Browsing by Author "Theron, K. I."
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- ItemAssessment of pre-harvest physiological infiltration methods for predicting commercial bitter pit in 'Braeburn' and 'Golden Delicious'(2010) Lotze, Elm.; Theron, K. I.; Joubert, J.Although management practices are followed to reduce the incidence of bitter pit in commercial orchards, this defect still surfaces and causes serious problems with fruit quality that lead to losses in especially export produce. Current methods e.g. fruit mineral analysis, magnesium (Mg) infiltration and ethylene forcing that were developed to predict bitter pit incidence, vary in reliability. However, there is still a need to predict bitter pit incidence, before it becomes visible. The effectiveness of ethylene forcing and Mg infiltration-were assessed under local conditions for 'Braeburn' and 'Golden Delicious' apples. The correlation coefficients for the two methods were compared, as well as the correlations between the bitter pit-like incidence induced by the individual methods and actual bitter pit after storage. During the first season, the coefficient determination for Mg infiltration and actual bitter pit (R2 = 0.45) was higher compared to the coefficient for ethylene forcing and actual bitter pit (R2= 0.13). The R2 for the linear relationship between bitter pit incidence with Mg-infiltration and ethylene forcing was 0.43. The actual bitter pit incidence per season influenced the accuracy of the methods.
- ItemChemical and phytochemical properties and antioxidant activities of three pomegranate cultivars grown in South Africa(Springer Verlag, 2011-02) Fawole, Olaniyi A.; Opara, Umezuruike Linus; Theron, K. I.A comparative study of chemical contents and antioxidant activities of three pomegranate cultivars (‘Arakta’, ‘Bhagwa’ and ‘Ruby’) grown in South Africa was conducted. Fresh pomegranate juice (PJ) of each cultivar were assessed for soluble solid contents (SSCs), pH and titratable acidity (TA), while extracted juice samples were evaluated for total phenolic (TP), including total tannins (TT), proanthocyanidins (Pcy), total flavonoids, anthocyanins and gallic acids (GA) using spectrophotometric methods. The antioxidant properties of the juice samples were evaluated against stable 2, 2– diphenyl–1–picryl hydrazyl, as well as in ferric reducing ability of plasma (FRAP) and QuantiChrom™ (TAC) antioxidant assays. There were significant differences in the chemical properties of the cultivars. SSC, TA and pH varied between the range of 14.07–15.10 °Brix, 0.22– 0.28 g/100 ml and 3.32–3.64, respectively. ‘Bhagwa’ had the highest TP (449.9 mg/100 ml), 1.3-fold and 1.6-fold higher than ‘Arakta’ and ‘Ruby’, respectively. The strongest total antioxidant activity was exhibited by ‘Bhagwa’ with an antioxidant index of 95.7%, followed by ‘Arakta’ (93.2%) and ‘Ruby’ (79.9%). PJ phytochemical properties (TP, TT, Pcy, GA) and antioxidant activity (FRAP and TAC) were significantly correlated (r2= 0.509–0.885) with each other.
- ItemThe effect of different rates of prohexadione-calcium and girdling on shoot growth and fruit quality when applied to different pear cultivars(International Society for Horticultural Science -- ISHS, 2005-04) Meintjes, J. J.; Stassen, P. J. C.; Theron, K. I.Prohexadione-Calcium (P-Ca) is a promising new shoot growth retardant that is already registered on apples in North America (Apogee®) and in Europe (Regalis®). This gibberellin biosynthesis inhibitor with limited persistence and low toxicity was tested on five Pyrus communis cultivars: ‘Rosemarie’, ‘Flamingo’, ‘Early Bon Chretien’, ‘Packham’s Triumph’ and ‘Forelle’. P-Ca was able to reduce shoot growth in all of the cultivars, but there was a marked difference in sensitivity towards different rates of P-Ca between the different cultivars. Fruit set was improved in ‘Rosemarie’, ‘Forelle’ and ‘Early Bon Chretien’, which led to a decrease in final fruit size of ‘Rosemarie’. P-Ca caused a decrease in return bloom in ‘Packham’s Triumph’ and ‘Forelle’. Girdling only reduced shoot growth in ‘Forelle’ but did not improve fruit set in any of the cultivars. Girdling improved final fruit weight of ‘Flamingo’, increased fruit length in ‘Early Bon Chretien’ and increased return bloom in all of the cultivars except ‘Packham’s Triumph’. The five cultivars are categorised according to their sensitivity towards P-Ca: ‘Rosemarie’ > ‘Flamingo’ = ‘Early Bon Chretien’ = ‘Packham’s Triumph’ > ‘Forelle’.
