Browsing by Author "Jacobs, G."
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- ItemBerry abscission in vitis vinifera L. cv. Waltham Cross : changes in abscission-related factors during berry development(South African Society for Enology and Viticulture, 2005) Burger, D. A.; Jacobs, G.; Huysamer, M.; Taylor, M. A.During the 1999 season, changes in total soluble solids (TSS), titratable acids (TA), pedicel diameter, berry diameter, berry mass and fruit removal force (FRF) were determined at biweekly intervals from 27 until 111 days after full bloom (DAFB) for Waltham Cross table grapes. In addition, at each assessment stage, grape bunches were detached and held in the dark at about 25°C for 80 h. Thereafter, moisture loss, FRF, berry abscission potential as well as percentage berry abscission were determined. During stages I and II of fruit growth (27 to 54 DAFB), TSS did not change significantly, while TA increased. FRF increased significantly during this early stage of berry development, indicating a strengthening of the abscission zone tissue. During stage III (after 54 DAFB), a decline in FRF occurred, which coincided with a perceptible increase in TSS and a decrease in TA. Berry mass increased significantly from 27 to 111 DAFB. Pedicel diameter only increased significantly for the period 27 to 41 DAFB, while berry diameter increased significantly for the period 27 to 97 DAFB. Grapes sampled at 27 DAFB had a significantly lower FRF and significantly higher levels of berry abscission and moisture loss after the 80-hour period in the dark, compared with grapes sampled at a later stage. At 27 DAFB, the abscission zone developed between the pedicel and the rachis, thereafter it developed between the pedicel and the berry. Although FRF did not change significantly as berries ripened (from 83 to 111 DAFB), abscission potential and percentage berry abscission were significantly higher for grapes harvested at 83 DAFB at a TSS of 12.3°Brix than for grapes harvested more mature, at a higher TSS. Moisture loss correlated significantly (P<0.0001) with berry abscission, with a correlation coefficient of 0.84. Berry abscission also correlated significantly (P<0.0001) with abscission potential, pedicel and berry diameter, FRF (at sampling), FRF (after 80 h) and berry mass, but not with TSS or TA.
- 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.
- ItemThe influence of storage duration and elevation of storage temperature on the development of berry split and berry abscission in vitis vinifera L. cv. Thompson seedless table grapes(South African Society for Enology and Viticulture, 2005) Burger, D. A.; Jacobs, G.; Huysamer, M.; Taylor, M. A.Thompson Seedless grapes, packed in non-perforated low density polyethylene bags, were cold stored at -0.5°C and RH 83% for 0, 1, 2, 4 and 8 weeks. After storage at -0.5°C for these periods, the grapes were stored for another 2 or 5 days at -0.5°C , or the grapes were transferred and stored at 10°C and RH 88% for 2 or 5 days. The polyliners were kept closed during the different storage periods. Fruit quality examinations were conducted after the specified periods at -0.5°C, and after each additional 2 and 5 days at both temperatures. Berry split increased with prolonged storage at -0.5°C. A linear function (y = 0.58x - 1.14; R2 = 0.97) described this increase in berry split over 61 days storage at -0.5°C. Transferring the grapes from -0.5°C to 10°C resulted in a further increase in berry split. Grapes stored for 0, 1, 2 and 4 weeks at -0.5°C followed by 5 days at 10°C, showed a significant increase in berry split, compared with grapes stored only at -0.5°C for the same period. Although significant differences in berry abscission occurred, no definite trend was observed that could be ascribed to storage period at -0.5°C or to an elevation in storage temperature from -0.5°C to 10°C.
- ItemMaterialism and indebtedness of low income consumers : evidence from South Africa's largest credit granting catalogue retailer(AOSIS, 2010) Jacobs, G.; Smit, E. van der M.In South Africa, studies have found changes in consumption and credit usage over time to be significant amongst low-income consumers. Yet, there has been limited empirical research on consumer behaviour in South Africa and even less on low-income consumerism. This study, which explores the relationship between materialism and indebtedness among a sample of low-income, instalment paying consumers of South Africa's largest catalogue retailer, aims to augment our understanding of these phenomena, whilst making some international comparisons. The study assesses whether (i) consumers display strong characteristics of materialism and (ii) whether materialism is a significant variable in predicting the consumers' propensity for incurring debt. It is concluded that low-income consumers are indeed highly materialistic. The study further suggests the presence of statistically significant relationships between consumers' levels of indebtedness and the demographic variables age and gender. However, materialism and monthly income are not significant in determining a consumer's level of indebtedness. While the decision to conduct the study on client data from one particular retailer, limits the extent to which the findings can be generalised to the larger South African population, the results do provide a number of important insights, which contribute to the scant body of literature on low-income consumer behaviour in the RSA.
- ItemRed colour development and loss in pears(International Society for Horticultural Science -- ISHS, 2005-04) Steyn, Willem J.; Wand, S. J. E.; Holcroft, D. M.; Jacobs, G.The endogenous and environmental regulation of red colour development in blushed and fully red pears is reviewed. Colour development in pears has an underlying developmental component. Generally, highest anthocyanin concentrations are attained in immature pears and colour tends to fade towards harvest. This is contrary to most other crop species where maximum pigmentation and colour are attained in ripe fruit and may relate to the photoprotective ability of anthocyanins. Because of this pigmentation pattern, net anthocyanin degradation at high temperatures results in pre-harvest red colour loss in susceptible pear cultivars. Susceptibility depends on the capacity to accumulate anthocyanin and on whether low temperatures are required for anthocyanin synthesis. Unlike apples, where red colour development in all cultivars seems to require or benefit from low temperatures, not all pear cultivars seem to respond to low temperatures. Light appears to have two opposing effects in pears, being required for anthocyanin synthesis, but also apparently increasing red colour loss through increased degradation of anthocyanin.
- 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.
- ItemUse of evaporative cooling to improve ' Rosemarie' and ' Forelle' pear fruit blush colour and quality(International Society for Horticultural Science -- ISHS, 2005-04) Wand, S. J. E.; Steyn, Willem J.; Holcroft, D. M.; Mdluli, M. J.; Van Den Dool, K.; Jacobs, G.In Pyrus communis ‘Rosemarie’, a potentially lucrative blushed pear cultivar, poor fruit colour has been ascribed to pre-harvest red colour loss during periods of high temperature. High temperatures combined with high irradiances also lead to sunburn on pome fruit. The use of pulsed overhead evaporative cooling (EC) to improve red colour and reduce sunburn in two blushed pear cultivars was evaluated over four seasons (2000/01 to 2003/04) in Stellenbosch, South Africa. ‘Rosemarie’ fruit blush was usually but not always improved under EC, with a late application (starting two weeks before harvest) yielding the best improvement. Peel anthocyanin concentrations were increased under EC. Incidence of sunburn was reduced during some years, but increased in EC-treated fruit during 2003/04 due to system failure on a hot day. EC initiated early in fruit development initially led to larger fruit with a lower TSS concentration and firmness, but this effect was gradually eliminated following reductions in EC water use. EC had no effect on ‘Forelle’ pear fruit colour or mass, but reduced firmness and TSS when started early in the season. Sunburn was only recorded in EC-treated fruit during 2002/03 due to system failure on a warm day. Though EC could be used to improve ‘Rosemarie’ fruit colour in warm production areas, its effect was relatively small compared to colour change in response to fluctuating temperature. The increased risk of sunburn during system ‘downtime’ highlights the requirement for a highly reliable system.