Orientador: Benedito Carlos Benedetti / Texto em português e Inglês / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Agrícola / Made available in DSpace on 2018-08-23T16:23:18Z (GMT). No. of bitstreams: 1 Teles_CesarSimas_D.pdf: 1939088 bytes, checksum: 585b37a053cde7606fc6da4a9aa803dc (MD5) Previous issue date: 2013 / Resumo: Botrytis cinerea Pers, causador da doença conhecida como mofo cinzento, é o principal problema para a conservação pós-colheita de uvas de mesa. A utilização do dióxido de enxofre (SO2) é a prática pós-colheita mais comum para o controle desta doença. Pesquisas buscam alternativas a este produto devido às reações que causa em pessoas alérgicas, danos que pode causar nos frutos e às restrições ao seu uso em sistemas de produção orgânico. Foram avaliados os efeitos da aplicação de uma atmosfera de 40% de CO2 por 24 ou 48 horas (pré-armazenagem) combinado com armazenagem em atmosfera controlada (AC) (12% O2 + 12% CO2) no controle de B. cinerea, e nos atributos de qualidade de uvas 'Flame Seedless' e 'Crimson Seedless'. Também foram avaliados, em uvas 'Crimson Seedless', e os efeitos da associação deste tratamentos com aplicações pré-colheita de cloreto de cálcio (CaCl2) ou dióxido de cloro (ClO2). Os tratamentos foram aplicados em uvas orgânicas infectadas de três formas: infectadas naturalmente, superficialmente inoculadas com conídios e inoculadas com uma baga coberta de micélio. Uvas 'Flame Seedless', naturalmente infectadas, tratadas com 40% de CO2 por 48 horas + AC apresentaram redução da podridão pós-colheita, de 22% para 0,6%, após 4 semanas, e de 100% para 7,4%, após 7 semanas. O pré-armazenamento em 40% de CO2 sozinho também limitou a incidência de mofo cinzento em frutos infectados naturalmente e em uvas inoculadas artificialmente, porém foi menos eficaz do que quando seguido pelo armazenamento em AC. A aplicação de CaCl2 ou ClO2 em pré-colheita reduziu a incidência do mofo cinzento em uvas 'Crimson Seedless' inoculadas com uma solução de conídios, porém não houve controle quando os cachos de uva foram inoculados com micélio. A aplicação de CaCl2 e ClO2 reduziram o mofo cinzento de 45% para 23,2% e 15.6%, respectivamente, em cachos inoculados com conídios e avaliados após 6 semanas armazenadas 0oC. O pré-tratamento com 40% CO2 + CA não afetou as características físico-químicas e sensoriais de uvas 'Crimson Seedless' ou 'Flame Seedless'. Em experimentos in vitro os tratamentos com 40% CO2 por 24 ou 48 h limitaram o crescimento micelial até 72 horas após o tratamento. A germinação dos conídios de B. cinerea foi retardada por 12h. Os resultados mostram que o pré-tratamento com 40% CO2 + CA possui grande potencial para ser adotado como prática comercial para conservação de uvas orgânicas / Abstract: Gray mold, caused by Botrytis cinerea Pers, is the main postharvest decay of table grapes. The use of sulfur dioxide (SO2) is the common post-harvest practice for its control. Several researchers are looking for alternative methods of control, because SO2 can cause allergic reactions, damage fruits and also it cannot be applied in organic production system. In this thesis, it was evaluated the effects of applying an atmosphere of 40% CO2 for 24 or 48 hours (pre-storage) combined with controlled atmosphere storage (CA = 12% O2 + 12% CO2) in the control of B. cinerea, and the effects in the quality and sensory attributes of 'Flame Seedless' and 'Crimson Seedless' table grapes. In addition, it was evaluated the efficacy of CaCl2 or ClO2 application in pre-harvest alone or in combination with pre-storage of 40% CO2 for 24 h + CA, to control gray mold on 'Crimson Seedless' table grapes, and the determination of the impact of these treatments on fruit quality. The treatments were applied in certified organic table grapes naturally infected, surface inoculated and nesting inoculated (inoculated with an infected berry). After 4 weeks of storage, the pre-storage in 40% CO2 for 48 hours + CA reduced postharvest rot from 22% to 0.6%, and after 7 weeks, the decay was reduced from 100% to 7.4% in 'Flame Seedless' naturally infected. The pre-storage in 40% CO2 alone also reduced the incidence of gray mold in fruits naturally infected and in artificially inoculated, but it was less effective than combined treatment. The application of CaCl2 or ClO2 pre-harvest reduced the incidence of gray mold on grapes 'Crimson Seedless' inoculated with a spore solution, but there was no control when fruits were nesting inoculated. After 6 weeks at 0oC, the application of CaCl2, and the ClO2 in fruits surface inoculated, reduced the gray mold from 45% to 23.2% and 15.6%, respectively. The pretreatment with 40% CO2 + CA did not affect quality and nor sensory attributes for both varieties tested. In vitro experiments, the treatment with 40% CO2 for 24 or 48 h limited mycelial growth for at least 72 hours after treatment. Conidial germination of B. cinerea was delayed for 12 hours. Our results showed the potential that pre-treatment with 40% CO2 associated with CA has to be adopted in commercial practice for preservation of organic grapes / Doutorado / Tecnologia Pós-Colheita / Doutor em Engenharia Agrícola

South African ‘Eureka’ lemon fruit must be exposed to chilling temperatures (± 0.6°C) as a mandatory quarantine treatment against insect pests for all its overseas markets. Chilling lemon fruit at such temperatures may develop chilling injury (CI) symptoms on the flavedo. This negative effect on fruit quality reduces fruit marketability. This study evaluated postharvest factors influencing physiological, biochemical and ultra-structural mechanisms involved in alleviating CI in lemon fruit. It was hypothesised that treatment with methyl jasmonate (MJ) and salicylic acid (SA) may enhance chilling tolerance in lemon fruit by maintaining cellular integrity and inducing synthesis of enzymatic and non-enzymatic antioxidants. Furthermore, fruit susceptibility to CI was associated with the source of fruit. Lemon fruit were harvested from three locations representative of moderate subtropical, warm temperate and cool subtropical environments. Harvested fruit were treated either with 10 μM MJ, 2 mM SA or 10 μM MJ plus 2 mM SA, stored either at -0.5, 2 or 4.5°C for 0, 7, 14, 21, or 28 days and afterwards transferred to 23°C for a week as shelf-life simulation. Thereafter, fruit were evaluated for alterations in physiological, biochemical and ultra-structural features involved in the manifestation of CI symptoms. Chilling damage was more severe in untreated lemon fruit than in treated lemon fruit. Storing lemon fruit at 4.5°C accelerated the manifestation of CI symptoms more so than at 2°C while storage at -0.5°C delayed the manifestation of CI symptoms. Lemon fruit of moderate subtropical origin were more chilling-tolerant than lemon fruit of warm temperate and cool subtropical origin. Treatment with 10 