- ItemEffect of pruning severity and branch quality on fruit set and fruit dry weight of Packham's Triumph pears (Pyrus communis L)(International Society for Horticultural Science -- ISHS, 2005-04) Reynolds, L. P.; Jacobs, G.; Theron, K. I.The effect of dormant pruning and the quality of 2-year-old bearing units(BU) on fruit set and mean fruit dry weight of ‘Packham’s Triumph’ pears wasdetermined during the 2002/03 season. Fruit set on short BU (28 cm long) was 20percent higher and mean fruit dry weight were 20 percent more than for long BUs(56 cm). On thick BU (14 mm basal diameter) 70 percent more fruit set than on thinBU (8 mm) and mean fruit dry weight was 20 percent more than on thick BU.
- ItemThe effect of scoring during flower induction or the initiation phase on return bloom in Pyrus communis L(International Society for Horticultural Science -- ISHS, 2005-04) Reynolds, L. P.; Jacobs, G.; Theron, K. I.The influence of scoring during the flower induction phase was investigated. Pear trees, Pyrus communis L. cv. Doyenne du Comice, Forelle and Rosemarie were used in the study, conducted in the Western Cape, South Africa. The yield of ‘Doyenne du Comice’ increased by 38% in scored trees compared to the control. The increase in yield was due to 50% more fruits on the scored trees than on the control trees. The increase in fruit number per tree was due to a higher percentage of reproductive buds per tree and the improved quality of these buds. Scoring of ‘Rosemarie’ at the correct time resulted in a 40% increase in reproductive buds. Scoring disrupts basipetal transport in the phloem, which results in the removal of apical dominance and an increase in root-derived cytokinins. More meristems can respond to inductive conditions and the higher concentration of cytokinins during inductive conditions leads to improved flower quality.
- ItemEffects of early winter gibberellic acid and mineral oil applications on flowering of young non-bearing Clementine (Citrus reticulata Blanco.) and Satsuma (Citrus unshiu Marc.) trees(2001) Mudzunga, J.; Theron, K. I.; Rabe, E.Gibberellic acid (GA₃) and heavy mineral oil (Bae-oil) treat ments, either individually or in combination, applied during the flower initiation period in early winter (April to July) were evalu ated as a means to reduce flowering levels in young non-bear ing citrus trees over four seasons (five trials). GA₃ and mineral oil, either individually or in combination applied late in May to late June, markedly reduced flowering. Peak response ib-Gf.J coincided with a significant reduction in bud sprouting. The winter application of GA₃, specifically, and possibly in combi nation with mineral oil to inhibit flowering, and enhance early vegetative growth on young trees may be utilised commer cially. Results from these experime_nts suggest that optimum application time seems to be during late May to late July. How ever, this time is likely to vary somewhat from year to year depending on prevailing climatic condit_ions.
- ItemEvaluating pre-harvest foliar calcium applications to increase fruit calcium and reduce bitter pit in 'Golden Delicious' apples(2008) Lotze, Elmi; Joubert, J.; Theron, K. I.In all major apple producing countries, applications of foliar calcium (Ca) products to increase fruit Ca content and reduce the incidence of bitter pit in apples are used. Calcium nitrate (Ca(NO3)2), Calcimax and Ca acetate were applied, commencing at three different developmental stages (early, mid and late) of fruit growth. Late Ca(NO3)2 (80 days after full bloom (dafb)) applications increased the Ca content of fruit at harvest more than early (six dafb) and mid (40 dafb) applications. There was a trend towards an increase in bitter pit from early to late applications of Ca(NO3)2 and Calcimax, confirming previous results obtained when applying only Ca(NO3)2. In spite of the very low incidences of bitter pit during these seasons (less than 7%), significant differences between treatments were found between Ca(NO3)2 Mid and other treatments in 2004/2005, as well as Ca(NO3)2 and Calcimax Early and other treatments in 2005/2006. Ca acetate applications did not show any trends in fruit Ca content or bitter pit incidence when applied during the three stages. Thus, products may differ in efficiency of Ca absorption and effectiveness in decreasing bitter pit in fruit when applied during different developmental stages. © 2008 Elsevier B.V. All rights reserved.
