Dry matter accumulation in citrus fruit is not limited by transport capacity of the pedicel

The vascularization of the pedicel in Marisol clementine (Citrus clementina Hort. ex Tanaka) has been characterized in relation to fruit growth. Phloem and xylem formation occurred during the first half of the period of fruit growth. Phloem cross-sectional area reached its maximum value by the end of fruitlet abscission, 78 d after anthesis (DAA), shortly after the rate of accumulation of dry matter in fruitlets reached its maximum value. Secondary xylem formation occurred until day 93, well after the end of fruitlet abscission. At fruit maturity, xylem accounted for 42-46 % of the cross-section of the pedicel. Vessels differentiated in this late-formed xylem. Formation of phloem and early xylem was directly related to fruitlet size (and growth rate). Differences in the rate of formation of conductive tissues in the pedicel of the developing fruitlets followed rather than preceded the differences in growth rate. Specific mass transfer (SMT) in the phloem was highest in the fastest growing fruitlets, and peaked during the late stages of fruitlet abscission (72-78 DAA) and during the main period of fruit growth (107-121 DAA). Application of a synthetic auxin to developing fruits, either at the end of flowering (2,4-D) or by day 64 after flowering (2,4-DP), increased the growth rate of the fruit and fruit size at maturity (8-13 % increase in fruit diameter at maturity). These auxin applications also enhanced the formation of conductive tissues in the pedicel, with a specific effect on phloem formation. Applying auxin at flowering resulted in a reduction in the phloem SMT by days 72-78, whereas auxin application on day 64 increased this parameter. Despite this difference in behaviour, which resulted from the different time-course of the growth response of the fruit to auxin applications, these applications increased fruit size to a similar extent. Severing 37 % of the phloem of the pedicel during the main period of fruit growth resulted in an increase in the specific mass transfer in the phloem but had no influence on fruit growth. These observations demonstrate that the transport capacity in the phloem of the pedicel does not limit fruit growth and, within the limits of our experiments, an increase in demand by the fruit appeared to be matched by an increase in SMT. The dependence of late xylem formation (after the period of fruitlet abscission) on fruitlet growth was demonstrated in Salustiana orange [Citrus sinensis (L.) Osbeck] by means of controlling fruit growth through the manipulation of leaf area. Fruit growth at this time was more closely related to leaf area than to carbohydrate levels, suggesting that it may be limited by current photosynthesis.     

Maximum Fruit Growth Potential and Seasonal Patterns of Resource Dynamics During Peach Growth

Maximum fruit growth potential, the growth attained by fruitswhen they are grown under optimal environmental conditions inthe presence of a non-limiting supply of resources, was estimatedfor two peach [Prunus persica (L.) Batsch] cultivars that differin the timing of resource demand for reproductive growth. Maximumpotential fruit growth was estimated on trees that were heavilythinned at bloom. On these trees, resource availability exceededresource demand for fruit growth. For both cultivars, the mean dry weights of fruits grown onunthinned trees were approximately half the mean dry weightsof fruits grown on trees that were heavily thinned at bloom,indicating that fruit growth was source-limited on unthinnedtrees. Comparison of the seasonal patterns of relative growthrate of fruits on unthinned and heavily thinned trees indicatedthe source-limited fruit growth occurred during distinct periodsof the growing season. On the early maturing cultivar, source-limitedfruit growth occurred from 300 degree-days after bloom untilharvest (4·5-10 weeks after bloom). On the late maturingcultivar, source-limited fruit growth occurred from 200-900and 1600-1900 degree-days (3·5-12 and 18-20 weeks) afterbloom. Although the final dry weight of fruits on the early maturingcultivar was only half that of fruits on the late maturing cultivar,the potential net sink strength of fruits was significantlyhigher on the early than the late maturing cultivar throughoutthe entire growth period of the early maturing cultivar. Resourceavailability for fruit growth was similar on the early and latematuring cultivars, indicating that selection for early maturingfruits has not changed the patterns of resource availabilityfor fruit growth.Copyright 1995, 1999 Academic Press Maximum fruit growth potential, carbon economy, partitioning, resource availability, resource limitation, source-limited growth, sink activity, sink strength, growth analysis, relative growth rate, Prunus persica (L.) Batsch, peach     

