Auswahl der wissenschaftlichen Literatur zum Thema „Citrus fruits Physiology“

AbstractCarotenoids in citrus contribute to the quality of the fruit, but the mechanism of its transcriptional regulation is fairly unknown. Here, we characterized a citrus FRUITFULL sub-clade MADS gene, CsMADS5, that was ripening-inducible and acted as a nucleus-localized trans-activator. Transient overexpression of CsMADS5 in citrus induced fruit coloration and enhanced carotenoid concentrations. The expression of carotenogenic genes including phytoene synthase (PSY), phytoene desaturase (PDS), and lycopene β-cyclase 1 (LCYb1) was increased in the peels of fruits overexpressing CsMADS5. Similar results were observed from stable overexpression of CsMADS5 in tomato fruits and citrus calli, even though the effect of CsMADS5 on carotenoid metabolism in transgenic citrus calli was limited. Further biochemical analyses demonstrated that CsMADS5 activated the transcription of PSY, PDS, and LCYb1 by directly binding to their promoters. We concluded that CsMADS5 positively regulates carotenoid biosynthesis in fruits by directly activating the transcription of carotenogenic genes. Moreover, CsMADS5 physically interacted with a positive regulator CsMADS6, indicating that CsMADS5 may form an enhancer complex with CsMADS6 to synergistically promote carotenoid accumulation. These findings expand our understanding of the complex transcriptional regulatory hierarchy of carotenoid biosynthesis during fruit ripening.

The increased consumption of fruits, vegetables, and whole grains contributes to the reduced risk of many diseases related to metabolic syndrome, including neurodegenerative diseases, cardiovascular disease (CVD), diabetes, and cancer. Citrus, the genus Citrus L., is one of the most important fruit crops, rich in carotenoids, flavonoids, terpenes, limonoids, and many other bioactive compounds of nutritional and nutraceutical value. Moreover, polymethoxylated flavones (PMFs), a unique class of bioactive flavonoids, abundantly occur in citrus fruits. In addition, citrus essential oil, rich in limonoids and terpenes, is an economically important product due to its potent antioxidant, antimicrobial, and flavoring properties. Mechanistic, observational, and intervention studies have demonstrated the health benefits of citrus bioactives in minimizing the risk of metabolic syndrome. This review provides a comprehensive view of the composition of carotenoids, flavonoids, terpenes, and limonoids of citrus fruits and their associated health benefits.

Abstract Indonesia is tropical country and has many islands, thus, postharvest problem arises from both inter-island and export in order shipping the tropical fruit from center of production to consumers. This review is an effort in making a contribution to solve the postharvest of fruit problem such as perishable short storage life. After review study, there are facts and recommendation been made. First one durian, citrus, mango, pineapples, papaya, banana, and salacca have big amount of production annually, thus, it required the most effort in distributing products. The potential but still lower production to boost the export. Second to study postharvest physiology properly of star fruit, duku, durian, citrus siam, pamelo, mango, mangosteen, jackfruit, rambutan, sapodilla, salacca, breadfruit, water melon, and grapes which true topical, mostly still limited data. Even though passion fruit, apple, and papaya have plenty research data there are still some needs of study. Third one, to study the senescent behaviour i.e. respiration and ethylene production, is still relevant in quick check for choosing postharvest treatment.

In this work, we assess the potential of waste products of Phlegrean mandarin (Citrus reticulata Blanco), namely seeds and peel, to be reutilized as a source of bioactive compounds beneficial for the human diet. Starting from the evidence that the by-products of this specific cultivar are the most powerful sources of antioxidants compared to pulp, we have investigated if and how the bioactive compounds in peel and seeds may be affected by fruit ripening. Three stages of fruit ripening have been considered in our study: unripe fruits = UF, semi-ripe fruits = SRF, ripe fruits = RF. The overall results indicated that RF showed the highest concentration of antioxidants. Among fruit components, peel was the richest in total antioxidant capacity, total polyphenol content, total flavonoids, total chlorophylls and carotenoids, while seeds exhibited the highest concentration of total condensed tannins and ascorbic acid. The liquid chromatography-tandem mass spectrometry (LC-MS/MS) assay indicates the occurrence, in peel extracts, of 28 phenolic compounds, mainly flavonoids (FLs); in seeds, 34 derivatives were present in the first stage (UF), which diminish to 24 during the ripening process. Our data indicated that the content of phytochemicals in citrus strongly varies among the fruit components and depends on the ripening stage. The higher antioxidant activity of peel and seeds, especially in RF, encourage a potential use of by-products of this specific citrus cultivar for industrial or pharmacological applications. However, to maximize the occurrence of desired bioactive compounds, it is important also to consider the ripening stage at which fruits must be collected.

