Source-sink Ratio Research Articles

Photosynthetic Responses in Annual Rye, Perennial Wheat, and Perennial Rye Subjected to Modest Source:Sink Ratio Changes

ABSTRACTNewly developed perennial cereals have been developed as alternatives to annual food crops. These provide novel contexts in which to study source vs. sink limitations of plant productivity. This is one of the first investigations of source:sink effects on photosynthesis, seed size, and regrowth in perennial cereal crops as well as in the commercially important annual rye (Secale cereale L.). Through experimental manipulations of field‐grown plants, we studied the effect of manipulations of source:sink ratio (25% decreases and 100% increases) on photosynthetic rate in perennial wheat [Triticum aestivum L. × Thinopyrum elongatum (Host) D. R. Dewey], perennial rye [S. cereale × Secale strictum (C. Presl) C. Presl subsp. strictum (syn. Secale montanum Guss.)], annual wheat (Triticum aestivum L.), and annual rye. We measured carbohydrate pools, seed size, and regrowth as further indices of source vs. sink limitation. Perennial wheat showed sink limitation throughout. Annual and perennial rye appeared to be colimited. Low source:sink ratios in perennial wheat and rye were associated with up to 25% higher photosynthetic rates while high source:sink ratios led to up to 20% decreases. Seed size showed more stability under source:sink manipulation in perennials than in annuals while regrowth of perennials was not affected by source sink ratio, and all three species showed more stability of seed size in response to source:sink manipulation than annual wheat. Our results are consistent with perennial cereals operating below their maximum photosynthetic capacity, in contrast to annual wheat, and following a conservative reproductive strategy. By selecting for greater sink strength in perennial wheat, breeders may be able to achieve higher rates of photosynthesis and support higher yields in this new crop.

Night Temperature and Source-sink Effects on Growth, Leaf Carbon Exchange Rate, and Carbohydrate Accumulation in Bell Pepper Ovaries

Low night temperatures and/or high source-sink ratios increase ovary swelling and subsequent fruit malformation in many sweet peppers (Capsicum annuum), including bell pepper. Although this response has been correlated with increased ovary carbohydrate accumulation, evidence for this is limited. Furthermore, it is unknown how the combined effects of night temperature and source-sink ratio affect ovary carbohydrate accumulation and ovary swelling. The objectives of the present work were to determine night temperature and source-sink effects on ovary swelling, net carbon exchange rate (CER), and soluble sugar and starch concentrations in bell pepper ovaries at anthesis. Source-sink and temperature effects were tested by comparing fruiting (low source-sink ratio or high sink demand) with non-fruiting (high source-sink ratio or low sink demand) ‘Legionnaire’ bell pepper plants grown at 22/20 °C [high night temperature (HNT)] or 22/12 °C [low night temperature (LNT)] day:night temperatures. Flowers that opened after imposition of the temperature and fruiting treatments were harvested at anthesis. Ovaries from harvested flowers were weighed and analyzed for non-structural carbohydrates. Leaf gas exchange measurements were performed every 3 days. Ovary fresh weight of flowers harvested at anthesis was highest in non-fruiting plants under LNT and lowest in plants grown under HNT regardless of fruiting status. Mean CER averaged over the experimental period was significantly higher in fruiting plants under HNT compared with all other treatments. There were no significant interactions between night temperature and fruiting status on ovary soluble sugar or starch concentrations. Low night temperature increased glucose, fructose, and starch concentration and decreased sucrose concentration in the ovary wall compared with HNT. There were no differences in soluble sugar or starch concentrations in the ovary wall between fruiting and non-fruiting plants. Thus, although both low temperature and high source-sink ratio (i.e., non-fruiting plants) resulted in ovary swelling, the mechanisms appear to differ. Whereas LNT effects on ovary swelling were associated with increased ovary carbohydrate accumulation, this association was not apparent when ovary swelling occurred in response to high source-sink ratios.

