Pruning has been used to reduce tree size, allow light penetration into trees, improve yield, improve fruit size and fruit quality, overcome alternate bearing, assist fruit harvest, and assist pest and disease control. The use of pruning has increased due to improving agricultural management techniques such as high planting densities, use of mechanical machinery in orchards and the need for effective pesticide and pathological chemical spray applications. The main objective of this study was to obtain a practical means of manipulating lemon trees at the right time. Pruning at the correct time to cultivate productive trees that produce quality fruit would have financial benefits. Lemon fruit quality is dependent on market demand and involves a number of features such as fruit shelf life, rind thickness, fruit size, rind colour, and juice content. The study was conducted on ’Eureka’ lemon trees budded on C. volkameriana rootstock, bearing the fifth and sixth commercial crops in 1999 and 2000 respectively. Twelve monthly pruning treatments per year were conducted on one row of trees starting in December 1997 (site 1) and repeated in the second year on the adjacent row of the same orchard starting in December 1998 (site 2). Selective pruning heading cuts were applied below the intercalation on the intercalary units. Potential branch bearing units were tagged and assessed during the harvest and flowering periods. Summer pruning between 16 to 19 months before the subsequent April/May harvest, resulted in the longest and most complex (intercalation sprouted per axil) vegetative response. The estimated crop value indicated that summer pruning treatments produced the highest income. This was ascribed not to differences in fruit size or quality, but to an increase in yield. The industry’s trend is to prune citrus from post-harvest to the pre-bloom stage. Results from this study have provided a beneficial cultural practice to prune during the summer months and provides a practice to optimise farm production and profit margins.

M.Tech.

Lenticels are macroscopic openings occurring on the surface of roots, shoots and some fruits like apples, pears, avocados and mangos and are responsible for gaseous exchange and transpiration. The discolouration of the lenticels of some mango cultivars is a serious problem, affecting the economic value of the fruit, especially in ‘TA’ and ‘Keitt’ while problems with lenticel discolouration are seldom found in ‘Kent’. Mango fruit lenticels develop from ruptured stomata on fruit from about 20 mm in ‘TA’ and ‘Keitt’ and 30 to 40 mm in ‘Kent’. Lenticels enlarge as the fruit grows due to stretching of the fruit surface, reaching their maximum size on adult fruit. Fully developed lenticels of ‘TA’ and ‘Keitt’ are larger in size than those of ‘Kent’. ‘Kent’ lenticels are also better insulated than ‘TA’ and ‘Keitt’, having a thick cuticle in the lenticel cavity and in some instances a phellogen is also present, while both of above mentioned characteristics are absent in ‘TA’ and ‘Keitt’. Resin present in the skin of the fruit plays an important role in the discolouration of ‘TA’ and ‘Keitt’ lenticels. The resin of both ‘TA’ and ‘Keitt’ fruit contain a considerable amount of an aggressive compound termed terpenes. These terpenes are volatile and are able to move out of the resin ducts via the sublenticellular cells to the outside of the fruit through the lenticels. The integrity of tonoplasts of the sublenticellular cells are lost due to the action of the terpenes, causing vacuolar bound phenols to come into contact with polyphenol oxidase present in the cell walls. The product of the resultant reaction is a quinone accumulating as a brownish deposit in the cell walls, visible from the outside as black markings around the lenticels. Lenticel discolouration may, however also occur due to maltreatment or rough handling of fruit, high temperatures in the warm water bath, extended brushing on packline or breaking of the cold chain and spilling of resin onto the surface of the fruit. Copyright 2005, University of Pretoria. All rights reserved. The copyright in this work vests in the University of Pretoria. No part of this work may be reproduced or transmitted in any form or by any means, without the prior written permission of the University of Pretoria. Please cite as follows: Bezuidenhout, JLJ 2005, Lenticel development and discolouration in the fruit of some mango (mangifera indica L.) cultivars, MSc(Agric) dissertation, University of Pretoria, Pretoria, viewed yymmdd < http://upetd.up.ac.za/thesis/available/etd-03072006-120414 / > / Dissertation (MSc (Agric))--University of Pretoria, 2007. / Plant Production and Soil Science / unrestricted

