Modulation of Competition between Fruits and Leaves by Flower Pruning and Water Fogging, and Consequences on Tomato Leaf and Fruit Growth

The effects of water fogging and reducing plant fruit load werestudied in a tomato crop grown in a glasshouse under Mediterraneansummer conditions. The objective of these treatments was toreduce competition between leaves and fruits for carbohydratesand water. Flower pruning increased plant leaf area and increasedfruit, stem, lamina and petiole dry mass (DM). This indicatesthat leaf area growth was limited during the summer due to competitionbetween fruits and leaves for assimilates. In contrast, reducingthe air vapour pressure deficit (VPD) by water fogging had noeffect on plant leaf area or aerial plant DM. Interestingly,there was a significant interaction between plant fruit loadand VPD: the higher the leaf[ratio]fruit ratio the greater theresponses to a reduction in VPD (increase in fruit DM, fruitdiameter, fruit and leaf expansion rate). The data suggest thatunder high fruit loads, water and carbohydrates limit growthunder Mediterranean summer conditions. However, reducing VPDwas not always sufficient to enhance fruit and leaf growth.This might be due to the lower leaf area under high fruit load.In contrast, reducing VPD under low fruit load triggered higherrates of leaf and fruit expansion; this is probably linked toa greater availability of water and carbohydrates. Copyright2001 Annals of Botany Company Assimilate competition, assimilate supply, flower pruning, fruit load, fruit growth, generative/vegetative growth, leaf growth, Lycopersicon esculentum, specific leaf weight, tomato, vapour pressure deficit, water stress     

Effect of temperature on biomass allocation in tomato (Lycopersicon esculentum)

Temperature may influence dry matter partitioning between fruits and vegetative plant parts either directly or indirectly through its influence on development, flower and/or fruit abortion. The objective of the present work was to investigate whether there is any direct effect of temperature on dry matter partitioning between fruits and vegetative plant parts in tomato. A greenhouse experiment was conducted, with alternating 3-week periods of high (23°C) and low (18°C) temperature setpoint. Dry matter partitioning during these 3-week periods was determined from destructive plant harvests at two levels of fruit pruning (3 and 7 fruits per truss). Indirect temperature effects on dry matter partitioning were excluded by fruit pruning.
On average, the fraction of dry matter distributed to the fruits during a 12-week period, starting with the flowering of the fifth truss (28 days after planting), was 0.53 (3 fruits per truss) and 0.70 (7 fruits per truss). These ratios were also calculated for every 3-week period separately and did not depend on the average temperature (18–24°C) during that period.
It is concluded that dry matter distribution in tomato is not significantly affected by temperature directly, which means that the temperature effect (18–24°C) on the generative sink strength is not much different from the temperature effect on the vegetative sink strength.     

Dry Matter Partitioning in Tomato: Validation of a Dynamic Simulation Model

A model for dynamic simulation of dry matter distribution betweenreproductive and vegetative plant parts and the distributionamong individual fruit trusses in glasshouse tomato, is validated.The model is part of the crop growth model TOMSIM and is basedon the hypothesis that dry matter distribution is regulatedby the sink strengths of the plant organs, quantified by theirpotential growth rates, i.e. the growth rates at non-limitingassimilate supply. Within the plant, individual fruit trussesare distinguished and sink strength of a truss is describedas a function of its development stage. Truss development rateis a function of temperature only. The same potential growthcurve, proportional to the number of fruits per truss, is adoptedfor all trusses. In a simple version of the model, vegetativeplant parts are lumped together as one sink with a constantsink strength. In a more detailed version, vegetative sink strengthis calculated as the sum of sink strengths of vegetative units(three leaves and stem internodes between two trusses). The model was validated for six glasshouse experiments, coveringeffects of planting date, plant density, number of fruits pertruss (pruning at anthesis), truss removal (every second trussremoved at anthesis), single- and double-shoot plants and atemperature experiment conducted in climate rooms at 17, 20or 23 °C. Daily increase in above-ground dry weight, averagedaily temperatures and number of set fruits per truss were inputsto the model. Both the simple and the more detailed model showedgood agreement between measured and simulated fraction of drymatter partitioned into the fruits over time. For the simpleversion of the model, the slope of the lines relating simulatedto measured fraction partitioned into the fruits (16 data sets),varied between 0.92 and 1.11, on average it was 1.04, implying4% over-estimation for this fraction. For the detailed modelthese numbers were slightly better: 0.89, 1.08 and 1.01, respectively.The temperature experiment revealed no important direct influenceof temperature on the ratio between generative and vegetativesink strength. Simulated truss growth curves showed reasonableagreement with the measurements, although both models over-estimated(17% on average) final dry weight of the lower trusses (truss1 –3) on a plant. Modelling dry matter partitioning basedon sink strengths of organs is promising, as it is a general,dynamic and flexible approach, showing good agreement betweenmeasurements and simulation for a range of conditions. Applicabilityof the model is, however, still limited as long as the numberof fruits per truss (flower and /or fruit abortion) is not simulated,as this is a major feedback mechanism in plant growth. Dry matter distribution; sink strength; glasshouse; model; partitioning; simulation; temperature; tomato; TOMSIM; validation     