Impact of the extension of black leaf streak disease on banana susceptibility to post-harvest diseases

Impact of the extension of black leaf streak disease on banana susceptibility to post-harvest diseases. Abstract - Introduction. The susceptibility of banana fruit to crown rot and anthracnose, the two main banana post-harvest diseases, is influenced by many pre-harvest abiotic factors. Mycosphaerella leaf spot diseases (MLSD) of bananas are biotic pre-harvest factors, which have an influence on fruit physiology. The fruit's susceptibility to post-harvest diseases may also be influenced by foliar diseases caused by M. fijiensis, responsible for black leaf streak disease (BLSD), and M. musicola, which causes sigatoka disease (SD). The aim of our study was to determine the influence of these biotic pre-harvest factors on banana fruit's susceptibility to crown rot and anthracnose. Materials and methods. A disease severity gradient was established in two experimental fields (Cameroon for BLSD and Guadeloupe for SD) where, at the flowering stage, six different levels of MLSD severity were selected. Fruit susceptibility was determined through necrotic surface assessments after artificial inoculation by Colletotrichum musae on the 3rd hand of harvested bunches. Results and discussion. BLSD significantly influenced banana sensitivity to crown rot (P 0.05) on banana susceptibility to either post-harvest disease. These results are discussed with emphasis on the influence of variations in the source-sink ratio on fruit physiology. The influence of BLSD on crown rot disease suggests the need to take into account the management of these foliar diseases for an alternative control method of post-harvest diseases through integrated pest management programs. Cameroon / Guadeloupe / Musa / fruits / Mycosphaerella fijiensis / Mycosphaerella musicola / black sigatoka / black leaf streak disease / anthracnoses / crown rots Impact de l'extension de la maladie des raies noires sur la sensibilite des bananes aux maladies post-recolte.

Seed abortion and the individual weight of castor seed (Ricinus communis L.)

The weight of each individual seed plays an important but often neglected role in the determination of castor (Ricinus communis L.) seed yield. Studies were made under field and greenhouse conditions to assess how seed abortion and the weight of individual castor seeds are influenced by: (i) water availability, (ii) position in the raceme, (iii) manipulation of source-sink ratio, and (iv) competition among seeds in the same capsule. Samples of 150 seeds were obtained from a field experiment in Lubbock, TX, USA with six cultivars under seven irrigation treatments. The seeds were individually weighed. Some racemes with mature fruits were harvested and kept with attached fruits for taking data on the position and weight of each seed. In a greenhouse experiment, castor plants of two cultivars were subjected to sink reduction (clipping of racemes) and source reduction (partial defoliation). The histogram of seed weight was not a bell-shape curve because there was a relatively high frequency of light (aborted) seeds. When more water was available, the plant increased the maximum seed weight and reduced the seed abortion rate. The lowest seed abortion rate was observed in the cv. BRS Nordestina (7.4%) and the highest in the cv. Hale (18.1%). The seed weight and the probability of seed abortion were not associated with the position in the raceme. No evidence was found that seeds in the same capsule compete for assimilates. The seed abortion rate increased in response to defoliation after flowering (source reduction), but it did not decrease in response to the racemes clipping (sink reduction). The sink reduction did not increase the number of seeds in the first raceme and the maximum and mean seed weight. Seed abortion was found to play an important role in adjustments of sink according to source capacity.

Understanding grain yield responses to source–sink ratios during grain filling in wheat and barley under contrasting environments

A better understanding of the effects of different source–sink ratio during the grain filling period on grain growth may be relevant in order to further increase cereal grain yield. The main objective of the present work was to determine the effect of different manipulations of the source–sink ratios in wheat and barley grown at four different environmental conditions on responsiveness of sinks (grain growth and yield) and sources (spike photosynthesis and water soluble carbohydrates in the stems). Four treatments were imposed 7 days after anthesis in two contrasting locations with low- and high-inputs conditions in wheat (cv. Soissons) and barley (cv. Sunrise): they were a control, a treatment removing all the spikelets from the upper half of the spikes (TS), and shadings decreasing incident radiation by 75% on the whole canopy (SW) or only on the leaves (having the top area of the meshes individual holes for each spike to be exposed to solar radiation, SL). As expected grain yield was closely related to grain number per m2. Average grain weight was reduced by shading treatments far more markedly in Sw than in SL. Interestingly, significant amounts of water soluble carbohydrates in the stems remained at maturity in SL and Sw treatments and spike photosynthesis in SL was consistently higher than in the unshaded controls in both species. These results may be an indication that wheat and barley are not source-limited during grain filling and that only when subjected to an extremely severe stress, grain size would be reduced due to lack of enough assimilates available to fill them.

