe vanaf die kouer produksie area het onmiddelik 'n verhooging in bot tempo getoon. Die data bevestig dat 'n koue behoefte 'n periode van dormansie induksie insluit. 'n Belangrike kultivaromgewing- interaksie, ten spyte van koue eenhede akkumulasie, is waargeneem wat verantwoordlik kan wees vir beëindiging van dormansie. Om die verandering van water status in dormante appel knoppe te bestudeer, was die volgende proef uitgevoer. Terminale apple knoppe van dieselfde vier kultivars en vanaf die selfde twee areas in die Wes Kaap as bogenoemde, is elke tweede week gedurende die winter 2001 gesny vanaf komersieële boorde. Daarna is die knoppe middel deur gesny en die skudblare verwyder voor die vars massa gemeet en daarna die waterpotensiaal bepaal is. Die data het bevestig dat daar veranderings in beskikbaarheid van vry water in dormante knoppe gedurende dormansie plaasvind. 'n Definitiewe invloed van temperatuur op waterpotensiaal is geïllustreer. Die waterpotensiaal van knoppe in die kouer produksie area toon 'n meer normale respons (gedurende die winter is die water in 'n gebonde vorm, wat later in die winter na vry water verander). Daar teenoor is daar in die knoppe van die warm produksie area nie veel verandering in waterpotensiaal of water massa getoon nie. Gedurende die winter van 2000 is twee jaar oue proleptiese vertakte 'Royal Gala' lote, ongeveer 500mm lank, gekies vanaf 'n boord in die Koue Bokkeveld. Die lote is verdeel en het twee koue behandelings ontvang. Koue kamer by 5-T'C en natuurlike koue in die boord. In 2001 is net die natuurlike koue behandeling herhaal. Daar is vyf dormante snoei behandeling op die lote gedoen; kontrole (geen), snoei terug tot die vierde lateraal voor en na die koue; verwydering van die 2de en 3de laterale voor en na koue. Na koue en snoei is die lote verwyder en in die groeikamer geforseer by 25°C en met konstante illuminasie. Die tempo waarteen die laterale gebot het is bereken (1\dae to 50% groen punt) waarna die laterale in klasse gedeel is; terminale knop, die vierde lateraal en die res van die laterale saam. Verwydering van distale weefsel d.m.V. snoei verhoog die tempo waarteen laterale knoppe groenpunt bereik. Snoei voor die koue behandeling was meer effektief as daarna. Die korrelatiewe fenomeen wat bot inhibeer van proksimale lote kan gemanipuleer word in die twee jaar apple loot. Die vertakkings gedrag van een jaar oue onvertakte 'Royal Gala', 'Cripps' Pink' apple en 'Rosemary' peer lote, 0.5m lank, is ondersoek na fisiese manipulasies gedoen is gedurende mid winter 2000. Vir die eerste vier behandelings (a,b,c,d) is die lote in 'n horisontale of vertikale possisie gelos as kontrole, of horisontale of vertikale gebuig en daar gehou d.m.v. binddraad. Behandelings e tot h het dieselfde behels maar die lote is ook nog in die helfte deur gesny (getop). Die hoeveelheid groei in mm vir elke node is aangeteken asook die posisie vanaf die terminale knop. Die 'Cripps' Pink' het 'n definitiewe veskuiwing vanaf 'n akrotoniese na 'n basitoniese vertakkingspatroon getoon. Die reaksies op die manipulasies of die gebrek daaraan ('Royal Gala' en 'Rosemary' ) kan 'n aanduiding wees dat genotipes verskillend reageer op die behandelings asook op die tyd wat dit gedoen was.