Photoperiodic and genetic control of carbon partitioning in peas and its relationship to apical senescence

Apical senescence but not flower initiation is delayed by short days (SD) compared to long days (LD) in pea plants (Pisum sativum L.) of genotype E Sn Hr. We recently reported that delay of senescence correlated with slower reproductive development, suggesting that fruits are weaker sinks for assimilates under delayed senescence conditions. Thus, we have examined assimilate partitioning in peas to determine if genotype and photoperiod regulate relative sink strength. Assimilate diversion by developing fruit has been implicated in senescence induction. A greater percentage of leaf-exported ¹⁴C was transported to fruits and a smaller percentage to the apical bud of G2 peas (genotype E Sn Hr) in LD than in SD. Relatively more of the ¹⁴C delivered to the apical bud of G2 peas was transported to flower buds than to young leaves in LD as compared to SD. There was no striking photoperiodic difference in carbon partitioning in genetic lines without the Sn Hr allele combination. The Sn Hr allele combination and photoperiod may regulate the relative strength of reproductive and vegetative sinks. Photoperiodic differences in sink strength early in reproduction suggest that these genes regulate sink strength by affecting the physiology of the whole plant. High vegetative sink strength in SD may maintain assimilate supply to the apical bud, delaying senescence.     

Phenology, growth and physiological adjustments of oil palm (Elaeis guineensis) to sink limitation induced by fruit pruning

Background and Aims

Despite its simple architecture and small phenotypic plasticity, oil palm has complex phenology and source–sink interactions. Phytomers appear in regular succession but their development takes years, involving long lag periods between environmental influences and their effects on sinks. Plant adjustments to resulting source–sink imbalances are poorly understood. This study investigated oil palm adjustments to imbalances caused by severe fruit pruning.

Methods

An experiment with two treatments (control and complete fruit pruning) during 22 months in 2006–2008) and six replications per treatment was conducted in Indonesia. Phenology, growth of above-ground vegetative and reproductive organs, leaf morphology, inflorescence sex differentiation, dynamics of non-structural carbohydrate reserves and light-saturated net photosynthesis (A_max) were monitored.

Key Results

Artificial sink limitation by complete fruit pruning accelerated development rate, resulting in higher phytomer, leaf and inflorescence numbers. Leaf size and morphology remained unchanged. Complete fruit pruning also suppressed the abortion of male inflorescences, estimated to be triggered at about 16 months before bunch maturity. The number of female inflorescences increased after an estimated lag of 24–26 months, corresponding to time from sex differentiation to bunch maturity. The most important adjustment process was increased assimilate storage in the stem, attaining nearly 50 % of dry weight in the stem top, mainly as starch, whereas glucose, which in controls was the most abundant non-structural carbohydrate stored in oil palm, decreased.