The effect of planting date on maize grain yields and yield components

Four experiments were established in the Waikato and Manawatu regions of New Zealand in 2006 and 2007 to determine planting date (PD) effect on maize (Zea mays L.) leaf growth, grain yield (GY) and yield components. Five or six hybrids of three maturity classes (early, mid and late) were sown on four or five PDs between 18 September and 15 December of each year. Increasing mean daily temperatures in the range 13–19°C immediately prior to tassel initiation reduced leaf number by 0.1 leaf°C−1. Highest leaf area indices were observed at mean daily temperatures of 17–19°C. In the lower latitude environment of Waikato, maximum GY was obtained with earlier plantings than Manawatu. Lower spring temperatures, and consequently smaller canopy sizes in Manawatu depressed yields of early plantings. When planted early, late hybrids generally outyielded early hybrids while a better balanced source–sink ratio meant that early hybrids yielded consistently across PDs, matching or outyielding late hybrids when both were planted late. Lower grain filling mean temperatures (15 vs. 18°C) and average radiation (11 vs. 20MJm−2d−1) reduced yields more for late than early plantings. Grain yield was highly correlated with kernel number (KN) (r=0.90***) and weight (KW) (r=0.76***). Lowest KN, KW and GY values were obtained under late plantings, low rainfall (<20mm) and/or radiation (<18MJm−2d−1) 10–20d either side of flowering, or when mean temperatures ≤15°C or irradiance <11MJm−2d−1 occurred during grain filling. Kernel number, KW and GY responses to late planting or water stress were more apparent in late than early hybrids. Kernel weight was more stable than KN under late planting or water stress conditions. Water stress during grain filling affected late PDs more than early PDs. Total biomass and harvest index decreased with delayed planting.

Principles of Cardiac Electric Propagation and Their Implications for Re-entrant Arrhythmias

The study of clinical electrophysiology essentially comprises examining how electric excitation develops and spreads through the millions of cells that constitute the heart. Given the enormous number of cells in a human heart, there is an extremely large number of possible ways that the heart can behave. We encounter rhythms across the spectrum from the organized and orderly behavior of sinus rhythm through repetitive continuous excitation (via reentry) in structurally defined circuits like atrial flutter and, finally, the complex, dynamic, and disorganized behavior of fibrillation. Despite these myriad possibilities, one can apply a basic understanding of the principles of propagation to predict how cardiac tissue will behave under varied circumstances and in response to various manipulations. In this article, we review the principles of propagation and how these can be used to understand reentry of all degrees of complexity. We use these principles to explain the mechanisms by which antiarrhythmic medications and ablation can terminate and prevent reentry. This article is not intended to be an exhaustive description of the physiology of cardiac propagation, rather, it is meant to capture the essence of propagation with sufficient detail to provide an intuitive feel for the interplay of the physiological features relevant to propagation. The figures and videos used in this article were created using a computational model of cardiac propagation (VisibleEP LLC, Colchester, VT). It is a hybrid between a physics-based and cellular automaton model. The model incorporates the fundamental features of propagation without modeling individual ion channels.1 The model manifests several relevant emergent properties, for example, electrotonic interactions, restitution of action potential duration, and conduction velocity as well as source–sink balance–dependent propagation. ### Cell Excitation A cell becomes excited when the balance of inward and outward currents passes a critical point after which inward currents exceed outward and an action potential ensues. …

Nutrient supply has greater influence than sink strength on photosynthetic adaptation to CO2 elevation in white birch seedlings

