Elmi Lötze

Evaluating the Effectiveness of Pre-Harvest Calcium Applications for Bitter Pit Control in ‘Golden Delicious’ Apples Under South African Conditions

ABSTRACT Pre-harvest foliar applications to increase fruit calcium (Ca) content and reduce bitter pit incidence, is a standard practice world wide. We re-evaluated the effectiveness of early season applications versus late applications of calcium nitrate (Ca(NO3)2) to reduce bitter pit in ‘Golden Delicious,’ under the present environmental conditions of the Western Cape, South Africa. Two periods of efficient uptake of external Ca were identified, viz., during cell division and the last few weeks before harvest. Foliar Ca applications during mid season (from 40 d after full bloom) were more effective in increasing fruit Ca content and reducing bitter pit incidence, than later applications. Thus, it is important to apply the bulk of the Ca(NO3)2 during the first few weeks after cell division to maximize the Ca content of ‘Golden Delicious’ apples.

Nutrient composition and content of various biological active compounds of three South African-based commercial seaweed biostimulants

Whenmineral content was considered, the significantly higher P and N concentrations reported in Afrikelp® and Basfoliar®Kelp compared to those in Kelpak®, may indicate an additional permissible enrichment of these products, all produced from E maxima, as natural levels in the freshly milled seaweed prior to processing were found to be much lower (Tables 1, 2). Similarly, significantly higher P levels in Afrikelp® and Basfoliar®Kelp products were reported in this study, also as pertaining to free phosphate levels (Tables 1, 2 and 3).

Evaluating the effectiveness of different strategies for calcium application on the accumulation of calcium in apple ( Malus X domestica Borkh. 'Braeburn') fruit

Summary Orchards displaying calcium (Ca) deficiency are a common phenomenon worldwide, despite the presence of sufficient Ca in the soil and the plant. A 3-year trial was conducted between the 2007 – 2008 and 2009 – 2010 growing seasons to evaluate the contributions of soil and foliar Ca applications to Ca concentrations in ‘Braeburn’ apple (Malus × domestica Borkh.) fruit. Ca(NO3)2 (Calflo; Yara Africa, Fourways North, South Africa) was applied as six separate foliar sprays until run-off. Applications were made at 1-week intervals between approx. 21 – 70 d after full bloom (DAFB) at 6.75 ml l–1. Soil applications of Ca (TropicoteTM; International ASA, Oslo, Norway) at 300 kg ha–1 were applied at fruit set, or after harvest, according to standard practice. Mineral analysis was conducted to assess the soluble Ca concentrations of whole fruit (without pips and stalks), to quantify the contribution of foliar sprays or soil-applied Ca. Fruit Ca concentrations were maintained at satisfactory levels (4.5 mg Ca 100 g–1 FW) at harvest by applying a series of six foliar sprays early in the season (for all seasons) during the trial period. Fruit Ca concentrations at 80 DAFB were highest in the treatments with foliar applications of Ca. In 2009 – 2010, Ca concentrations in apple fruit were lowest (8.38 mg 100 g–1 FW) for soil application of Ca at fruit set. Ca applications to soil after harvest in the previous season, and soil applications shortly after fruit set in the current season, did not significantly increase Ca concentrations in current-season fruit, providing soil Ca levels were above the minimum requirement for apple trees. A possible explanation is that apple trees regulate their uptake of Ca through the roots when soil Ca is available in sufficient quantities. This confirms the importance of active root growth for efficient Ca uptake by apple trees when applying Ca to the soil.

Are the attitudes and practices of foodservice managers, catering personnel and students contributing to excessive food wastage at Stellenbosch University?

Objective: The aim was to investigate factors contributing to food wastage by Stellenbosch University (SU) students in selected residences, and to determine the attitudes and practices of students and catering personnel impacting on food waste and a sustainable environment. Design: Cross-sectional, descriptive study. Setting: Stellenbosch University, Western Cape. Subjects: Six foodservice managers, 63 catering personnel and 517 students participated in the study. Outcome measures: A weighed-food wastage study was conducted at seven selected residences during lunch and supper on three non-consecutive weekdays. Food service managers (FSMs) and catering personnel completed interviewer-administered questionnaires, while SU students completed an electronic survey. Results: Ninety percent of students preferred the standard menu options, despite a relatively high average plate waste of 16.9%. More production waste was generated during lunch than supper. The male residence generated more plate waste. Even though students requested larger servings of vegetables, the wastage of these items was high. Factors contributing to wastage were the booking system, menus and serving style, meal plan stipulating the serving of dessert and serving of a large starch portion. All FSMs and 88.5% catering personnel considered it important to reduce food wastage to a minimum. Conclusion: Education of catering personnel and students regarding food waste reduction measures is crucial. A representative forum including students, catering companies and faculty management should be involved when seeking solutions to reduce food wastage and improve communication. By implementing these strategies, a university-wide culture of sustainability with a focus on food waste reduction can be developed and nurtured.