Thesis (MScAgric)--University of Stellenbosch, 2001. / ENGLISH ABSTRACT: Delayed foliation is commonly observed in apple and pear producing countries with warm and/or short winter climates, resulting in less synchronised budburst, of fewer buds and reduced yield. Applications of rest-breaking agents minimise the symptoms of delayed foliation. According to chilling models used in fruit producing areas of the world, the climate of South Africa is not suitable for deciduous fruit production, however fruit has been successfully produced here for a long time. This study aimed to quantify the effects of freezing temperatures, different chilling temperatures and the period of chilling, to obtain a better knowledge of bud dormancy release on apple and pear shoots. The chilling period was the most important factor influencing the progression of dormancy. While in some cases the chilling temperature and the freeze treatment effects were significant, the contribution to differences in the progression of dormancy was negligible. Our findings indicate that currently used chilling models should emphasise the time of exposure to low temperatures more than the difference in temperatures between I to ro-c. The South African apple and pear industry made good progress in moving towards high density plantings, but large variation in soil types, non-optimum growing conditions, replant situations and a lack experience with dwarfing rootstocks limited further development. However, there is sti II an urgency to obtain higher early yields of good quality fruit applying the most efficient production practices. We aimed to quantify the field performance of locally available apple and pear rootstocks, in particular from data outside of previously reported local trials, as well as early production of newly planted trials. Information obtained form the industry indicates that BPI and BP3 are the preferred pear rootstocks. From production records of 'Packham's Triumph' pears, it appeared that BP3 and OHxF97 produced the best yields compared to the other rootstocks. Production of 'Doyenne du Cornice' was the best on QA and BP3. In newly planted 'Rosemarie', 'Flamingo', and 'Forelle' trials, different rootstocks were evaluated. 'Rosemarie' showed indications 01 incompatibility with QA and QC5 I, but on BPI and QA with a 'Beurre Hardy' interstock produced good initial yields although BPI induced slightly larger trees. 'Flamingo' on QA and QC51 produced the best yields. 'Forelle' on BPI, BP3, and QA produced similar yields up to the 4th leaf. For apples M793 seems to be the preferred rootstock in the South African industry. From production records of 'Golden Delicious' and 'Granny Smith' apples, it appeared that M793 and MM 106 produced the best yields when compared to Seedling rootstock. In a 'Cripps' Pink' trial, MMI09, M793 and M25 were more vigorous than M7, MMlll and MMI06. MMI06 was cumulatively, over four years from planting, the most yield efficient, although no consistent trend regarding fruit quality was observed between the rootstocks evaluated. / AFRIKAANSE OPSOMMING: Vertraagde bot word algemeen opgemerk in appel en peer produserende lande met n' warm enlof kort winter klimaat, wat veroorsaak dat bot van minder knoppe, meer ongelyk plaasvind en gevolglik lei tot swakker opbrengste. Toediening van rus-breek middels beperk die simptome van vertraagde bot. Volgens koue modelle wat in vrugte produserende areas in die wereld gebruik word, is Suid Afrika se klimaat nie geskik vir die verbouing van sagtevrugte nie alhoewel sagtevrugte al vir n lang tyd met groot sukses hier verbou word. Hierdie studie is daarop gemik om die effek van vries temperature, verskillende koue temperature en die periode van koue op die vrystelling van dormansie op knoppe van appel en peer lote te kwantifiseer. Die peri ode van koue was die mees belangrikste faktor wat die ontwikkeling van dormansie beinvloed het. In sommige gevalle was die effek van die koue temperature betekenisvol, maar die bydrae tot die verskille in die ontwikkeling van dormansie was weglaatbaar klein. Ons bevindinge dui aan dat die huidige koue modelle wat gebruik word, meer klem moet le op die periode van blootstelling aan koue as aan die effek van verski llende temperature tussen 1 en 10°e. Die Suid Afrikaanse appel en peer bedryf het goeie vordering in die beweging na hoe digtheid aanplantings gemaak, maar groot verskille in grond tipes, sub-optimale groei toestande, herplant probleme en n' tekort aan ondervinding met dwergende onderstamme het verdere ontwikkeling beperk. Ten spyte hiervan is daar steeds n' dringendheid om hcer produksies, van goeie kwaliteit vrugte so vroeg as moontlik te kry deur die toepassing van die mees effektiewe produksie praktyke. Ons het gepoog om die prestasie van plaaslik beskikbare appel en peer onderstamme te kwantifiseer, in besonder deur data wat nog nie van tevore oor verslag gedoen is nie en ook deur te meld van vroee produksies op nuut aangeplante proewe. lnformasie uit die bedryf het aangedui dat BP 1 en BP3 die voorkeur peer onderstamme is. Deur na die produksie geskiedenis van 'Packham's Truimph' pere te kyk kom dit voor of BP3 en OHxF97 die beste produksies in vergelyking met die ander onderstamme gelewer het. Die produksie van 'Doyenne du Com ice' was die beste op QA en BP3. In nuut geplante 'Rosemarie', 'Flamingo', en 'Forelle' pro ev e was verskillende onderstammc gecvalueer. 'Rosemarie' het tekens van onverenigbaarheid getoon met QA en Q 51, maar op BP 1 en QA met n 'Beurre Hardy' tussenstam het 'Rosemarie' goeie aanvanklike opbrengste gel ewer, al was bome op BP 1 effens grater. 'Flamingo' op QA en QCS 1 het die beste opbrengste gelewer. 'Forelle' op BP 1, BP3, en QA het ongeveer ewe veel tot die 4dc blad geproduseer. By appels is M793 die voorkeur onderstam van die Suid-Afrikaanse appel bedryf. M793 en MM 106 gee beter opbrengste as Saailing onderstam wanner die produksie geskiedenis van 'Golden Delicious' en 'Granny Smith' appels evalueer word. In n' 'Cripps' Pink' proefwas MMI09, M793 en M2S meer groeikragtig as M7, MMlil en MMI06. MM I 06 het kumulatief meer geproduseer en was ook meer produsie doeltreffend tot en met die 4de blad na plant. Daar was egter geen konstante neiging rakende vrug kwaliteit tussen die verskillende onderstamme wat getoets is nie.