μM MJ plus 2 mM SA significantly (P < 0.05) improved chilling tolerance in lemon fruit. This treatment effectively maintained membrane integrity, thereby retarding electrolyte leakage and membrane lipid peroxidation as well as mass loss and respiration rate. Treatment with 10 μM MJ plus 2 mM SA was also effective in enhancing the antioxidant concentrations of vitamin E and carotenoids. The production of these antioxidants could have been part of a defence system against chilling damage, reducing CI and maintaining fruit quality. Treatment with 10 μM MJ plus 2 mM SA enhanced the concentration of compounds involved in chilling resistance, such as proline, soluble sugars, ascorbic acid and total phenolics as well as the enzyme phenylalanine ammonia-lyase (PAL). The enhancement of the defence mechanisms may have played a role in enhancing chilling tolerance in lemon fruit. The treatment also inhibited certain enzymes involved in tissue browning, such as peroxidase (POD) which might have contributed to delaying manifestation of symptoms. Polyphenol oxidase (PPO) was found to not be a good biochemical marker of the occurrence of CI. Treatment with 10 μM MJ plus 2 mM SA appeared to be able to enhance chilling tolerance in lemon fruit by maintaining the ultra-structure of the cuticle, cell wall integrity, cell membrane of parenchyma cells of the flavedo. This treatment also preserved the mineral nutrients of the flavedo (carbon, oxygen, phosphorus, potassium, calcium, magnesium, sulphur, sodium, silicon and aluminium) during cold storage. This could have played a role in protecting the fruit against chilling stress and maintaining fruit quality. Treatment with 10 μM MJ plus 2 mM SA reduced ROS production, while the activity of enzymatic antioxidants such as catalyse (CAT), ascorbate peroxidase (APX) and glutathione reductase (GR), and accumulation of essential proteins was enhanced. This increase in activity of enzymatic antioxidants and the presence of stress-responsive proteins in the lemon flavedo could have been directly involved in enhancing chilling tolerance. The CI symptoms were accompanied by an increase in membrane permeability, membrane lipid peroxidation as well as phospholipase D (PLD) and lipoxygenase (LOX) activity; however, treatment with 10 μM MJ plus 2 mM SA effectively reduced the membrane permeability, membrane lipid peroxidation, and PLD and LOX activity induced by the cold treatment. This could have contributed to the efficacy of 10 μM MJ plus 2 mM SA in inhibiting the manifestation of CI symptoms. Treatment with 10 μM MJ plus 2 mM SA enhanced flavedo total antioxidant capacity measured by ferric reducing ability of plasma; 2,2-diphenyl-1-picrylhydrazyl; 2,2-azinobis (3-ethyl-benzothiazoline-6-sulfonic acid) and the oxygen radical absorption capacity assays. The enhancement of antioxidant capacity in lemon flavedo could have contributed to the fruit’s chilling tolerance. Therefore, the effect of 10 μM MJ plus 2 mM SA treatment, enhancing chilling tolerance, may be attributed to its ability to enhance enzymatic and non-enzymatic antioxidants; activate essential proteins and mitigate the effect of ROS accumulation. With the use of 10 μM MJ plus 2 mM SA treatments, the South African citrus industry will be able to meet the quarantine temperature requirements for exportation of lemon fruit whilst reducing economic losses, depending on the preharvest conditions experienced by the fruit in each shipment. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2013.

A Podridão Mole, causada por espécies do gênero Rhizopus, sendo a espécie R. stolonifer a mais comum, é uma das principais doenças pós-colheita de pêssegos. O desenvolvimento do patógeno prejudica a comercialização de pêssegos em mercados atacadistas e varejistas, consistindo em uma das principais causas de rejeição de frutos e da redução do preço de venda da caixa de pêssego. O fungo pode causar podridões em outros frutos e vegetais com níveis similares de perdas. Essa doença está intimamente relacionada à presença de danos físicos ou mecânicos, exemplificados pela presença de injúrias na superfície do fruto, já que Rhizopus é conhecido por penetrar seus hospedeiros via ferimentos. Poucos trabalhos investigaram os mecanismos de penetração do patógeno em pêssegos. Alguns concluíram que o fungo não produz enzimas que auxiliem na penetração direta de frutos. No entanto, observações da ocorrência da doença em pêssegos aparentemente não injuriados sugerem que a penetração direta pode ocorrer. A principal medida de controle da doença consiste no manejo cuidadoso dos frutos justamente para evitar ferimentos. O objetivo desse trabalho consistiu em avaliar os mecanismos de penetração de R. stolonifer em pêssegos, injuriados ou intactos, e caracterizar o progresso espaço-temporal da Podridão Mole nesses frutos. A atividade de enzimas esterases produzidas pelo fungo foi avaliada qualitativamente, a partir da reação de discos de micélio e suspensões de esporos do patógeno em água ou solução nutritiva em diferentes períodos de incubação (0, 4 e 8 horas) com substrato indoxil acetato, para observação da produção de cristais de coloração azul índigo. Os tratamentos que continham discos de micélio e suspensão de esporos em solução nutritiva, após 8 horas de incubação, adquiriram tonalidades mais escuras de azul, devido à formação de cristais oriundos da reação entre enzimas esterases e substrato. Avaliações ao espectrofotômetro foram conduzidas para determinar a quantidade de enzimas produzidas por R. stolonifer quando cultivado em meios com glicose ou cutina, como únicas fontes de carbono. O patógeno foi capaz de crescer em ambos os meios e observou-se maior atividade de enzimas esterases quando o patógeno foi cultivado em meio com cutina. Solução de diisopropil fluorofosfato, inibidor de enzimas cutinases, foi depositada sobre frutos e impediu a manifestação da Podridão Mole em pêssegos inoculados com suspensão de esporos do fungo em solução nutritiva. Pêssegos feridos ou não foram inoculados com suspensão de esporos de R. stolonifer em água e solução nutritiva para estudo do progresso espaço-temporal da Podridão Mole. Frutos sadios colocados próximos a frutos inoculados artificialmente apresentaram sintomas da doença, a qual se disseminou com mesma taxa de progresso em todos os tratamentos. O processo infeccioso de R. stolonifer em pêssegos e nectarinas também foi observado em microscopia óptica e eletrônica de varredura e verificou-se a penetração direta de tecidos intactos pelo fungo. Os resultados obtidos nesse trabalho demonstraram que R. stolonifer é capaz de penetrar diretamente frutos intactos através de esporos germinados em aporte nutritivo externo ao fruto e estolões miceliais. Essas estruturas produzem enzimas esterases, principalmente cutinases, que auxiliam no processo infeccioso. / Soft Rot, caused by Rhizopus stolonifer, is