Thesis (MScAgric)--University of Stellenbosch, 2000. / ENGLISH ABSTRACT: Ineffective pollination of the main cultivar with the pollinator cultivar is due to either an incompatibility problem between the main and pollinator cultivar, or because the flowering times of the main and pollinator cultivars do not overlap adequately. Three trials were conducted to try and find a more effective way to determine cultivar compatibility and to group cultivars together according to their budburst reaction to chilling. Most apple cultivars are self-incompatible and need cross-pollination for fruit set. Due to differences in the genetically defined fertilisation compatibility between the pollen from the male parent (pollinator) and the egg cell of the female parent, various apple pollinators differ in their ability to set fruit with viable seed. Fruit weight and size are positively correlated with seed set although it has been found that the pollinator can have a direct influence on fruit quality. 'African Red' apple trees on M7 rootstock in an evaluation block on a commercial farm in the Koue Bokkeveld region (32°55'N 19°27'E, Mediterranean climate, ;::::1060Utah chill units, and ;::::530mm rainfall annually; altitude 966 m) were used to assess the influence of 5 pollinators ('Granny Smith', 'Winter Banana', 'Cripps' Pink', 'Cripps' Red' and 'Simpson Crab') on fruit set, fruit weight and length and diameter. The degree to which 'African Red' is self-compatible was also assessed and the effect of flowering position ("king" vs. lateral) on fruit quality was determined. None of the pollinators showed a significantly higher fruit set. No differences in fruit set were found between the "king" and lateral flowering positions. No significant differences were found in the average number or weight of well developed seeds between pollinators. In both years fruit weight was significantly correlated to seed number for all five pollinator cultivars. In 1998 'Simpson crab' gave fruit that were significantly more elongated than those of 'Cripps' Pink'. 'African Red' is highly self incompatible. Compatibility assessments that are based on the number of fruit that develop after the flowers ofthe main cultivar had been hand pollinated in field trials are a time-consuming process. Allele-specific PCR amplification for some of the known S-alleles of the incompatibility S-gene (S2, S3, S5, S7 and S9) was carried out to successfully predict the compatibility of genotypes. The results compared well with that found in literature. For all the Malus domestica cultivars tested at least one, but in some instances both alleles of the S-gene were determined. 'Simpson crab' (Malus baccata) did, however, not possess any of the tested S-alleles. One-year-old, ca. 40 mm long shoots of various apple cultivars were selected from commercial orchards in both the Elgin [34°S, 305 m, ca. 750 chill units (CU) (Richardson et al., 1974)] and Koue Bokkeveld (33°S, 945 m, ca. 1300 CU) regions of the Western Cape, South Africa in two consecutive years (1998 and 1999). Shoots were forced at a constant 25°C with continuous illumination after receiving their allocated chill units. The effect of chilling period on the budburst of each cultivar in both regions was estimated by determining, 1) the total proportion of budburst (%Bb), 2) the proportion of shoots with terminal budburst (%TBb), and 3) the rate of budburst [lI(days to 25% budburst)]. It was found that these indices differed significantly between cultivars, and within cultivars between areas, as far as budburst patterns, in reaction to chilling, were concerned. The rate of budburst was the most consistent in describing the reaction of buds to different chilling periods and could be used to group cultivars together according to their budburst reaction to chilling. / AFRIKAANSE OPSOMMING: KRUISBESTUIWINGSBIOLOGIE VAN APPELS MET SPESIALE VERWYSING NA 'AFRICAN RED'. Oneffektiewe kruisbestuiwing III die boord kan toegeskryf word aan Of onverenigbaarheid tussen die hoof- en bestuiwingskultivar Of as gevolg van die blomtyd van die kruisbestuiwer wat nie genoegsaam oorvleuel met die van die hoofkultivar nie. Drie proewe is uitgevoer om 'n meer effektiewe proses daar te stel vir die toets van kultivarverenigbaarheid en om kultivars te probeer groepeer na gelang van hul reaksie op bepaalde hoeveelhede koue. Meeste appelkultivars is selfonverenigbaar en benodig kruisbestuiwing vir genoegsame vrugset. As gevolg van verskille III die geneties gedefinieerde bevrugtingsverenigbaarheid tussen die stuifmeel van die manlike ouer (bestuiwer) en die eiersel van die vroulike ouer (hoofkultivar), verskil bestuiwers in hul vermoë om vrugte met sade te set. Vruggrootte en -massa is positief gekorreleerd met saadset alhoewel dit al gevind is dat die bestuiwer op sig self ook 'n invloed op vrugkwaliteit kan hê. 