13C-photosynthate accumulation in Japanese pear fruit during the period of rapid fruit growth is limited by the sink strength of fruit rather than by the transport capacity of the pedicel

In Japanese pear, the application of GA3+4 during the period of rapid fruit growth resulted in a marked increase in pedicel diameter and bigger fruit at harvest. To elucidate the relationship between pedicel capacity and fruit growth and to determine the main factor responsible for larger fruit size at harvest, fruit growth and pedicel vascularization after GA application were examined and the carbohydrate fluxes were monitored in a spur unit by non-invasive techniques using 13C tracer. Histological studies of fruit revealed that GA increased the cell size of the mesocarp but not the cell number and core size. The investigation of carbon partitioning showed that an increase in the specific rate of carbohydrate accumulation in fruit or the strength of fruit should be responsible for an increase of fruit weight in GA-treated trees. Observation of pedicel vascularization showed that an increase in pedicel cross-sectional area (CSA) by GA application mainly resulted from phloem and xylem CSA, but it is unlikely that an increase in the transport system is the direct factor for larger fruit size. Therefore, it can be concluded that larger fruit size resulting from GA application during the period of rapid fruit growth caused an increase in the cell size of the mesocarp and increased carbon partitioning to the fruit. Although GA is closely involved with pedicel vascularization, it seems that photosynthate accumulation in fruit is limited by the sink strength of fruit rather than by the transport capacity of the pedicel.     

Carbohydrate Availability in Relation to Fruitlet Abscission in Citrus

Abscission of flowers and fruitlets in the Washington navelorange (Citrus sinensis [L.] Osbeck) has been characterizedin relation to carbohydrate availability. A main wave of flowerabscission occurs shortly after anthesis while the carbohydratereserves in the tree are high. Fruitlet abscission starts approx.30 d after the commencement of flowering, while carbohydrates(mainly starch) are being accumulated in the leaves. Flowerand early fruitlet abscission are not caused by carbohydrateshortage. During late fruitlet abscission sucrose concentrationin the leaves falls to a low value demonstrating a limitationin supply and competition among the developing fruitlets forcarbohydrates. Concentrations of sucrose and reducing sugarsin the peel of the fruitlets also fall to low values, and arelationship could be demonstrated between these free sugarlevels and abscission. Ringing increases carbohydrate supplyto fruit and reduces late fruitlet abscission, but only hasa marginal effect on the growth of the fruitlets, which seemsless sensitive than abscission to carbohydrate shortage. Thelimitation of carbohydrate supply to the fruitlets occurs whilestarch levels in the leaves remain high. Slow mobilization ofstarch reserves may be one factor limiting set in Citrus. Copyright2001 Annals of Botany Company Carbohydrate supply, citrus, fruit growth and abscission, ringing, navel orange, starch, sugar metabolism     

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     

Effect of Pulp Cell Number and Assimilate Availability on Dry Matter Accumulation Rate in a Banana Fruit [ Musa sp. AAA group 'Grande Naine' (Cavendish subgroup)]