one of the main postharvest diseases on peaches. The pathogen development is prejudicial to the stone fruit commercialization in wholesale and retail markets and the disease can cause reduction in the price of peaches, being one of the main causes of fruit rejection. The pathogen has been responsible for causing rots in other types of fruit and vegetables, with similar level of losses. The disease is related to the occurrence of mechanical and physical damages and the presence of injuries on the fruit surface contributes to the infection by Rhizopus, which is known as a strictly wound parasite. Few studies have investigated the mechanisms of the pathogen penetration in peaches. Some have concluded that the fungus does not produce enzymes that assist in the direct penetration of fruit. However, observations of disease occurrence on apparently uninjured peaches suggest that direct penetration can occur. Careful management to avoid injuries on the fruit is the most important disease control measure. The objective of this research was to evaluate the penetration mechanisms of R. stolonifer on injured or uninjured peaches and characterize the spatio-temporal progress of Soft Rot on these fruit. To determine the esterase enzymes activity, produced by the pathogen, micelial discs and spore suspensions of R. stolonifer on water or nutrient solution in different incubation periods (0, 4 and 8 hours) were added to indoxyl acetate solution, to observe the presence of crystals of indigo blue color. The treatments with micelial discs or spore suspensions on nutrient solution, after 8 hours of incubation, showed darker shade of blue, because of the production of crystals from the reaction between the esterase enzymes and the indoxyl acetate. Spectrophotometer evaluations were carried out to determine the amount of enzymes produced by R. stolonifer when it was grown on culture media with glucose or cutin, as sole carbon sources. The pathogen was able to grow on both media and higher esterase activity was observed when the fungus was grown on cutin media. Diisopropyl fluorophosphate solution, a cutinase inhibitor, was placed over the fruit and prevented Soft Rot development on peaches inoculated with the fungus spore suspension on nutrient solution. Injured or uninjured peaches were inoculated with R. stolonifer spore suspensions on water or nutrient solution to study the spatiotemporal progress of Soft Rot. Healthy fruit placed next to artificially inoculated peaches showed symptoms of the disease, which has spread with the same rate of progress in all treatments. The infectious process of R. stolonifer on peaches and nectarines was also studied on optic and scanning electron microscopy and direct penetration of intact tissues by the fungus was observed. The results of this work showed that R. stolonifer is capable of direct penetration on uninjured peaches by spores germinated on external nutrient support and by micelial stolons. These structures produce esterase enzymes, especially cutinase, that help in the infectious process.

Thesis (MscAgric (Horticulture))--University of Stellenbosch, 2007. / More and more markets develop around the world for South African grapes and it becomes a challenge to store grapes for longer and reach the market with superior quality. The most destructive decay fungus, Botrytis cinerea can cause huge economic losses and successful postharvest control in the table grape industry relies on SO2. This gas not only controls the fungus but also causes losses due to phytotoxicity. SO2 also creates allergic reactions amongst certain people. In modern times the focus is on food safety and governments consequently impose certain regulations and restrictions to restrict the use of chemicals and ensure “cleaner” produce. The objective of this study was to find a steriliser to reduce B. cinerea inoculum on the berry surface prior to storage,to be used in conjunction with the current method of control – the SO2 generator pad.

A Podridão Mole, causada por espécies do gênero Rhizopus, sendo a espécie R. stolonifer a mais comum, é uma das principais doenças pós-colheita de pêssegos. O desenvolvimento do patógeno prejudica a comercialização de pêssegos em mercados atacadistas e varejistas, consistindo em uma das principais causas de rejeição de frutos e da redução do preço de venda da caixa de pêssego. O fungo pode causar podridões em outros frutos e vegetais com níveis similares de perdas. Essa doença está intimamente relacionada à presença de danos físicos ou mecânicos, exemplificados pela presença de injúrias na superfície do fruto, já que Rhizopus é conhecido por penetrar seus hospedeiros via ferimentos. Poucos trabalhos investigaram os mecanismos de penetração do patógeno em pêssegos. Alguns concluíram que o fungo não produz enzimas que auxiliem na penetração direta de frutos. No entanto, observações da ocorrência da doença em pêssegos aparentemente não injuriados sugerem que a penetração direta pode ocorrer. A principal medida de controle da doença consiste no manejo cuidadoso dos frutos justamente para evitar ferimentos. O objetivo desse trabalho consistiu em avaliar os mecanismos de penetração de R. stolonifer em pêssegos, injuriados ou intactos, e caracterizar o progresso espaço-temporal da Podridão Mole nesses frutos. A atividade de enzimas esterases produzidas pelo fungo foi avaliada qualitativamente, a partir da reação de discos de micélio e suspensões de esporos do patógeno em água ou solução nutritiva em diferentes períodos de incubação (0, 4 e 8 horas) com substrato indoxil acetato, para observação da produção de cristais de coloração azul índigo. Os tratamentos que continham discos de micélio e suspensão de esporos em solução nutritiva, após 8 horas de incubação, adquiriram tonalidades mais escuras de azul, devido à formação de cristais oriundos da reação entre enzimas esterases e substrato. Avaliações ao espectrofotômetro foram conduzidas para determinar a quantidade de enzimas produzidas por R. stolonifer quando cultivado em meios com glicose ou cutina, como únicas fontes de carbono. O patógeno foi capaz de crescer em ambos os meios e observou-se maior atividade de enzimas esterases quando o patógeno foi cultivado em meio com cutina. Solução de diisopropil fluorofosfato, inibidor de enzimas cutinases, foi depositada sobre frutos e impediu a manifestação da Podridão Mole em pêssegos inoculados com suspensão de esporos do fungo em solução nutritiva. Pêssegos feridos ou não foram inoculados com suspensão de esporos de R. stolonifer em água e solução nutritiva para estudo do progresso espaço-temporal da Podridão Mole. Frutos sadios colocados próximos a frutos inoculados artificialmente apresentaram sintomas da doença, a qual se disseminou com mesma taxa de progresso em todos os tratamentos. O processo infeccioso de R. stolonifer em pêssegos e nectarinas também foi observado