Abstract The aim of this work was to evaluate the general role of the vacuolar pyrophosphatase proton pump (V-PPase) in sucrose accumulation in citrus species. First, three citrus V-PPase genes, designated CsVPP-1, CsVPP-2, and CsVPP-4, were identified in the citrus genome. CsVPP-1 and CsVPP-2 belonging to citrus type I V-PPase genes are targeted to the tonoplast, and CsVPP-4 belonging to citrus type II V-PPase genes is located in the Golgi bodies. Moreover, there was a significantly positive correlation between transcript levels of type I V-PPase genes and sucrose, rather than hexose, content in fruits of seven citrus cultivars. Drought and abscisic acid treatments significantly induced the CsVPP-1 and CsVPP-2 transcript levels, as well as the sucrose content. The overexpression of type I V-PPase genes significantly increased PPase activity, decreased pyrophosphate contents, and increased sucrose contents, whereas V-PPase inhibition produced the opposite effect in both citrus fruits and leaves. Furthermore, altering the expression levels of type I V-PPase genes significantly influenced the transcript levels of sucrose transporter genes. Taken together, this study demonstrated that CsVPP-1 and CsVPP-2 play key roles in sucrose storage in the vacuole by regulating pyrophosphate homeostasis, ultimately the sucrose biosynthesis and transcript levels of sucrose transport genes, providing a novel lead for engineering or breeding modified taste in citrus and other fruits.

Abstract Chromoplast-specific lycopene β-cyclase (LCYb2) is a critical carotenogenic enzyme, which controls the massive accumulation of downstream carotenoids, especially provitamin A carotenoids, in citrus. Its regulatory metabolism is largely unknown. Here, we identified a group I ethylene response factor, CsERF061, in citrus by yeast one-hybrid screen with the promoter of LCYb2. The expression of CsERF061 was induced by ethylene. Transcript and protein levels of CsERF061 were increased during fruit development and coloration. CsERF061 is a nucleus-localized transcriptional activator, which directly binds to the promoter of LCYb2 and activates its expression. Overexpression of CsERF061 in citrus calli and tomato fruits enhanced carotenoid accumulation by increasing the expression of key carotenoid pathway genes, and increased the number of chromoplasts needed to sequester the elevated concentrations of carotenoids, which was accompanied by changes in the concentrations of abscisic acid and gibberellin. Electrophoretic mobility shift and dual-luciferase assays verified that CsERF061 activates the promoters of nine other key carotenoid pathway genes, PSY1, PDS, CRTISO, LCYb1, BCH, ZEP, NCED3, CCD1, and CCD4, revealing the multitargeted regulation of CsERF061. Collectively, our findings decipher a novel regulatory network of carotenoid enhancement by CsERF061, induced by ethylene, which will be useful for manipulating carotenoid accumulation in citrus and other plants.

This study was conducted to perform symptomological identification of Citrus Psorosis Virus (CPsV) in Northern Cyprus. This is the oldest known citrus virus disease, which causes huge decrease in citrus fruits’ quality. The first symptoms of the disease were found in Florida and California in the 1890s. The most important and well known symptoms of CPsV are dehiscence and spalling of the trunk and branches of old trees. Chlorotic spotting and ringspot may also be caused on the leaves of infected young trees.There were reports not to kill the infected trees in the Mediterranean basin and America, but the disease leads to an important reduction in yield and fruit quality in time. Recent available verbal information among the farmers in Northern Cyprus claims that there is an increase in the symptoms of chlorotic spotting on leaves and spalling on tree trunks, which are thought to be caused by CPsV. Grafting is a common management technique on citrus trees in Northern Cyprus, where most of the varieties have been grafted on sour orange; and grafting is among the major ways of transmitting this virus, together with other mechanical practices.The results of the present study showed that the virus disease in different citrus species and varieties of Northern Cyprus are mostly symptomatic. In the current work, citrus orchards which showed disease symptoms were all recorded and a detailed database was prepared for future molecular analyses. Thus, it is revealed that further molecular studies should be carried in order to perform a scientific investigation into the presence of this virus disease in Northern Cyprus and prove it molecularly.

Includes bibliographical references (leaves 152-164) Microscopy investigations into the oil glands, localisation of the rind oils and the development of oleocellosis have been carried out in Washington navel orange (Citrus sinensis [L.] Osbeck). Aims to develop an improved understanding of the physiological basis of the rind disorder.