Fruit position on the bunch (inflorescence) is an importantpart of variability in banana fruit weight at harvest, as fruitsat the bottom of the bunch (distal fruits) are approx. 40% smallerthan those at the top (proximal fruits). In this study, therespective roles of cell number and cell filling rate in thedevelopment of pulp dry weight are estimated. To this end, thesource/sink ratio in the plant was altered at different stagesof fruit development. Leaf shading (reducing resource availability),bunch bagging (increasing sink activity by increasing fruittemperature), and bunch trimming (decreasing sink size by fruitpruning), applied once cell division had finished, showed thatthe pulp filling rate depends on resource availability. Bunchbagging and bunch trimming were also carried out before theend of cell division to estimate the role of pulp cell numberin the development of pulp dry weight. A sampling method wascalibrated to evaluate pulp cell number from the digestion ofa fixed portion of the pulp in a solution of chromic and nitricacids. A relationship was found between pulp cell number andfruit length at the end of cell division. It was observed thatpulp cell number is a determining factor in pulp dry weightvariability within a bunch. On the other hand, the cell fillingrate was identical for all fruits in the bunch and was influencedby the source/sink ratio. A Michaelis-Menten relationship wasinvoked to relate the cell filling rate in a bunch to the source/sinkratio during bunch filling. Copyright 2001 Annals of BotanyCompany Banana fruit, Musa sp., fruit growth, cell number, cell filling rate, source/sink ratio, temperature     

Phloem in developing cotton fruits: 6(5)carboxyfluorescein as a tracer for functional phloem

Carbohydrate and water transport into developing cotton (Gossypiumhirsutum L.) fruits is essential for normal fruit development,and phloem has been suggested to play a major role in this transport.To study transport into cotton fruits of different developmentalstages, a phloem tracer [6(5)carboxyfluorescein] was appliedto sympodial leaves. Tracer distribution into the subtendedfruit was determined using epifluorescence microscopy. Phloemthroughout the entire capsule wall and central column was functionalfrom early stages of fruit development. Vasculature of the capsulewall consisted of a complex three-dimensional network. Vascularbundles ended in radially-oriented club-shaped structures, whichconsisted mainly of fibres, with phloem on the outside of thesestructures. The vascular system of the capsule wall was connectedto the central column by amphicribral bundles in the partitions.The central column had two adaxial (ventral) vascular bundlesper carpel. These vascular bundles branched into the placentalregion of the central column, and connected to the seeds viathe funiculi. Amphicribral vascular bundles diverged from theseadaxial bundles into the partition. The results of this studyconfirmed previous observations on the vascular anatomy of thecapsule wall and describe the vascular anatomy of the centralcolumn of cotton fruits Key words: Cotton, Gossypium hirsutum L., phloem, fruit, carboxyfluorescein, vasculature     

Maximum Fruit Growth Potential Following Resource Limitation During Peach Growth

To achieve its maximum organ growth potential, an organ mustgrow at its potential relative growth rate (RGR) throughoutdevelopment. When resource availability limits growth, the RGRis reduced below the potential RGR. This study examines whether,following a period of resource-limited growth, the RGR is ableto increase to the potential RGR when sufficient resources areavailable. Fruit RGRs of a late maturing peach cultivar wereexamined following removal of most of the fruits (heavy thinning)from previously unthinned trees in Apr., May, and Jun. The fruitRGRs after imposition of the thinning treatments were higherthan those on unthinned trees during source-limited periodsof the growing season, suggesting that fruit RGR can increasein response to increased resource availability. In general,the RGRs of fruits of trees thinned in Apr., May, and Jun. didnot exceed those of fruits on trees thinned at bloom, suggestingthat heavy thinning at bloom provides a reasonable estimateof the potential RGR. There were times, however, when the effectsof competition with vegetative sinks were apparent, suggestingthat the RGR of fruits on trees that were heavily thinned atbloom may underestimate the potential RGR during these times.The absolute growth rates of fruits on thinned trees were greaterthan those on unthinned trees, but generally were not greaterthan those on trees that were thinned at bloom, suggesting thatpeach fruits are unable to recover potential growth lost duringresource-limited growth periods.Copyright 1995, 1999 AcademicPress Prunus persica (L.) Batsch, peach, maximum fruit growth potential, relative growth rate, absolute growth rate, thinning, fruit-fruit competition, resource availability, resource limitation, growth analysis     

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 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     

