Dissertationen zum Thema „Ripening“

This thesis presents a theoretical approach to Ostwald ripening of droplets in arbitrary dimensions. A mean-field theory is constructed to incorporate screening effects among the competing droplets. The mean-field equations are solved to all orders in the volume fraction to provide analytic expressions for the coarsening rate, the droplet distribution function, and the time-dependent droplet number. These results are in agreement with experiments in three-dimension and with very large scale and extensive numerical studies in both two and three dimensions undertaken in this thesis. The numerical study also provides the time evolution of the structure factors, wherein lengths scale with the average droplet radius. Finally, the mean-field theory is extended to exciton systems and surfactant systems.

Thesis (MSc)--Stellenbosch University, 2002.
ENGLISH ABSTRACT: 'Forelle' is one of three blushed pear cultivars produced in South Africa. A mandatory minimum cold storage duration of 12 weeks at -0.5°C to ensure even ripening, prevents 'Forelle' from being marketed earlier. Since earlier marketing can result in premium prices (in excess of 50% morê per carton) research in recent years has been directed at reducing this 12 week cold storage period. Intermittent warming treatments, controlled atmosphere (CA) storage in combination with regular atmosphere (RA) storage intervals, and ethylene treatments, have been tested as alternatives to the 12 week cold requirement. However, none of these treatments delivered a better internal quality in terms of mealiness and astringency. Fruit harvested from the Warm Bokkeveld and Theewaterskloof areas at commercial maturity were stored at -0.5°C for up to 21 and 22 weeks, respectively, to understand the changes in ripening and mealiness of 'Forelle' pears after cold storage (Paper 1). Samples were removed every third weev, placed at 15°C, and maturity factors, total ACC concentration, ethylene production and respiration rates monitored every third day for 12 days. Fruit from the Warm Bokkeveld and the Theewaterskloof areas ripened after 6 and 7 weeks at -0.5°C, respectively. However, after 6 weeks of cold storage followed by 6 days at 15°C, all fruit harvested in the Warm Bokkeveld, and 70 % of the fruit harvested in the Theewaterskloof area, were mealy. With extended storage at -0.5°C (> 15 weeks) the incidence of mealiness declined in fruit from both areas, but never disappeared, when evaluated at 15°C over 12 days. Since harvest maturity affects the incidence of mealiness in other pear cultivars, the effect of harvest maturity on 'Forelle' pears with regard to mealiness development was examined (Paper 2). Fruit were harvested from the Ceres area, in weeks 8 (preoptimum), 10 (optimum), 12 and 14 (both post optimum). Maturity indices, juice content, mealiness, total ACC content, ethylene production and internal ethylene were monitored at harvest, after 6 weeks of storage at -0.5°C and again after 7 days at 15°C. Fruit harvested 2 weeks before commercial harvest (week 8) had the highest total ACC concentration, ethylene production and the potential to ripen, but also developed the highest incidence of mealiness (80%). However, fruit of all harvest maturities (except where contamination with 1-MCP occurred) were mealy. It would appear that factor(s), other than harvest maturity, play a more important role in the initiation of mealiness in 'Forelle' pears. Although ethylene has been shown to shorten the cold requirement of 'Forelle', there are conflicting reports as to its effectiveness in reducing mealiness. Consequently, the aim of the third paper was to evaluate the effect of ethylene on ripening and mealiness of 'Forelle' pears. Fruit harvested from the Elgin area at commercial maturity were stored for 3 weeks at -0.5°C, treated with ethylene (100 Jl L.L·l , 24h, 20°C) and held at 20°C for a further 2 days (without ethylene). Control fruit were held at 20°C for 3 days. Fruit were returned to -0.5°C for a further 3 weeks. After a subsequent 3 days at 20°C, flesh firmness was 4.6 kg in treated fruit compared to 6.1 kg for control fruit. At this point all fruit treated with ethylene were mealy. Control fruit all exhibited mealiness after a further 3 weeks at -0.5°C followed by 7 days at 15°C. Ethylene treatment advanced fruit maturity, but did not prevent or alleviate mealiness. Mealiness is a textural disorder recognized by a dry soft pulp. This has previously been recorded in 'd'Anjou' pears, as a result of storing the fruit for too long at -1.1°C, but has also been the result of a chilling injury in fruit like nectarines, kiwi and persimmon. The role of storage temperature on ripening, and specifically mealiness, of 'Forelle' was thus investigated (Paper 4). Fruit harvested from the Elgin area at commercial maturity were stored at -0.5°C, 4.0°C and 7.5°C for 0, 3 and 6 weeks. Samples were removed every third week, placed at 15°C, and maturity indices, extractable juice content, mealiness, total ACC content, internal ethylene concentration and ethylene production were monitored on removal and after 7 days. Flesh firmness of the 4°C stored fruit was 0.5 kg lower than fruit stored at -0.5°C, on removal from storage. Fruit stored at 4°C and 7.5°C ripened with little to no mealiness (0 and 8% respectively) in contrast to fruit stored at -0.5°C (70% mealy). Total ACC accumulation and ethylene production were higher for fruit stored at 4°C and 7.5°C than fruit stored at -0.5°C. Storage temperature appears to playa role in the development of mealiness. Although storage temperatures influenced mealiness development, this research should be repeated before this can recommended as a commercial treatment. The underlying mechanism of action in the development of mealiness should be investigated. By examining fruit grown in different climatical areas, harvested at different maturities, treated with exogenous ethylene and stored at different temperatures, this research has helped to a better understanding of the role of factors affecting ripening and development of mealiness in 'Forelle'.
AFRIKAANSE OPSOMMING: Forelle' is een van drie blos peer kultivars wat in Suid Afrika geproduseer word. 'n Minimum van 12 weke by -0.5°C opberging, is deur wetgewing vasgestel, om eweredige rypheid van 'Forelle' te verseker. Vroeër bemarking van 'Forelle' kan daartoe lei dat vrugte premium pryse, van 50% meer per karton behaal. Aangesien die vasgestelde koue periode verhoed dat 'Forelle' vroeër bemark kan word, het onlangse navorsing gefokus op vermindering van die vasgestelde opberging van 12 weke by -0.5°C. Afwisselende verwarmmgs behandelings gedurende koue opberging, beheerde atmosfeer (BA) opberging in kombinasie met gewone atmosfeer (GA) opbergings intervalle, en etileen behandelings, is _getoets as alternatiewe vir die 12 weke opbergings vereiste by -0.5°C. Geen van die bogenoemde behandelings kon egter 'n beter interne kwaliteit in terme van meleringheid en frankheid as 'n alternatief verseker nie. Die doel van die eerste proef was om die invloed van koue opberging by -0.5°C op rypwording en melerigheid van 'Forelle' te bepaal. Vrugte is in die Warm Bokkeveld and Theewaterskloof areas geoes tydens kommersiële oesrypheid, waarna hulle vir 21 en 22 weke, respektiewelik, by -0.5°C opgeberg is. Monsters is elke derde week vanaf die -0.5°C koue opberging geneem en by 15°C geplaas, waarna rypheids indeksering, totale ACC konsentrasie, etileen produksie and respirasie tempos elke derde dag vir 12 dae gemonitor is. Vrugte wat in dieWarm Bokkeveld en Theewaterskloof areas geoes is, het rypgeword by 15°C, na 6 and 7 weke by -0.5°C, respektiewelik. Alle vrugte vanaf die Warm Bokkeveld en 70% vrugte vanaf die Theewaterskloof area, het egter na die 6 en 7 weke by -0.5°C, respektiewelik, en 6 dae by 15°C, melerigheid ontwikkel. Vrugte wat vir langer as 15 weke by -0.5°C opgeberg is, het in albei areas 'n afname in melerigheid getoon, maar die defek het nooit heeltemal verdwyn tydens evaluasie by 15°C nie. Oes rypheid affekteer die ontwikkeling van melerigheid in ander peer kultivars. Die tweede proef was dus gefokus op dip. invloed van oes rypheid op 'Forelle' se ontwikkeling van melerigheid. Vrugte is in die Warm Bokkeveld area geoes in week 8 (pre-optimum), 10 (optimum), 12 and 14 (albei post-optimum). Rypheids indekse, uitdrukbare sapinhoud, meleringheid, totale ACC konsentrasie, interne etileen vlakke en etileen produksie is gemonitor, na opberging vir 6 weke by -0.5°C en 7 dae by 15°C. Vrugte wat 2 weke voor kommersiële rypheid geoes is (week 8) het die hoogste totale ACC konsentrasie en etileen produksie gehad, en het reeds die potensiaal gehad om ryp te word. Die hoogste vlakke van melerigheid (80%) is ook in vrugte wat tydens hierdie oes verkry is, waargeneem. Vrugte wat op alle tye geoes is, het melerigheid ontwikkel, behalwe waar kontaminasie met 1-MCP plaasgevind het. Dit wil voorkom asof 'n ander faktor 'n belangriker rol in die ontwikkeling van melerigheid in 'Forelle' speel as oes rypheid. Etileen is bewys om die vereiste koue opberging vir 'Forelle' te kan verkort, maar daar is konflik oor die effektiwiteit van etileen op die verlaging van melerigheid in 'Forelle'. Die doel van die derde proef was dus om die effek van eksterne etileen behandeling op rypheid en melerigheid van 'Forelle' te toets. Vrugte wat in die Elgin area by kommersiële oesrypheid geoes is, is vir 3 weke gestoor by -0.5°C, met etileen behandel (100 Il L.L-1, 24h, 20°C) en vir 'n verdere 2 dae by 20°C gehou (sonder etileen). Kontrole vrugte is vir 3 dae by 20°C gehou. Daarna is vrugte weer vir 'n verdere 3 weke by -0.5°C opgeberg. Na 'n verdere 3 dae by 20°C, was vlees fermheid van etileen behandelde vrugte 4.6 kg .n vergelyking met 6.1 kg vir die kontrole vrugte. Alle vrugte wat met etileen behandel is, was melerig op hierdie stadium. Die kontrole vrugte het ook almal melerig geword, maar slegs na 'n verdere 3 weke by -0.5°C en 7 dae by 15°C. Etileen behandeling het dus die rypheid van 'Forelle' bevorder, maar het nie melerigheid voorkom nie. Melerigheid is 'n tekstuur probleem, wat gekenmerk word aan sagte droë pulp. Hierdie tekstuur probleem is voorheen waargeneem in 'd'Anjou' pere wat te lank by -Ll=C opgeberg is, maar is ook kenmerkend by vrugte soos nektariens, kiwi en persimmon wat aan koue skade ly. Lie gevolg is dat die effek van opbergings temperatuur op 'Forelle' rypwording en melerigheid getoets moes word. Vrugte is geoes van die Elgin area tydens kommersiële oesrypheid en gestoor by -0.5°C, 4.0°C en 7.5°C vir 0, 3 en 6 weke. Vrug monsters is geneem, na verwydering van bogenoemde stoor temperature en na 7 dae by 15°C, waarby rypheids indekse, uitdrukbare sapinhoud, meleringheid, totale ACC konsentrasie, interne etileen vlakke en etileen produksie gemonitor is. Vlees fermheid van vrugte wat vir 6 weke by 4°C opgeberg was, was 0.5 kg laer as vrugte wat by -0.5°C opgeberg was. Vrugte wat by 4°C and 7.5°C vir 6 weke gestoor is en by 15°C ryp geword het, het min tot geen melerigheid ontwikkel (0 and 8%, respektiewelik) nie. Vrugte wat by -0.5°C opgeberg was het egter hoë vlakke van melerigheid bereik (70% melerig). Totale ACC akkumulasie en etileen produksie was hoër vir vrugte wat by 4°C en 7.5°C gestoor was, teenoor vrugte wat gestoor was by -0.5°C. Dit wil voorkom asof na-oes opbergings temperature wel 'n rol speel in die ontwikkeling van melerigheid. Alhoewel dit voorkom asof na-oes temperature wel 'n rol speel in die ontwikkeling van melerigheid in 'Forelle' pere, is meer basiese navorsing nodig om die meganisme van werking in melerigheid ontwikkeling te verstaan. Na-oes temperatuur as 'n faktor wat melerigheid kan beïnvloed, moet oor 'n reeks van seisoene nagevors word. Laasgenoemde is van uiterste belang aangesien die invloed van seisoenale variasies op melerigheid nog nie gekwantifiseer is nie. Die navorsing was gefokus daarop om vas te stel watter faktore 'n fisiologiese rol speel in rypwording en melerigheid van 'Forelle' pere. Deurdat vrugte van twee areas met verskillende klimate, vrugte met verskye oesryphede, ekterne etileen behandeling, en vrugte van verskillende opbergings temperature ondersoek is, het hierdie navorsing gehelp om 'n beter begrip te vorm van die rol van hierdie faktore op die rypwording en die ontwikkeling van melerigheid in 'Forelle'.