Thesis (MScAgric)--University of Stellenbosch, 2004.
ENGLISH ABSTRACT: Rind colour is one of the most important external quality characteristics of citrus fruit and plays an important role in purchasing decisions by consumers. Consumers perceive brightlycoloured fruit to be sweet and mature, whereas citrus with a green rind is perceived to be sour and immature. However, there is a poor correlation between rind colour and internal quality, contradicting what is generally assumed by the fruit-buying public. In general, a bright orange rind colour improves consumer acceptance. Thus, it is important to ensure that the rind of citrus fruit is well-coloured on arrival at the market. Various pre-harvest cultural practices and postharvest techniques can be applied to improve rind colour. Degreening with ethylene gas is the most commonly used postharvest technology to improve rind colour, but has various negative side-effects. Degreened fruit are more prone to decay, have rinds which appear dull and flaccid, have been reported to develop off-flavours and have a shorter shelf-life period. Therefore, it is necessary to find alternatives to ethylene degreening and to extend shelf-life of citrus fruit. Under normal orchard conditions, rind colour development is associated with low night temperatures, usually experienced during autumn or following the passing of a cold front. To simulate cold front conditions, a hydrocooler and cold room were used to rapidly drop fruit temperature to 4 ºC for 6 hours, and then fruit were incubated at 20 to 22 ºC for 72 hours. This “cold shock” treatment of ‘Nules Clementine’ mandarin improved rind colour to a level similar to that of degreened fruit in the 2002 season due to a decrease in chlorophyll content and increase in carotenoid content. However, this result could not be repeated. Storage temperature is one of the most important postharvest factors affecting rind colour. Citrus fruit shipped to export markets requiring low temperatures (-0.6 ºC) for pest disinfestations purposes have been reported to arrive with poor rind colour. Shipping under low temperatures results in poor rind colour of fruit on arrival in the market. To comply with the USA’s phytosanitary requirement for imported citrus, fruit is held at -0.6 ºC for a minimum of 22 days. The effect of shipping at various temperatures (-0.6 ºC or 4.5 ºC), durations and the influence of initial rind colour, “orange” or “yellow”, on fruit colour upon arrival in the market was evaluated. Fruit shipped at a higher temperature (4.5 ºC) had a marginally better rind colour than fruit shipped at -0.6 ºC. The perceived loss of rind colour following shipping at sub-zero temperatures is probably due to carotenoid degradation. Therefore, initial rind colour plays a critical role in final product quality. Depending on market destination and shipping temperature, pale-coloured fruit should not be packed for markets sensitive to rind colour. Holding temperature after shipping can be effectively used to improve the rind colour of fruit arriving in the market with undesirable rind colour. An intermediate holding temperature of between 11 and 15 ºC resulted in the greatest improvement in rind colour after 2 weeks. A high holding temperature (20 ºC) caused colour degradation, whereas a low holding temperature (4.5 ºC) resulted in the maintenance of rind colour. By selecting the correct holding temperature, even after shipping at sub-zero temperatures, final colour can be improved.
AFRIKAANSE OPSOMMING: Tyd-temperatuur interaksie op na-oes skilkleur ontwikkeling by sitrus Skilkleur is een van die belangrikste eksterne kwaliteitseienskappe van die sitrusvrug en spëel ʼn belangrikke rol in wat verbruikers koop. Verbruikers verwag dat heldergekleurde vrugte soet en ryp sal wees, terwyl sitrus met ʼn groen skil geassosieer word met onrypheid en ʼn suur smaak. In teenstelling hiermee is daar egter ʼn swak korrelasie tussen skilkleur en interne kwaliteit. Aangesien ʼn heldergekleurde oranje skil verbruikersaanvaarding verbeter, is dit dus belangrik om te verseker dat die sitrusvrug ʼn goeie skilkleur het teen die tyd wat dit die mark bereik. Verskeie voor-oes bestuurspraktyke en na-oes tegnieke kan toegepas word om die skilkleur te verbeter. Ontgroening met etileen gas is die tegnologie wat mees algemeen gebruik word om skilkleur na oes te verbeter, maar dit het egter verskeie newe effekte tot gevolg. Ontgroende vrugte is meer vatbaar vir bederf en verwelkde skille met ʼn dowwe voorkoms. Afsmaake kan voorkom en ʼn verkorte rakleeftyd is al gerapporteer. Dit is dus noodsaaklik om ʼn alternatief vir etileen ontgroening te ontwikkel en die rakleeftyd van sitrusvrugte te verleng. Onder normale boordomstandighede word skilkleur ontwikkeling geassosieer met lae nag temperature wat gewoonlik in die herfs of na ʼn kouefront ondervind word. Om soortgelyke omstandighede na te boots, was ʼn “hydrocooler” en koelkamers gebruik om die temperatuur vinnig te laat daal tot by 4 °C en dit vir 6 uur daar te hou. Die vrugte was dan by 20 tot 22 °C geinkubeer vir 72 uur. Hierdie “koueskok” behandeling van ‘Nules Clementine’ mandaryn het skilkleur verbeter tot ʼn vlak vergelykbaar met ontgroende vrugte in die 2002 seisoen wat ontstaan het weens ʼn verlaging in chlorofil en ʼn toename in die karotinoïed inhoud van die skil. Opbergingstemperatuur is een van die belangrikste na-oes faktore wat skilkleur beinvloed. Sitrusvrugte wat verskeep word na uitvoermarkte wat lae temperature (-0.6 °C) vir disinfestasie vereis arriveer soms by die mark met ʼn swak skilkleur. Om die fitosanitêre vereistes vir die invoer van sitrus deur die VSA na tekom, was vrugte vir ʼn minimum van 22 dae by -0.6 °C gehou. Die effek van verskeping by verskeie temperature (-0.6 °C of 4.5 °C), tydperke en die invloed van aanvanklike skilkleur, “oranje” of “geel” was geevalueer by aankoms in die mark. Vrugte wat by hoër temperature (4.5 °C) verskeep was het ʼn effens beter skilkleur as vrugte by -0.6 °C getoon. Die verlies in skilkleur wat waargeneem word na verskeping onder vriespunt kan moontlik toegeskryf word aan karotenoiëd afbraak. Daarom speel aanvanklike skilkleur ʼn kritieke rol in finale produk kwaliteit. Die finale mark bestemming en verskepingstemperatuur sal bepaal of swakgekleurde vrugte verpak kan word. Opbergingstemperatuur na verskeping kan effektief gebruik word om die skilkleur van vrugte wat swak gekleur was met aankoms by die mark te verbeter. Matige temperature tussen 11 en 15 °C het na 2 weke die beste verbetering in skilkleur gelewer. Hoër temperature (20 °C) het skilkleur nadelig beinvloed, terwyl lae temperature skilkleur behou het. Deur die korrekte temperatuur te kies, selfs na verskeping by temperature onder vriespunt, kan uiteindelike skilkleur steeds verbeter word.