em microscopia óptica e eletrônica de varredura e verificou-se a penetração direta de tecidos intactos pelo fungo. Os resultados obtidos nesse trabalho demonstraram que R. stolonifer é capaz de penetrar diretamente frutos intactos através de esporos germinados em aporte nutritivo externo ao fruto e estolões miceliais. Essas estruturas produzem enzimas esterases, principalmente cutinases, que auxiliam no processo infeccioso. / Soft Rot, caused by Rhizopus stolonifer, is one of the main postharvest diseases on peaches. The pathogen development is prejudicial to the stone fruit commercialization in wholesale and retail markets and the disease can cause reduction in the price of peaches, being one of the main causes of fruit rejection. The pathogen has been responsible for causing rots in other types of fruit and vegetables, with similar level of losses. The disease is related to the occurrence of mechanical and physical damages and the presence of injuries on the fruit surface contributes to the infection by Rhizopus, which is known as a strictly wound parasite. Few studies have investigated the mechanisms of the pathogen penetration in peaches. Some have concluded that the fungus does not produce enzymes that assist in the direct penetration of fruit. However, observations of disease occurrence on apparently uninjured peaches suggest that direct penetration can occur. Careful management to avoid injuries on the fruit is the most important disease control measure. The objective of this research was to evaluate the penetration mechanisms of R. stolonifer on injured or uninjured peaches and characterize the spatio-temporal progress of Soft Rot on these fruit. To determine the esterase enzymes activity, produced by the pathogen, micelial discs and spore suspensions of R. stolonifer on water or nutrient solution in different incubation periods (0, 4 and 8 hours) were added to indoxyl acetate solution, to observe the presence of crystals of indigo blue color. The treatments with micelial discs or spore suspensions on nutrient solution, after 8 hours of incubation, showed darker shade of blue, because of the production of crystals from the reaction between the esterase enzymes and the indoxyl acetate. Spectrophotometer evaluations were carried out to determine the amount of enzymes produced by R. stolonifer when it was grown on culture media with glucose or cutin, as sole carbon sources. The pathogen was able to grow on both media and higher esterase activity was observed when the fungus was grown on cutin media. Diisopropyl fluorophosphate solution, a cutinase inhibitor, was placed over the fruit and prevented Soft Rot development on peaches inoculated with the fungus spore suspension on nutrient solution. Injured or uninjured peaches were inoculated with R. stolonifer spore suspensions on water or nutrient solution to study the spatiotemporal progress of Soft Rot. Healthy fruit placed next to artificially inoculated peaches showed symptoms of the disease, which has spread with the same rate of progress in all treatments. The infectious process of R. stolonifer on peaches and nectarines was also studied on optic and scanning electron microscopy and direct penetration of intact tissues by the fungus was observed. The results of this work showed that R. stolonifer is capable of direct penetration on uninjured peaches by spores germinated on external nutrient support and by micelial stolons. These structures produce esterase enzymes, especially cutinase, that help in the infectious process.

[EN] Citrus spp. (Rutaceae) are the most widely produced fruits and they are grown in over a hundred countries. During postharvest, major losses are caused by fungal diseases, that for decades have been controlled by treatments with synthetic fungicides. However, their use is continuously more restricted by distributors and supermarket chains, which lower the Maximum Residue Level (MRL) to one third of the authorized or even ban the use of certain fungicides. This has loss of efficacy of treatments and development of resistant strains of pathogens. Alternatives are necessary to substitute or combine the use of synthetic fungicides. The objective of the present work was to evaluate alternative treatments against green and blue molds, caused by Penicillium digitatum (Pers.: Fr.) Sacc. and Penicillium italicum Wehmer, respectively. Food additives and GRAS substances were tested in in vivo preliminary tests against green and blue molds. Potassium sorbate (PS) (Chapter 2) and sodium benzoate (SB) (Chapter 1) were the most effective. 60-s dips in 3% (w/v) SB above 50°C reduced by 90% green and blue mold incidence on 'Valencia' oranges after 7 days at 20°C. This treatment was also effective on 'Lanelate' oranges, 'Fino' lemons and 'Ortanique' mandarins, but not on 'Clemenules' mandarins. Heated solutions combining SB with low doses of imazalil (IMZ) were synergistic. In semi-commercial trials with 'Marisol' Clementine mandarins, the combination PS+IMZ at 20°C allowed a significant reduction of the IMZ doses still controlling green mold. A new colorimetric method that employed extraction of PS from macerated fruit, followed by reaction with 2-thiobarbituric acid (Chapter 3) showed that in oranges treated with PS and stored at 15°C, residues declined initially rapidly and later more slowly, until residues stopped declining after 6 d. A brief double-dip rinse in tap water, immediately after immersion of lemons in a 2% (w/v) PS, removed more than 90% of PS residue. Exposure at 33ºC with 15 kPa CO2 for 24 h or 30 kPa O2 for 48 h effectively controlled both green and blue molds after 7 days of incubation at 20ºC, but control of both diseases lowered after 15 days (Chapter 4). Combining PS dip treatments with gas exposure showed a synergistic effect, that maintained the efficacy of combined treatments during 15 days. In cold storage, after 14, 28, and 42 days, green mold incidence on 'Clemenules' and 'Ortanique' mandarins treated with PS dips and 30kPa O2 for 48h was reduced by 100, 96 and 68%, and 100, 97 and 79%, respectively. Again, a synergistic effect between treatments was observed (Chapter 5). Postharvest green mold and blue molds were effectively controlled by fumigation of lemons and oranges for 6 h at 22ºC with two applied dosages of 3000 ¿L L-1 of ammonia that was injected initially and again 2 h later (Chapter 6). Ammonia fumigation controlled an IMZ-resistant isolate of P. digitatum. When fruit were first immersed in 10 or 30 mg L-1 IMZ (about 10% of typical commercial rates) before ammonia fumigation, a single fumigation with 1500 ¿L L-1 of ammonia was adequate to control both diseases and the increase in effectiveness was additive or synergistic. All these treatments, at different degrees, could replace synthetic fungicides or augment IMZ performance in citrus postharvest decay management. The development of green