Conclusions

The development rate of oil palm is in part controlled by source–sink relationships. Although increased rate of development and proportion of female inflorescences constituted observed adjustments to sink limitation, the low plasticity of plant architecture (constant leaf size, absence of branching) limited compensatory growth. Non-structural carbohydrate storage was thus the main adjustment process.Key words: Carbon allocation, non-structural carbohydrates, source–sink relationships, Elaeis guineensis, phenotypic plasticity, photosynthesis     

Dry matter partitioning models for the simulation of individual fruit growth in greenhouse cucumber canopies

Background and Aims

Growth imbalances between individual fruits are common in indeterminate plants such as cucumber (Cucumis sativus). In this species, these imbalances can be related to differences in two growth characteristics, fruit growth duration until reaching a given size and fruit abortion. Both are related to distribution, and environmental factors as well as canopy architecture play a key role in their differentiation. Furthermore, events leading to a fruit reaching its harvestable size before or simultaneously with a prior fruit can be observed. Functional–structural plant models (FSPMs) allow for interactions between environmental factors, canopy architecture and physiological processes. Here, we tested hypotheses which account for these interactions by introducing dominance and abortion thresholds for the partitioning of assimilates between growing fruits.

Methods

Using the L-System formalism, an FSPM was developed which combined a model for architectural development, a biochemical model of photosynthesis and a model for assimilate partitioning, the last including a fruit growth model based on a size-related potential growth rate (R_P). Starting from a distribution proportional to R_P, the model was extended by including abortion and dominance. Abortion was related to source strength and dominance to sink strength. Both thresholds were varied to test their influence on fruit growth characteristics. Simulations were conducted for a dense row and a sparse isometric canopy.

Key Results

The simple partitioning models failed to simulate individual fruit growth realistically. The introduction of abortion and dominance thresholds gave the best results. Simulations of fruit growth durations and abortion rates were in line with measurements, and events in which a fruit was harvestable earlier than an older fruit were reproduced.

Conclusions

Dominance and abortion events need to be considered when simulating typical fruit growth traits. By integrating environmental factors, the FSPM can be a valuable tool to analyse and improve existing knowledge about the dynamics of assimilates partitioning.     

A Simulation Model for Dry Matter Partitioning in Cucumber

A dynamic model is developed for the simulation of the dailydry matter distribution between the generative and vegetativeplant parts and the distribution among individual fruits ingreenhouse cucumber. The model is based on the hypothesis thatdry matter partitioning is regulated by the sink strengths ofthe plant organs. The sink strength of an organ is defined hereas its potential growth rate, i.e. the growth rate at non-limitingassimilate supply. The sink strength of each individual fruitis described as a function of its temperature sum after anthesisand the actual temperature, that of the vegetative plant partsas a function of actual temperature only. The formation rateof non-aborting fruits is essentially a function of the source/sinkratio. Model results agreed well with the measured fluctuating distributionof dry matter between fruits and vegetative parts. The measuredeffects of three intensities of fruit removal were also simulatedsatisfactorily. When simulating the partitioning among individualfruits the final fruit size was simulated quite well. However,the growth rate of young fruits was usually overestimated andthat of old fruits underestimated, because of dominance amongfruits. This phenomenon could be accounted for by incorporatingpriority functions into the model. Finally, a sensitivity analysisof the model was performed to investigate the effects of someclimatic factors, manipulations of the number of fruits on aplant and model parameters on dry matter distribution. Strategiesto manipulate the dry matter distribution are discussed.Copyright1994, 1999 Academic Press Cucumber, Cucumis sativus (L.), dry matter distribution, fruit growth, partitioning, simulation model, source-sink     

Partitioning of (13)C-photosynthate from spur leaves during fruit growth of three Japanese pear (Pyrus pyrifolia) cultivars differing in maturation date

BACKGROUND AND AIMS: In fruit crops, fruit size at harvest is an important aspect of quality. With Japanese pears (Pyrus pyrifolia), later maturing cultivars usually have larger fruits than earlier maturing cultivars. It is considered that the supply of photosynthate during fruit development is a critical determinant of size. To assess the interaction of assimilate supply and early/late maturity of cultivars and its effect on final fruit size, the pattern of carbon assimilate partitioning from spur leaves (source) to fruit and other organs (sinks) during fruit growth was investigated using three genotypes differing in maturation date. METHODS: Partitioning of photosynthate from spur leaves during fruit growth was investigated by exposure of spurs to (13)CO(2) and measurement of the change in (13)C abundance in dry matter with time. Leaf number and leaf area per spur, fresh fruit weight, cell number and cell size of the mesocarp were measured and used to model the development of the spur leaf and fruit. KEY RESULTS: Compared with the earlier-maturing cultivars 'Shinsui' and 'Kousui', the larger-fruited, later-maturing cultivar 'Shinsetsu' had a greater total leaf area per spur, greater source strength (source weight x source specific activity), with more (13)C assimilated per spur and allocated to fruit, smaller loss of (13)C in respiration and export over the season, and longer duration of cell division and enlargement. Histology shows that cultivar differences in final fruit size were mainly attributable to the number of cells in the mesocarp. CONCLUSIONS: Assimilate availability during the period of cell division was crucial for early fruit growth and closely correlated with final fruit size. Early fruit growth of the earlier-maturing cultivars, but not the later-maturing ones, was severely restrained by assimilate supply rather than by sink limitation.     