The effect of Roundup on lemon trees was evaluated by repeatedly spraying 0.5, 0.75, 1, 1.25, and 1.5 lb a.i/acre on the bottom 20 to 24 inches of the tree canopies. Leaf injury symptoms, flower and fruit counts, and yield data were collected The Roundup applications caused significant leaf injury in the sprayed area of the canopies and there was significant defoliation of branches at the higher Roundup rates. In 1996, flower and fruitier counts were not affected by the Roundup applications. However, flower and fruitier counts in 1997 in the sprayed zone of the canopy were significantly reduced by Roundup and the effect increased with increasing Roundup rate. The 1996 yield data indicated that the Roundup applications did not significantly affect lemon yield, however, the effect of Roundup on the 1997 flower and fruitier counts suggests that there may be a yield effect in 1997. The preliminary data suggest that accidental drift of Roundup on to lemon trees when spraying weeds on the orchard floor has no short-term effect on grove productivity but this conclusion must be substantiated by further data collection.

Conhecimentos sobre fisiologia da produção de mudas cítricas sob condições de deficiência hídrica são necessários para fomentar as práticas de irrigação em viveiros telados. O objetivo deste trabalho foi avaliar o efeito de deficiência hídrica induzido por polietileno glicol (PEG) e por interrupção da irrigação sobre o desenvolvimento e variáveis fisiológicas de mudas de laranja Valência (Citrus sinensis L. Osbeck) enxertada sobre limão Cravo (Citrus limonia Osbeck) e citrumelo Swingle (Poncirus trifoliata (L.) Raf x Citrus paradisi Macf). As mudas foram produzidas em sacolas plásticas de 4,5L contendo substrato a base de casca de pinus e submetidas à deficiência hídrica durante três fases fenológicas, e em duas estações do ano (outono-inverno e primavera-verão). O trabalho foi dividido em dois experimentos. No primeiro, avaliaram-se plantas mantidas em capacidade de container e submetidas à interrupção intermitente da irrigação, até o potencial hídrico do substrato atingir -15kPa, e a duas concentrações de PEG, correspondentes ao potencial hídrico no substrato de respectivamente -15 e -25kPa. No segundo experimento, avaliaram-se plantas mantidas em capacidade de container e submetidas a interrupção intermitente da irrigação até o potencial hídrico do substrato atingir respectivamente -15 e -25kPa. Dados coletados incluíram variáveis biométricas, concentrações foliares de nutrientes, de prolina e de clorofila, concentração de carboidratos em raízes, caule e folhas, aproveitamento comercial de mudas, taxa de assimilação de CO2, condutância estomática, transpiração e eficiência do uso da água. O delineamento adotado foi o de blocos ao acaso, seguindo o esquema fatorial 2 x 3 x 4 (porta-enxerto x fase de crescimento x deficiência hídrica), perfazendo 24 tratamentos e cinco repetições para o primeiro experimento, e esquema fatorial 2 x 3 x 3, com 18 tratamentos e seis repetições no segundo experimento. A parcela experimental foi constituída de seis plantas. Mudas de laranja Valência enxertadas sobre limão Cravo e citrumelo Swingle apresentam crescimento e características fisiológicas distintas, sendo que maior vigor é induzido por aquele porta-enxerto. O emprego de PEG como osmólito em estudos para indução de deficiência hídrica in vivo não é indicado para citros em vasos, já que este material acarreta efeitos fisiológicos distintos daqueles apresentados por plantas submetidas à interrupção da irrigação. Mudas sobre ambos porta-enxertos são afetadas pela interrupção da irrigação entre a retirada do fitilho e a maturação do segundo fluxo de crescimento do enxerto, sendo os prejuízos proporcionais à duração da deficiência hídrica. Os efeitos da seca temporária são mais intensos