Search

Brown rot in stored stone fruits, caused by Monilinia spp., may be due to preharvest and storage factors, but the combined effect of these factors has yet to be investigated. We set up two experiments to monitor the progression of brown rot during the storage of nectarines subjected to various preharvest and storage conditions. We assessed the effects of different agricultural practices (irrigation regimen × fruit load) and harvest dates on brown rot progress during storage in 2018 and the effect of different storage temperatures in 2019. We found that the cumulative incidence of brown rot during storage increased with individual fruit mass, which was influenced by agricultural practices, and for later harvest dates. It also increased with storage temperature. We observed that during storage no secondary infections developed in nectarines not in direct contact with fruits infected with Monilinia laxa . These findings led to the identification of candidate variables describing the brown rot risk on nectarines during storage, such as individual fruit mass, meteorological conditions before fruit harvest, prevalence of brown rot at harvest, and storage temperature. We used these variables to build a mathematical model for estimating the time-to-appearance of brown rot symptoms in stored nectarines. This model fitted the experimental data well, highlighting the need to pay greater attention to the interaction between preharvest and storage conditions. This model could be used to evaluate management strategies for reducing the impact of brown rot in nectarines during storage.

Productivity of fruit tree crops depends on the interaction between plant physiology, environmental conditions and agricultural practices. We develop a mechanistic model of fruit tree crops that reliable simulates the dynamics of variables of interest for growers and consequences of agricultural practices while relying on a minimal number of inputs and parameters. The temporal dynamics of carbon content in the different organs (i.e., shoots-S, roots-R and fruits-F) are the result of photosynthesis by S, nutrient supply by R, respiration by S, R and F, competition among different organs, photoperiod and initial system conditions partially controlled by cultural practices. We calibrate model parameters and evaluate model predictions using unpublished data from a peach (Prunus persica) experimental orchard with trees subjected to different levels of branch pruning and fruit thinning. Fiinally, we evaluate the consequences of different combinations of pruning and thinning intensities within a multi-criteria analysis. The predictions are in good agreement with the experimental measurements and for the different conditions (pruning and thinning). Our simulations indicate that thinning and pruning practices actually used by growers provide the best compromise between total shoot production, which impacts next year's abundance of shoots and fruits, and current year's fruit production in terms of quantity (yield) and quality (average fruit size). This suggests that growers are not only interested in maximizing current year's yield but also in its quality and its durability. The present work provides for modelers a system of equations based on acknowledged principles of plant science easily modifiable for different purposes. For horticulturists, it gives insights on the potentialities of pruning and thinning. For ecologists, it provides a transparent quantitative framework that can be coupled with biotic and abiotic stressors., (© The Author(s) 2021. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

We develop a model based on the biophysical representation of water and sugar flows between the pedicel, fruit xylem and phloem, and the fruit apoplast and symplast in order to identify diurnal patterns of transport in the pedicel-fruit system of peach. The model predicts that during the night water is mainly imported to the fruit through the xylem, and that fruit phloem-xylem transfer of water allows sugar concentrations in the phloem to be higher in the fruit than in the pedicel. This results in relatively high sugar transport to the fruit apoplast, leading to relatively high sugar uptake by the fruit symplast despite low sugar concentrations in the pedicel. At midday, the model predicts a xylem backflow of water driven by a lower pressure potential in the xylem than in the fruit apoplast. In addition, fruit xylem-to-phloem transfer of water decreases the fruit phloem sugar concentration, resulting in moderate sugar uptake by the fruit symplast, despite the high sugar concentration in the pedicel. Globally, the predicted fruit xylem-phloem water transfers buffer the sugar concentrations in the fruit phloem and apoplast, leading to a diurnally regulated uptake of sugar. A possible fruit xylem-to-apoplast recirculation of water through the fruit phloem reduces water lost by xylem backflow at midday., (© The Author(s) 2020. Published by Oxford University Press on behalf of the Society for Experimental Biology.)

The development of a new organ is the result of coordinated events of cell division and expansion, in strong interaction with each other. This study presents a dynamic model of tomato fruit development that includes cell division, endoreduplication, and expansion processes. The model is used to investigate the potential interactions among these developmental processes within the context of the neo-cellular theory. In particular, different control schemes (either cell-autonomous or organ-controlled) are tested and compared to experimental data from two contrasting genotypes. The model shows that a pure cell-autonomous control fails to reproduce the observed cell-size distribution, and that an organ-wide control is required in order to get realistic cell-size variations. The model also supports the role of endoreduplication as an important determinant of the final cell size and suggests that a direct effect of endoreduplication on cell expansion is needed in order to obtain a significant correlation between size and ploidy, as observed in real data., (© Society for Experimental Biology 2019.)

Agronomic practices can alter plant susceptibility to diseases and represent a promising alternative to the use of pesticides. Yet, they also alter crop quality and quantity so that the evaluation of their efficacy is not straightforward. Here we couple a compartmental epidemiological model for brown rot diffusion in fruit orchards with a fruit-tree growth model explicitly considering the role of agronomic practices over fruit quality. The new modelling framework permits us to evaluate, in terms of quantity and quality of the fruit production, management scenarios characterized by different levels of regulated deficit irrigation and crop load. Our results suggest that a moderate water stress in the final weeks of fruit development and a moderate fruit load provide effective control on the brown rot spreading, and eventually guarantee monetary returns similar to those that would be obtained in the absence of the disease.

