The vase life of cut flowers is determined by various physiological factors that determine the rate of their senescence. A thorough understanding of these factors is required in order to design treatments that will extend the vase life and delay senescence of cut flowers. Senescence of climacteric flowers such as carnations (Dianthus caryophyllus L. cv. Nordika and cv. Snow White) and freesias (Freesia refracta cv. Athena) is characterized by a climacteric rise in respiration rate and ethylene synthesis during the late stages. The increase in ethylene production is preceded by an increase in the sensitivity of the flowers to ethylene. Pulse treatments with sucrose caused a delay and suppression of the climacteric rise in ethylene synthesis and a delay in the climacteric maximum of the respiration rate. A pulse treatment for 24 hours with a 20% sucrose solution was most effective in extending the longevity of both carnations and freesias. The ability of the receptor molecules to bind ethylene is greatly reduced when flowers are pulse-treated with sucrose. In freesias, the ability to bind ethylene is reduced even further when flowers are treated with STS or 1-MCP. Ethylene synthesis in freesias is suppressed and inhibited when treated with STS or 1-MCP but longevity of the freesias and number of open florets on the stem is not increased. The uptake and distribution of sucrose in the buds of freesias is seen by the distribution of sucrose from the first bud on the stem to the next bud after the bud opens. The distribution of sucrose from one bud to the next results in more buds opening on the stem than that on the stems of STS or 1-MCP treated freesias. It is thus clear from the results of the study, that pulsing senescing climacteric flowers with sucrose increases the vase life of the flowers and suppresses ethylene sensitivity of the flowers, thus delaying the autocatalytic process of ethylene production. It is also evident from the results that the osmolality in the flowers has a direct influence on the metabolic processes of the flowers. In freesias, pulse treatment with sucrose increases the number of open buds on the stem and delays senescence of the florets. / Mr. C.S. Whitehead

No description available.

Bibliography: leaves 280-300. / xix, 338 leaves : ill. (chiefly col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Horticulture, Viticulture and Oenology, 2000

Yeast biocontrol agents that were applied to 'Bose' and 'Anjou' pears in the field up to three weeks prior to harvest were found to survive on the fruit at high population levels on both pear varieties. Cryptococcus infirmo-miniatus, Cryptococcus laurentii, and Rhodotorula glutinis maintained populations averaging 5 x 10��� cfu/fruit for three weeks. Candida oleophila had high initial populations, but the population size quickly declined to levels similar to the total yeast populations on untreated fruit. After a storage period of 2-4 months, fruit that were treated with C. infirmo-miniatus three weeks before harvest showed significantly lower incidence of decay at wounds than did untreated fruit. Combinations of biocontrol agents with reduced rates of the postharvest fungicides captan and thiabendazole were effective in reducing incidence and severity of blue mold decay caused by Penicillium expansum on 'Bosc' pears. Calcium chloride was also effective in combination with some biocontrol agents. Chitosan caused reductions in decay when used alone, but not when combined with most biocontrol agents. The compounds L-asparagine, L-proline, and 2-deoxy-D-glucose were not consistently effective either alone or combined with biocontrol agents. Storage of 'Bosc' and 'Anjou' pears in atmospheres with carbon dioxide concentrations of 12% or 20% for up to six weeks significantly reduced incidence and severity of gray mold decay caused by Botrytis cinerea, but decay was not reduced when the atmospheres was only 3% CO���. In contrast, the 12% or 20% CO��� atmospheres did not have significant effects on decay caused by P. expansum. Use of the biocontrol agents C. infirmo-miniatus, C. laurentii, or R. glutinis led to reductions in decay in all atmospheres, with C. infirmo-miniatus being the most consistently effective. The biocontrol products BioSave-110 (EcoScience Corp.) and Aspire (Ecogen Corp.) were less effective than the yeasts C. laurentii, R. glutinis, and C. infirmo-miniatus which were grown in the lab. / Graduation date: 1999