quando aplicados isoladamente a partir da maturação do primeiro fluxo de crescimento, devido ao maior tamanho das plantas. A interrupção da irrigação até que o potencial hídrico do substrato seja de -15kPa permite produção satisfatória de mudas de laranja Valência sobre limão Cravo e citrumelo Swingle, independentemente do período em que ocorra a deficiência hídrica. A interrupção da irrigação até que o potencial hídrico do substrato atinja -25kPa afeta significativamente a produção das mudas cítricas. O limão Cravo induziu maior aclimatação à copa, apresentando grande capacidade de recuperação do crescimento e do desempenho fisiológico após sucessivos ciclos de suspensão / restauração da irrigação.
Physiological aspects of citrus nursery tree production submitted to water deficit are necessary to support irrigation management in screen houses. This work evaluated water stress induced either by polyethylene glycol (PEG) or irrigation suspending on growth and physiological traits of Valencia sweet orange (Citrus sinensis L. Osbeck) budded on Rangpur lime (Citrus limonia Osbeck) and Swingle citrumelo (Poncirus trifoliata (L.) Raf x Citrus paradisi Macf). Nursery trees were produced in 4.5L containers filled with composted pine bark, and submitted to water stress in three phenological phases in two seasons (autumn-winter and spring-summer). Experimental works were divided in two trials. In the first one, evaluation was carried on plants submitted to container capacity, irrigation suspending when substrate water potential dropped to -15kPa, and two PEG concentrations in water equivalents to substrate water potential of -15 and -25kPa. In the second trial, evaluation was carried on plants submitted to container capacity and irrigation suspending when substrate water potential dropped to -15 and -25kPa. Data collected included biometric variables, leaf concentrations of nutrients, proline and chlorophyll, carbohydrates concentrations in roots, stems and leaves, commercial feasibility of nursery trees, CO2 assimilation rate, stomatal conductance, leaf transpiration and temperature, and water use efficiency. Experimental design was randomized blocks with a 2 x 3 x 4 factorial (rootstock x phenological phase x water stress), performing 24 treatments and five replicates for the first experiment, and a 2 x 3 x 3 factorial with 18 treatments and six replicates for the second experiment. Experimental unit consisted of six nursery plants aligned on concrete benches. Valencia sweet orange budded on Rangpur lime and Swingle citrumelo had different growth and physiological behavior, with the first rootstock inducing higher vigor. PEG should not be used for in vivo water stress studies in containerized citrus, as a result of toxicity and physiological effects distinct from those observed in plants submitted to suspended irrigation. Nursery trees on both materials are affected by suspended irrigation from unwrapping to the maturation of scion second growth flush. Damages to plant development due to water deficit are proportional to stress duration. However, temporary drought is more harmful when partially induced after the scion first growth flush, probably because of higher plant size and container restriction. Substrate water potential of -15kPa can be used as adequate irrigation threshold for Valencia sweet orange nursery production on Rangpur lime and Swingle citrumelo rootstocks regardless of phenological phase. On the other hand, substrate water potential of -25kPa significantly reduces horticultural value of citrus nursery trees. Rangpur lime induces higher morphological and physiological acclimation to the scion due to irrigation suspending, and it also has great plasticity and recovery of growth and physiological performance after successive suspending / restoring irrigation cycles.