Effect of assimilate supply on the growth of individual cucumber fruits

The effects of assimilate supply on the growth of individual fruits during different stages of fruit development were analysed in cucumber ( Cucumis sativus L. cv. Corona). The assimilate supply was varied by maintaining different numbers of fruits per plant or maintaining different irradiances. The growth rate of a cucumber fruit strongly increased with increasing assimilate supply, but its growing period was not noticeably affected. At a low assimilate supply both cell number and cell size were reduced. Increasing the assimilate supply at different stages of fruit development showed that the early development of a cucumber fruit was not crucial for setting its growth potential. A small number of cells, due to a low assimilate supply, during early fruit development, was to a great extent compensated by an increased expansion rate of individual cells. It is concluded that cell number is not an important determinant of fruit size in cucumber, although fruit size is often positively correlated with cell number. In the early stages of fruit development the effect of irradiance on the fruit growth rate depends on the presence of an earlier developed fruit because of dom-inance between fruits. In later stages of fruit development, a decrease in irradiance reduced the growth rate of all fruits relatively to the same extent independent of age or presence of other fruits.     

Genetic differences in fruit-set patterns are determined by differences in fruit sink strength and a source : sink threshold for fruit set

Background and Aims

Fruit set in indeterminate plant species largely depends on the balance between source and sink strength. Plants of these species show fluctuations in fruit set during the growing season. It was tested whether differences in fruit sink strength among the cultivars explained the differences in fruit-set patterns.

Methods

Capsicum was chosen as a model plant. Six cultivars with differences in fruit set, fruit size and plant growth were evaluated in a greenhouse experiment. Fruit-set patterns, generative and vegetative sink strength, source strength and the source : sink ratio at fruit set were determined. Sink strength was quantified as potential growth rate. Fruit set was related to total fruit sink strength and the source : sink ratio. The effect of differences observed in above-mentioned parameters on fruit-set patterns was examined using a simple simulation model.

Key Results

Sink strengths of individual fruits differed greatly among cultivars. Week-to-week fruit set in large-fruited cultivars fluctuated due to large fluctuations in total fruit sink strength, but in small-fruited cultivars, total fruit sink strength and fruit set were relatively constant. Large variations in week-to-week fruit set were correlated with a low fruit-set percentage. The source : sink threshold for fruit set was higher in large-fruited cultivars. Simulations showed that within the range of parameter values found in the experiment, fruit sink strength and source : sink threshold for fruit set had the largest impact on fruit set: an increase in these parameters decreased the average percentage fruit set and increased variation in weekly fruit set. Both were needed to explain the fruit-set patterns observed. The differences observed in the other parameters (e.g. source strength) had a lower effect on fruit set.

Conclusions

Both individual fruit sink strength and the source : sink threshold for fruit set were needed to explain the differences observed between fruit-set patterns of the six cultivars.     

How plant allometry influences bud phenology and fruit yield in two Vaccinium species