and blue molds on the most commercially important citrus species and cultivars was assessed for four consecutive harvest seasons and associated with fruit quality parameters (Chapter 7). Fruit susceptibility of the cultivars to green mold in increasing order was Nova, Sanguinelli, Ortanique, Lanelate, Navelate, Fortune, Clemenules, Valencia, W. Navel, Oronules, Clemenpons, Marisol, Salustiana, Hernandina, and Nadorcott. Peel characteristics were the most influencing quality parameters on the susceptibility of citrus fruit to green and blue molds. / [ES] Los cítricos (Citrus spp. fam. Rutaceae) son la fruta más consumida a nivel mundial y se cultivan en más de un centenar de países. Durante el manejo en poscosecha, la mayor parte de las pérdidas se deben a enfermedades fúngicas, que durante décadas se han controlado mediante tratamientos con fungicidas de síntesis. Sin embargo, su uso está continuamente más restringido por parte de los distribuidores y cadenas de supermercados, que reducen el Límite Máximo de Residuos (LMR) a un tercio del establecido o incluso prohíben el uso de ciertos fungicidas. Esto ha provocado la pérdida de eficacia de los tratamientos y el desarrollo de cepas de patógenos resistentes a los fungicidas. Se necesitan pues alternativas para sustituir o combinar con el uso de fungicidas de síntesis. El objetivo de este trabajo fue evaluar tratamientos alternativos contra las podredumbres verde y azul, causadas por Penicillium digitatum (Pers.: Fr.) Sacc. y Penicillium italicum Wehmer, respectivamente. Aditivos alimentarios y sustancias GRAS se probaron en test in vivo preliminaries contra los mohos verde y azul. El benzoato sódico (BS; Capítulo 1) y el sorbato potásico (SP; Capítulo 2) fueron los más eficaces. Baños de 60 s en 3% (p/v) BS sobre 50°C redujeron en un 90% la incidencia de las podredumbres verde y azul en naranjas 'Valencia Late' tras 7 días a 20°C. Estos tratamientos fueron también efectivos en naranjas 'Lanelate', limones 'Fino' y mandarinas híbridas 'Ortanique', pero no en mandarinas 'Clemenules'. La combinación de baños calientes de BS con dosis bajas de imazalil (IMZ) fueron sinérgicas. Un nuevo método colorimétrico que empleó la extracción del SP de la fruta macerada, seguido de una reacción con ácido 2-tiobabitúrico (Capítulo 3) mostró que en naranjas tratadas con SP almacenadas a 15°C, los residuos descendieron rápidamente al inicio y lentamente más tarde, hasta que dejaron de descender tras 6 días. Un doble aclarado rápido con agua corriente inmediatamente después de la inmersión de limones en SP al 2% (p/v), eliminó más del 90% del residuo de SP. Los choques gaseosos a 33ºC y 15kPa CO2 durante 24 h o 30 kPa O2 durante 48 h controlaron de manera eficaz las podredumbres verde y azul tras 7 días de incubación a 20ºC, pero el control de las dos podredumbres descendió tras 15 días (Capítulo 4). En almacenamiento en frío, tras 14, 28 y 42 días, la incidencia de moho verde en mandarinas 'Clemenules' y 'Ortanique' tratadas con baños con SP y 30kPa O2 durante 48h se redujo en un 100, 96 y 68%, y 100, 97 y 79%, respectivamente. De nuevo, una fuerte sinergia se observó entre los tratamientos (Capítulo 5). Las podredumbres verde y azul se controlaron eficazmente mediante la fumigación de limones y naranjas durante 6 h a 22ºC con dos dosis de 3000 ¿L L-1 amoniaco, inyectadas al inicio del tratamiento y 2 h después (Capítulo 6). El tratamiento con amoniaco controló una cepa de P. digitatum resistente a IMZ. Cuando la fruta se bañó en 10 o 30 mg L-1 IMZ (un 10% de la dosis comercial) antes de la fumigación con amoniaco, una sola aplicación con 1500 ¿L L-1 amoniaco fue suficiente para controlar las dos podredumbres, y el incremento en la eficacia fue aditivo o sinérgico. Todos estos tratamientos, a diferentes niveles, podrían sustituir a los fungicidas de síntesis o aumentar la eficacia de los tratamientos con IMZ en el manejo poscosecha de los cítricos. El desarrollo de las podredumbres verde y azul en las especies y variedades de cítricos más importantes comercialmente se evaluó durante cuatro campañas consecutivas y se relacionó con los parámetros de calidad de la fruta (Capítulo 7). La susceptibilidad de los cultivares en orden creciente fue Nova, Sanguinelli, Ortanique, Lanelate, Navelate, Fortune, Clemenules, Valencia, W. Navel, Oronules, Clemenpons, Marisol, Salustiana, Hernandina, y Nadorcott. Las características de la corteza fueron los parámetros de calidad / [CAT] Els cítrics (Citrus spp. fam. Rutaceae) son la fruita més consumida a nivell mundial i es cultiven en un centenar de països. Durant la poscollita, la major part de les pèrdues es deuen a malalties fúngiques, que durant dècades s'han controlat mitjançant tractaments amb fungicides de síntesi. No obstant, l'ús d'aquestes pràctiques està contínuament més restringit per part dels distribuïdors y cadenes de supermercats, que redueixen el Límit Màxim de Residus (LMR) a un terç del permès per la legislació o inclús prohibeixen l'ús d'alguns fungicides. Açò ha provocat la minora de l'eficàcia dels tractaments poscollita i el desenvolupament de soques dels patògens resistents als fungicides. Es necessari per lo tant trobar i implementar alternatives per a substituir o combinar l'ús de fungicides de síntesi. L'objectiu d'aquest treball ha sigut avaluar tractaments alternatius contra les podridures verda i blava, causades per Penicillium digitatum (Pers.: Fr.) Sacc. i Penicillium italicum Wehmer, respectivament. Additius alimentaris i substàncies GRAS es provaren en test in vivo preliminars contra les podridures verda i blava. El benzoat sòdic (BS; Capítol 1) i el sorbat potàsic (SP; Capítol 2) foren els més eficaços. Solucions calentes de BS combinades amb baixes dosis d'imazalil (IMZ) foren sinèrgiques. Esta combinació va reduir l'incidència de les podridures verda i blava en quasi el 100% en taronges 'Valencia Late' després de 8 setmanes a 5°C i 7 dies a 20°C. En assajos semicomercials mandarines 'Marisol', la combinació SP+IMZ a 20°C va permetre una baixada significativa de la dosis de IMZ sense perdre eficàcia contra la podridura verda. Un nou mètode colorimètric que inclou l'extracció del SP de la fruita macerada, seguit d'una reacció amb àcid 2-tiobabitúric (Capítol 3) mostrà que en taronges tractades amb SP conservades a 15°C, els residus descendiren ràpidament al inici i lentament mes tard, fins que deixaren de descendir després de 6 dies. Un doble rentat ràpid amb aigua corrent immediatament després de d'immersió de llimones en SP al 2% (p/v), eliminà més del 90% del residu de SP. Els xocs gasosos a 33ºC i 15kPa CO2 durant 24 h o 30 kPa O2 durant 48 h controlaren de manera eficaç les podridures verda i blava després de 7 dies d'incubació a 20ºC, però el control de les dos podridures descendí després de 15 dies (Capítol 4). La combinació de banys amb SP i xocs gasosos mostrà un efecte sinèrgic, que