The nutritional quality and antioxidant activity of organic and conventional green beans were compared in a series of experiments. Firmness, percent dry matter, carotenoids and chlorophyll contents, respiration rate, vitamin C and proteins were evaluated. Hydroxyl radical scavenging activity, SOD, APX and POX were also analysed. In a second experiment, organic green beans treated with hexanal formulations were stored with untreated at 12⁰C in the refrigerator for a period of three weeks during two seasons. The results of the experiment showed higher levels of most of the parameters measured in organic green beans (with significant differences in firmness, carotenoids and chlorophyll b), except for respiration, vitamin C, antioxidant activity(hydroxyl radical scavenging) and APX where conventional green beans were higher and showed significant differences in respiration and vitamin C. The storage experiment showed a decrease in firmness and fresh weight and increase in respiration during storage for both seasons. Carotenoids and chlorophyll contents showed decrease in concentrations during the first week and increased during the second week of storage.

Volatile metabolites from headspace gas of mango cultivars Tommy Atkins and Keitt, wounded and inoculated with two pathogens, Colletotrichum gloeosporioides and Lasiodiplodia theobromae or non-inoculated controls were profiled using a GC/MS to develop a technology to discriminate diseases. Several disease discriminatory compounds were identified and classified into three groups: (i) compounds unique to only one treatment; (ii) compounds common to two or more treatments but not to all; and (iii) compounds common to all treatments but with varying in their abundance. 1-pentanol and boronic acid ethyl were detected in only Lasiodiplodia-inoculated mangoes while thujol was observed only in Colletotrichum-inoculated mangoes. Models based on significant mass ions classified up to 100% of the diseases/inoculations. The disease discriminatory compounds and discriminant analysis models developed here could be used in the early detection of postharvest diseases of mango fruit, after validation under commercial conditions.

Advanced research in Controlled/Modified Atmosphere storage systems has shown that open channels of different lengths and cross sectional areas, connected to an air tight storage chamber, are able to maintain variable stable gas concentrations which could be near optimal concentrations for CA/MA storage of various commodities. / This study was geared towards assessing the suitability of the diffusion channels in maintaining a desired gas concentration for CA storage of spinach. Initially, the respiratory behaviour of spinach was studied in gas sealed chambers (replicated four times) stored at four different temperatures, 2$ sp circ$C, 8$ sp circ$C, 15$ sp circ$C and 23$ sp circ$C. The respiration rate of spinach was 20 mgCO$ sb2$/kg.h, 66 mgCO$ sb2$/kg.h, 163 mgCO$ sb2$/kg.h and 271 mgCO$ sb2$/kg.h for 2$ sp circ$C, 8$ sp circ$C, 15$ sp circ$C and 23$ sp circ$C, respectively. A model was developed based on principles of enzymatic kinetics which could reliably predict the respiration rate of spinach at any given storage temperature. / Two other sets of experiments were carried in a cold room set at 2$ sp circ$C. (Abstract shortened by UMI.)

The use of sulphur as a method of postharvest disease control and colour retention in litchis is soon to be restricted by the European Union. It is therefore essential that new postharvest treatments and packaging techniques be developed in order to retain internal and external fruit qualities and thus allow for export. Good litchi quality is not only important for the export market but also for use on the local market. In this study, alternative methods for postharvest quality control were investigated with the aim of extending the litchi storage life to 40 days under modified storage. Packaging the fruit in polypropylene bags significantly decreased fruit water loss and resulted in an increase in shelf life, as determined by red colour and overall rind appearance. There was no distinct advantage of amodified atmosphere. The use of a punnet, lined with absorbent sheeting and placed within the sealed polypropylene bag, further improved the shelf life. The absorbent sheeting reduced the amount of free water and resulted in little pathogen infection, while the punnet was effective in protecting the fruit from damage. It was notable that most water loss occurred within the first 10 days of storage and that the majority would actually take place during the cooling phase. A hydrocooling technique was therefore investigated and was found to not significantly decrease water loss, possibly due to not hydrocooling the fruit for a long enough period of time. Temperature management was extremely important for both colour retention and pathogen control. It was found that treatments stored at 5.5QC showed better colour retention after the 40 days storage than the 1QC storage treatment. The higher storage temperature, however, enhances the potential for postharvest diseases. Three compounds, namely ISR 2000, 'Biosave' and F10, were tested for pathogen control. 'Biosave' showed the best results with the most effective concentration being 100 mill water and good pathogen control occurred when storage was at 10 C. Polyphenol oxidase (PPO) activity in the litchi rind was evaluated as it is thought to be closely related to browning of litchi fruit, probably due to the degradation of phenolics by PPO. Brown fruit had a high PPO activity whilst red fruit had much lower activity. It was also shown that PPO activity decrease over storage time, possibly due to product inhibition of the enzyme. The internal quality of the fruit was determined using the T88: acid ratio of the pulp, as it is well correlated to mean eating quality. For fruit to have excellent taste, it must have a T88: acid ratio of between 31:1 and 60:1. All the fruit had a ratio that met this criterion and would therefore ensure good eating quality. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2006.