Various techniques for accelerating mature flavour development in Cheddar cheese were compared. Control cheese ( c) was manufactured by using Streptococcus cremor is AM2, a starter used in normal commercial manufacture. A combination of S. cremoris AM2 and Streptococcus lactis C2 Lac- Prt- mutant was used in the manufacture of test cheeses (M). §._. lactis C2 mutant was grown in glucose broth at 30°c and pH 6 .O for 16 hours, followed by concentration and diafiltration to 1011cfu mL - 1 using microfiltration equipment. The control cheesemilk was inoculated to 6x107 streptococci pe mL with S. cremoris AM2 and the mutant vat cheesemilk to 2x109 per mL with a combination of ~ cremoris AM2 and ~ lactis C2 mutant. The starter population in cheese containing mutant starter was 100 times that in control cheese (1010 compared to 10a). Cheeses were also made with added bacterial neutral proteinase (Neutrase, N) and stored at a0c (a) and 15°c ( 15) for 32 weeks. This resulted in cheese being subjected to the following treatments: ca (control), C15, CNa, CN15, Ma·, M15, MNa, and MN15. Cheddaring times were slightly reduced and milling acidities slightly higher in the vat . containing mutant starter. However the composition of all cheese was satisfactory. Bacteriological counts, proteolysis, rheological properties and flavour development of these cheeses were monitored at regular intervals throughout maturation. The order of the effectiveness of the treatment in accelerating ripening was MN15, >M15,> CN15,> C15,> MNa,> Ma,> CNa,> ca. Cheeses from these treatments attained the characteristics of control cheese stored at a0 c (Ca) for 6 months after 1.4, 1.7, 2.0, 2.6, 2.8, 3.2, 4.3 and 6.0 months respectively. Cheese quality was not adversely affected except for bitterness in CN8 cheese and overmaturity in CN15 cheese late in the storage period. The possible mechanisms and relative merits of the various treatments are discussed with special reference to an "active role" theory of starter bacteria in flavour development.