Os objetivos deste trabalho foram determinar o efeito do processamento mínimo e da temperatura de armazenamento na fisiologia do tangor ‘Murcott’ minimamente processado e determinar os recobrimentos comestíveis que promovam a manutenção da qualidade microbiológica, sensorial e físicoquímica de tangor ‘Murcott’ minimamente processado. No primeira etapa foram testados dois níveis de processamento (tangores inteiros sem a casca e tangores em gomos) e cinco temperaturas de armazenamento (1º, 6º, 11º, 21º e 31ºC). Frutos intactos foram utilizados como controle. No segundo experimento os tangores em gomos foram tratados com diversos recobrimentos comestíveis e armazenados sob duas temperaturas (6º e 12ºC). Os recobrimentos utilizados foram: gelatina a 4% p/p, gelatina a 8% p/p, concentrado protéico de soro de leite a 8% p/p e emulsão a base de parafina. Tangores sem recobrimentos foram utilizados como controle. No primeiro experimento foram determinadas as taxas respiratórias e de produção de etileno a cada hora durante as 10 primeiras horas após o processamento e, em seguida, a cada 24 horas por sete dias. Determinaram-se também os quocientes de temperatura (Q10). No segundo experimento determinaram-se: as características físico-químicas a cada dois dias por um período de seis dias; a taxa respiratória diariamente por oito dias; as características microbiológicas no quarto e sétimo dias após o processamento e as características sensoriais no quarto dia após o processamento. Os níveis de etileno foram baixos e inconstantes ao longo do tempo de avaliação. O aumento da temperatura de armazenamento e o nível de processamento mínimo influenciaram a taxa respiratória. Os recobrimentos comestíveis foram pouco efetivos na redução da taxa respiratória e na manutenção das características físico-químicas, microbiológicas e sensoriais de gomos de tangor ‘Murcott’.
The objectives of this work were to determine the effect of minimally processing and the storage temperature on the physiology of fresh-cut tangor ‘Murcott’ and to determine the edible coatings that maintain the microbiological, sensorial and physico-chemical qualities of fresh-cut tangor ‘Murcott’. In the first experiment two processing levels (peeled fruits and segments) and five storage temperatures (1º, 6º, 11º, 21º and 31ºC) were tested. Whole fruits were used as control. In the second experiment the segments were treated with several edible coatings and stored under two temperatures (6º and 12ºC). The edible coatings were: gelatin 4% w/w, gelatin 8% w/w, whey protein 8% w/w and paraffin wax emulsion. Segments without recovering were used as control. In the first experiment the respiratory rate and the ethylene production were determined every hour for 10 hours and then, every day for 7 days. The temperature quotients (Q10) were also determined. In the second experiment were determined: the physico-chemical properties every two day for six days; the respiratory rate daily for eight days; the microbiological analysis on the fourth and seventh days of storage; and the sensorial analysis on the fourth day of storage. The storage temperature and the processing level did influence the respiratory rate. The ethylene levels were low and inconstant during the study. The edible coatings were little effective on reducing the respiratory rate and on maintaining the physico-chemical, microbiological and sensorial properties of fresh-cut tangor ‘Murcott’.

Includes bibliographical references (leaves 152-164)
x, 165 leaves : ill. (chiefly col.), plates ; 30 cm.
Microscopy investigations into the oil glands, localisation of the rind oils and the development of oleocellosis have been carried out in Washington navel orange (Citrus sinensis [L.] Osbeck). Aims to develop an improved understanding of the physiological basis of the rind disorder.
Thesis (Ph.D.)--University of Adelaide, Dept. of Horticulture, Viticulture and Oenology, 2002

The South African Citrus Industry is the second largest exporter of citrus, after Spain. The industry is under pressure to supply high quality fruit as well as to expand into new, high paying markets. However, high paying markets such as Japan and the USA require cold sterilised fruit as obligatory quarantine treatments against Mediterranean fruit fly (Ceratitis capitata) in order to reduce any possible spread of the pest. Citrus fruit originated from tropical climates and hence are chilling susceptible. Chilling injury symptoms appear as dark brown spots, pitting and/or decay when fruit are transferred to shelf temperatures; thus reducing the marketability of citrus fruit. Therefore, there is need for methods to mitigate chilling injury. Previous studies have shown silicon to mitigate many forms of stress without any hazardous effect on human health. Thus, the aim of the study was to investigate the potential of post-harvest silicon dips in mitigating chilling symptoms in citrus fruit. Briefly, fruit from two sources (Ukulinga Research Farm and Ithala Farm) were dipped in different silicon concentrations (0, 50, 150, and 250 mg ℓ-1) for 30 minutes and thereafter stored at -0.5 or 2⁰C for up to 28 days with weekly evaluation for chilling injury symptoms. Total antioxidants were determined using FRAP, ABTS, and DPPH assays under spectrophotometer. In addition, sugars, ascorbic acid, phenolics and flavonoids were analysed using High Performance Liquid Chromatography (HPLC). Fruit from Ukulinga Research Farm showed significantly higher total antioxidants (ascorbic acid total phenolics and specific flavonoids hesperidin and naringin) and sugars relative to fruit from Ithala Farm. Low concentrations of silicon dips significantly reduced the appearance of chilling injury symptoms by inducing an enzymatic conversion of glucose to ascorbic acid, thereby increasing the antioxidant capacity of chilling susceptible fruit. Moreover, silicon increased the concentration of total antioxidants, total phenolics and total flavonoids. High silicon concentrations had a negative effect on post-harvest quality of lemons by increasing fruit weight loss and electrolyte leakage, resulting in appearance of chilling symptoms. In conclusion, the study showed that silicon had potential to reduce chilling injury. However, high silicon concentrations raised concern, in particularly, on fruit appearance.
Thesis (M.Sc.Agric.)-University of KwaZulu-Natal, Pietermaritzburg, 2012.