Effects of Sink Demand on Photosynthesis in Cucumber

In Cucumis sativus L. net photosynthesis of leaf number 12 increaseduntil 12 d after its unfolding and then decreased gradually. Sink demand was varied by imposing the number of fruits perplant without changing the number of leaves per plant. Net leafphotosynthesis did not respond to sink demand during the first16 d of fruit growth. Subsequently, a substantial reductionin photosynthesis was found only when all fruits were removed.This reduction was accompanied by a decrease in the rate oftranspiration, indicating a higher stomataL resistance. Neither starch nor mono- and disaccharides accumulated noticeablyat reduced sink demand, suggesting that there was no end-productinhibition of photosynthesis. Dry matter content of the leaves increased and specific leafarea decreased when sink demand was reduced. When modelling cucumber production, effects of sink demand onleaf photosynthesis can be ignored. Key words: Cucumis sativus, photosynthesis, sink-source, sink demand     

Contrasted responses to carbohydrate limitation in tomato fruit at two stages of development

The metabolic consequences of long‐term carbohydrate depletion have been well documented in many sink organs but not extensively in fruit. Therefore, in the present study the response to sugar limitation in tomato fruit (Lycopersicon esculentum Mill.) was investigated at two developmental stages; during the cell division and cell expansion phases. First, the response in excised fruit cultured in vitro was characterized. Sugar depletion caused an arrest of growth and an exhaustion of carbon reserves. The proteins that were degraded and the nitrogen released was transiently stored as asparagine and glutamine in both developmental stages and also as γ ‐aminobutyric acid (GABA) in expanding fruit. Fruit at the cell division stage appeared to be more sensitive to sugar limitation. The response to sugar depletion was then characterized in fruit from plants submitted to extended darkness. In planta, the effects of sugar‐limitation were similar to those described in vitro but much more attenuated, especially in expanding fruit, which still accumulated dry matter. The expression of cell cycle genes, sugar‐ and nitrogen‐related genes was reduced by darkness. Only asparagine synthetase gene expression was induced in both dark‐treated fruit. Together the present data revealed that the effects of the carbon limitation are more pronounced in the youngest fruits as it is probably controlled by the relative sink strength of the fruit.     

Re-interpretation of an Experiment on the Role of Assimilated Transport Resistance in Partitioning in Tomato

The importance of transport resistance (distance between sourceand sink) on assimilate partitioning in tomato is questioned.Slack and Calvert ( Journal of Horticultural Science 52 : 309–315,1977) concluded that, in tomato, excising of fruit trusses showeda direct influence of distance from source on assimilate partitioning.A dry matter distribution model for tomato, based on the hypothesisthat distribution is regulated by the sink strengths of theplant organs and that no influence of transport resistance onpartitioning exists, has been described and validated by Heuvelink( Annals of Botany 77 : 71–80, 1996). Using this model,it is shown that the results of Slack and Calvert (1977) canbe explained more simply on the basis of the succession of trusseswith growth shifted with respect to time. Therefore, their resultsdo not prove that transport resistance plays a role in assimilatepartitioning. Allocation; distance; dry matter distribution; model; assimilate pool; partitioning; simulation; transport resistance; tomato     