Background and AimsUnderstanding how plant allometry, plant architecture and phenology contribute to fruit production can identify those plant traits that maximize fruit yield. In this study, we compared these variables and fruit yield for two shrub species, Vaccinium angustifolium and Vaccinium myrtilloides, to test the hypothesis that phenology is linked to the plants’ allometric traits, which are predictors of fruit production.MethodsWe measured leaf and flower phenology and the above-ground biomass of both Vaccinium species in a commercial wild lowbush blueberry field (Quebec, Canada) over a 2-year crop cycle; 1 year of pruning followed by 1 year of harvest. Leaf and flower phenology were measured, and the allometric traits of shoots and buds were monitored over the crop cycle. We hand-collected the fruits of each plant to determine fruit attributes and biomass.Key ResultsDuring the harvesting year, the leafing and flowering of V. angustifolium occurred earlier than that of V. myrtilloides. This difference was related to the allometric characteristics of the buds due to differences in carbon partitioning by the plants during the pruning year. Through structural equation modelling, we identified that the earlier leafing in V. angustifolium was related to a lower leaf bud number, while earlier flowering was linked to a lower number of flowers per bud. Despite differences in reproductive allometric traits, vegetative biomass still determined reproductive biomass in a log–log scale model.ConclusionsGrowing buds are competing sinks for non-structural carbohydrates. Their differences in both number and characteristics (e.g. number of flowers per bud) influence levels of fruit production and explain some of the phenological differences observed between the two Vaccinium species. For similar above-ground biomass, both Vaccinium species had similar reproductive outputs in terms of fruit biomass, despite differences in reproductive traits such as fruit size and number.     

Quantifying sink and source limitations on dry matter partitioning to fruit growth in peach trees

We describe an approach for determining the degree of sink and source limitations on peach ( Prunus persica L. Batsch) fruit growth during several growth periods. Source limitations on fruit growth may be due to either a shortfall in assimilate supply within the tree (supply limitation) or to a deficiency in the capacity of the translocation system to deliver assimilates in sufficient quantity to support the maximum fruit growth rate (transport/competition limitation). To ascertain the potential maximum rate of fruit growth, fruit thinning treatments were used. One month after bloom, the number of fruits per tree was adjusted to between 50 and 700 on an early and a late maturing peach cultivar (cvs Spring Lady and Cal Red, respectively). Rates of potential sink demand, potential source supply and actual fruit growth were estimated from sequential harvests of all fruits on 42 trees on two (Spring Lady) and three (Cal Red) dates. These values were used to estimate the proportion of potential growth achieved, and the supply and transport/competition limitations on fruit growth. The results indicated that source limitations were significant on trees with moderate to high fruit numbers. These source limitations were due to supply limitations during all harvest intervals and to transport/competition limitations during the early harvest intervals. Sink limitations occurred to the greatest extent during the mid-period of fruit growth on the later maturing cultivar.     

The Dynamics of Growth and Dry Matter Distribution in Cucumber

The dynamics of growth and proportional dry matter distributionbetween the vegetative parts and fruits of cucumber were studieddaily during a growing season. Most of the changes in dailyintegral of total solar radiation were reflected by changesin plant growth rate. Sometimes a time lag of a few days occurred,indicating the plants were adapting to radiation. The proportional dry matter distribution between fruits andvegetative parts showed a cyclic pattern. The daily proportionaldry matter distribution to the fruits varied between 40 and90% of the total dry matter. However, the cumulative dry weightof the fruits was fairly constant at 60% of the cumulative plantdry weight. The daily proportional dry matter distribution did not seemto be linked directly to the climate conditions (temperature,CO₂ concentration, relative humidity or daily light integral).The proportional distribution to the fruits showed a clear positivecorrelation with the fruit load (number and weight of fruits)on a plant. The number of fruits on a plant changed considerablyduring the growing season. This number was limited not by theformation of new fruits but by abortion of fruits within about10 d after flowering. The number of young fruits that did notabort appeared to correlate positively with the growth rateof the vegetative parts. Cucumis sativus (L.), cucumber, biomass allocation, partitioning, vegetative-generative growth, fruit growth, fruit abortion     

Effect of number and configuration of fruits, photon flux and age on the growth and dry matter distribution of fruits of Pisum sativum L.