Background: One of the key goals of fruit biology is to understand the factors that influence fruit growth and quality, ultimately with a view to manipulating them for improvement of fruit traits., Scope: Primary metabolism, which is not only essential for growth but is also a major component of fruit quality, is an obvious target for improvement. However, metabolism is a moving target that undergoes marked changes throughout fruit growth and ripening., Conclusions: Agricultural practice and breeding have successfully improved fruit metabolic traits, but both face the complexity of the interplay between development, metabolism and the environment. Thus, more fundamental knowledge is needed to identify further strategies for the manipulation of fruit metabolism. Nearly two decades of post-genomics approaches involving transcriptomics, proteomics and/or metabolomics have generated a lot of information about the behaviour of fruit metabolic networks. Today, the emergence of modelling tools is providing the opportunity to turn this information into a mechanistic understanding of fruits, and ultimately to design better fruits. Since high-quality data are a key requirement in modelling, a range of must-have parameters and variables is proposed.

Citrate is one of the most important organic acids in many fruits and its concentration plays a critical role in organoleptic properties. The regulation of citrate accumulation throughout fruit development, and the origins of the phenotypic variability of the citrate concentration within fruit species remain to be clarified. In the present study, we developed a process-based model of citrate accumulation based on a simplified representation of the TCA cycle to predict citrate concentration in fruit pulp during the pre- and post-harvest stages. Banana fruit was taken as a reference because it has the particularity of having post-harvest ripening, during which citrate concentration undergoes substantial changes. The model was calibrated and validated on the two stages, using data sets from three contrasting cultivars in terms of citrate accumulation, and incorporated different fruit load, potassium supply, and harvest dates. The model predicted the pre and post-harvest dynamics of citrate concentration with fairly good accuracy for the three cultivars. The model suggested major differences in TCA cycle functioning among cultivars during post-harvest ripening of banana, and pointed to a potential role for NAD-malic enzyme and mitochondrial malate carriers in the genotypic variability of citrate concentration. The sensitivity of citrate accumulation to growth parameters and temperature differed among cultivars during post-harvest ripening. Finally, the model can be used as a conceptual basis to study citrate accumulation in fleshy fruits and may be a powerful tool to improve our understanding of fruit acidity.

A detailed study of the diurnal compositional changes was performed in tomato (Solanum lycopersicum cv. Moneymaker) leaves and fruits. Plants were cultivated in a commercial greenhouse under two growth conditions: control and shaded. Expanding fruits and the closest mature leaves were harvested during two different day/night cycles (cloudy or sunny day). High-throughput robotized biochemical phenotyping of major compounds, as well as proton nuclear magnetic resonance and mass spectrometry metabolomic profiling, were used to measure the contents of about 70 metabolites in the leaves and 60 metabolites in the fruits, in parallel with ecophysiological measurements. Metabolite data were processed using multivariate, univariate, or clustering analyses and correlation networks. The shaded carbon-limited plants adjusted their leaf area, decreased their sink carbon demand and showed subtle compositional modifications. For source leaves, several metabolites varied along a diel cycle, including those directly linked to photosynthesis and photorespiration. These metabolites peaked at midday in both conditions and diel cycles as expected. However, transitory carbon storage was limited in tomato leaves. In fruits, fewer metabolites showed diel fluctuations, which were also of lower amplitude. Several organic acids were among the fluctuating metabolites. Diel patterns observed in leaves and especially in fruits differed between the cloudy and sunny days, and between the two conditions. Relationships between compositional changes in leaves and fruits are in agreement with the fact that several metabolic processes of the fruit appeared linked to its momentary supply of sucrose., (© The Author 2015. Published by Oxford University Press on behalf of the Society for Experimental Biology.)

Background: The literature abounds with the impacts of drought conditions on the concentration of non-structural compounds (NSC) in peach fruits without distinction as to the direct effect of drought on fruit metabolism and its indirect effect through dilution. Moreover, there is a need to investigate the sensitivity of the fruit composition to progressive water deficit in semi-arid conditions, as well as the origin of variations in fruit composition - not only in carbohydrates and organic acids, but also in secondary metabolites such as polyphenols., Results: The increase in stress intensity resulted in smaller fruits and a reduction in yield. Drought increased fruit dry matter content, structural dry matter (SDM) content and firmness due to lower water import to fruits, although drought reduced fruit surface conductance and its transpiration. Drought significantly affected the concentrations of each NSC either through the decrease in dilution and/or modifications of their metabolism. The increase in hexoses and sorbitol concentrations of fruits grown under drought conditions resulted in an increase in the sweetness index but not near harvest. Malic acid concentration and content:SDM ratio increased as drought intensified, whereas those of citric and quinic acids decreased. Polyphenol concentration and content increased under severe drought., Conclusion: The increase in stress intensity strongly affected fruit mass. The concentration of total carbohydrates and organic acid at harvest increased mainly through a decrease in fruit dilution, whereas the concentrations of polyphenols were also strongly affected through an impact on their metabolism., (© 2014 Society of Chemical Industry.)