To study the effects of source–sink ratio and nutrient supply on photosynthetic acclimation to CO2 elevation, we subjected white birch seedlings to two levels of nutrient supply (high vs. low) and CO2 concentrations (ambient vs. doubled [CO2]) for two months and then shaded the lower canopy on half of the seedlings to reduce source/sink ratio for an additional month. The CO2 elevation significantly increased Pn and IWUE at both nutrient levels but the increase was greater in the high than low nutrient treatment. The CO2 elevation resulted in a down-regulation of Vcmax in the low nutrient treatment but up-regulation of Jmax, TPU, (F′m−F)/F′m and Jc in the high nutrient after 3 months of treatment. Both the CO2 elevation and high nutrient supply increased the partition of total electron transport to carboxylation at the expense of oxidation. The seedlings responded to the shading of the lower canopy by reducing biomass allocation to roots rather than making physiological adjustments to unshaded leaves in the upper canopy. Our results suggest that the direction of photosynthetic acclimation to CO2 elevation in white birch was nutrient-dependent and an increase in sink strength could reduce the feedback inhibition of photosynthesis.

Night temperature and source-sink effects on overall growth, cell number and cell size in bell pepper ovaries.

Ovary swelling, and resultant fruit malformation, in bell pepper flowers is favoured by low night temperature or a high source-sink ratio. However, the interaction between night temperature and source-sink ratio on ovary swelling and the contribution of cell size and cell number to ovary swelling are unknown. The present research examined the interactive effects of night temperature and source-sink ratio on ovary size, cell number and cell size at anthesis in bell pepper flowers. Bell pepper plants were grown in growth chambers at night temperatures of either 20 °C (HNT) or 12 °C (LNT). Within each temperature treatment, plants bore either 0 (non-fruiting) or two developing fruits per plant. Ovary fresh weight, cell size and cell number were measured. Ovary fresh weights in non-fruiting plants grown at LNT were the largest, while fresh weights were smallest in plants grown at HNT with fruits. In general, mesocarp cell size in ovaries was largest in non-fruiting plants grown at either LNT or HNT and smallest in fruiting plants at HNT. Mesocarp cell number was greater in non-fruiting plants under LNT than in the rest of the night temperature/fruiting treatments. These responses were more marked in ovaries sampled after 18 d of treatment compared with those sampled after 40 d of treatment. Ovary fresh weight of flowers at anthesis increased 65 % in non-fruiting plants grown under LNT compared with fruiting plants grown under HNT. This increase was due primarily to increases in mesocarp cell number and size. These results indicate that the combined effects of LNT and high source-sink ratio on ovary swelling are additive. Furthermore, the combined effects of LNT and low source-sink ratio or HNT and high source-sink ratio can partially overcome the detrimental effects of LNT and high source-sink ratio.

Analyzing wildfire exposure and source–sink relationships on a fire prone forest landscape

We used simulation modeling to analyze wildfire exposure to social and ecological values on a 0.6millionha national forest in central Oregon, USA. We simulated 50,000 wildfires that replicated recent fire events in the area and generated detailed maps of burn probability (BP) and fire intensity distributions. We also recorded the ignition locations and size of each simulated fire and used these outputs to construct a fire source–sink ratio as the ratio of fire size to burn probability. Fire behavior was summarized for federal land management designations, including biological conservation reserves, recreational sites, managed forest, and wildland urban interface. Burn probability from the simulations ranged from 0.00001 to 0.026 within the study area (mean=0.0023), and exhibited substantial variation among and within land designations. Simulated fire behavior was broadly related to gradients in fire regimes, although the combined effects of fuel, topography, and simulated weather resulted in fine scale patterns not reflected in ecological and vegetation data. Average BP for the northern spotted owl (Strix occidentalis caurina) nesting sites ranged from 0.0002 to 0.04. Among the 130 different wildland urban interface areas, average BP varied from 0.0001 to 0.02. Spatial variation in the source–sink ratio was pronounced, and strongly affected by the continuity and arrangement of surface and canopy fuel. We discuss the management implications in terms of prioritizing fuel management activities and designing conservation strategies on fire prone landscapes within the 177millionha national forest network.