Tomatoes are the fourth most valuable commodity in agriculture after rice, wheat and soybeans globally with 151 million tonnes of fruit being produced in 2012. The tomato fruit is also a model system for fleshy fruit development. During ethylene-regulated fruit ripening there are complex changes in fruit chemical composition due to degradation and synthesis of a number of soluble and volatile metabolites. Ultimately, these changes control the composition of the ripe fruit and dictate its flavour and texture. It is known that ripening can proceed when mature green fruit are removed from the plant (and indeed this is standard commercial practice) but the extent to which metabolic changes are sustained when fruit are ripened in this way has yet to be established. A modelling approach such as constraints-based modelling can provide system-level insights into the workings of the complex tomato metabolic network during ripening. The first aim of this thesis was therefore to construct a genome-scale metabolic network model for tomato and to use this model to explore metabolic network flux distributions during the transitions between the stages of fruit ripening. The flux distributions predicted provided insight into the production and usage of energy and reductants, into routes for climacteric CO₂ release, and the metabolic routes underlying metabolite conversions during ripening. The second aim of this thesis was to use the model to explore metabolic engineering strategies for increased production of lycopene in tomato fruit. The model predictions showed that rearrangement of dominant metabolic fluxes were required to cope with the increased demand for reductants at high lycopene accumulation, which came at a cost of a lower accumulation of other secondary metabolites. Overall the thesis provides an approach to connect underlying metabolic mechanisms to the known metabolic processes that happen during ripening.

A cell culture system was developed to study the production of prostaglandins by cervical cells from late pregnant guinea pigs. This permitted the examination of the influence of various substances on the synthesis of the prostaglandins, including progesterone and the anti-progesterone drug RU486 (Mifepristone/RU38486). RU486 has been found to promote cervical ripening in humans and guinea pigs. It is thought to increase the sensitivity of the uterus to prostaglandins and thereby promote muscle activity. It is licensed in the United Kingdom as an abortifacient. Since this antiprogestin can provoke cervical ripening alone an accessible source of tissue from an animal with a similar physiology to the human seemed to be an appropriate starting point from which to investigate the effects of this steroidal derivative and how it may affect prostaglandin production. The results show that prostaglandin output can be provoked in vitro by agents such as lipopolysaccharide and phorbol ester. The observed effects by RU486 were mixed. Giving the animals examined, there were, however, some instances where a significant increase was detected, apparently associated with the calcium ionophore A23187, and others where there appeared to be a reduction. The inclusion of RU486 in the culture medium with other treatments did not produce any significant differences compared to the treatment on its own, and alone RU486 only produced a significant difference where the animal had been given the drug in vivo.

Mango fruit ripen quickly. It is highly perishable. Short shelf life of mango fruit limits its transportation to distant domestic and international markets. The objective of my research was to elucidate the role of changes in endogenous levels of brassinosteroids (BRs), ethylene, abscisic acid (ABA) and/or indole-3-acetic acid (IAA) in modulating the ripening processes of 'Kensington Pride' mango fruit. The endogenous levels of these regulators were regulated using inhibitors of their biosynthesis and/or action to unfold their mechanism in delaying/hastening mango fruit ripening, extending storage life and improving fruit quality as well as to underpin the mode of action of ABA and NO in modulating ethylene biosynthesis and activities of fruit softening enzymes in the pulp during ripening and/or alleviating chilling injury (CI) during cool storage.Higher endogenous level of ABA at the climacteric-rise stage triggered the climacteric peak of ethylene production coupled with a significant quadratic relationship between both of them; suggest that ABA play a key role in modulating mango fruit ripening. The exogenous application of ABA (1.0 - 2.0 mM) promoted skin colour development and fruit softening during ripening, and the trend was reversed with its inhibitor of biosynthesis - nordihydroguaiaretic acid (0.1 - 0.2 mM NDGA). The endogenous level of IAA was higher at the initial stage of ripening and decline over ripening period. The exogenous application of 45 - 60 ng g-1 FW Epi- BL increased the climacteric peak of ethylene and respiration, promoted skin colour, but the changes in the endogenous level of BRs (castasterone and brassinolide) are unlikely to modulate mango fruit ripening as it is present in a trace amounts in mango pulp tissues throughout the ripening period.Exogenous postharvest application of ABA (1.0 mM) increased the climacteric peak of ethylene production through promoting the activities of 1- aminocyclopropane-1-carboxylic acid (ACC) synthase (ACS), ACC oxidase (ACO) enzymes, and ACC content, decreased the fruit firmness with increased exopolygalacturonase (exo-PG), endo-PG and endo-1,4-_-D-glucanase (EGase) activities, decreased pectinesterase (PE) activity in the pulp, higher total sugars and sucrose, advanced degradation of total organic acids, citric and fumaric acid. The application of 0.2 mM NDGA showed reverse trends for these ripening indicator parameters.NO fumigation (20 μL L-1 or 40 μL L-1) was more effective in delaying fruit ripening when applied at the pre-climacteric (PC) stage, than at the climacteric-rise (CR) stage. NO (20 μL L-1) fumigation delayed and suppressed the endogenous ethylene production, activities of ACS and ACO enzymes, and ACC content, rate of respiration, higher pulp rheological properties (firmness, springiness, cohesiveness, chewiness, adhesiveness, and stiffness) with lower activities of exo-, endo-PG, EGase, but maintained higher PE activity in pulp tissues during ripening at 21°C and cool storage (13°C). NO treatments (20 and 40 μL L-1) significantly alleviated CI index during ripening at ambient temperature following 2- or 4-week of cold-stored (5°C) period. All NO fumigation treatments significantly suppressed ethylene production and respiration rates irrespective of cold storage period. NO–fumigated with above 5 μL L-1 significantly delayed fruit softening up to 2 days and retarded colour development, reduced total sugar and fructose concentrations, increased tartaric and shikimic acid at fully ripe stage during ripening period irrespective of cold-stored fruit.In conclusion, the higher levels of endogenous IAA in fruit pulp during the PC stage and the accumulation of ABA prior to the climacteric stage might switch on ethylene production that triggers fruit ripening. There is a significant quadratic relationship between endogenous level of ABA in the pulp and ethylene production during fruit ripening period. Exogenous Epi-BL promoted fruit ripening, whilst, the changes in endogenous levels of BRs are unlikely to modulate mango fruit ripening. Moreover, the exogenous application of ABA (1.0 mM) promoted the activities of ethylene biosynthesis enzymes (ACS and ACO) and ACC content and ethylene biosynthesis as well as endo-PG activity in the pulp, whilst, the NDGA-treated fruit showed the reverse trends. The application of NO fumigation (20 L L-1) at PC stage can be effectively used to delay the fruit ripening up to 2 days at ambient temperature (21°C) and cool-storage (13°C) through suppression the activity of ethylene biosynthesis and softening enzymes and alleviate CI following 2- and 4-week cold storage (5°C) without any adverse effects on fruit quality.