- ItemHarvest and post-harvest apple fruit quality following applications of kaolin particle film in South African orchards(2006) Wand, S. J. E.; Theron, K. I.; Ackerman, J.; Marais, S. J. S.Sunburn on apples in the Western Cape region of South Africa can result in yield losses of up to 50%. Application of kaolin-based particle film (Surround® WP) increases leaf and fruit surface reflectivity, thus potentially reducing heat load and sunburn. Trials were performed during 2002/2003 and 2003/2004 to assess the effectiveness of kaolin particle film in controlling sunburn on 'Granny Smith', 'Braeburn', 'Fuji', 'Royal Gala' and 'Cripps' Pink' apples. Fruit quality and ripening were monitored following 1-4 months in regular atmosphere cold storage at -0.5°C. Sunburn on exposed fruit was significantly reduced in 'Granny Smith' and 'Fuji'. Kaolin treatment improved fruit colour of 'Granny Smith' and 'Royal Gala', and delayed starch conversion in 'Granny Smith' at harvest and during the early storage period but not thereafter. Incidence of watercore at harvest was significantly reduced by kaolin treatment, but this disorder disappeared during cold storage in both treatments. There were no effects on skin anthocyanin or phenolic concentrations in any cultivar compared to unsprayed fruit. © 2005 Elsevier B.V. All rights reserved.
- ItemPhysiological and horticultural studies on the phenomenon of apical dominance in apple trees(Stellenbosch : Stellenbosch University, 1984) Theron, K. I.; Stellenbosch University. Faculty of . Dept. of .
- ItemReproductive bud development of pears (Pyrus communis L.) with emphasis on the bourse shoot(International Society for Horticultural Science -- ISHS, 2005-04) Reynolds, L. P.; Jacobs, G.; Theron, K. I.For consistent yields in pear fruit production, knowledge of the development of the reproductive bud is required. The aim of this study was to gain more insight into the development of the primordial bourse shoot. The bourse shoot is important because of the ability of a bourse shoot to become reproductive, which can lead to bourse-over-bourse bearing. The progression of reproductive bud development in ‘Forelle’ and ‘Rosemarie’ was studied from primordial bourse shoot initiation until dormancy the following season. The primordial bourse shoot development in the reproductive bud before full bloom is poorly documented. The primordial bourse shoot was initiated in February 2003. The primordial bourse shoot development progressed during dormancy with a plastochron length of 60 to 80 days in June. The rate of preformed leaf formation increased rapidly until August, when the plastochron was 5 days. ‘Rosemarie’s’ primordial bourse shoot development was more advanced at full bloom. This is one of the possible reasons for the higher bourse-over-bourse bearing habit of the cultivar. The number of leaves of the bourse shoot of ‘Rosemarie’ was significantly greater than with ‘Forelle’, which has a low tendency for bourse-over-bourse bearing. Flower initiation of the terminal bud of the bourse shoot was 56 and 77 days after full bloom for ‘Forelle’ and ‘Rosemarie’, respectively. Initiation was well correlated with the cessation of bourse shoot growth. An increase in mitotic activity occurred during flower differentiation of the terminal bourse bud, with a peak of floral appendage formation during December and January. From February until dormancy enlargement of the floral parts took place.
- ItemStudies on the growth and development of Nerine bowdenii W. Watson (Amaryllidaceae)(Stellenbosch : Stellenbosch University, 1993) Theron, K. I.; Stellenbosch University. Faculty of . Dept. of .