Anthocyanin content of grains in purple wheat is affected by grain position, assimilate availability and agronomic management

Purple wheat grains are a promising source of anthocyanins and have been proposed as raw material for baking. However, little information is available about the effect of physiological and management variables on grain anthocyanins. This research aimed to (i) characterize the anthocyanin dynamic of grains set at different positions within the spikelet, (ii) evaluate the effect of different source–sink ratios on anthocyanins, and (iii) assess the response of anthocyanins to magnesium fertilization and harvest timing. Four source–sink ratios (pre- and post-anthesis spike halving, spike-shading and control) and two agronomic practices (Mg fertilization and early harvesting) were evaluated in field trials. Grain position affected grain weight and anthocyanin content, decreasing at distal positions. Both variables showed positive response to higher source–sink ratio. Pre-anthesis halving increased anthocyanin content by 54 and 37% (Exps. 1 and 2), while post-anthesis halving increased this trait by 31 and 29%. Source reduction decreased anthocyanin content by 26% and 51%. Changes in anthocyanin content associated with source–sink treatments and with grain positions were the result of different maximum anthocyanin content reached by physiological maturity. Magnesium fertilization and early harvesting increased anthocyanin content and concentration by 65 and 39%, respectively, seeming promising to increase anthocyanins in purple wheat.

EFFECT OF LEAF-TO-FRUIT RATIO AND GIRDLING ON GAS EXCHANGES, FRUIT GROWTH AND CARBOHYDRATE CONTENTS AT DIFFERENT STAGES OF FRUIT DEVELOPMENT OF OLEA EUROPAEA L. 'PICHOLINE'

ISHS XXVIII International Horticultural Congress on Science and Horticulture for People (IHC2010): Olive Trends Symposium - From the Olive Tree to Olive Oil: New Trends and Future Challenges EFFECT OF LEAF-TO-FRUIT RATIO AND GIRDLING ON GAS EXCHANGES, FRUIT GROWTH AND CARBOHYDRATE CONTENTS AT DIFFERENT STAGES OF FRUIT DEVELOPMENT OF OLEA EUROPAEA L. 'PICHOLINE'

Variation in dry matter and nitrogen accumulation and remobilization in barley as affected by fertilization, cultivar, and source–sink relations

Barley ( Hordeum vulgare L.) is one of the most important cereals worldwide and is being increasingly grown in many areas of the world, but there is a lack of information about the physiological processes limiting grain yield. A two-year field study was conducted with the objective of determining the effect of different rates of nitrogen (N) (control, 60 kg N ha −1, and 120 kg N ha −1) on source–sink relations, dry matter and N remobilization, and grain yield. Therefore, the source–sink ratio was manipulated to examine the factor(s) limiting grain filling under rainfed conditions. The treatments were: I, control; II, half of the spike was removed; III, the entire spike was removed. The distribution of dry matter, N among grains, and culms and leaves were analyzed at anthesis and harvest. Dry matter accumulation and partitioning into different plant parts were affected by the fertilization treatments and increased as the N level increased. At anthesis, the amount of leaf + culm dry matter was greater than the amount of spike dry matter. N fertilization slightly affected the N concentration of the different plant parts at anthesis and at maturity. N content was affected by the fertilization treatments and was increased by 62% over the two years of the study compared with the control. In addition, dry matter remobilization was an average of 40% higher in the fertilized treatments compared with the control, which indicates that fertilization led plants to translocate higher amounts of dry matter. N remobilization was affected by the fertilization treatment and by the sink reduction. The spike reduction treatment increased the pre-anthesis assimilates and contribution to grain, indicating that the dry matter remobilization from vegetative tissues were very important for grain development. In contrast, N translocation efficiency was similar under sink reduction. Grain yield was determined by biomass and harvest index, and at the half spikes, there was a higher contribution at the harvest index. In addition, grain N yield was determined more by grain yield and less by the N concentration. The present study indicates that N fertilization and sink size can affect dry matter and N accumulation, partitioning, and remobilization in barley, which can affect grain yield.