Bacteriocins (BCNs) are ribosomally synthesized polypeptides or proteins with antimicrobial activity, produced by different groups of bacteria. Many lactic acid bacteria (LAB) produce BCNs with broad spectra of inhibition. The antimicrobial activity of BCNs against spoilage organisms (SPOs) has raised considerable interest in their application in juice preservation. The objectives of the study were to: (i) isolate, identify and screen BCN producing bacteria for antimicrobial activity against spoilage bacteria and fungi, (ii) optimize production of BCN from selected producers and (iii) investigate the industrial application of the BCN as a preservative in fruit juice. Eleven LAB strains of BCN producers were screened for antimicrobial activity. BCNs from Lactobacillus plantarum and Pediococcus pentosaceus 34 were the most effective against juice spoilage bacteria and fungi. The effect of medium components on bacteriocin production in L. plantarum and P. pentosaceus 34 was also determined. Clementine:Valencia (1:1) juice was used for the first time as the growth medium for L. plantarum and P. pentosaceus 34. The BCN from L. plantarum showed the highest activity and was, therefore, chosen for juice fermentation studies. The identification of L. plantarum was confirmed by biochemical tests, polymerase chain reaction (PCR) and sequencing of the recA gene. The highest BCN activity was observed for L. plantarum grown in De Man-Rogosa-Sharpe (MRS) and a combination of all supplements (i.e. peptone, MnSO4.H2O, Tween 80, glucose and whey), followed by MRS and Tween 80, peptone, MnSO4.H2O and MRS alone. MRS was a better medium for BCN production than juice [Clementine:Valencia (1:1)]. Size exclusion chromatography (SEC) was used to isolate the active L. plantarum BCN fraction which corresponded to an approximate molecular weight of 3.2 kDa and was proteinaceous in nature. Plantaricin structural genes (plnEF, plnJ, plnK, plnN) were detected in the L. plantarum strain by PCR and sequenced, and were chromosomally encoded as no plasmids could be detected. This implies that the BCN from L. plantarum is most likely a type of class IIa plantaricin which is responsible for the broad inhibitory activity observed. For the industrial application studies, L. plantarum BCN-containing cell free supernatant (BCNsup) added to “Ready to Drink” (RTD) Clementine:Valencia (1:1) juice at concentrations of 3 600 - 500 000 ppm decreased growth of SPOs, Lactobacillus acidophilus and Streptococcus thermophilus. At 250 000 ppm, the L. plantarum BCNsup achieved 5.3 and 6.8 log reductions of the L. acidophilus, after 24 and 48 h, respectively, which is larger than the USFDA (2001) requirement of a 5 log reduction in SPO activity, for preservation of fruit juices. However, there was a decrease in the activity when the BCNsup was applied to industrial (Valor) RTD juice (mango-orange) at decreasing concentrations of 100 000, 50 000 and 25 000 ppm. Organoleptic tests showed that the BCN did not alter flavor or taste of the juice and did not cause toxicity or allergic reactions. A food safety risk assessment was conducted in order to determine the Critical Control Point(s) [CCP(s)] at which the BCN could be applied to control identified microbiological hazards, and a Hazard Analysis and Critical Control Point (HACCP) plan was developed. This is the first report on the optimisation of L. plantarum BCN production in juice [Clementine:Valencia (1:1)], followed by inoculation into RTD juice (mango-orange), including a HACCP plan for the application of the BCN as a preservative in juice.