Background: Malate is one of the most important organic acids in many fruits and its concentration plays a critical role in organoleptic properties. Several studies suggest that malate accumulation in fruit cells is controlled at the level of vacuolar storage. However, the regulation of vacuolar malate storage throughout fruit development, and the origins of the phenotypic variability of the malate concentration within fruit species remain to be clarified. In the present study, we adapted the mechanistic model of vacuolar storage proposed by Lobit et al. in order to study the accumulation of malate in pre and postharvest fruits. The main adaptation concerned the variation of the free energy of ATP hydrolysis during fruit development. Banana fruit was taken as a reference because it has the particularity of having separate growth and post-harvest ripening stages, during which malate concentration undergoes substantial changes. Moreover, the concentration of malate in banana pulp varies greatly among cultivars which make possible to use the model as a tool to analyze the genotypic variability. The model was calibrated and validated using data sets from three cultivars with contrasting malate accumulation, grown under different fruit loads and potassium supplies, and harvested at different stages., Results: The model predicted the pre and post-harvest dynamics of malate concentration with fairly good accuracy for the three cultivars (mean RRMSE = 0.25-0.42). The sensitivity of the model to parameters and input variables was analyzed. According to the model, vacuolar composition, in particular potassium and organic acid concentrations, had an important effect on malate accumulation. The model suggested that rising temperatures depressed malate accumulation. The model also helped distinguish differences in malate concentration among the three cultivars and between the pre and post-harvest stages by highlighting the probable importance of proton pump activity and particularly of the free energy of ATP hydrolysis and vacuolar pH., Conclusions: This model appears to be an interesting tool to study malate accumulation in pre and postharvest fruits and to get insights into the ecophysiological determinants of fruit acidity, and thus may be useful for fruit quality improvement.

Managing fruit quality is complex because many different attributes have to be taken into account, which are themselves subjected to spatial and temporal variations. Heterogeneous fruit quality has been assumed to be partly related to temperature and maturity gradients within the fruit. To test this assumption, we measured the spatial variability of certain mango fruit quality traits: colour of the peel and of the flesh, and sourness and sweetness, at different stages of fruit maturity using destructive methods as well as vis-NIR reflectance. The spatial variability of mango quality traits was compared to internal variations in thermal time, simulated by a physical model, and to internal variations in maturity, using ethylene content as an indicator. All the fruit quality indicators analysed showed significant spatial and temporal variations, regardless of the measurement method used. The heterogeneity of internal fruit quality traits was not correlated with the marked internal temperature gradient we modelled. However, variations in ethylene content revealed a strong internal maturity gradient which was correlated with the spatial variations in measured mango quality traits. Nonetheless, alone, the internal maturity gradient did not explain the variability of fruit quality traits, suggesting that other factors, such as gas, abscisic acid and water gradients, are also involved., (Copyright © 2014 Elsevier GmbH. All rights reserved.)

Fruit physiology is strongly affected by both fruit temperature and water losses through transpiration. Fruit temperature and its transpiration vary with environmental factors and fruit characteristics. In line with previous studies, measurements of physical and thermal fruit properties were found to significantly vary between fruit tissues and maturity stages. To study the impact of these variations on fruit temperature and transpiration, a modelling approach was used. A physical model was developed to predict the spatial and temporal variations of fruit temperature and transpiration according to the spatial and temporal variations of environmental factors and thermal and physical fruit properties. Model predictions compared well to temperature measurements on mango fruits, making it possible to accurately simulate the daily temperature variations of the sunny and shaded sides of fruits. Model simulations indicated that fruit development induced an increase in both the temperature gradient within the fruit and fruit water losses, mainly due to fruit expansion. However, the evolution of fruit characteristics has only a very slight impact on the average temperature and the transpiration per surface unit. The importance of temperature and transpiration gradients highlighted in this study made it necessary to take spatial and temporal variations of environmental factors and fruit characteristics into account to model fruit physiology.

To assess the influence of the environment on fruit metabolism, tomato (Solanum lycopersicum 'Moneymaker') plants were grown under contrasting conditions (optimal for commercial, water limited, or shaded production) and locations. Samples were harvested at nine stages of development, and 36 enzyme activities of central metabolism were measured as well as protein, starch, and major metabolites, such as hexoses, sucrose, organic acids, and amino acids. The most remarkable result was the high reproducibility of enzyme activities throughout development, irrespective of conditions or location. Hierarchical clustering of enzyme activities also revealed tight relationships between metabolic pathways and phases of development. Thus, cell division was characterized by high activities of fructokinase, glucokinase, pyruvate kinase, and tricarboxylic acid cycle enzymes, indicating ATP production as a priority, whereas cell expansion was characterized by enzymes involved in the lower part of glycolysis, suggesting a metabolic reprogramming to anaplerosis. As expected, enzymes involved in the accumulation of sugars, citrate, and glutamate were strongly increased during ripening. However, a group of enzymes involved in ATP production, which is probably fueled by starch degradation, was also increased. Metabolites levels seemed more sensitive than enzymes to the environment, although such differences tended to decrease at ripening. The integration of enzyme and metabolite data obtained under contrasting growth conditions using principal component analysis suggests that, with the exceptions of alanine amino transferase and glutamate and malate dehydrogenase and malate, there are no links between single enzyme activities and metabolite time courses or levels.

A model of kiwifruit berry development is presented, building on the model of Fishman and Génard used for peach fruit. That model has been extended to incorporate a number of important features of kiwifruit growth. First, the kiwifruit berry is attached to the stem through a pedicel/receptacle complex which contributes significantly to the hydraulic resistance between the stem and the fruit, and this resistance changes considerably during the season. Second, much of the carbohydrate in kiwifruit berries is stored as starch until the fruit matures late in the season, when the starch hydrolyses to soluble sugars. This starch storage has a major effect on the osmotic potential of the fruit, so an existing model of kiwifruit starch dynamics was included in the model. Using previously published approaches, we also included elasticity and extended the modelling period to cover both the cell division and cell expansion phases of growth. The resulting model showed close simulation of field observations of fresh weight, dry matter, starch, and soluble solids in kiwifruit. Comparison with continuous measurements of fruit diameter confirmed that elasticity was needed to adequately simulate observed diurnal variation in fruit size. Sensitivity analyses suggested that the model is particularly sensitive to variation in inputs relating to water (stem water potential and the humidity of the air), and to parameters controlling cell expansion (cell wall extensibility). Some limitations in the model structure were identified, suggesting that a revised model including current apoplastic/symplastic concepts needs to be developed.