The South African fresh fruit industry is a significant exporter, accounting for approximately 45% of the country’s agricultural exports. Of the total exported fruit in the 2005/06 season, 60% was subtropical fruit. However, certain physiological rind disorders such as mango lenticel damage and citrus rind pitting are frequently observed, reducing the commercial value of the fruit. This thesis deals with the epidemiology of these rind physiological disorders, in an attempt to obtain basic information that could serve as a guideline to predict and manage the fruit susceptibility to these disorders. The study further investigated the relative effects that certain pre-harvest factors have on the postharvest development of these disorders. Factors of particular interest were harvest maturity, climate and the mineral content of the fruit. Rind pitting is a physiological disorder of citrus that develops during storage. A study was conducted to investigate the relative effects that certain pre-harvest factors have on the post-harvest development of superficial rind pitting in ‘Benny Valencia’ oranges. Factors of particular interest were harvest maturity, climate and the mineral content of the fruit. In addition, trees were treated with two different formulations of nitrogen viz. limestone ammonium nitrate (LAN) and a slow release nitrogen fertilizer (Horticote®), during March 2006. The fruit were then sampled on a two-weekly basis over a period of three months. On each sampling date a set of quality related readings, such as juice sugar and titratable acid concentration were taken, after which the mineral concentration of the exocarp and mesocarp was measured. Fruit were also stored under export simulation conditions. The results indicate that fruit from trees that received additional N were more susceptible to rind pitting than those from control trees. Of the two N applications, fruit from trees that received slow release N were more susceptible to rind pitting than fruit from trees that received the LAN treatment. Another important observation made was that the nitrogen concentration of oranges from trees that received extra nitrogen fertilizer was lower than that from the controls. In addition, experimental fruit were smaller than control fruit. Fruit from trees that received the slow release nitrogen treatment were smallest. A sink/source hypothesis aimed at explaining this phenomenon has been formulated and is currently being investigated. A number of control mechanisms are also being explored. Mango lenticel damage is a serious defect that occurs on the rind of the fruit. This condition causes fruit to attain a speckled appearance and become unattractive to the buyer. Each season, the disorder reduces the packout of fresh fruit by about 16%. Several preharvest factors play a critical role in the postharvest development of lenticel damage. Preliminary studies have shown that the incidence of lenticel damage has some relationship to fruit moisture and fruit nutrient concentration, depending on which of these factors first achieve a critical threshold. A study was conducted to develop appropriate skin moisture content parameters to predict lenticel damage potential before harvest. The study further aimed to provide certain biological markers regarding appropriate nitrogen fertilization practices to reduce lenticel damage. To do this, two trials were conducted approximately a month before harvest. Firstly, a plastic ground cover to restrict water supply was laid under ‘Tommy Atkins’ trees at Numbi Estates in the Hazyview area of the Mpumalanga province, South Africa. Secondly, additional nitrogen was applied as three different formulations, viz. limestone ammonium nitrate (LAN), potassium nitrate (KNO3), and a slow release nitrogen fertilizer under trade name Horticote®, to two ‘Tommy Atkins’ and two ‘Keitt’ orchards at Bavaria Estates in the Hoedspruit area of the Limpopo province, South Africa. Fruit samples were harvested, packed and stored at different intervals after rain during January 2006. With regard to lenticel damage on ’Tommy Atkins’ fruit from Numbi, there was no significant difference between the control and plastic cover treatments. However, when compared to fruit from other localities, the Numbi fruit had the highest incidence of lenticel damage, followed by the conventional orchard at Bavaria. The Numbi fruit, which had the highest incidence of lenticel damage, also had the highest pulp and skin nitrogen concentration. Of the four treatments at Bavaria, the LAN treatment had the highest incidence of lenticel damage, but the pulp and skin nitrogen concentrations of this treatment were comparable with the other treatments. The organic fruit had significantly lower lenticel damage incidence and also had the lowest pulp and rind nitrogen concentrations. Similarly, ‘Keitt’ results showed that the intensity of lenticel damage was significantly higher in the orchard that received additional nitrogen in the form of LAN. From the results it was, however, not possible to formulate nitrogen-lenticel damage correlations. The study failed to prove the case for a direct relationship between the disorder and with nitrogen, as there were no significant or consistent correlations with nitrogen content. An interesting relationship was nevertheless observed between lenticel damage and the time of harvest before and after rainfall. The results indicated that both ‘Tommy Atkins’ and ‘Keitt’ fruit become more susceptible to lenticel damage when harvested a day after rainfall and this gradually reduces afterwards. The effect of rainfall in this regard and a sink-source hypothesis arising from these observations are also discussed. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2008.