mantingué l'eficàcia dels tractaments combinats durant 15 dies. En conservacions en fred, després de 14, 28 i 42 dies, d'incidència de podridura verda en mandarines 'Clemenules' i 'Ortanique' tractades en banys amb SP i 30kPa O2 durant 48h es reduí en un 100, 96 i 68%, i 100, 97 i 79%, respectivament. De nou, una forta sinergia s'observà entre els tractaments (Capítol 5). Les podridures verda i blava es controlaren eficaçment mitjançant la fumigació de llimones i taronges durant 6 h a 22ºC amb dos dosis de 3000 ¿L L-1 amoníac, injectades al inici del tractament i 2 h després (Capítol 6). El tractament amb amoníac controlà una soca de P. digitatum amb un alt nivell de resistència a IMZ. Tots estos tractaments, a diferents nivells, podrien substituir als fungicides de síntesis o augmentar l'eficàcia dels tractaments amb IMZ en el maneig poscollita dels cítrics. El desenvolupament de les podridures verda i blava en les especies y varietats de cítrics més importants comercialment s'avaluà durant quatre campanyes consecutives i es relacionà amb els paràmetres de qualitat de la fruita (Capítol 7). La susceptibilitat dels distints cultivars en ordre creixent fon Nova, Sanguinelli, Ortanique, Lanelate, Navelate, Fortune, Clemenules, Valencia, W. Navel, Oronules, Clemenpons, Marisol, Salustiana, Hernandina, i Nadorcott. Les característiques de la pell foren els paràmetres de qualitat més influents en la susceptibilitat dels cítrics a les pod / Montesinos Herrero, CI. (2016). Evaluation of alternatives to synthetic fungicides to control citrus postharvest diseases [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/63662 / TESIS

Ph.D. (Agriculture)) -- University of Limpopo, 2021 / The rind physiological disorders incidence such as rind pitting is a challenge to the citrus industry as it affects appearance; and ultimately, acceptability and purchase in both local and international markets. Although the internal quality is not directly affected by rind pitting, fruit damaged by this disorder are rejected in the fresh fruit market. The susceptibility to this disorder varies among citrus fruit cultivars. Other factors impacting rind physiological disorders include; pre-harvest environmental conditions and postharvest storage conditions. However, the main cause of this disorder is still unknown. In South Africa, ‘Benny’ valencias are the most prone orange cultivars to rind pitting disorder within the sweet-orange-type. Therefore, the aim of this study was to investigate production site and postharvest treatments’ effect on physico-chemical, biochemical properties, antioxidants, rind soluble sugars and gene expression in relation to rind pitting development of ‘Benny’ valencia citrus fruit. During 2016 and 2017 seasons, the study was conducted, whereby, ‘Benny’ valencia citrus fruit were harvested from Tzaneen, Groblersdal and Musina in South Africa. After harvesting, the fruits were transported to the Agricultural Research Council- Tropical and Subtropical Crops (ARC-TSC) postharvest laboratory in Nelspruit for sorting, grading treatment, cold storage and post-storage quality evaluation. After sorting and grading, fruits were subjected to the following treatments: T1 = no wax plus dehydration, T2 = wax plus dehydration and T3 = wax plus no dehydration. Dehydrated treatments were applied for 3 days at relative humidity of ±45%, thereafter, fruit were stored at -0.6 and 4.5°C for 28 days plus 7 days shelf-life. After removal from cold storage plus 7 days shelf-life, fruit were analysed for rind pitting incidence (RPI), weight loss percentage (WL), firmness, total electrolyte leakage (TEL), total soluble solids (TSS), titratable acidity (TA) and TSS: TA ratio. xxvi Afterwards, fruit were peeled to remove flavedo, thereafter; the flavedo peels were freeze-dried, milled and stored at -21°C for further physiological analysis. Freeze dried flavedo peel was analysed for total flavonoids, total phenolics, vitamin C, soluble sugars (glucose, fructose and sucrose), antioxidant assays (FRAP, DPPH, ABST and ORAC) and genes. The results showed that rind pitting incidence was high on fruit subjected to wax plus no dehydration across all storage temperatures and production sites. Furthermore, results showed that fruit harvested from Musina exposed to T1 had higher incidence of rind pitting than those from Groblersdal and Tzaneen, irrespective of storage temperature. Meanwhile, fruit harvested from Musina had the highest TEL when compared with Groblersdal and Tzaneen irrespective of treatments and storage temperatures. A significantly higher (P<0.05) WL was observed in Musina fruit harvested from Tzaneen exposed to T3 at both storage temperatures. Moreover, increased TSS was observed after storage across all production site and postharvest treatments. The study showed that production site and postharvest treatments had a significant influence on rind pitting and total electrolyte leakage. Additionally, fruit treated with no wax + dehydration was found to be more susceptible to rind pitting. However, fruit sourced from Tzaneen had significantly (P<0.0001) high TPC and TFC, irrespective of postharvest treatments therefore, low rind pitting incidence. While rind vitamin C was higher in fruit from Groblersdal when compared with Tzaneen and Musina. However, low RPI was also observed in fruit sourced from Groblersdal. Fruit from Musina subjected to wax plus dehydration had higher RSA and low RPI at both temperatures when compared with fruit sourced from Groblersdal and Tzaneen. Therefore, wax plus dehydration resulted in low rind pitting with an increased accumulation of rind biochemical concentrations, xxvii irrespective of cold storage temperatures. These results suggested that there is a link between rind pitting and rind biochemical concentrations in the ‘Benny’ valencia citrus fruit. Moreover, fruit from Musina subjected to wax plus dehydration had higher antioxidant measured by DPPH and low RPI at both low storage temperatures when compared with fruit harvested from Groblersdal and Tzaneen. Furthermore, fruit harvested from Musina and treated with no wax plus dehydration, thereafter, stored at -0.6°C had low RPI with high antioxidant activity measured by FRAP than Tzaneen and Groblersdal regions in both seasons. With respect to sugars, fructose was not significantly (P<0.05) affected by production sites, postharvest treatments and cold storage temperature, hence, the low pitting incidence. The highest glucose was observed in fruit harvested from Groblersdal, irrespective of treatments and cold storage temperatures when compared with those from Tzaneen and Musina, low RPI was also observed in fruit harvested from Groblersdal. However, fruit harvested from Groblersdal treated with wax plus dehydration and stored at 4.5°C had higher sucrose and low RPI when compared with Tzaneen and Musina. Moreover, this study