Understanding what determines the size and composition of fruit, grain and seed in response to the environment and genotype is challenging, as these traits result from several linked processes controlled at different levels of organization, from the subcellular to the crop level, with subtle interactions occurring at or between the levels of organization. Process-based simulation models (PBSMs) implement algorithms to simulate metabolic and biophysical aspects of cell, tissue and organ behaviour. In this review, fruit, grain and seed PBSMs describing the main phases of growth, development and storage metabolism are discussed. From this concurrent work, it is possible to identify generic storage organ processes which can be modelled similarly for fruit, grain and seed. Spatial heterogeneity at the tissue and whole-plant level is found to be a key consideration in modelling the effects of the environment and genotype on fruit, grain and seed end-use value. In the future, PBSMs may well become the main link between studies at the molecular and whole-plant levels. To bridge this phenotype-to-genotype gap, future models need to remain plastic without becoming overparameterized., (© 2011 INRA. New Phytologist © 2011 New Phytologist Trust.)

A mechanistic model predicting the accumulation of tomato fruit sugars was developed in order (i) to dissect the relative influence of three underlying processes: assimilate supply (S), metabolic transformation of sugars into other compounds (M), and dilution by water uptake (D); and (ii) to estimate the genetic variability of S, M, and D. The latter was estimated in a population of 20 introgression lines derived from the introgression of a wild tomato species (Solanum chmielewskii) into S. lycopersicum, grown under two contrasted fruit load conditions. Low load systematically decreased D in the whole population, while S and M were targets of genotype × fruit load interactions. The sugar concentration positively correlated to S and D when the variation was due to genetic introgressions, while it positively correlated to S and M when the variation was due to changes in fruit load. Co-localizations between quantitative trait loci (QTLs) for sugar concentration and QTLs for S, M, and D allowed hypotheses to be proposed on the processes putatively involved at the QTLs. Among the five QTLs for sugar concentration, four co-localized with QTLs for S, M, and D with similar allele effects. Moreover, the processes underlying QTLs for sugar accumulation changed according to the fruit load condition. Finally, for some genotypes, the processes underlying sugar concentration compensated in such a way that they did not modify the sugar concentration. By uncoupling genetic from physiological relationships between processes, these results provide new insights into further understanding of tomato fruit sugar accumulation.

The present study aimed to clarify the relationship between sugars and vitamin C in fruit. The objective was to determine whether vitamin C content was regulated by sugar content due to the role of sugar as a precursor for vitamin C. During summer, maximal content in sugar and vitamin C were found in both genotypes tested Solanum lycopersicon 'Cervil' and 'Levovil'. During autumn, fruit pruning increased fruit size and hexose content but fruit vitamin C content did not increase. Therefore sugar substrate was not limiting for vitamin C synthesis during autumn. We demonstrated for two cultivars, 'Cervil' and 'Levovil', with different sugar accumulation profiles during ripening, that sugar content was not determinant in the regulation of vitamin C content. The strong correlation observed between sugars and vitamin C in 'Cervil' was due to their concomitant increase during fruit ripening., (2010 Elsevier Masson SAS. All rights reserved.)

Tomato fruit growth and composition depend on both genotype and environment. This paper aims at studying how fruit phenotypic responses to changes in carbon availability can be influenced by genotype, and at identifying genotype-dependent and -independent changes in gene expression underlying variations in fruit growth and composition. We grew a parental line (Solanum lycopersicum) and an introgression line from Solanum chmielewskii harbouring quantitative trait loci for fresh weight and sugar content under two fruit loads (FL). Lowering FL increased fruit cell number and reduced fruit developmental period in both genotypes. In contrast, fruit cell size was increased only in the parental line. Modifications in gene expression were monitored using microarrays and RT-qPCR for a subset of genes. FL changes induced more deployments of regulation systems (transcriptional and post-transcriptional) than massive adjustments of whole primary metabolism. Interactions between genotype and FL occurred on 99 genes mainly linked to hormonal and stress responses, and on gene expression kinetics. Links between gene expression and fruit phenotype were found for aquaporin expression levels and fruit water content, and invertase expression levels and sugar content. In summary, the present data emphasized age- and genotype-dependent responses of tomato fruit to carbon availability, at phenotypic as well as gene expression level.

Simulation models can be used to perform virtual profiling in order to analyse eco-physiological processes controlling plant phenotype. To illustrate this, an eco-physiological model has been used to compare and contrast the status of a virtual fruit system under two situations of carbon supply. The model simulates fruit growth, accumulation of sugar, citric acid and water, transpiration, respiration and ethylene emission, and was successfully tested on peach (Prunus persica L. Batsch) for two leaf-to-fruit ratios (6 and 18 leaves per fruit). The development stage and the variation in leaf number had large effects of the fruit model variables dealing with growth, metabolism and fruit quality. A sensitivity analysis showed that changing a single parameter value, which could correspond to a genotypic change induced by a mutation, either strongly affects most of the processes, or affects a specific process or none. Correlation analysis showed that, in a complex system such as fruit, the intensity of many physiological processes and quality traits co-varies. It also showed unexpected co-variations resulting from emergent properties of the system. This virtual profiling approach opens a new route to explore the impact of mutations, or naturally occurring genetic variations, under differing environmental conditions.