New emerging markets such as Japan and the United States require cold sterilisation of South African citrus fruit as a phytosanitary standard against fruit fly. However, citrus fruit are chilling susceptible, with lemons being the second-most chilling susceptible after grapefruit. Chilling injury is a physiological rind disorder; the occurrence of which is despite its prevalence in horticultural commodities, not well understood. Therefore, the aim of this study was to investigate physiological compounds regulating chilling susceptibility or resistance in citrus fruit, with special emphasis on lemons. Furthermore, the potential of hot water dips or “molybdenum soaks” to maintain a certain level of physiological compounds which determine manifestation of chilling injury symptoms in citrus fruit was investigated. Moreover, it was attempted to create an understanding of the order in which physiological compounds mitigate chilling injury. Lemon fruit from different farms known to be chilling susceptible or resistant were obtained during the 2007 and 2008 harvest season. Thereafter, fruit were treated by soaking for 30 min in 1μM NaMo04.2H20 solution followed by a 2 min HWD 47 or 53°C. Treated fruit were waxed, weighed and stored at -0.5°C for up to 28 days and sampled for chilling injury evaluation 7, 14, 21, or 28 days into cold storage. A second evaluation was carried out five days after withdrawal from cold storage to allow development of chilling injury symptoms as a shelf-life simulation. After the second evaluation fruit were peeled, peel freeze-dried, milled using mortar and pestle and stored at -21°C for further physiological analysis. Freeze-dried peel was analysed for soluble sugars (glucose, fructose, sucrose), vitamin C (ascorbic acid), vitamin E (α-tocopherol), β-carotene, polyamines (putrescine, spermine, spermidine), specific flavanones (naringin and hesperidin) using HPLC-UV-Vis detector and proline, total antioxidant assays (FRAP, ABTS, DPPH), total phenolics, total flavonoids, lipid peroxidation using spectrophotometry, as well as for the heat shock protein (HSP70) using electrophoresis and silver-staining. Chilling susceptibility of lemon fruit varied with fruit source; those sourced from Ukulinga and Eston Estates were chilling resistant, while fruit from Sun Valley Estates showed chilling injury symptoms after 28 days of cold storage plus five days shelf-life. Furthermore, hot water dips (HW) 53°C, 1 μM Molybdenum (Mo) and 10 μM Mo plus HW 53°C significantly reduced chilling injury symptoms compared with the control and HW 47°C. In addition, Sun Valley Estates fruit also showed higher fruit weight loss compared with non-chilling resistant lemons. The alignment of higher fruit weight loss during storage with chilling susceptibility ascertains the use of weight loss as a non-destructive parameter for chilling susceptibility. With respect to flavedo sugars, glucose was found to be the dominant soluble sugar with multi-functional roles during cold storage. This plays a significant role in mitigating cellular stress. Chilling susceptible lemons from Sun Valley Estates had low flavedo glucose concentrations and, therefore, little conversion of glucose to ascorbic acid was possible resulting in a low antioxidant capacity. However, treatments with HW 53°C and Mo soaks seemed to enhance the enzymatic conversion of glucose to ascorbic acid leading to a higher antioxidant capacity in the flavedo of such treated fruit. Furthermore, glucose also feeds into the pentose phosphate pathway which is coupled with the shikimate pathway synthesizing secondary metabolites, especially of the phenolics group. The decrease in glucose was aligned to the levels of total phenolics, but not to that of β-carotene, naringin and hesperidin through 28 days into cold storage period. Moreover, as glucose also feeds into shikimate pathway, simultaneously an increase in proline flavedo concentration was observed. Proline is an antioxidant synthesized from glutamate; as cellular glucose decreases so does the total antioxidant capacity during cold storage. Ascorbic acid is a dominant and potent antioxidant in lemon flavedo as proven with the FRAP, ABTS and DPPH assays. Chilling resistant fruit have significantly higher ascorbic acid conversion. Furthermore, ascorbic acid also acts to generate the α-tocopheroxy radical to further important membrane-bound antioxidant, vitamin E (α-tocopherol equivalent). Furthermore, the DPPH assay was found to be effective in quantifying total antioxidants in lemon flavedo since it detects both lipophilic and hydrophilic antioxidants compared with the ABTS and FRAP assays which are bias to the estimation of liphophilic or hydrophilic antioxidants, respectively. The hot water and molybdenum treatments increased total antioxidants (DPPH assay) with reduced lipid peroxidation 7 days into cold storage and therefore, reduced chilling symptoms in fruit from Sun Valley Estates. The capacity of antioxidant to scavenge reactive oxygen species (ROS) was increased during cold storage and membrane stability significantly improved. Furthermore, putrescine as low valency polyamine was reduced as such compound acted as precursor to the synthesis of the high valency polyamines, spermine and spermidine. Chilling susceptible lemons from Sun Valley Estates showed increased soluble-conjugated polyamines as a response to stress. Furthermore, HW 53°C, 1 μM Mo and 10 μM Mo plus HW 53°C significantly increased the protein concentration and, therefore, likely also the occurrence of proteins with 70kDa (as estimator of HSP70). Additionally, the concentration of conjugated high valency polyamines was also increased, resulting in reduced chilling injury symptoms. The effect of ROS has only been viewed as damaging, while recently their role has also been viewed as stress acclamatory signalling compounds when produced concentrations below critical damaging threshold. Therefore, hot water dips seems to signals synthesis of total protein which include HSPs which then act throughout cold stress to protect other protein and channel other damaged proteins towards proteolysis. While molybdenum increased ROS production below damaging critical threshold, with ROS signalling stress acclimation by further signalling production of bioactive compound with antioxidant properties.
Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2012.