Abstract. In experiments with Pisum sativum cv. Sleaford Orbiter in a controlled environment, the effect of fruit number and position, photon flux density and developmental stage on fruit growth was studied. During early development (up to 22 d from anthesis) growth of the first fruit was unaffected by the presence of one or two additional fruits irrespective of their position. When grown to maturity in competition with fruits at the same node a small decrease in weight of this fruit was observed. Where plants retained a full complement (20-30) of fruits the growth of the first fruit was markedly decreased at all stages of development (6-40 d). In all instances where competition was observed, the pericarp was more affected than the seeds. This was particularly so when photon flux was decreased 18-22 d from anthesis compared with a decrease at an earlier stage. Partition of dry matter between fruits showed a progressively increasing allocation to the later-formed fruits with time for all treatments. The actual proportions allocated to different fruits were not changed by the number of competing fruits. Decreasing photon flux by more than two-thirds decreased fruit growth rates but had little effect on dry matter partitioning in most cases, although where all fruits were retained, there was a tendency for fruits at the lower reproductive nodes to be less affected. These findings are discussed in relation to known sources of assimilate for fruits, assimilate transport and sink demand. It is suggested that partition of dry matter between fruits can be estimated on the basis of fruit size and the developmental trend in relative growth rate of fruits grown in the absence of competition for assimilate from other fruits.     

The Effect of the Fruit and Exogenous Hormones on Leaf Expansion and Composition in Citrus

Sanz, A., Martinez Cortina, C. and Guardiola, J. L. 1987. Theeffect of the fruit and exogenous hormones on leaf expansionand composition in Citrus.—J. exp. Bot. 38: 2033-2042. The effect of the developing flowers and fruitlets on leaf expansionand composition has been determined in leafy inflorescencesof Citrus sinensis L. Osbeck. During leaf expansion the developingflowers do not compete with the leaves, and their early removaldoes not affect leaf size and composition. Competition for mineralelements is established after flower opening, once leaf expansionis complete. No effect of the fruit on metabolizable carbohydratesin the leaves was found up to day 22 after flower opening. The response to exogenously applied growth regulators suggeststhat the differences in weight and composition between inflorescenceleaves and leaves from vegetative sprouts may be due to hormonally-mediateddifferences in sink strength. Gibberellic acid enhances laminaexpansion and increases the sink strength of the leaves. Kinetinenhances lamina expansion without affecting sink strength. Leafgrowth is directly related to both soluble and wall-bound acidinvertase activities; however, the GA₃ effects on leaf growthand sink strength are unrelated to invertase activity and tothe rate of starch accumulation. Key words: Acid invertase, amylase, carbohydrates, Citrus, leaf growth     

Partitioning of assimilates in fruiting tomato plants

Tomato is a potentially high-yield crop with a harvest index of about 65%. During fruiting, fruit growth accounts for 80 to 90% of the plant fresh weight gain and fruits are therefore the strongest sinks for assimilate.At initiation, an inflorescence is a weak sink in comparison with apical shoots. When assimilate supply is inadequate, the inflorescence has a reduced level of endogenous cytokinin and the degree of abortion is inversely related to the activity of sucrose hydrolase. Application of cytokinin plus gibberellins to the inflorescence increases its capacity to attract assimilate at the expense of apical shoots.At fruit set, cell division is activated and the ovary starts to accumulate reducing sugars and starch. Both the final cell number and the potential cell size are determined in the first two weeks and may be related to the levels of cytokinin and auxin.At the early stage of rapid growth a fruit accumulates imported assimilates, mainly in the forms of hexoses and starch. The rate of starch accumulation increases with the absolute fruit growth rate and affects the final soluble solids content of a fruit. The change in the fruit growth rate during fruit development does not coincide with the changes in the endogenous hormone levels of the fruit. A fruit competes for assimilate with others mainly in the same truss.     