suggested that soluble sugars in ‘Benny’ valencia flavedo during cold storage is involved in rind pitting tolerance mediated by wax plus dehydration treatment. Three homologic genes: CsCP gene; CsNAC-domain protein gene; CsCP-F gene; were chosen to examine the relationship between their expression and citrus rind pitting through quantitative RT-PCR analysis in pitting and no-pitting fruits. Results showed that the expression of CsCP, CsNAC and CsCP-F genes were all higher in the pitting rind fruit harvested from Tzaneen and low in fruit with low pitting. Groblersdal and Musina fruit had low expression of genes and low rind pitting was observed. Therefore, findings suggested that CsCP, CsNAC and CsCP-F genes may xxviii be linked to non-chilling rind pitting and could serve as targets for future investigation. Generally, the overall results obtained in this study provided an understanding into the previous unknown complexities of citrus non-chilling rind pitting. Moreover, the study revealed that the studied factors had an influence on non-chilling rind pitting and physico-chemical properties of ‘Benny’ valencia citrus fruit. In addition, postharvest treatments resulted in low non-chilling rind pitting with an increased accumulation of rind biochemical concentrations. The fruit with high antioxidant capacity were found to be tolerant to rind pitting, whereas, fruit with low antioxidant capacity were found to be susceptible to rind pitting. Furthermore, soluble sugars are believed to be involved in the defence mechanisms against non-chilling rind pitting in the fruit. Gene expression changes also provided clues about the possible mechanisms involved in non-chilling rind pitting development. / National Research Fund, Agricultural Research Council Tropical and Subtropical Fruit Crops and Citrus Academy

Thesis (M.Sc.( Agriculture (Horticulture)) -- University of Limpopo, 2022 / Avocado fruit ‘Hass’ exocarp changes colour from green to purple and black during ripening. However, uniform purple or black exocarp colour is not achieved during ripening, leading to consumers' rejection of fruit for not meeting quality standards. Avocado ‘Hass’ fruit harvested early remain green or develop a multicoloured appearance, concurrently devaluing their commercial value; and, therefore, unattractive to consumers. Therefore, this study aimed to investigate the role of sucrose and calcium postharvest pulsing on early matured ‘Hass’ avocado exocarp colour change during ripening. In this study, early matured ‘Hass’ avocado fruit were harvested from Halls and Sons, Mataffin farm (25°25’39.13” S, 30°55’52.84” E), Nelspruit, South Africa with 10 cm pedicel at commercial dry matter content (22%). Thereafter, the fruit were transported to the University of Mpumalanga laboratory. In the laboratory, the study was divided into two experiments: Experiment 1 ‘Hass’ fruit were continuously infused through the pedicel with different sucrose concentrations; 0 (control), 0.2 and 0.5 mM L-1. Experiment 2 fruit were infused with different calcium chloride (CaCl2) concentrations; 0 (control), 2 and 3 mM L-1. In both experiments, treated and untreated fruit were stored at 5.5°C for 28 days. After removal from cold storage, fruit were ripened at room temperature (±25°C) and evaluated every other day for firmness, subjective colour (visual colour), objective colour parameters (lightness-L*, chroma-C* and hue angle- h°), external chilling injury and ripening percentage. The results showed that Su (0.2 mM L-1) pulsing extended the ripening period by one day, corresponding with maintained fruit firmness. Furthermore, Su (0.2 mM L-1) treated fruit reduced the ‘Hass’ avocado fruit chilling injury index (CII) during cold storage. With respect to colour change, Su (0.5 mM L-1) treated fruit developed purple colour when compared with Su (0.2 mM L-1), which only developed to olive colour on the final ripening day (day 6). In addition, the results showed that all sucrose concentrations had a significant decreasing effect (P < 0.05) on objective colour parameters (L*, C* and h°) and increasing visual colour rating. With respect to CaCl2 treatments, fruit firmness decline was significantly delayed, which resulted in extended ripening time. Moreover, CaCl2 (2 and 3 mM L-1) significantly decreased (P < 0.05) pericarp objective colour parameters (L*, C* and h°) and increased visual colour rating and developed purple colour on the final ripening day (days 6 and 8, respectively). In addition, pulsing with CaCl2 (2 and 3 mM L-1) concentration reduced chilling injury during storage compared with control fruit. In conclusion, the results of this study indicated that Su and CaCl2 applied as postharvest treatments may contribute to avocado colour development by increasing anthocyanin accumulation. However, future research is required to investigate whether these treatments affect anthocyanin biosynthesis at the gene level.

Thesis (MEng) -- Stellenbosch University, 2014. / ENGLISH ABSTRACT: As overpopulation threatens the world’s ability to feed itself, food has become an invaluable resource. Unfortunately, almost a third of the food produced for human consumption is lost annually. Pests including insects, phytopathogens and weeds are responsible for more than a third of the annual major crop losses suffered around the world. The majority of current post-harvest control strategies employ synthetic agents. These compounds, however, have been found to be detrimental to the environment as well as human health, which has led researchers to investigate alternative strategies. Biocontrol agents are environmentally compatible, have a lower toxicity and are biodegradable, making them an attractive alternative to the synthetic control agents. The lipopeptides produced by Bacillus spp. in particular, have shown great potential as biocontrol agents against various post-harvest phytopathogens. Most biocontrol strategies apply the biocontrol organism, for example Bacillus, directly, whereas this study focused on the use of the lipopeptide itself as an antifungal agent. This is advantageous as the lipopeptides are less sensitive to their surroundings, such as temperature and pH, compared to living organisms, allowing for the production of a standardized product. This study investigated the production of the Bacillus lipopeptides surfactin, fengycin and iturin under controlled batch conditions. Parameters increasing lipopeptide production were quantified, focussing on antifungal lipopeptides (iturin and fengycin), and lipopeptide production was optimized. Experiments were performed in a fully instrumented 1.3 L bench-top bioreactor and lipopeptide analyses were performed via high pressure liquid chromatography (HPLC) and liquid chromatography-mass spectroscopy (LC-MS). After screening four Bacillus spp., Bacillus amyloliquefaciens DSM 23117 was found to be the best antifungal