'African Red' appelbome op M7 onderstamme, in 'n evaluasie blok op 'n kommersiële plaas in die Koue Bokkeveld (32°55'N 19°27'E, Meditereense klimaat, ::::1060 Utah koue eenhede, en ::::530mmjaarlikse reënval; ligging 966 m), is gebruik om die invloed van 5 bestuiwers ('Granny Smith', 'Winter Banana', 'Cripps' Pink', 'Cripps' Red' and 'Simpson Crab') op vrugset, vrugmassa, -lengte en -deursnee oor twee seisoene te bepaal. Die mate waartoe 'African Red' self onverenigbaar is en die effek van blomposisie ("king" vs laterale blom) op vrugkwaliteit is ook bepaal. Geen een van die bestuiwers het vrugset beduidend beïnvloed nie. Ook is daar geen verskille gevind tussen die "king" en laterale blomposisies t.o.v. vrugset nie. Geen beduidende verskille is tussen bestuiwers gevind in die gemiddelde aantal of gewig van volsade geset nie .. In albei jare was die vrugmassa beduidend gekorreleerd met saadset vir al vyf bestuiwerkultivars. In 1998 het 'Simpson Crab' vrugte geset wat beduidend langer was as vrugte wat geset het toe 'Cripps' Pink' as bestuiwer gebruik is. Daar is ook gevind dat 'African Red' hoogs selfonverenigbaar is. Verenigbaarheidstoetse wat gebaseer is op die aantal vruggles wat ontwikkel nadat blomme van die hoofkultivar met die hand bestuif is, is 'n tydsame proses. Allele spesifieke PCR amplifikasie vir bekende S-allele van die onverenigbaarheids S-geen (S2, S3, S5 S7en S9) is suksesvol uitgevoer om die verenigbaarheid van genotipes vooraf te bepaal. Die resultate het goed vergelyk met wat in literatuur gevind is. Vir al die Malus domestica spesies wat getoets is, is ten minste een, en in sommige gevalle twee, van die S-allele gevind. Die blomappel 'Simpson' (Malus baccata) het egter nie een van die vyf S-allele opgelewer nie Een-jaar-oue, 40 mm lang lote van verskeie appelkultivars, is in twee opeenvolgende jare (1998 en 1999) vanuit kommersiële boorde in beide die Elgin [34°S, 305 m, ca. 750 koue eenhede (CU) (Richardson et al., 1974)] and Koue Bokkeveld (33°S, 945 m, ca. 1300 CU) areas van die Wes Kaap gsny. Die lote is geforseer om te bot by 'n konstante temperatuur van 25°C met deurlopende beligting, nadat elke groep lote aan 'n bepaalde hoeveelheid koue blootgestel is. Die effek van koue op bot van elke kultivar in beide areas is bepaal deur, 1) die totale persentasie knoppe wat gebot het, 2) die persentasie terminale knoppe wat gebot het, en 3) die tempo van bot [l/(dae tot 25% bot)] te meet. Daar is gevind dat bo-genoemde parameters beduidend tussen kultivars, en binne kultivars tussen areas, verskil. As 'n beskrywing van die reaksie van knoppe op koue het die tempo van bot die mees konstante resultate oor die twee opeenvolgende seisoene gelewer en kon hierdie parameter gebruik word om kultivars in groepe, na gelang van hul reaksie op koue, in te deel.

Thesis (PhD(Agric) (Horticulture))--Stellenbosch University, 2008. / Lack of winter chilling is a major problem in producing temperate-zone fruit in warm climates. Delayed foliation and protracted bud burst and flowering are the main problems necessitating artificial means to break dormancy. In South Africa (SA), most apple production areas receive insufficient winter chilling, and an annual application of rest breaking (RB) agents is included as standard practice. The most used RB agent in SA was dinitro-o-cresol (DNOC) but its use was discontinued. Hydrogen cyanamide (HC) became the replacement. It has been effective in apple, but variable effects on fruit set, blossom, yield and fruit quality have been reported. Thidiazuron (TDZ) has also shown the ability to break dormancy in apples. Another important practice in apple production is chemical thinning (CT). However, results are highly influenced by the type of chemical, weather conditions, cultivar and blossom pattern. With the increasing efficacy of RB and by identifying its effects on vegetative and reproductive development, it will be possible to determine more effective chemical thinning treatments. The objective of this study was to determine appropriate RB treatments for apple trees in a warm winter climate, identifying their effect on vegetative and reproductive development and the influence on CT efficacy. The research was performed in the Elgin area (34°S, 300 m) SA, over a period of three years, on ‘Golden Delicious’ and ‘Royal Gala’. In evaluating the effect of different HC concentrations and oil, no synergistic or antagonistic effects were observed on budburst and yield. Mineral oil at 4% plus 1 to 2% Dormex® combined were sufficient to break dormancy. Dormex® at 4% (2.08% HC) reduced fruit set and yield. In general, the rest breaking treatments (DNOC, HC and TDZ) enhanced the final vegetative bud burst compared to the control, while reproductive bud burst in 2002 and 2003 was not significantly influenced. The treatments compressed and advanced flowering periods, but this effect was not always evident when the spring was warm. The treatments synchronised flowering on the tree and between the two cultivars. The mixture of 0.245% HC and 4% oil was less effective in terms of increasing bud burst in ‘Royal Gala’ compared to other rest-breaking treatments. The mixture of 0.49% HC and 4% oil effectively compressed and synchronised flowering in ‘Golden Delicious’. TDZ-oil used at the lower rates also increased bud burst and concentrated flowering. However, it appears that after a cooler winter, higher rates could result in an exacerbated bud burst effect with excessive vegetative growth. The rate and timing of TDZ-oil application influenced the reproductive development of apples and therefore fruit quality. In ‘Golden Delicious’ increased fruit set, number of seeds, and reduced fruit russeting appear as beneficial results of TDZ-oil, whereas fruit set and russeting was not affected in ‘Granny Smith’. TDZ-oil, when applied late and at increasing rates, led to an increase in the malformation of calyx cavities, especially when chemical thinning was performed using the cytokinin-like compound benzyladenine. The effect seemed to be cultivar specific, with ‘Golden Delicious’ being the most severely affected. Increased return bloom in response to late TDZ application in ‘Golden Delicious’ and ‘Royal Gala’ appeared to be beneficial.