Seed-yield and yield components response to source–sink ratio in annual and perennial species of Lesquerella (Brassicaceae)

Although the annual Lesquerella fendleri is the prime candidate for the development of a lesquerolic rich oil-seed crop, within this genus there are other species available to breeders, some of which are perennials. However, the feasibility of a perennial crop of Lesquerella is not clear because increases in seed-yield tend to reduce perennially. The objective of this work was to determine the effect of the source–sink ratio on seed yield and yield components in annual and perennial species of Lesquerella. We predicted that (i) due to differences in allocation patterns of annual and perennial species, seed-yield and yield components in perennials would be less affected by the source–sink ratio (higher stability) than in annuals and (ii) since seed-weight has been found to be the most stable yield component in other crops and their wild relatives, most of the variation in seed-yield as a consequence of source–sink ratios would be determined by changes in the number fruits per plant and the number of seeds per fruit. A field experiment was carried out in Chubut, Patagonia Argentina in a complete randomized design with four treatments to examine source–sink relationships in four species of Lesquerella, two annuals ( L. angustifolia, L. gracilis) and two perennials ( L. pinetorum, L. mendocina) . We used either shading (reduction of source) or removal of flower-buds (reduction of sink) to develop a range of source–sink relationships. All four species showed a similar yield response to source–sink variations. Seed-yield was lower in shaded plants, although the timing of shading influenced this response. Flower-bud removal resulted in a significant increase in seed-yield. Seed-yield differences among source–sink treatments were best explained by changes in the number of fruits per plant than by the number of seeds per fruit. Source–sink manipulations had no affect on seed weight. Flower-bud removal significantly increased the number of fruits per plant in all species except for L. mendocina. The number of seeds per fruits increased only in L. pinetorum. Our results show that carbon stored during pre-anthesis plays a key role in reproduction both in annual and perennial Lesquerella. The increase in the seed-yield components found with bud removal could potentially reduce longevity in perennial species. The results also show that the number of fruits per plant is a good proxy for seed-yield within a species.

Crop management affects dry-milling quality of flint maize kernels

Dry-milling performance of maize ( Zea mays, L.) kernels primarily depends on their hardness. The flint type is harder than the dent and semi-dent maize, yielding a higher proportion of big endosperm pieces in the mill. Nevertheless, crop growing conditions could modify milling properties. The objective of this work was to analyze the effect of different crop environments and management practices on dry-milling quality of flint maize kernels. Two orange-flint hybrids from different eras of breeding differing in flint type expression and grain yield potential were evaluated. They were grown at three different locations of the Argentina's main maize-production area under different sowing dates, plant densities, and fertilization rates during two growing seasons. Crop post-silking growth, grain yield and its components (kernel number and weight), kernel size and hardness-associated properties (test weight, percent floaters and milling ratio), and flaking-grit yield were analyzed. Most of observed differences in physical properties of kernels, particularly for the high-yielding new hybrid with unstable flint expression, were associated with the source–sink ratio established during the post-silking period (explored range from 154 to 617 mg kernel −1). This variable mainly results from changes in crop growth during that period. Increases in weight per kernel improved hardness-associated properties. High crop grain yields together with top dry-milling quality were achieved when the new high-yielding hybrid was cropped with an appropriated crop management.

Lodging yield penalties as affected by breeding in Mediterranean wheats

Stem lodging, a permanent displacement of cereal stems which may reduce wheat yields significantly, affects wheat crops in both developed and developing countries, mainly under high-yielding conditions. Although breeding has decreased these losses by reducing the likelihood of the plant lodging through reduced height (mainly by the introgression of dwarfing genes), lodging continues to affect wheat yields. We aimed to quantify how wheat breeding has modified the sensitivity of yield to lodging, identifying physiological causes for yield reductions. Two field experiments were carried out in Mediterranean Spain during the 2006/07 and 2007/08 growing seasons. The first season two genotypes (Aragon 03 and ID-2151) and two lodging treatments (control and lodged near anthesis) were analysed. The second season four genotypes (Aragon 03, Estrella, Anza and ID-2151) and three lodging treatments (control, lodged from either jointing to maturity or anthesis to maturity) were imposed. In addition, in the 2007/08 experiment the source–sink ratios of five representative spikes of each plot were modified through hand trimming all spikelets from one side of each spike soon after anthesis. Yield losses due to early lodging were reduced by wheat breeding: yield penalties in the oldest and newest genotypes were 61% and 43% (mean values of both lodging treatments), respectively while it was 57% in intermediate cultivars (mean value of both lodging treatments and cultivars). Lodging decreased both the number of grains per m 2 and the average grain weight (AGW). The decrease of the number of grains per m 2 was associated with reductions in the crop growth, while the AGW loss seemed related to both a reduction of the availability of assimilates to fill grains and a direct effect on grain size potential. Lodged plants exhibited stronger source-limitation during grain filling than those un-lodged, while the response of the grain weight to sink-strength reductions in lodged plants was very similar to that in the un-trimmed controls, indicating that grain filling in un-lodged and in strongly lodged canopies was similarly balanced in terms of source–sink ratios.