candidate. This was based on it outperforming other candidates in terms of maximum antifungals produced, Yp/x,antifungals (yield per cells), and antifungal productivity. Nitrate, in the form of NH4NO3, was critical for lipopeptide production and an optimum concentration was observed above which the CDW (cell dry weight) no longer increased significantly and both μmax (maximum specific growth rate, h-1) and lipopeptide production decreased. For μmax, the optimum NH3NO4 concentration was 10 g/L and for lipopeptides it was 8 g/L. At these respective NH4NO3 concentrations μmax = 0.58 (h-1), the maximum antifungals (fengycin and iturin) were 285.7 mAU*min and the maximum surfactin concentration was 302 mg/L. The lipopeptides produced by B. amyloliquefaciens, the antifungals (fengycin and iturin) and surfactin, are secondary metabolites, regardless of the optimization treatment, i.e. increased NH4NO3 concentrations. Using 30% enriched air extended the nitrate utilization period, suggesting that when increasing supply concentration, more oxygen was available to act as electron acceptors, allowing nitrate to be used for lipopeptide production. The number of iturin and fengycin homologues generally increased with an increase in nitrate concentration. This suggested that process conditions, such as nitrate concentration, can be used to manipulate homologue ratios, allowing for the possibility to tailor-make biocontrol-agent upstream, during the production process, and possibly increase the efficacy of the biocontrol strategy. The lipopeptides produced by B. amyloliquefaciens showed complete inhibition against Botryotinia fuckeliana and diminished the growth capabilities of Botrytis cinerea. No inhibition was observed against Penicillium digitatum. These results indicate potential of the biocontrol strategy, although scale-up and fed-batch studies are recommended, especially when considering commercial implementation. Studies regarding the lipopeptide application method, i.e. a single application or multiple applications, should also be investigated as this will influence the efficacy of the lipopeptides against the target organisms. / AFRIKKANSE OPSOMMING: Met oorbevolking wat die wêreld se vermoë om die groeiende bevolking te onderhou belemmer, het dit noodsaaklik geword om huidige voedselbronne te beskerm. Daar word beraam dat een derde van die voedsel wat wêreldwyd geproduseer word vir menslike verbruik verlore gaan elke jaar. Verder is insekte, plantpatogene en onkruide verantwoordelik vir meer as ‘n derde van die verliese rakend jaarlikse oeste. Meeste bestaande na-oes beheermetodes maak gebruik van sintetiese stowwe. Ongelukkig kan hierdie verbindings nadelig wees vir die omgewing sowel as menlike gesondheid. Navorsers het hulsef dus toespits daarop om alternatiewe beheermetodes te ondersoek. Bio-beheermetodes is omgewingsvriendelik sowel as bio-afbreekbaar, wat hulle ideale alternatiewe maak vir die sintetiese stowwe. Bacillus spp. lipopeptiede het veral hoë potensiaal getoon as bio-beheermiddels teen verskeie na-oes plantsiektes. Meeste bio-beheermetodes wend die biobeheer organisme, soos Bacillus, direk aan, waar hierdie studie op die gebruik van lipopeptiede as ‘n beheermiddel gefokus het. Die voordeel is dat lipopeptidiede minder sensitief is vir hul omgewings, soos temperatuur en pH, i.v.m. organismes en die moontlikheid bied van ‘n gestandardiseerde produk. Hierdie studie het die produksie van spesifieke Bacillus lipopeptide, naamlik surfactin, fengycin en iturin, onder beheerde lottoestande ondersoek. Parameters wat lipopeptied produksie verhoog is gekwantifiseer, spesifiek antifungiese middels (iturin en fengycin) en lipopeptied produksie is geoptimeer. Eksperimente is uitgevoer in ‘n 1.3 L bioreaktor en lipopeptiedanaliese is met behulp van hoë druk vloeistof chromatografie en vloeistofchromatografie-massa spektroskopie uitgevoer. Van die vier moontlike Bacillus spp., was Bacillus amyloliquefaciens DSM 23117 die mees belowende antifungus-produserende kandidaat. Dit het beter resultate gelewer in terme van maksimale antifungiese produksie, Yp/x,antifungies (opbrengs per sel) asook antifungiese produktiwiteit. Nitraat, in hierdie geval NH4NO3, was noodsaaklik vir lipopeptied produksie en ‘n optimale konsentrasie is waargeneem waarbo die seldigtheid nie meer beduidend toegeneem het nie en beide die μmax (maksimale spesifieke groei tempo, h-1) en lipopeptied produksie afgeneem het. Die optimale NH4NO3 konsentrasie vir μmax was 10 g/L en vir lipopeptiedproduksie was 8 g/L. By 10 g/L NH4NO3 was μmax = 0.58 (h-1) en by 8 g/L was die maksimale antifungiese produksie (fengycin en iturin) 285.7 mAU*min en die maksimale surfactin produksie 302 mg/L onderskeidelik. Die lipopeptide, die antifungiese middels (fengycin en iturin) en surfactin, geproduseer deur B. amyloliquefaciens is sekondêre metaboliete, ongeag van die optimerings-behandelinge wat toegepas word, soos ‘n verhoging in NH4NO3 konsentrasie. Die gebruik van 30% verrykte suurstof het die nitraat verbruikingsperiode verleng, wat voorgestel het dat met die verryking, meer suurstof beskikbaar was om te dien as finale elektron ontvanger en sodoende die nitraat beskikbaar te stel vir lipopeptied produksie. Iturin en fengycin homoloë, oor die algemeen, het toegeneem soos wat die nitraat konsentrasie verhoog is. Hierdie resultate dui daarop dat prosestoestande, soos nitraat konsentrasie, gebruik kan word om die verhouding waarin lipopeptied homoloë geproduseer word te manipuleer. Hierdie resultate dui op die potensiaal vir die stroomop produksie van ‘n unieke bio-beheermiddel, wat die effektiwiteit van die bio-beheermetode moontlik sal verhoog. Die geproduseerde lipopeptiede het totale inhibisie getoon teen Botryotinia fuckeliana en ook fungiese aktiwiteit belemmer met Botrytis cinerea. Geen inhibisie is getoon teen Penicillium digitatum nie. Hierdie resultate toon die potensiaal van die bio-beheermetode, maar ‘n opskalerings-studie asook ‘n voerlot studie word aanbeveel, veral met die oog op moontlike kommersiële implementering van die strategie. Verdere studies met betrekking tot die aanwendingsmetode van die lipopeptiede moet ook verder ondersoek word, m.a.w. enkel teenoor menigte aanwendigs, aangesien dit die effektiwiteit van die lipopeptiede teen die teikenorganismes sal beïnvloed.

M. Tech. Agriculture / Brown rot caused by Monilinia laxa is the main pre and postharvest disease of peaches; it affects the shelf life and marketability of peaches. Increasing consumer concern regarding food safety makes it necessary to search for natural environmentally friendly alternative products for postharvest disease control. The objective of this study is to develop an environmentally friendly essential oil technology for the control of brown rot (M. laxa) in peaches at postharvest stage to replace the currently used synthetic fungicide (Iprodione)