Determining the probability of bitter pit in ‘Golden Delicious’ apples through the post-harvest mineral content of individual fruit

Summary Bitter pit fruit in commercial consignments of apples still poses an economic threat to exporters from South Africa. Mineral analysis of fruit has been used with variable success to predict bitter pit prior to harvest. The possibility of increasing the accuracy of existing predictive models by using analysis of individual fruit rather than pooled samples was investigated. By improving the normality of the distributions of the different minerals and decreasing the overlap between pitted and non-pitted fruit classes, we attempted to improve the reliability of predictions based on variable threshold values. Even though our model produced a correct classification of 85% for non-pitted fruit which can be useful, this was still below the required tolerance expected on the market which, at present, is less than 2% bitter pit in an overseas consignment. The classification for pitted fruit, 63%, was not satisfactory.

Efficacy of Foliar Application of Calcium Products on Tomatoes as Defined by Penetration Depth of and Concentration within Fruit Tissues

The efficacy of ion absorption through the cuticle of a leaf of fruit has been related the conditions whilst applying (i.e., environmental) and the receiving surface exposure (i.e., area covered, capacity of absorption). The influence of the products physical chemical properties like point of deliquescence should be taken under consideration while quantifying penetration. The present study compares traditional and recent calcium formulations (total of 10) by evaluating calcium penetration and distribution on tomato fruits as well as comparing plant health and fruit quality. Elemental analysis through Wavelength Dispersive X-ray Spectrometer (WDS) analysis, using a Zeiss EVOR_MA15 SEM (Carl Zeiss Pty. Ltd., Cape Town, South Africa) and mineral analysis were used to quantify calcium content in the fruit. In addition, maturity index parameters were taken before and after storage (10 days at 15°C). Nitrogen, phosphorus, magnesium and calcium did not differ significantly after treatment according to elemental and mineral analysis. Calcium concentration in the fruit was successfully increased.

Re-Visiting Calcium Concentration and Distribution in Apple Fruit (Malus domestica Borkh.)

Distribution of calcium in the apple has been quantified using mineral analyses of fruit sections during the mid-1900s by various researchers. Most of the work was done either at harvest, or after storage. We used Proton-induced X-ray spectrometry (PIXE) and Scanning Electron Microscopy to correlate Ca distribution in apples to results obtained from mineral analyses (MA). For fruit at harvest transverse distribution of Ca in ‘Braeburn’ apples determined by PIXE confirmed similar analyses with MA. It was not possible to establish a significant relationship between the total Ca concentration determined by PIXE and soluble Ca concentration from MA in this paper, either at harvest, or 80 days after full bloom (dafb). A significant correlation was found between PIXE and SEM results 80 dafb.

Foliar application of calcium plus boron reduces the incidence of sunburn in ‘Golden Delicious’ apple

Summary Losses of apple fruit due to sunburn damage under South African climatic conditions can reach up to 40% per annum for specific cultivars in certain years. Various approaches to reduce the incidence and severity of sunburn resulted in temporary effects but, at present, no single remedy is available to provide a significant and consistent reduction in sunburn damage on a commercial scale. ‘Golden Delicious’ apple trees that received both calcium (Ca) and boron (B) as foliar applications on a weekly basis, when applied from approx. 21 – 70 d after full bloom (DAFB), showed significantly less sunburn in two consecutive seasons (P = 0.0500 and P = 0.0247 respectively) than untreated control fruit, or treatments based on Ca alone. The minerals were applied as supplements of sugar-alcohol complexed with Ca and B, trading as Manni-Plex® Ca [10% (w/w) Ca] and Manni-Plex® B [3.3% (w/w) B], respectively. The mode of action by which the incidence of sunburn was reduced using combined sprays of Manni-Plex® Ca plus Manni-Plex® B remains to be elucidated.

Evaluating the Streif index against commercial subjective predictions to determine the harvest date of apples in South Africa

For the local deciduous fruit industry, which mainly exports fruit, determination of the optimum physiological harvest maturity for apples to ensure high fruit quality after long-term storage is still an important goal. This is performed by a subjective determination based on a weekly rate of change of all or some of the ripening parameters such as fruit firmness. In Europe, the Streif index (SI) has been implemented to reduce this subjectivity. The aim of this project was to evaluate this index under local conditions. Historical physiological data for Golden Delicious and Starking apples (Malus domestica Borkh.) from various orchards in the Ceres area were analysed. Significant correlations were obtained between the SI and subjective predictions of the release date for harvesting, after adapting the local starch breakdown values. However, during seasons when the starch conversion rates were very low during the early season, the SI alone may not be sufficient to indicate the release date for harvesting. A multilinear regression equation was also fitted to the maturity data. Likewise the accuracy of this model was influenced by season and variation between individual sites. Both methods can be applied commercially to support the otherwise subjective determination of the harvest dates.