Detailed information has arisen from research at gene and cell levels, but it is still incomplete in the context of a quantitative understanding of whole plant physiology. Because of their integrative nature, process-based simulation models can help to bridge the gap between genotype and phenotype and assist in deconvoluting genotype-by-environment (GxE) interactions for complex traits. Indeed, GxE interactions are emergent properties of simulation models, i.e. unexpected properties generated by complex interconnections between subsystem components and biological processes. They co-occur in the system with synergistic or antagonistic effects. In this work, different kinds of GxE interactions are illustrated. Approaches to link model parameters to genes or quantitative trait loci (QTL) are briefly reviewed. Then the analysis of GxE interactions through simulation models is illustrated with an integrated model simulation of peach (Prunus persica (L.) Batsch) fruit mass and sweetness, and with a model of wheat (Triticum aestivum L.) grain yield and protein concentration. This paper suggests that the management of complex traits such as fruit and grain quality may become possible, thanks to the increasing knowledge concerning the genetic and environmental regulation of organ size and composition and to the development of models simulating the complex aspects of metabolism and biophysical behaviours at the plant and organ levels.

The objective of this study was to determine the impact of lowering nitrogen supply from 12 to 6 or 4 mM NO(3)(-) on tomato fruit yield and quality during the growing season. Lowering nitrogen supply had a low impact on fruit commercial yield (-7.5%), but it reduced plant vegetative growth and increased fruit dry matter content, improving consequently fruit quality. Fruit quality was improved due to lower acid (10-16%) and increased soluble sugar content (5-17%). The content of some phenolic compounds (rutin, a caffeic acid glycoside, and a caffeic acid derivate) and total ascorbic acid tended to be higher in fruit with the lowest nitrogen supply, but differences were significant in only a few cases (trusses). With regard to carotenoids, data did not show significant and univocal differences related to different levels of nitrogen supply. Thus, reducing nitrogen fertilization limited environmental pollution, on the one hand, and may improve, on the other hand, both growers' profits, by limiting nitrogen inputs, and fruit quality for consumers, by increasing tomato sugars content. It was concluded that primary and secondary metabolites could be affected as a result of a specific response to low nitrogen, combined with a lower degree of vegetative development, increasing fruit irradiance, and therefore modifying fruit composition.

Background and Aims: The mechanisms involving light control of vitamin C content in fruits are not yet fully understood. The present study aimed to evaluate the impact of fruit and leaf shading on ascorbate (AsA) accumulation in tomato fruit and to determine how fruit sugar content (as an AsA precursor) affected AsA content., Methods: Cherry tomato plants were grown in a glasshouse. The control treatment (normally irradiated fruits and irradiated leaves) was compared with the whole-plant shading treatment and with leaf or fruit shading treatments in fruits harvested at breaker stage. In a second experiment, the correlation between sugars and AsA was studied during ripening., Key Results: Fruit shading was the most effective treatment in reducing fruit AsA content. Under normal conditions, AsA and sugar content were correlated and increased with the ripening stage. Reducing fruit irradiance strongly decreased the reduced AsA content (-74 %), without affecting sugars, so that sugar and reduced AsA were no longer correlated. Leaf shading delayed fruit ripening: it increased the accumulation of oxidized AsA in green fruits (+98 %), whereas it decreased the reduced AsA content in orange fruits (-19 %), suggesting that fruit AsA metabolism also depends on leaf irradiance., Conclusions: Under fruit shading only, the absence of a correlation between sugars and reduced AsA content indicated that fruit AsA content was not limited by leaf photosynthesis or sugar substrate, but strongly depended on fruit irradiance. Leaf shading most probably affected fruit AsA content by delaying fruit ripening, and suggested a complex regulation of AsA metabolism which depends on both fruit and leaf irradiance and fruit ripening stage.

Many quantitative trait loci (QTLs) for quality traits have been located on the tomato genetic map, but introgression of favourable wild alleles into large fruited species is hampered by co-localizations of QTLs with antagonist effects. The aim of this study was to assess the growth processes controlled by the main QTLs for fruit size and composition. Four nearly isogenic lines (NILs) derived from an intraspecific cross between a tasty cherry tomato (Cervil) and a normal-tasting large fruit tomato (Levovil) were studied. The lines carried one (L2, L4, and L9) or five (Lx) introgressions from Cervil on chromosomes 1, 2, 4, and 9. QTLs for fruit size could be mainly associated with cell division processes in L2 and L9, whereas cell expansion was rather homogeneous among the genotypes, except Cervil for which the low expansion rate was attributed to low cell plasticity. The link between endoreduplication and fruit size remained unclear, as cell or fruit sizes were positively correlated with the cell DNA content, but not with the endoreduplication factor. QTLs for fruit composition reflected differences in water accumulation rather than in sugar accumulation, except in L9 for which the up-regulation of sucrose unloading and hexose transport and/or starch synthesis was suggested. This may explain the increased amount of carbon allocated to cell structures in L9, which could be related to a QTL for fruit texture. In Lx, these effects were attenuated, except on fruit size and cell division. Finally, the region on top of chromosome 9 may control size and composition attributes in tomato, by a combination of QTL effects on cell division, cell wall synthesis, and carbon import and metabolism.