A Space-time Model of Carbon Translocation along a Shoot Bearing Fruits

A carbon-based model is described of the source-sink relationshipsof a stem bearing fruits in space and time and focusing on growthvariability along the branch. The novelty of the model comesfrom the aggregation of physiological processes taking intoaccount spatial aspects. The stem is represented as a set ofcompartments (metamers) connected to source (leafy shoots) andsink (fruits) compartments. Each leafy shoot forms one compartment.The fruit consists of three compartments involved in translocation(cytoplasm), structure (cell wall) and storage (vacuole). Physiologicalprocesses considered are photosynthesis, respiration of fruitsand leaves, translocation of assimilates and fruit growth. Assimilateproduction is regulated by sink strength. Carbon translocationbetween two compartments depends on the gradient of assimilateconcentration. The gradient induces carbon translocation fromthe most to the least concentrated compartment, except for thevacuole compartment into which translocation is possible whateverthe concentration gradient. Fruit growth, in terms of freshweight, results from the phloem water supplied to the fruitaccording to the concentration gradient between the fruit andthe stem. The model is calibrated for peach trees by comparingobserved and simulated fruit dry and fresh weights for a shootwith normal fruit load. The model simulates variability betweenpeach fruits and the effect of contrasting fruit loads. Accordingto this model, photosynthesis increases and assimilate concentrationsin leaves and phloem decrease with decreasing leaf:fruit ratioas reported in the literature. Simulated concentrations of assimilatesin the phloem range from 2 to 14%. Simulated concentration gradientsand specific mass transfer for peach trees range from 0.05 to0.17 g cm^-3m^-1and from 0 to 3 g cm^-2h^-1, respectively, and areof the same order of magnitude as those reported for variousother tree species. The model is used to analyse the effectof fruit position relative to the leaves. Copyright 1999 Annalsof Botany Company Peach tree, Prunus persica (L.) Batsch, model, carbohydrates, translocation, source-sink, fruit.     

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.     

Influence of Sink-Source Interaction on Dry Matter Production in Tomato

Sink-source ratio in tomato was manipulated, in six glasshouseexperiments, by fruit pruning (trusses pruned to two to sevenfruits immediately after fruit set of each truss), truss pruning(removal of every other truss at anthesis) and truss pruningin plants with two shoots. Periodic destructive harvest wereconducted for about 100 d after flowering of the first truss.Dry matter production was not influenced by sink-source ratio,whereas dry matter distribution between fruits and vegetativeparts was greatly affected. The fraction of dry matter distributedto the fruits at the end of the fruit pruning experiments (F_fruits)could be described accurately as a saturation-type functionof number of fruits retained per truss (N_f): F_fruits = 0.660(l-e^-0.341N_f). Specific leaf area and internode length decreasedand plant leaf area increased when sink-source ratio was reduced.Removal of every other truss at anthesis did reduce dry matterpartitioning into the fruits, but it did not influence internodelength. Plant development (number of visible leaves at the endof the experiments) was not influenced by sink-source ratio.In four experiments some plants were pruned to one fruit pertruss. Final dry matter production was 8-24% lower for theseplants, compared with plants with more than one fruit per truss.This was, at least party, the result of less light interceptionby these plants, which had strongly curled leaves pointing downwards. Results indicate that effects of sink demand on dry matter productionper unit of intercepted radiation and probably on leaf photosyntheticrate in commercial tomato production can be ignored.Copyright1995, 1999 Academic Press Dry matter production, feedback control, glasshouse, growth analysis, Lycopersicon esculentum, pruning, sink demand, sink-source ratio, tomato     

Pollination and Resource Constraints on Fruit Set and Fruit Size ofPersoonia rigida(Proteaceae)

Flower and immature fruit abscission can be caused by proximatefactors preventing the development of all flowers into maturefruits. Two potential limiting factors, pollen supply and carbohydrateavailability, were assessed as relative constraints on accumulationof fruit dry matter inPersoonia rigida(Proteaceae). Naturalpollen transfer was highly efficient, and no evidence of self-incompatibilitywas found. Levels of fruit set (67.4% following open-pollinationand 50.4–58.8% following hand-pollinations) may be thehighest recorded for a species of Proteaceae with hermaphroditicflowers. Fruit abscission occurred principally in a single phasefrom 4–10 weeks post-anthesis, with a peak during theeighth week post-anthesis, and this early abscission was theresult of fertilization failure in some flowers. Manipulationof carbohydrate availability by girdling and/or defoliationof branches provided evidence that carbohydrate supply affectedfruit set only when supply was very low. Fruit abscission dueto very low carbohydrate availability on defoliated brancheswas evident during the early abscission phase but was more pronouncedduring the second half of the fruit development period (>17weeks post-anthesis), coinciding with the period of greatestdry matter demand by the fruits. Minimal fruit abscission occurredduring this later period on leaf-bearing branches. Increasesin carbohydrate supply had no effect on fruit set, but fruitsize was highly sensitive to carbohydrate availability. Subtendingand adjacent leaves were identified as major contributors tothe carbohydrate supply of fruits, although some carbohydratecould be obtained from beyond the fruiting branch. Despite thehigh levels of natural fruit set, both pollen supply and resourceavailability were indicated as potential constraints on accumulationof fruit dry matter inP. rigida.Copyright 1999 Annals of BotanyCompany. Persoonia rigidaR.Br., Proteaceae, pollination, carbohydrates, fruit set, fruit size, abscission, girdling.     