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.

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.

Citrus Huanglongbing (HLB) or citrus greening disease has been in Florida since at least 2005 and has spread to all of the citrus producing regions. The Asian citrus psyllid (Diaphorina citri) is the insect that transmits the suspected causal bacterium which is tentatively named Candidatus Liberibacter asiaticus. Symptoms of the disease are first the yellow shoot (huanglongbing) and the development of the blotchy mottle symptom in the leaves. Mineral deficiency symptoms are often found on infected trees and may mimic normal deficiency symptoms. Fruit on infected trees may be small and lopsided and may abscise prematurely and therefore productivity is reduced. Tree decline eventually occurs. The suspected causal bacterium has not been obtained in pure culture and a polymerase chain reaction (PCR) test along with symptoms, is the only way to verify infected trees. All citrus cultivars appear susceptible. Current management strategies are chemical and biological control to reduced psyllid populations, inspections for infected trees and removal of infected trees to reduce the available pathogen inoculum. Current research on psyllid control, psyllid transmission, symptomology, detection, culturing the causal agent, development of new detection methods, alternative hosts of the psyllid and the causal agent, physiology of the disease, resistant or tolerant cultivar development and more is discussed. HLB is a major problem for citrus production and often limits commercial production. Paper published with permission.

The proposal was aimed to identify and functionally characterize key genes/enzymes in the citrus flavanone neohesperidoside biosynthetic pathway and to use them as tools for metabolic engineering to decrease bitterness levels in grapefruit. The proposed section on fruit seediness was dropped as suggested by the reviewers of the proposal. Citrus flavor and aroma is composed of complex combinations of soluble and volatile compounds. The former includes mainly sugars, acids and flavanones, a subgroup of flavonoids that includes bitter compounds responsible for the bitter flavor of grapefruit and pummelo. Bitter species contain mostly bitter flavanone neohesperidosides, while non-bitter species contain mostly tasteless flavanone rutinosides. Both flavanone versions are diglycosides consisting of a rhamnose-glucose oligosaccharide a-linked at position 7 to the flavanone skeleton. However, in the bitter neohesperidosides the rhamnose is attached at position 2 of the glucose moiety, while in the tasteless rutinosides the rhamnose is attached at position 6 of the glucose moiety. Thus, the position of the rhamnose moiety, determined by the specificity of the last enzymes in the pathway- rhamnosyltransferase (1,2 or 1,6 specificity), is the determinant of the bitter flavor. Flavanones, like all flavonoids are synthesized via one of the branches of the phenylpropanoid pathway; the first committed step is catalyzed by the enzyme Chalcone synthase (CHS) followed by Chalcone isomerase (CHI). During the course of the work a key gene/enzyme in the biosynthesis of the bitter flavanones, a 1,2 rhamnosyltransferase (1,2RT), was functionally characterized using a transgenic cell-culture biotransformation system, confirming that this gene is a prime candidate for metabolic engineering of the pathway. This is the first direct functional evidence for the activity of a plant recombinant rhamnosyltransferase, the first confirmed rhamnosyltransferase gene with 1,2 specificity and the second confirmed rhamnosyltransferase gene altogether in plants. Additional genes of the flavanone pathway that were isolated during this work and are potential tools for metabolic engineering include (I) A putative 1,6 rhamnosyltransferase (1,6RT) from oranges, that is presumed to catalyze the biosynthesis of the tasteless flavanones. This gene is a prime candidate for use in future metabolic engineering for decreased bitterness and is currently being functionally characterized using the biotransformation system developed for characterizing rhamnosyltransferases. (2) A putative 7-0-glucosyltransferase presumed to catalyze the first glycosylation step of the flavanone aglycones. Silencing of gene expression in grapefruit was attempted using three genes: (1) The "upstream" flavonoid biosynthesis genes CHS and CHI, by antisense and co-suppression; and (2) The "downstream" 1,2R T, by an RNAi approach. CHS and CHI silencing resulted in some plants with a dramatically decreased level of the bitter flavanone neohesperidoside naringin in leaves. We have yet to study the long-term effect of silencing these genes on tree physiology, and on the actual bitterness of fruit. The effect of 1,2RT silencing on naringin content in grapefruit has yet to be examined, but a slow growth phenotype for these plants was noted. We speculate that silencing of the final glycosylation step of the flavanones delays their evacuation to the vacuole, resulting in accumulation of flavanones in the cytoplasm, causing inhibitory effects on plant growth. This speculation is yet to be established at the product level. Future metabolic engineering experiments are planned with 1,6RT following functional characterization.