Evaluation of a Dynamic Simulation Model for Tomato Crop Growth and Development

A dynamic simulation model for tomato crop growth and development,TOMSIM, is evaluated. Potential crop growth and daily crop grossassimilation rate (P_gc,d) is computed by integration of leafassimilation rates over total crop leaf area throughout theday. Crop growth results fromP_gc,dminus maintenance respirationrate (R_m), multiplied by the conversion efficiency. Dry matterdistribution is simulated, based on the sink strength of theplant organs, which is quantified by their potential growthrate. Within the plant, individual fruit trusses and vegetativeunits (three leaves and stem internodes between two trusses)are distinguished. Sink strength of a truss or a vegetativeunit is described as a function of its developmental stage.In this paper, emphasis is on the interactions between the twosubmodels of, respectively, dry matter production and dry matterdistribution. Sensitivity analysis showed that global radiation,CO₂concentration, specific leaf area (SLA) and the developmentalstage of a vegetative unit at leaf pruning had a large influenceon crop growth rate, whereas temperature, number of fruits pertruss, sink strength of a vegetative unit and plant densitywere less important. Leaf area index (LAI) was very sensitiveto SLA and the developmental stage of a vegetative unit at leafpruning. Temperature did not influence the simulated R_m, asincreased respiration rate per unit of biomass at higher temperatureswas compensated by a decrease in biomass. The model was validatedfor four glasshouse experiments with plant density and fruitpruning treatments, and on data from two commercially growncrops. In general, measured and simulated crop growth ratesfrom 1 month after planting onwards agreed reasonably well,average overestimation being 12%. However, crop growth ratesin the first month after planting were overestimated by 52%on average. Final crop dry mass was overestimated by 0–31%,due to inaccurate simulation of LAI, resulting partly from inaccurateSLA prediction, which is especially important at low plant densityand in a young crop.Copyright 1999 Annals of Botany Company Crop growth, dry matter production, glasshouse, leaf area,Lycopersicon esculentum, partitioning, simulation model, tomato, TOMSIM.     

The relationship between tomato fruit growth,incidence of blossom-end rot and phytohormone content as affected by sink/source ratio

Blossom-end rot is generally considered a calcium-related physiological disorder. The results of the previous studies show that several factors such as plant conditions can be effective on the blossom-end rot incidence. Therefore, the present study was undertaken to investigate the effect of the sink/source ratio on the incidence of the blossom-end rot of two greenhouse tomato (Solanum lycopersicum L.) cultivars: ‘Grandella’ and ‘Isabella’. To this end, four treatments were applied: saving one fruit per truss (1F), two fruits per truss (2F), three fruits per truss (3F), and no fruit pruning (control). The results showed that the tomato cultivar ‘Isabella’ was more susceptible to the blossom-end rot than ‘Grandella’. Decreasing the sink/source ratio increased the incidence of the blossom-end rot and the relative fruit growth rate. The correlation between the blossom-end rot incidence and the relative fruit growth rate showed that the fruit growth rate could be regarded as an important factor in the incidence of this disorder. Endogenous auxin and cytokinin concentrations acted as the regulators of the fruit growth rate and influenced it. Slowing down the relative growth rate by keeping proper sink/source ratio based on tomato cultivar is, therefore, an effective, cheap and healthy way to control the incidence of the blossom-end rot, especially in organic farming.     

Effect of Fruit Load on Partitioning of Dry Matter and Energy in Cantaloupe (Cucumis melo L.)

Cantaloupe (Cucumis melo L.) plants set groups of fruits whichgenerate large variations in the reproductive:vegetative dryweight balance. We studied the influence of fruit number onthe partitioning of dry matter and energy between the vegetativeand reproductive organs and among the seeds and the variousfruit tissues during the development of the first fruits. Over2 years and on two Charentais cantaloupe cultivars, fruit numberwas either limited to one or left unrestricted, which led tothe setting of two to six fruits. Because of the high lipidcontent in seeds, the distribution of assimilates was studiedin terms of energy equivalent as well as dry weight. Measureddry weights were converted into energy equivalents by calculatingthe construction cost of tissues from their elemental composition.Seeds differed from other tissues in showing an increase inconstruction cost, from 1.1 to 1.8 g CH₂O g^-1d. wt between 10and 30 d after pollination. For this reason, during the secondhalf of fruit development on plants with unrestricted fruitload, they made up to 31% of the fruit and 12% of the aerialpart of the whole plant in terms of dry weight, but 39 and 18%in terms of energy (glucose equivalents). The fraction of assimilatesallocated to the fruits showed a saturation-type response tothe number of fruits per plant. It did not increase in cultivarTalma above two fruits per plant, which could be due to a decreasingsink strength with fruit rank, whereas cultivar Galoubet maintaineda more homogeneous fruit size within plants. At a similar fruitload, the reproductive:vegetative dry weight balance differedbetween the 2 years of the experiment, probably because of variationin the fruit sink strength. Copyright 1999 Annals of BotanyCompany Charentais cantaloupe, Cucumis melo L., assimilate distribution, construction cost, development, dry matter partitioning, fruit load, seeds, sink strength.