Parthenocarpic Fruit Growth Reduces Yield Fluctuation and Blossom-end Rot in Sweet Pepper

The aim of this work was to investigate whether parthenocarpicfruit growth could avoid flushing, i.e. an irregular yield pattern,in sweet pepper. Plants were grown in a greenhouse compartmentfrom April until August. Half of the plants were grown withouta fruit set treatment (control), whereas parthenocarpic fruitswere allowed to develop on the other plants by preventing self-pollinationand applying auxin to the stigma. For node positions 3 to 17,fruit set per node varied between 21 and 55% for control plants[coefficient of variation (CV) = 11%], whereas auxin-treatedplants showed much less variation in fruit set (41–57%;CV = 5%) and average fruit set was higher. In agreement withfruit set, fruit yield was also much more regular in the auxin-treatedplants. Fruit fresh yield varied between 0.2 and 1.0 kg m^-2forcontrol plants (CV = 20%), and between 0.4 and 0.8 kg m^-2forauxin-treated plants (CV = 9%). Results showed that developingseeds in sweet pepper fruits are the main cause of the abortionof new flowers, and irregular fruit set and yield. Parthenocarpicfruit growth resulted in flatter, 30% smaller fruits, becauseof a reduction in fruit growth rate; the duration of fruit growthwas 1 week longer than for fruits from control plants. Parthenocarpicfruits were hardly affected by blossom-end rot (BER) with only1% of fruits being affected compared to 31% in the control.Total dry mass production was the same for treated and controlplants; however, in auxin-treated plants, 50% of the total drymass was allocated to the fruits, compared to 58% in controlplants. Copyright 2001 Annals of Botany Company Abortion, auxin, BER, blossom-end rot, Capsicum annuum L., flushing, fruit set, irregular yield pattern, parthenocarpy, sweet pepper     

Effects of Seed Number on Competition and Dominance among Fruits in Capsicum annuum L.

The effects of seed number on set, development and growth ofa fruit, and on inhibition of later-developed fruits were studiedby varying the pollen load on the stigma of sweet pepper flowers(Capsicum annuum L.). Despite much variation, a linear increasein individual fruit weight with seed number could be observed.Seed number affected the growth rate rather than the growingperiod of fruit. When seed numbers were low, the probabilityof fruit setting was positively related to seed number. However,a relatively low seed number (50–100 seeds/fruit: 20–30%of the maximum seed number) was sufficient for maximal fruitset. An increase in seed number increased the inhibitory effect ofa fruit on set and growth of later-developing fruits. As a result,when pollination treatments were applied to all the flowersof a plant, results could be quite different to those obtainedwhen only a limited number of flowers were treated. Fruit setof the second fruit was reduced by the application of a highpollen load to the first flower, even when the first fruit abortedbefore it had accumulated much dry matter. Our results suggestthat growth inhibition of the second fruit by seed number ofthe first fruit is controlled both by competition for limitedassimilates, as well as by dominance due to the production ofplant growth regulators by the developing fruit. Sweet pepper; Capsicum annuum L.; pollination; fruit set; abortion; abscission; fruit growth; first-fruit dominance; sink strength