Throughout tomato domestication, a large increase in fruit size was associated with a loss of dry matter and sugar contents. This study aims to dissect the contributions of genetic variation and the physiological processes underlying the relationships between fruit growth and the accumulation of dry matter and sugars. Fruit quality traits and physiological parameters were measured on 20 introgression lines derived from the introgression of Solanum chmielewskii into S. lycopersicum, under high (HL, unpruned trusses) and low (LL, trusses pruned to one fruit) fruit load conditions. Inter- and intra-genotypic correlations among traits were estimated and quantitative trait loci (QTL) for size, composition, and physiological traits were mapped. LL increased almost all traits, but the response of sugar content was genotype-dependent, involving either dilution effects or differences in carbon allocation to sugars. Genotype x fruit load interactions were significant for most traits and only 30% of the QTL were stable under both fruit loads. Many QTL for fresh weight and cell or seed numbers co-localized. Eleven clusters of QTL for fresh weight and dry matter or sugar content were detected, eight with opposite allele effects and three with negative effects. Two genotypic antagonistic relationships, between fresh weight and dry matter content and between cell number and cell size, were significant only under HL; the second could be interpreted as a competition for carbohydrates among cells. The role of cuticular conductance, fruit transpiration or cracking in the relationship between fruit fresh weight and composition was also emphasized at the genetic and physiological levels.

The number of cells and the mean cell volume in the mesocarps of fruits from peach genotypes with different percentages of the genome of Prunus davidiana, a wild, related, species, were evaluated. The mesocarp mass varied greatly between the four groups of genotypes. The mean cell volume and the number of cells were negatively correlated within each group. This correlation can be interpreted as a relationship of competition between cells. In order to describe the type of competition in the different groups, we tried to adjust a model of competition for resources proposed by Lescourret and Génard (Ecoscience 10:334-341, 2003). To estimate the values of the three parameters of the model for the different groups, we applied model selection. Within nested models, we identified a single best model with six parameter values. This model was roughly accurate, but it allowed us to describe the general relationship for each group. The parameter values revealed a strong and under-compensating density-dependence effect for all groups. The percentage of P. davidiana genome appeared to influence the maximal number of cells and the strength of the competition, but no effect was found on the maximal mean volume of cells.

Changes in elastic and plastic components of mango (Mangifera indica L. cv 'Cogshall') fruit growth were analyzed with a model of fruit growth over time and in response to various assimilate supplies. The model is based on water relations (water potential and osmotic and turgor pressures) at the fruit level. Variation in elastic fruit growth was modeled as a function of the elastic modulus and variation in turgor pressure. Variation in plastic fruit growth was modeled using the Lockhart (1965) equation. In this model, plastic growth parameters (yield threshold pressure and cell wall extensibility) varied during fruit growth. Outputs of the model were diurnal and seasonal fruit growth, and fruit turgor pressure. These variables were simulated with good accuracy by the model, particularly the observed increase in fruit size with increasing availability of assimilate supply. Shrinkage was sensitive to the surface conductance of fruit peel, the elasticity modulus and the hydraulic conductivity of fruit, whereas fruit growth rate was highly sensitive to parameters linked to changes in wall extensibility and yield threshold pressure, regardless of the assimilate supply. According to the model, plastic growth was generally zero during the day and shrinkage and swelling were linked to the elastic behavior of the fruit. During the night, plastic and elastic growths were positive, resulting in fruit expansion.

Endoreduplication is a phenomenon, widespread among plants, which consists of an incomplete cell cycle without mitosis and leads to the increase of the nuclear DNA content. In this work, a model was developed describing cell proliferation and DNA endoreduplication over the whole fruit development, from the pre-anthesis period until maturation. In each mitotic cycle of duration tau, the proportion of cells proceeding through division depends on a constant parameter rho and on the progressive decline of the proliferating capacity . The non-dividing cells may either stop the reduplication fully, or switch to repeated syntheses of DNA without cell division, resulting in cell endoreduplication. A single constant parameter sigma describes the proportion of cells that moves from one to the next class of DNA content after each lapse of time tauE, considered to be the minimum time required for an endocycle. The model calculates the total number of cells and their distribution among eight classes of ploidy level. The dynamic patterns of cell proliferation and ploidy were compared with those obtained experimentally on two contrasting tomato genotypes. The approach developed in this model should allow the future integration of new knowledge concerning the genetic and environmental control of the switch from complete to incomplete cell cycle.

This work proposed a model of tomato growth adapted from the Fishman and Génard model developed to predict carbon and water accumulation in peach fruit. The main adaptations relied on the literature on tomato and mainly concerned: (i) the decrease in cell wall extensibility coefficient during fruit development; (ii) the increase in the membrane reflection coefficient to solute from 0 to 1, which accounted for the switch from symplasmic to apoplasmic phloem unloading, and (iii) the negative influence of the initial fruit weight on the maximum rate of active carbon uptake based on the assumption of higher competition for carbon among cells in large fruits containing more cells. A sensitivity analysis was performed and the model was calibrated and evaluated with satisfaction on 17 experimental datasets obtained under contrasting environmental (temperature, air vapour pressure deficit) and plant (plant fruit load and fruit position) conditions. Then the model was used to analyse the variations in the main fluxes involved in tomato fruit growth and accumulation of carbon in response to virtual carbon and water stresses. The conclusions are that this model, integrating simple biophysical laws, was able to simulate the complex fruit behaviour in response to external or internal factors and thus it may be a powerful tool for managing fruit growth and quality.