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Controlled environment experiments were conducted to study the influence of four night/day temperature regimes; 17.8/25.6, 7.2/18.3, 4.4/15.6 and 2.8/13.9°C on the quality of tomato fruits, Lycopersicon esculentum Mill. c.v. Early Red Chief, measured objectively at three harvest dates. Temperature effects on vegetative and reproductive growth and fruit cracking were also examined. In addition, the stability of carotenoid pigments of macerated and cubed fruit stored at -20° for 0, 10, 20 and 40 days was studied. Low air temperatures decreased plant growth, caused chlorosis of vegetative growth, and reduced the frequency of fruit cracking but had little effect on fruit weight. Flower formation continued at all temperatures with the exception of the 2.8/13.9 environment while fruit set occurred only at the two highest thermal regimes. Fruits harvested at 17.8/25.6 were considerably lower in total solids, reducing sugars and titratable acidities and had substantially higher pH values than fruit exposed to 7.2/18.3, 4.4/15.6 and 2.8/13.9. Temperature had little or no effect on fruit refractive indices and total pectic substances. The failure of total pectic substances to reflect the apparent firmness differences between treatments indicates that total pectic substances are not a satisfactory index of this quality parameter. Surface and internal lightness and yellowness declined with increasing temperatures and later harvests, while redness values increased. Fruit harvested at 17.8/25.6 attained a full red coloration in 7 days, while those exposed to 7.2/18.3 required about 14 days to reach a comparable level of colour development. Fruit exposed to 2.8/13.9 were of inferior colour as evidenced by high L and bL values and low aL values. The high degree of association between lightness and yellowness values under all treatment conditions suggests that surface colour and, to a lesser extent, internal colour can be adequately specified in terms of a constant and two, rather than three, variables. The high overall correlation coefficient obtained between surface and internal Lb/a ratios immediately indicated the possibility of utilizing surface Lb/a ratios to predict internal colour. Temperature and harvest dates influenced the relationship between internal and surface colour ratios as evidenced by the decrease in correlation coefficients with higher temperatures and later harvests. The effect of decreasing temperatures on tomato colour was found to be largely a function of temperature effects on lycopene synthesis. Colour values showed marked changes as total carotene concentrations increased up to about 55 μg/g fresh weight. Continued increases above this level were not accompanied by parallel changes in surface or internal colour. Temperatures and harvest dates affected all pigment concentrations with the exception of Ƴ-carotene and, for the most part, β-carotene. The temperature regimes ranked in order of decreasing fruit quality were as follows: 7.2/18.3; 17.8/25.6; 4.4/15.6; 2.8/13.9. Although of satisfactory coloration, fruits harvested at 17.8/25.6 were rated below the 7.2/18.3 fruit for reasons of lower dry matter, sugar and acid contents. Storage duration had little effect on carotenoid concentrations of cubed samples. In macerated samples, phytoene, phytofluene and ζ-carotene concentrations decreased with storage time. When fresh samples were analysed, all pigment concentrations with the exception of lycopene were found to be much lower in macerated than in cubed samples. / Land and Food Systems, Faculty of / Graduate

Fruit-growers in the lower mainland of British Columbia are facing a potential labor shortage for hand harvesting of fruit. Prices paid to hand picking labor have increased by more than 100 percent in the last three years. These factors have prompted interest in mechanical harvesting methods. The purpose of this research was to investigate the feasibility of introducing mechanical harvesting methods in raspberry production and to determine optimum machine parameters. A review of methods used for determining the optimum size of agricultural equipment was conducted and the methods were summarized. Due to the nature of small fruit production some commonly used methods were not applicable and modifications were necessary. A fruit yield function and a timeliness function were developed for Willamette raspberries. The fruit yield function based on actual yield data, was used for determining the potential income from a raspberry plantation. The timeliness function, based on the reduction of fruit quality due to variations in the length of the interval between subsequent harvests, was used to determine a suitable charge for untimeliness at any part of the harvest season. An optimum fruit removal efficiency for mechanical harvesting of Willamette raspberries was determined by assessing the loss in potential income due to the removal of green fruit and the production of over mature fruit. This was based on published results of mechanical harvesting trials. Results indicated that the mechanical harvesting of raspberries could be potentially much more profitable than hand harvesting. A machine with a fruit removal efficiency of 80 percent and with an operating speed of 1.5 miles per hour, or greater, appeared to be optimum. At operating speeds above 1.5 miles per hour, the cost of mechanical harvesting was not significantly influenced by the purchase price of the harvester. The cost of untimely operation was large. Extending the interval between subsequent harvests by one day resulted in an annual profit reduction of approximately 200 dollars per acre. / Applied Science, Faculty of / Chemical and Biological Engineering, Department of / Graduate

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