The ripening stage of apple fruits at harvest is the main factor influencing fruit quality during the cold storage period that lasts several months and give rise to physiological disorders in fruits of susceptible cultivars. In particular, superficial scald is connected to α-farnesene oxidation, leading to fruit browning. Therefore, the assessment of the optimal ripening stage at harvest is considered to be crucial to control the overall quality, the length of storage life and the scald incidence. However, the maturity indexes traditionally used in the horticultural practice do not strictly correlate with fruit maturity, and do not account for the variability occurring in the field. Hence, the present work focused on the determination of apple fruit ripening with the use of an innovative, non-destructive device, the DA-meter. The study was conducted on ‘Granny Smith’ and ‘Pink Lady’ cultivars, which differ in scald susceptibility. Pre- and post- harvest ripening behavior of the fruits was studied, and the influence of ripening stage and treatments with 1-MCP were evaluated in relation to scald development and related metabolites. IAD was shown to be a reliable indicator of apple ripening, allowing cultivar-specific predictions of the optimal harvest time in different growing seasons. IAD may also be employed to segregate apple fruits in maturity classes, requiring different storage conditions to control flesh firmness reduction and scald incidence. Moreover, 1-MCP application is extremely effective in reducing superficial scald, and its effect is influenced by fruit ripening stage reached at harvest. However, the relation between ethylene and α-farnesene was not entirely elucidated. Thus, ethylene can be involved in other oxidative processes associated with scald besides α-farnesene regulation.

The ripening stage of apple fruits at harvest is the main factor influencing fruit quality during the cold storage period that lasts several months and give rise to physiological disorders in fruits of susceptible cultivars. In particular, superficial scald is connected to α-farnesene oxidation, leading to fruit browning. Therefore, the assessment of the optimal ripening stage at harvest is considered to be crucial to control the overall quality, the length of storage life and the scald incidence. However, the maturity indexes traditionally used in the horticultural practice do not strictly correlate with fruit maturity, and do not account for the variability occurring in the field. Hence, the present work focused on the determination of apple fruit ripening with the use of an innovative, non-destructive device, the DA-meter. The study was conducted on ‘Granny Smith’ and ‘Pink Lady’ cultivars, which differ in scald susceptibility. Pre- and post- harvest ripening behavior of the fruits was studied, and the influence of ripening stage and treatments with 1-MCP were evaluated in relation to scald development and related metabolites. IAD was shown to be a reliable indicator of apple ripening, allowing cultivar-specific predictions of the optimal harvest time in different growing seasons. IAD may also be employed to segregate apple fruits in maturity classes, requiring different storage conditions to control flesh firmness reduction and scald incidence. Moreover, 1-MCP application is extremely effective in reducing superficial scald, and its effect is influenced by fruit ripening stage reached at harvest. However, the relation between ethylene and α-farnesene was not entirely elucidated. Thus, ethylene can be involved in other oxidative processes associated with scald besides α-farnesene regulation.

Pawpaw (Asimina triloba (L.) Dunal) has significant potential as a new fruit crop. During ripening, loss of firmness is extremely rapid, and this trait may be the biggest obstacle to the development of a broader market as handling without injury is difficult. Cold storage of pawpaw seems limited to 4 weeks at 4 C. A study of several cultivars with commercial appeal showed that ripening traits such as ethylene production, respiration and loss of firmness were similar in all genotypes, and that no cultivar showed superior responses to cold storage. Cold storage for longer than 4 weeks caused the development of cold injury symptoms such as black discoloration, rapid loss of firmness, impaired respiration, tissue acidification, decrease in antioxidant content, decrease in volatile ester production and development of off-flavor volatile compounds. Overall cold storage injury symptoms observed in pawpaw may be due to oxidative damage linked to the failure of the two major antioxidant systems that could protect against such damage: phenolics and the ascorbateglutamate system. With the aim of enhancing pawpaw low temperature tolerance and prolonging cold storage length, different techniques such as hot air exposure and hot water dips of fruit prior to beginning cold storage, and intermittent warming periods during cold storage, were evaluated. Despite positive results with these techniques for other commodities, all the strategies failed to appreciably alter fruit ripening, loss of firmness or maintain fruit quality during and/or after cold storage.

Oligosaccharides were isolated directly from tomato fruit tissue; a series of homo-oligogalacturonides with a DP of 2-6 was identified in red-ripe and over-ripe fruit. Two glucose disaccharides, identified as gentiobiose and nigerose, were isolated from both mature green (MG) and red-ripe fruit. Gentiobiose was able to accelerate the initiation of ripening when vacuum infiltrated into MG tomato fruit, particularly when co-infiltrated with nigerose. The possible origin of these disaccharides is discussed. The potential role of organic acids (ascorbate, citrate and oxalate) in fruit softening was evaluated in vitro on MG tomato fruit alcohol-insoluble residue (AIR). The hydroxyl radical (^•OH), produced via a Fenton reaction in which ascorbate acts as a pro-oxidant, released pectin into solution in the presence of oxygen. ^•OH production in vivo may be localised in the PCW by the positioning of metal ions such as Cu²⁺ on pectins or glycoproteins. Probes used to detect ^·OH in the tomato fruit apoplast produced inconclusive results but suggested that this active oxygen species is present during ripening. The incubation of tomato fruit AIR with naturally occurring chelators such as citrate and oxalate also led to solubilisation of uronate-containing material. The alteration of the PCW during ripening is likely to be the result of a number of processes. These processes may occur throughout the PCW or may occur in specific areas but their contribution to the softening process should not be over-looked in favour of processes only involving hydrolytic enzymes, as this could lead to an over-simplified view fruit ripening.