A virtual fruit model simulating seasonal changes in several peach (Prunus persica (L.) Batsch) fruit quality traits during the final growth stage is presented. The quality traits considered are fruit size, the proportion of total fruit mass consisting of fruit flesh, dry matter content of the flesh and the concentrations of sucrose, glucose, fructose and sorbitol in the flesh, which are used to calculate a sweetness index. The virtual peach fruit model was developed by adapting and integrating three existing process-based models describing fruit dry mass growth, fruit fresh mass growth and sugar accumulation in the flesh into one complex system. Data sets of peach fruit growth and quality obtained from one field site over several years were used to estimate parameters and evaluate the virtual peach fruit model. Output from the model showed good agreement with the field data. Insight into the complex nature of the virtual peach fruit model, i.e., its ability to show emergent properties, was accomplished by conducting a series of theoretical experiments. The virtual peach fruit model was shown to be sensitive to management and environmental factors (leaf:fruit ratio, stem water potential and, to a lesser extent, weather). Its ability to generate simple laws relating to physiological variables and quality parameters was also demonstrated. Finally, the virtual peach fruit model was able to reveal complex behaviors resulting from changes in water potentials or leaf:fruit ratios over time.

A theory of fruit climacteric ethylene emission was developed and used as the basis of a simulation model called ETHY. According to the theory, the biosynthetic pathway of ethylene is supplied by ATP and is regulated by 1-aminocyclopropane-1-carboxylic acid (ACC) synthase and ACC oxidase. The conjugation of ACC with malonate to form MACC was taken into account as a way to decrease the availability of ACC. Because of the seasonal increase of fruit volume, the dilution of biochemical compounds used in ETHY was taken into account. Finally, the ethylene diffusion across the skin was considered. The theory took into account the effect of temperature and O(2) and CO(2) internal concentrations on ethylene. The model was applied to peach (Prunus persica) fruit over 3 years, several leaf:fruit ratios, and irrigation conditions. An adequate ethylene increase was predicted without considering any increase in respiration during the ripening period, which suggests that the respiratory climacteric may not be required for ripening. Another important result of this study is the high sensitivity of ETHY to the parameters involved in the calculation of ACC oxidase and ACC synthase activities, ATP production, and skin surface and permeability. ETHY was also highly sensitive to changes in fruit growth and temperature.

Increasing fruit load (from no berries present to 25, 50 and 100% of the initial fruit load) significantly decreased branch growth on 5-year-old coffee (Coffea arabica L.) trees of the dwarf cultivar 'Costa Rica 95', during their third production cycle. Ring-barking the branches further reduced their growth. Berry dry mass at harvest was significantly reduced by increasing fruit load. Dry matter allocation to berries was four times that allocated to branch growth during the cycle. Branch dieback and berry drop were significantly higher at greater fruit loads. This illustrates the importance of berry sink strength and indicates that there is competition for carbohydrates between berries and shoots and also among berries. Leaf net photosynthesis (P(n)) increased with increasing fruit load. Furthermore, leaves of non-isolated branches bearing full fruit load achieved three times higher P(n) than leaves of isolated (ring-barked) branches without berries, indicating strong relief of leaf P(n) inhibition by carbohydrate demand from berries and other parts of the coffee tree when excess photoassimilates could be exported. Leaf P(n) was significantly higher in the morning than later during the day. This reduction in leaf P(n) is generally attributed to stomatal closure in response to high irradiance, temperature and vapor pressure deficit in the middle of the day; however, it could also be a feedback effect of reserves accumulating during the morning when climatic conditions for leaf P(n) were optimal, because increased leaf mass ratio was observed in leaves of ring-barked branches with low or no fruit loads. Rates of CO(2) emission by berries decreased and calculated photosynthetic rates of berries increased with increasing photosynthetic photon flux (PPF) especially at low PPFs (0 to 100 micromol m(-2) s(-1)). The photosynthetic contribution of berries at the bean-filling stage was estimated to be about 30% of their daily respiration costs and 12% of their total carbon requirements at PPF values commonly experienced in the field (200 to 500 micromol m(-2) s(-1)).

We modeled the effects of weather and source-sink factors on mango fruit growth. The peach fruit-growth model "Cashoo" was adapted for mango fruit. The model accounts for the main processes of fruit growth, i.e., leaf photosynthesis, fruit demand, fruit respiration, and storage and mobilization of leaf and stem reserves. Simulations for three successive years and for various leaf-to-fruit ratio treatments showed good agreement with observed fruit growth data. Simulations of fruit growth under different climatic conditions, especially with contrasting temperature and radiation, and for different values of initial fruit dry mass and leaf-to-fruit ratio, showed that variations in fruit growth among years can be partly explained by climatic variations through their effects on leaf photosynthesis, fruit demand and fruit growth rate. However, climatic changes contribute substantially less to observed variability in fruit growth than to initial fruit dry mass and leaf-to-fruit ratio.

Background and Aims: A model of fruit surface conductance to water vapour diffusion driven by fruit growth is proposed. It computes the total fruit conductance by integrating each of its components: stomata, cuticle and cracks., Methods: The stomatal conductance is computed from the stomatal density per fruit and the specific stomatal conductance. The cuticular component is equal to the proportion of cuticle per fruit multiplied by its specific conductance. Cracks are assumed to be generated when pulp expansion rate exceeds cuticle expansion rate. A constant percentage of cracks is assumed to heal each day. The proportion of cracks to total fruit surface area multiplied by the specific crack conductance accounts for the crack component. The model was applied to peach fruit (Prunus persica) and its parameters were estimated from field experiments with various crop load and irrigation regimes., Key Results: The predictions were in good agreement with the experimental measurements and for the different conditions (irrigation and crop load). Total fruit surface conductance decreased during early growth as stomatal density, and hence the contribution of the stomatal conductance, decreased from 80 to 20 % with fruit expansion. Cracks were generated for fruits exhibiting high growth rates during late growth and the crack component could account for up to 60 % of the total conductance during the rapid fruit growth. The cuticular contribution was slightly variable (around 20 %). Sensitivity analysis revealed that simulated conductance was highly affected by stomatal parameters during the early period of growth and by both crack and stomatal parameters during the late period. Large fruit growth rate leads to earlier and greater increase of conductance due to higher crack occurrence. Conversely, low fruit growth rate accounts for a delayed and lower increase of conductance., Conclusions: By predicting crack occurrence during fruit growth, this model could be helpful in managing cropping practices for integrated plant protection.

