Masters Degrees (Horticulture)
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Browsing Masters Degrees (Horticulture) by browse.metadata.advisor "De Kock, Arrie"
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- ItemMoisture loss studies in Japanese plums (Prunus salicina Lindl.)(Stellenbosch : Stellenbosch University, 2015-12) Theron, Jacobus Adriaan; Jooste, Mariana; Theron, K. I.; De Kock, Arrie; Stellenbosch University. Faculty of Agrisciences. Dept. of Horticulture.ENGLISH ABSTRACT: The export of Japanese plums from South Africa is challenging. Exporting late season plums require fruit to last as long as 8 weeks in cold-storage. Prolonged storage periods can cause some cultivars to develop a shrivelled appearance due to moisture loss. Moisture loss from perishable commodities manifests mainly as shrivelling due to a loss in the turgidity of the surface cells of the fruit, or weight loss. ‘African DelightTM’ (highly susceptible to shrivel), ‘Laetitia’ (shrivel susceptible), ‘Sapphire’ (shrivel susceptible) and ‘Songold’ (not shrivel susceptible) plums were investigated by means of fluorescent microscopy for cracks and openings in the fruit peel. Only ‘African DelightTM’ had open hairline cracks in its peel, and fruit with wider cracks were associated with higher water vapour permeabilities. Open lenticels were found in the peels of ‘African DelightTM’, ‘Laetitia’ and ‘Sapphire’ plums. For ‘Songold’ no peel cracking or open lenticels were observed. The fact that the cuticle of this cultivar is mostly intact may be the reason why it is not susceptible to postharvest shrivel manifestation. The water vapour permeance of the fruit peel determines how easily fruit lose moisture. In this study it was determined to what extent fruit, trees, orchards, harvest date and cultivar contribute to the total variation in plum peel water vapour permeability. The permeabilities of ‘African DelightTM’, ‘Laetitia’, and ‘Songold’ were determined weekly from 4 weeks before harvest until post optimum maturity. Fruit to fruit variation made the largest contribution towards the total variation (> 45%), followed by harvest date (> 20%) and orchard (> 15%) effects. The permeability across all cultivars increased two-fold as fruit became over mature. The contribution of cultivar differences to fruit peel permeability varied greatly between seasons (42% in 2013/2014 and 5% in 2014/2015). Differences between cultivars may include cuticle thickness and composition, micro cracks in the peel and/or open lenticels. Current handling protocols suggest that fruit should be cooled as soon as possible after harvest, but this is not always possible. ‘African DelightTM’ plums were exposed to various handling scenarios in order to determine the handling protocol with the least risk of moisture loss. The control consisted of packaging and cooling the fruit within 6 h of harvest. Fruit quality was comparable or even better than the control when the fruit were pre-cooled to 0 °C and 15 °C for up to 72 h. High vapour pressure deficits caused fruit to lose more moisture, especially when fruit were exposed to ambient temperatures for 48 h and 72 h. It is recommended that handling protocols for plums should be followed stringently in order to reduce mass loss and shrivel manifestation. Since other studies found that silicate (Si) has positive effects on fruit quality, we applied potassium silicate preharvest to ‘African DelightTM’ trees. However, we did not find significant differences between treatments regarding crack width or crack incidence in the fruit peel, shrivel, decay, internal browning, gel breakdown or aerated tissue levels. Currently preharvest potassium silicate applications are not recommended to improve plum quality.
- ItemMoisture loss studies in nectarine (Prunus persica var. necterina)(Stellenbosch : Stellenbosch University, 2016-12) Chigwaya, Kenias; Theron, K. I.; De Kock, Arrie; Jooste, Mariana; Stellenbosch University. Faculty of AgriSciences. Dept. of Horticulture.ENGLISH ABSTRACT: Moisture loss studies in nectarines (Prunus persica var. nectarina) Moisture loss during long term storage is one of the main post-harvest problems in nectarines. The long handling chain to which fruit are exposed to, from harvest until the end of shelf-life, exposes fruit to moisture loss. Moisture loss occurs as a result of the vapour pressure deficit (VPD) between the fruit and surrounding atmosphere. In addition to causing loss of saleable weight, moisture loss also results in fruit having a shrivelled appearance. Moisture is lost from fruit through various openings in the fruit peel such as micro-cracks and lenticels. In this study we investigated the effect of fruit to fruit variation, harvest date, tree and orchard effects and cultivar differences on the variation in water vapour permeance (P’H2O) of three nectarine cultivars namely ‘Alpine’, ‘Summer Bright’ and ‘August Red’. The study showed that large fruit to fruit differences were the main contributor (>45%) to the variation in P’H2O, followed by harvest date (>35%), cultivar differences (>7%) and orchard effects (>3%) whilst tree effects did not contribute to P’H2O. Generally, the P’H2O of all three cultivars increased steadily as the harvest date approached and continued to increase post-harvest, but P’H2O at optimum harvest was not closely correlated to their susceptibility to shrivel. In addition, ‘August Red’ nectarines were exposed to different handling chains from harvest until the end of shelf-life to determine the VPD at different stages in the handling chain in order to establish the point which is most effective in reducing moisture loss and shrivel. The results indicated that none of the proposed handling chains performed better than the current standard handling protocol in reducing moisture loss and shrivel. This protocol stipulates that nectarines should be harvested during the cooler time of the day and field heat should be removed as soon as possible after harvesting. Furthermore, the handling protocol requires that nectarines should be packed within 12 hours of arrival at the pack-house. Several researchers have reported that silicon containing fertilizers improve fruit quality and we therefore also investigated whether pre-harvest applications of potassium silicate (K2SiO3) can reduce post-harvest moisture loss, shrivel and split pit in ‘Southern Glo’ nectarines. The results showed that both soil and foliar K2SiO3 applications were not effective in reducing post-harvest moisture loss, shrivel or the incidence of split pit in ‘Southern Glo’ nectarines. For future studies, it is recommended to increase the frequency of K2SiO3 applications. The study also looked at the effectiveness of different packaging films in reducing moisture loss and shrivel in ‘August Red’ and ‘Alpine’ nectarines. Failure to package fruit optimally may result in weight loss, shrivel, decay and the incidence of internal defects such as woolliness, pulpiness and over-ripeness. The results showed that the use of Xtend® and high density poly-ethylene (HDPE) bags significantly reduced moisture loss and shrivel in nectarines in both pulp trays and plastic punnets. The standard nectarine HDPE wrappers resulted in significantly higher percentage mass loss as well as shrivel incidence in ‘Alpine’ nectarines. It is therefore important to reduce moisture loss at harvest by following the standard handling protocol and by packing fruit optimally.