L'éthylène est synthétisé et perçu par toutes les plantes. C'est l'une des phytohormones les plus importantes contrôlant la maturation des fruits. L'éthylène est perçu par les protéines localisées au niveau du réticulum endoplasmique (RE), appelées récepteurs éthylène (ETR), qui régulent le développement et la maturation des fruits, mais les mécanismes par lesquels ils fonctionnent ne sont pas encore tous connus. Premièrement, pour étudier si les ETRs régulent le mûrissement des fruits climactériques et non climactériques, nous avons comparé les ETRs et les protéines apparentées des deux catégories de fruits et en analysant à nouveau des données RNAseq déjà publiées. Nous avons constaté que les ETRs atteignaient leur maximum d’expression au début du mûrissement à la fois dans les fruits climactériques et non climactériques, mais dans ces derniers, les ETRs ont un pic d’expression plus précoce par rapport à l’accumulation de sucres. Dans cette étude, nous avons également comparé la structure des ETRs et des protéines apparentées dans les deux classes de fruits, établissant ainsi une base pour l'annotation de gènes liés à la perception de l'éthylène. Enfin, les résultats ont montré qu'il y avait un plus grand nombre de gènes ETRs dans les fruits climatériques que dans les fruits non climatériques. Deuxièmement, chez la tomate, qui est un modèle de maturation des fruits charnus, un septième ETR a été trouvé récemment, suite au séquençage du génome. La caractérisation de ce SlETR7 a été réalisée. Nous avons montré que l’éthylène se lie à la partie transmembranaire de SlETR7. L'expression de SlETR7 augmente dans le péricarpe lorsque les fruits mûrissent, comme pour d’autre ETRs. Les profils d’expression des 7 ETRs au cours de la maturation des fruits peuvent être divisés en 2 groupes: le groupe 1, ETR3, ETR4 et ETR6 qui sont exprimés plus tôt à Breaker + 2 jours que les ETRs du groupe 2, ETR1, ETR2, ETR5 et ETR7. Nous avons construit des lignées de tomates Knock Out (KO) et OverExpressed (OE) pour SlETR7, et nous avons observé certains changements de phénotypes prouvant que SlETR7 est un ETR fonctionnel. Alors que les plantes et les fruits KO ne présentaient qu'un faible changement phénotypique: production d'éthylène supérieure à Br et 2 jours comparée à Wild Type (WT), les lignées OE montraient une floraison précoce, des plantes plus courtes et des fruits plus petits que WT. Les analyses de l'expression de 7 ETRs dans les lignées KO et OE ont révélé que d'autres ETR sont régulées positivement chez les mutants de KO, ce qui peut expliquer l'absence de phénotype évident. Et cela suggère que SlETR7 n'est peut-être pas essentiel pour la maturation des fruits. Troisièmement, en ce qui concerne les études des 7 ETRs de tomate, l’absence de méthode fiable pour les quantifier, au niveau protéine, constitue un obstacle majeur. Une méthode protéomique ciblée a été développée, PRM pour Parallel Reaction Monitoring, et cela a permis l'identification et la quantification relative des sept ETRs de tomate. Ce développement appliqué à l’étude des tomates WT et des mutants Never Ripe (NR) montre qu’il existe une sur-accumulation de ETR3 mutée qui pourrait être la cause de l’inhibition de maturation des tomates NR, qui restent oranges. En effet cette protéine ETR3 mutée, gain-de-fonction, bloque la signalétique éthylène même en présence d’éthylène. Enfin, les ARNm et les protéines d'ETRs ont été analysés au sein des mêmes échantillons, ce qui nous a amenés à suggérer l'existence d'une corrélation positive entre les ARNm et les protéines d'ETR, controversée dans la littérature précédente
Ethylene is synthesized and perceived by all plants, and it is one of the most important phytohormone controlling fruit ripening. Ethylene is perceived by endoplasmic reticulum (ER)- localized proteins, called Ethylene Receptors (ETRs), which regulate fruit development and ripening, however the mechanisms by which ETRs regulate fruit ripening are not fully explained. Firstly, to study if ETRs regulate the ripening of climacteric and non-climacteric fruits, we compared ETRs and related protein members of both classes of fruit and by re-analyzing RNAseq data, already published, we found that ETRs were peaking at the inception of ripening in both climacteric and non- climacteric fruits, but in these data, the ETRs showed an earlier ETR expression peak relative to sugar accumulation. In this review, we also compared the structure of the ethylene receptors and related proteins in both classes of fruit, establishing a basis for the annotation of genes related to ethylene perception. Finally, the results show that there was a higher number of ETR genes in climacteric fruits than in non-climacteric fruits. Secondly, in tomato which is a fleshy fruit ripening model, a seventh ETR has been reported recently, following the genome sequencing. Characterization of this SlETR7 was carried out. We showed that ethylene binds to the transmembrane part of SlETR7. Like other ETR expression patterns during fruit ripening, SlETR7 expression in pericarp also goes up when fruit ripens. The profiles of the seven ETR expression during fruit ripening can be divided in 2 groups: group 1, ETR3, ETR4, and ETR6 are expressed earlier at Breaker+2 days than group 2, SlETR1, SlETR2, SlETR5, and SlETR7 that are expressed at a later stage of ripening. We constructed Knock Out (KO) and OverExpressed (OE) tomato lines for SlETR7, and we observed some phenotype changes proving that SlETR7 is a functional ETR. While there was only a small phenotype change in KO plants and fruits: more ethylene production at Br and Br+2days compared to Wild Type (WT). The OE lines showed early flowering, shorter plants, and smaller fruit than WT. The analyzes of the 7 ETR expression in KO and OE lines, revealed that other ETR expression is upregulated in KO mutants, which may explain the absence of obvious phenotype. and this suggest that SlETR7 maybe not critical in fruit ripening. Thirdly, regarding the studies of the seven tomato ETRs, one major bottleneck is the absence of reliable method to quantify them at the protein level. A targeted proteomic method was developed, PRM for Parallel Reaction Monitoring, and allow the identification and relative quantification of the seven tomato ETRs. This development applied to the study of the WT and Never Ripe mutant tomatoes showed that there is an over-accumulation of SlETR3, affected by a gain-of-function mutation in NR, while the NR tomatoes undergo ripening, which may be a cause of further ripening inhibition, as NR fruit stay orange. Finally, ETR mRNAs and proteins were analyzed within the same samples, and this led us to propose that there is a positive correlation between ETR mRNAs and proteins, which was controversial in the previous literature