South Africa is the second largest exporter of citrus fruit in the world. There has recently emerged a strong demand for lemons in the world market due to their nutritional value, culinary and non-culinary uses. During exportation, fruit are subjected to low temperature (-0.5°C) for varying periods of time as an obligatory quarantine treatment. However, lemons are sensitive to low temperatures and easily develop chilling injury during this obligatory quarantine treatment. This has become a major limitation to the expansion of South Africa’s lemon industry. Postharvest treatments with methyl jasmonate (MJ) and / or salicylic acid (SA) have been successfully used in horticultural crops to reduce chilling injury. A similar treatment was applied to ‘Eureka’ lemons. During the 2008 harvest season, postharvest fruit were either dipped in 10 or 50 μM MJ or 2 or 2.5 mM SA solutions. A control or no dip treatment was also applied. Three replicates of 15 fruits per treatment were used. During the 2009 harvest season the following postharvest treatments were applied as dips: 10 μM MJ, 2 mM SA, 10 μM MJ & 2 mM SA, 1 μM MJ & 0.2 mM SA, or 0.1 μM MJ & 0.02 mM SA solutions. A control or no dip treatment was also applied. Three replicates of 15 fruits per treatment were used. Subsequently fruit were stored at -0.5ºC for 0, 7, 14, 21, 28, 35, and 42 days, before being transferred to room temperature (25°C) for 7 days where after chilling injury was rated. Treatments with 10 μM MJ and / or 2 mM SA reduced chilling injury symptoms in lemons harvested during the 2009 season. Although no visual symptoms of chilling injury were observed during the 2008 harvest season, treatments with 10 μM MJ and / or 2 mM SA reduced fruit mass loss, delayed the occurrence of stress symptoms such as lipid peroxidation and suppressed accumulation of ROS in the rind. Treatments with 10 μM MJ and / or 2 mM SA were more effective in inducing antioxidant capacity and other defence compounds such as phenolics, ascorbic acid, carbohydrates and chilling injury responses such as accumulation of proline in the rind. This may have increased the chilling tolerance of fruit during the cold storage. Therefore, this study revealed that MJ and SA have the potential to reduce and delay symptoms of chilling injury in lemons. This lead to the suggestion that both, MJ and SA dips should be further tested as treatments to mitigate chilling injury in lemons. Future studies should focus more on preventing the injury itself or preventing the primary event of chilling injury. This could probably reduce the chances of secondary events to take place. / Thesis (M.Sc.Agric.)-University of KwaZulu-Natal, Pietermaritzburg, 2010.