The size of fruit cells, seeds and fruits depends on their number. Could this density-dependence effect result from sugar resource sharing and, if so, does it involve phloem sugar flow or the intensity of sugar unloading to the sink? A density-dependence model (DDM) describing these processes was designed and parameterised for six species at five levels of organisation: cells and seeds within fruits, fruits within clusters, fruits within plants and plants within plots. Sugar flow was driven by phloem conductance, determined by parameters α, governing the shape of its relationship to population size, and κ, its value for a population size of one. Sugar unloading followed Michaelis–Menten kinetics with parameters Vm (maximal unloading rate) and Km (Michaelis constant). The DDM effectively reproduced the observed individual mass dynamics, the undercompensating density dependence observed in most species at all sub-plant levels and the undercompensating, exact and overcompensating density dependence observed at the plant level. Conductance (κ) was a scaling factor varying with the level of organisation. Vm was positively correlated with density dependence, and α was negatively correlated with density dependence only if the plant-within-plot level was not considered. Analysis of the model’s behaviour indicates that density dependence of fruit growth could be a result of sugar sharing, and that both phloem sugar flow and sugar unloading contribute to these effects. [ABSTRACT FROM AUTHOR]

Background and Aims Sugar concentration is a key determinant of fruit quality. Soluble sugars and starch concentrations in fruits vary greatly from one species to another. The aim of this study was to investigate similarities and differences in sugar accumulation strategies across ten contrasting fruit species using a modelling approach. Methods We developed a coarse-grained model of primary metabolism based on the description of the main metabolic and hydraulic processes (synthesis of compounds other than sugar and starch, synthesis and hydrolysis of starch, and water dilution) involved in the accumulation of soluble sugars during fruit development. Key Results Statistical analyses based on metabolic rates separated the species into six groups according to the rate of synthesis of compounds other than sugar and starch. Herbaceous species (cucumber, tomato, eggplant, pepper and strawberry) were characterized by a higher synthesis rate than woody species (apple, nectarine, clementine, grape and kiwifruit). Inspection of the dynamics of the processes involved in sugar accumulation revealed that net sugar importation, metabolism and dilution processes were remarkably synchronous in most herbaceous plants, whereas in kiwifruit, apple and nectarine, processes related to starch metabolism were temporally separated from other processes. Strawberry, clementine and grape showed a distinct dynamic compared with all other species. Conclusions Overall, these results provide fresh insights into species-specific regulatory strategies and into the role of starch metabolism in the accumulation of soluble sugars in fleshy fruits. In particular, inter-specific differences in development period shape the co-ordination of metabolic processes and affect priorities for carbon allocation across species. The six metabolic groups identified by our analysis do not show a clear separation into climacteric and non-climacteric species, possibly suggesting that the metabolic processes related to sugar concentration are not greatly affected by ethylene-associated events. [ABSTRACT FROM AUTHOR]

Although fleshy fruit is mainly made up of water, little is known about the impact of its water status on sugar metabolism and its composition. In order to verify whether fruit water status is an important driver of carbohydrate composition in tomato fruit, an adaptation of the SUGAR model proposed previously by M. Génard and M. Souty was used. Two versions of the model, with or without integrating the influence of fruit water content on carbohydrate metabolism, were proposed and then assessed with the data sets from two genotypes, Levovil and Cervil, grown under different conditions. The results showed that, for both genotypes, soluble sugars and starch were better fitted by the model when the effects of water content on carbohydrate metabolism were taken into consideration. Water content might play a regulatory role in the carbon metabolism from sugars to compounds other than sugars and starch in Cervil fruit, and from sugars to starch in Levovil fruit. While water content influences tomato fruit carbohydrate concentrations by both metabolism and dilution/dehydration effects in the early developmental stage, it is mainly by dilution/dehydration effects in the late stage. The possible mechanisms underlying the effect of the fruit water content on carbohydrate metabolism are also discussed. [ABSTRACT FROM AUTHOR]

Process-based models are effective tools to predict the phenotype of an individual in different growing conditions. Combined with a quantitative trait locus (QTL) mapping approach, it is then possible to predict the behavior of individuals with any combinations of alleles. However the number of simulations to explore the realm of possibilities may become infinite. Therefore, the use of an efficient optimization algorithm to intelligently explore the search space becomes imperative. The optimization algorithm has to solve a multi-objective problem, since the phenotypes of interest are usually a complex of traits, to identify the individuals with best tradeoffs between those traits. In this study we proposed to unroll such a combined approach in the case of peach fruit quality described through three targeted traits, using a process-based model with seven parameters controlled by QTL. We compared a current approach based on the optimization of the values of the parameters with a more evolved way to proceed which consists in the direct optimization of the alleles controlling the parameters. The optimization algorithm has been adapted to deal with both continuous and combinatorial problems. We compared the spaces of parameters obtained with different tactics and the phenotype of the individuals resulting from random simulations and optimization in these spaces. The use of a genetic model enabled the restriction of the dimension of the parameter space toward more feasible combinations of parameter values, reproducing relationships between parameters as observed in a real progeny. The results of this study demonstrated the potential of such an approach to refine the solutions toward more realistic ideotypes. Perspectives of improvement are discussed. [ABSTRACT FROM AUTHOR]