Thesis (MSc. Agriculture (Horticulture)) -- University of Limpopo, 2016
The Agricultural Research Council-Institute for Tropical and Subtropical Crops (ARC-ITSC) is continuously developing new avocado selections, in order for the South African Avocado Industry (SAAI) to remain competitive in various international avocado markets. However, information on the response of some of these selections, including ‘Fuerte 2 and 4’, ‘BL1058’ and ‘H287’ to low temperature storage and ripening physiology, has not been investigated. Thus, the objective of this study was to evaluate the effect of harvest season and ripening duration on the physico-chemical properties of newly developed ‘Fuerte-type’ avocado fruit selections during ripening. ‘Fuerte-type’ avocado fruit were indexed for maturity using moisture content, thereafter harvested and stored at 5.5°C for 28 days during the 2014 and 2015 harvest seasons. The experiment comprised five treatments: control (commercial ‘Fuerte’), ‘Fuerte 2 and 4’, ‘BL1058’ and ‘H287’ arranged as a factorial in a completely randomised design (RCD) with 3 replicates. The treatment factors were: (i) 2 x harvest seasons, (ii) 5 x selections and (iii) 6 x ripening days. After withdrawal from low storage temperature, fruit were ripened at ambient temperature. During ripening, the following physico-chemical properties were evaluated; external chilling injury, electrolyte leakage, mass loss, firmness, respiration rate and peel colour. Results showed that selections and harvest seasons had no significant effect (P=0.668) on the moisture content of the evaluated ‘Fuerte-type’ avocado fruit. After withdrawal from low storage temperature, there was a significant interaction (P˂0.05) between selections and harvest seasons on external chilling injury and electrolyte leakage. Results further showed that external chilling injury correlated with electrolyte leakage during both harvest seasons. Treatment factors had no significant effect (P=0.997) on mass loss. Similarly, treatment factors had no significant effect (P=0.139) on firmness. However, selection ‘H287’ had hard skin with an average firmness of 83.44 densimeter units during ripening in both harvest seasons. Treatment factors were highly significant (P˂0.05) on respiration rate. Respiration rate followed a climacteric pattern and the magnitude of climacteric peak and day of occurrence varied amongst selections during both harvest seasons. Ripening percentage differed significantly (P˂0.05) amongst harvest seasons, selections and ripening days. Treatment factors had no significant effect on lightness (P=0.711), chroma (P=0.378) and hue angle (P=0.536) skin colour parameters,however, variations were recorded as a result of the cold damage black spots. The results indicated that the ‘Fuerte-type’ avocado selections had poor storage qualities. Further studies are required to evaluate physico-chemical properties during low storage temperature and the effect of season, production conditions and maturity level on development of chilling injury. In addition, studies on application of treatments to reduce chilling injury symptoms and analysis of bioactive compounds should be considered for conclusive recommendations. Thereafter, the selections can be planted in different production regions to assess and select the best producing and quality combinations for a given region as part of phase III of the project
Agricultural Sector Education Training Authority (AgriSeta) and National Research Foundation (NRF)

Ostwald ripening and chemotaxis are two different mechanisms that describe particle motion throughout a domain. Ostwald ripening describes the redistribution of a solid solution due to energy potentials while chemotaxis is a cellular phenomenon where organisms move based on the presence of chemical gradients in their environment. Despite the two systems coming from disparate fields, they are connected by the late-stage dynamics of interfacial motion. For the Ostwald ripening system we consider the case of N droplets in the asymptotic limit of small radii [formula omitted]. We first derive a system of ODEs that describe the motion of the droplets and then improve this calculation by including higher order terms. Certain properties, such as area preservation and finite time extinction of certain droplets are proved and a numerical example is presented to support the claims. In the chemotaxis model we look at the asymptotic limit of diffusive forces being small compared to that of chemotactic gradients. We use a boundary-fitted coordinate system to derive an equation for the velocity of an arbitrary interface and analyze a few specific examples. The asymptotic results are also explored and confirmed using the finite element and level set methods. Our analysis reveals the mechanism of movement to be motion by curvature in Ostwald ripening and a surface diffusion law in chemotaxis. The governing rules of motion may be different in the two systems but the end result is typically characteristically similar- exchange of mass and smoothing in favor of a larger and more stable configuration of drops.
Science, Faculty of
Mathematics, Department of
Graduate

Thesis (MscAgric (Viticulture and Oenology))--Stellenbosch University, 2008.
The effect of various irrigation strategies on grapevine water relations during the berry ripening period was investigated in a Shiraz/Richter 99 vineyard. Comparisons between different irrigation strategies (full/seasonal, véraison+post véraison, post véraison and no irrigation) were made. During the day, the seasonally irrigated vines experienced less water stress than the deficit treatments. Non-irrigated vines seemed to maintain higher diurnal leaf water potentials. Lower leaf water potentials indicated lower water contents in the vegetative and reproductive tissue. Full irrigation seemed to stimulate primary shoot length. Longer water deficit induced earlier and more complete shoot maturation (reserve accumulation). Re-distribution of leaf area on the shoot may occur when vines are subjected to water deficit. Extended water deficit seemed to induce earlier and restricted water loss from vegetative tissue. The water relations were reflected in the berry size. Irrigation during ripening seemed to induce a continuation of berry water loss. Transpiration losses were apparently much higher in fully irrigated vines whereas stomatal control efficiently maintained water relations in non-irrigated vines. Water deficit seemed to have enhanced the soluble solid accumulation. Irrigation treatments did not seem to affect the titratable acid and pH. The post véraison irrigation in particular seemed to favour a wide window for harvesting. Irrigation at post véraison and especially véraison+post veraison seemed to have a greater effect on the synthesis and extraction of phenolics, anthocyanins and tannins in the berry skins. Different irrigation strategies may affect grapes in such a way that different wine styles are obtained.

Changes in cell walls and in the levels of polysaccharide-degrading enzymes, in mesocarp of mango fruit during ripening were investigated. Total, insoluble cell wall content declined with ripening. Galactose, arabinose, xylose and mannose were lost from the wall during ripening and autolysis of ripe mango mesocarp released arabinose and xylose into the soluble fraction. Galacturonic acid was also removed from the wall but polygalacturonase (which degrades pectic galacturonan in fruits of many other species) could not be detected. Several glycosidase activities were present in the mesocarp and, of these, a-d-galactosidase and mannosidase increased markedly during ripening. The increase in the former may be significant in the removal of wall-bound galactose accompanying ripening. Enzyme extracts prepared from ripe mangoes released galactose from cell walls isolated from unripe fruits but soluble polysaccharides released from the wall by enzyme action In vitro could not be detected by electrophoresis. Polysaccharides, composed mainly of xylose and glucose, were co-extracted with enzymic protein from mango mesocarp and there was evidence that these polymers underwent degradation during ripening. They may be derived, partly at least, from wall hemi-celluloses. It is proposed that one process contributing to cell wall breakdown and resultant tissue softening in the mango may be the enzymic hydrolysis of polysaccharides containing arabinose and galactose (possibly neutral pectic polymers) and that polygalacturonase activity probably does not contribute significantly to tissue softening The mechanism for removal of galacturonan from the wall was not established but this may result from prior removal of polysaccharides containing arabinose and galactose. Data obtained also suggest that hemi-celluloses in the wall may be degraded during ripening, Critical appraisal was made of the limitations of both preparatory and analytical methods employed and proposals made for employing better methods in further work.

Fruit quality traits are the result of genetic, agronomic and environmental factors that, alone or in combination, modulate metabolic processes during both pre- and post-harvest phases and affect fruit development and ripening processes. Productivity, size and organoleptic quality should be the main quality criteria adopted by fruit growers: in this context, harvesting time is crucial. Too early harvested fruit may be stored for a long time but their flavour quality is low, whereas late harvested fruit are of better quality but do not withstand long storage periods and theirs shelf-life is reduced. This is particularly true for peaches and nectarines characterized by a quick ripening evolution and a reduced aptitude to prolonged storage: this induces growers to anticipate harvesting and represents the main constraints for supplying high-quality standard level peaches to the consumers. Elucidating mechanisms and basic processes characterizing ripening and responsible for the evolution of quality parameters is the prerequisite to develop strategies aimed to produce high-quality fruit and to maintain these standards throughout the postharvest chain. In climacteric fruit, including peaches, ethylene is a key factor in coordinating and regulating the evolution of several processes characterizing the ripening syndrome. Thus, studying aspects related to ethylene action has been a challenge during the last few decades. Improvements of the basic knowledge of ethylene physiology also came from the identification of specific inhibitors of its biosynthesis and/or action, and from the use of mutants. The development of highthroughput molecular tools (i.e. microarray) and functional genomics approaches represent a great opportunity for a better understanding of the ripening process and the basic mechanisms governing quality-related metabolisms in fruit. Considering peach, the first step toward a functional approach is represented by the development of an Expressed Sequences Tag (ESTs) repertoire, that, together with other ESTs isolated by other units and available in public databases, allowed to select 4806 oligos, corresponding to an equal number of genes expressed in peach fruit, and construct the first peach microarray (?PEACH 1.0). ?PEACH 1.0 has been used to study the effects of exogenous ethylene on different peach genotypes, a "melting flesh" cv and two ripening mutants, Slow Ripening (SR) and Stony Hard (SH). Microarray analysis revealed marked differences in transcript profiling possibly related to the nature of mutation and differences in ethylene physiology. SH fruit has also been used for expression analyses of two elements involved in the ethylene signalling pathway. Besides mutants, specific inhibitors of ethylene biosynthesis and/or action represent invaluable tools for elucidating the ethylene role in the ripening process. One of the most powerful inhibitor of ethylene function is 1-methylcyclopropene (1-MCP) that is practically used on different fruit species, but not on peaches, to prolong shelf-life. Using ?PEACH 1.0, a large-scale analysis of transcriptome has been performed on nectarine fruit treated with 1-MCP in order to elucidate the molecular mechanisms responsible for the limited effect of the inhibitor on this climacteric fruit species. At the end of the treatment (24h) and 48h hours later, a number of genes involved in quality-related ripening processes (such as softening, sugar metabolism and colour development) appeared to be deeply modified in their expression. Changes in the expression profile of Transcription Factors related to ethylene and auxin action confirmed the importance of "cross-talk" between the two hormones in the modulation of the ripening process in peach. In the context of a functional genomics, three different genes (two from peach and one from tomato), identified following transcriptomics approaches, have been used for transgenic experiments in tomato plants.

Objectives of the first part of research program were the effect of some environmental and physiological aspects on the intensity of flavonoid synthesis. The trial was carried out during the 2011 growing season in the commercial vineyard of the Plantaze, Podgorica (Montenegro). Two grapevine cultivars were compared: Vranac and Cabernet Sauvignon. The following experimental treatments were compared: early leaf removal (flowering time), cluster thinning (veraison time) and combination of both treatments. The early defoliation reduced yield per vine in Cabernet Sauvignon and Vranac. In Cabernet Sauvignon defoliation initially delayed berry growth. In cultivar Vranac defoliation did not modify the berry growth and berry weight. In the treatments “defoliated-thinned” is observed reduction of the cluster weight, berry weight and berry number per cluster. Early defoliation and cluster thinning in both varieties raised the concentration of anthocyanins and proanthocyanidins. The enhanced contents of these compounds per berry in variety Vranac is the result of increased synthesis. The objective of second study was to improve the knowledge of the eco-physiological basis of the genotype x environmental interaction. The experimental plan included the study of the Sangiovese grapes, a variety by a particular responsiveness to changing environmental conditions, and Cabernet Sauvignon grapes, a so called international cultivar characterized by more stable features. It was operated within the framework of Appellations of Origin Bolgheri (Tuscany coast), Montalcino (Tuscany Apennines) and Misano (Romagna coast). The experiment was conducted during two growing seasons (2011-2012) through grape development and ripening from fruit set to ripe stage. Since carotenoids are the precursors to C13-norisoprenoid aroma compounds in wine, relationship between carotenoid and norisoprenoid levels in grapes was investigated. In the first phase of berry ripening, before veraison, sites with greater global solar radiation (Montalcino and Bolgheri) showed positive correlation with the intensity of total carotenoids accumulation. Location Montalcino was also characterized by a greater water stress. Correlation between carotenoids accumulation prior to veraison and accumulation of norisoprenoids were not observed. Sangiovese showed a greater reactivity to the environment compared to Cabernet Sauvignon. The norisoprenoids levels in variety Sangiovese largely varied between different years and sites. The synthesis of norisoprenoids appears to be more related to the specific ecophysiological conditions that occur during maturation, rather than to the carotenoids content at veraison.

El melón (Cucumis melo L.) es un importante cultivo a nivel mundial, con una producción de 31 millones de toneladas durante el año 2016. Aunque tradicionalmente los programas de mejora genética se han focalizado en el comportamiento agronómico del cultivo, la calidad de fruto se ha convertido recientemente en un objetivo principal. La calidad del fruto es un concepto complejo, que incluye diversos caracteres relacionados con la apariencia visual del fruto y su calidad nutricional y organoléptica. Muchos de estos caracteres están asociados a la maduración de fruto, que es el proceso que sufre el fruto para transformarse en un alimento atractivo para promover la dispersión de la semilla. Los frutos son clasificados, en base a su comportamiento durante la maduración, en climatéricos, cuando la hormona vegetal etileno es sintetizada de manera autocatalítica al comienzo del proceso de maduración, y no climatéricos, para los cuales el etileno no tiene un papel importante. El principal objetivo de este trabajo ha sido estudiar las bases genéticas de la calidad y la maduración del fruto en melón. Hemos desarrollado una población de líneas puras recombinantes (RIL) a partir del cruce entre dos variedades élite, “Védrantais”, altamente climatérica, y “Piel de Sapo” (PS), no climatérica. La diversidad fenotípica en la calidad de fruto y los caracteres asociados a la maduración, incluyendo la producción de etileno, han sido estudiados en profundidad. Un mapa genético de alta densidad ha sido construido usando variantes obtenidas a través de un experimento de genotyping-by-sequencing. Un experimento de mapeo de QTLs reveló cinco genes mayores y 33 QTLs implicados en la apariencia visual del fruto (color, presencia de suturas, moteado), morfología de fruto, contenido en azúcares y peso de semilla. Un segundo experimento de mapeo de QTLs identificó 14 QTLs implicados en la producción de etileno y otros caracteres asociados a la maduración, como degradación de clorofila o formación de una capa de abscisión. Entre ellos, podemos destacar un QTL mayor, ETHQV8.1, implicado en la producción de etileno que afectó a prácticamente todos los caracteres estudiados, localizado en un intervalo de 500 kb del cromosoma VIII. Para diseccionar genéticamente la maduración del fruto, además de la mencionada población de RILs, estudiamos la línea casi isogénica (NIL) climatérica 8M35, con el fondo genético de PS y una introgresión de la accesión exótica PI 161375. 8M35 porta el QTL ETHQB3.5, delimitado en una región de 5Mb del cromosoma III. Se ha seguido una estrategia de clonaje posicional para el mapeo fino de ETHQB3.5, generando un juego diverso de subNILs. Tras múltiples evaluaciones de diferentes subNILs, determinamos que al menos dos factores genéticos diferentes deben estar implicados en el desencadenamiento de la maduración climatérica en la línea 8M35. Uno de ellos, nombrado ETHQB3.5.1, es responsable de la mayor parte del fenotipo y fue delimitado a una región de 500 kb que contiene 63 genes anotados. Finalmente, dos colecciones de introgresiones recíprocas fueron desarrolladas, utilizando “Védrantais” y PS, ambos como líneas parentales recurrente y donante, respectivamente. Se efectuaron retrocruzamientos recurrentes en las dos direcciones y se realizó una selección asistida por marcadores en cada generación, para seleccionar tanto la introgresión diana como el fondo genético deseado. Las colecciones actuales, que cubren el 95% del genoma de la línea parental donante, están formadas por 38 líneas de introgresión. Hemos realizado un fenotipado preliminar que ha permitido validar algunos de los QTLs mapeados en la población de RILs. Además, dos familias segregantes de líneas de introgresión con el fondo genético de PS se han usado para el mapeo fino de ETHQV8.1, permitiendo reducir la región a un intervalo de 150 kb que contiene 14 genes candidatos.
Melon (Cucumis melo L.) is an important crop worldwide, with a production of around 31 million tons during 2016. Although traditionally breeding programs have been focused on agronomic traits, fruit quality has become a main goal recently. Fruit quality is a complex concept, including diverse traits related to fruit appearance, nutritional and organoleptic traits. Many of these traits are associated to fruit ripening, which is the process that the fruit undergoes to become edible to promote seed dispersal. Fruits are classified according to their ripening behavior into climacteric, when the plant hormone ethylene is synthesized in an autocatalytic way at the onset of ripening, and non-climacteric, in which ethylene has not a major role. The main goal of this work was to study the genetic basis of fruit quality and fruit ripening in melon. We have developed a Recombinant Inbred Line (RIL) population from a cross between two elite cultivars, “Védrantais”, highly climacteric, and “Piel de Sapo”, non-climacteric. The phenotypic diversity in fruit quality and ripening-associated traits, including ethylene production, has been thoroughly studied. A high-density genetic map was constructed using SNPs and INDELs obtained through a genotyping-by-sequencing experiment. A first QTL mapping experiment revealed five major genes and 33 QTLs governing fruit appearance (flesh and rind color, presence of sutures, mottled rind), fruit morphology, sugar content and seed weight. A second QTL mapping experiment identified 14 QTLs modifying ethylene production and ripening-associated traits, as chlorophyll degradation and abscission layer formation. Among them, we highlight a major QTL, ETHQV8.1, involved in ethylene production that was affecting almost all the studied traits, located in a 500-kb interval in chromosome VIII. In order to genetically dissect the fruit ripening process in melon, in addition to the mentioned RIL population, we studied a climacteric near-isogenic line, 8M35, with “Piel de Sapo” background and containing an introgression from the exotic accession PI 161375. 8M35 carries a QTL, ETHQB3.5, delimited in a region of 5 Mb in chromosome III. A positional cloning strategy was followed to fine map ETHQB3.5, generating a diverse set of subNILs. After multiple evaluations of different subNILs, we determined that at least two different genetic factors should be involved in triggering climacteric ripening in 8M35. One of them, named ETHQB3.5.1, which is responsible for the major part of the variation, was delimited to a 500-kb region containing 63 annotated genes. Finally, two reciprocal introgression line (IL) collections were developed, using both “Védrantais” and “Piel de Sapo” as recurrent and donor parental lines, respectively. Recurrent backcrosses were performed in both directions and marker-assisted selection was performed in each generation to select both the target introgressions and the desired background. The current IL collections, covering approximately 95% of the donor parental genome, are formed by 38 ILs. We performed a preliminary phenotyping that allowed to validate some of the QTLs mapped in the RIL population for both fruit quality and fruit ripening traits. In addition, two segregating families of ILs with “Piel de Sapo” background were used to fine map ETHQV8.1, allowing to narrow down the region to a 150-kb interval containing 14 candidate genes. As a summary, this PhD thesis has contributed to improving our knowledge about the genetics of fruit quality and particularly fruit ripening in melon, proposing some important QTLs that will be further explored in the future. Our work suggests that climacteric behavior in melon is a complex and quantitative trait controlled by polygenic inheritance, rather than a qualitative class as described traditionally in the literature.

Vineyards in New Zealand suffer bird damage caused by several avian species, including blackbirds and silvereyes. The introduced European Blackbird takes whole grapes which reduces yield. The self-introduced Australasian Silvereye pecks on grapes, leaving them on the vine to be further attacked by fungi and bacteria, and the subsequent off-odours can cause grapes to be refused by the winery or to suffer a price-reduction. Bird control methods remain primitive and largely ineffective during the long ripening period of wine grapes. An ecologically sound method to manage and reduce bird pressure requires deeper understanding of why some birds eat grapes, especially since grapes are not particularly nutritious. This work investigated the extent to which blackbirds and silvereyes are attracted by various compounds in ripening grapes. Since in natural grapes these compounds develop and change simultaneously, I developed an artificial grape in which a single parameter could be investigated. Artificial grapes (and sometimes nectar) were presented on a bird feeder table and the responses of birds to hexose sugars, the aromas 2-3-isobutylmethoxypyrazine and geraniol, tartaric and malic acids, grape tannins, and purple and green colour were recorded on timelapse video and analysed.

Vineyards in New Zealand suffer bird damage caused by several avian species, including blackbirds and silvereyes. The introduced European Blackbird takes whole grapes which reduces yield. The self-introduced Australasian Silvereye pecks on grapes, leaving them on the vine to be further attacked by fungi and bacteria, and the subsequent off-odours can cause grapes to be refused by the winery or to suffer a price-reduction. Bird control methods remain primitive and largely ineffective during the long ripening period of wine grapes. An ecologically sound method to manage and reduce bird pressure requires deeper understanding of why some birds eat grapes, especially since grapes are not particularly nutritious. This work investigated the extent to which blackbirds and silvereyes are attracted by various compounds in ripening grapes. Since in natural grapes these compounds develop and change simultaneously, I developed an artificial grape in which a single parameter could be investigated. Artificial grapes (and sometimes nectar) were presented on a bird feeder table and the responses of birds to hexose sugars, the aromas 2-3-isobutylmethoxypyrazine and geraniol, tartaric and malic acids, grape tannins, and purple and green colour were recorded on timelapse video and analysed.