Correlation between dynamic tomato fruit-set and source-sink ratio: a common relationship for different plant densities and seasons?

It is widely accepted that fruit-set in plants is related to source-sink ratio. Despite its critical importance to yield, prediction of fruit-set remains an ongoing problem in crop models. Functional-structural plant models are potentially able to simulate organ-level plasticity of plants. To predict fruit-set, the quantitative link between source-sink ratio and fruit-set probability is analysed here via a functional-structural plant model, GreenLab. Two experiments, each with four plant densities, were carried out in a solar greenhouse during two growth seasons (started in spring and autumn). Dynamic fruit-set probability was estimated by frequent observation on inflorescences. Source and sink parameter values were obtained by fitting GreenLab outputs for the biomass of plant parts (lamina, petiole, internode, fruit), at both organ and plant level, to corresponding destructive measurements at six dates from real plants. The dynamic source-sink ratio was calculated as the ratio between biomass production and plant demand (sum of all organ sink strength) per growth cycle, both being outputs of the model. Most sink parameters were stable over multiple planting densities and seasons. From planting, source-sink ratio increased in the vegetative stage and reached a peak after fruit-set commenced, followed by a decrease of leaf appearance rate. Fruit-set probability was correlated with the source-sink ratio after the appearance of flower buds. The relationship between fruit-set probability and the most correlated source-sink ratio could be quantified by a single regression line for both experiments. The current work paves the way to predicting dynamic fruit-set using a functional structure model.

Simulation of fruit-set and trophic competition and optimization of yield advantages in six Capsicum cultivars using functional–structural plant modelling

Many indeterminate plants can have wide fluctuations in the pattern of fruit-set and harvest. Fruit-set in these types of plants depends largely on the balance between source (assimilate supply) and sink strength (assimilate demand) within the plant. This study aims to evaluate the ability of functional-structural plant models to simulate different fruit-set patterns among Capsicum cultivars through source-sink relationships. A greenhouse experiment of six Capsicum cultivars characterized with different fruit weight and fruit-set was conducted. Fruit-set patterns and potential fruit sink strength were determined through measurement. Source and sink strength of other organs were determined via the GREENLAB model, with a description of plant organ weight and dimensions according to plant topological structure established from the measured data as inputs. Parameter optimization was determined using a generalized least squares method for the entire growth cycle. Fruit sink strength differed among cultivars. Vegetative sink strength was generally lower for large-fruited cultivars than for small-fruited ones. The larger the size of the fruit, the larger variation there was in fruit-set and fruit yield. Large-fruited cultivars need a higher source-sink ratio for fruit-set, which means higher demand for assimilates. Temporal heterogeneity of fruit-set affected both number and yield of fruit. The simulation study showed that reducing heterogeneity of fruit-set was obtained by different approaches: for example, increasing source strength; decreasing vegetative sink strength, source-sink ratio for fruit-set and flower appearance rate; and harvesting individual fruits earlier before full ripeness. Simulation results showed that, when we increased source strength or decreased vegetative sink strength, fruit-set and fruit weight increased. However, no significant differences were found between large-fruited and small-fruited groups of cultivars regarding the effects of source and vegetative sink strength on fruit-set and fruit weight. When the source-sink ratio at fruit-set decreased, the number of fruit retained on the plant increased competition for assimilates with vegetative organs. Therefore, total plant and vegetative dry weights decreased, especially for large-fruited cultivars. Optimization study showed that temporal heterogeneity of fruit-set and ripening was predicted to be reduced when fruits were harvested earlier. Furthermore, there was a 20 % increase in the number of extra fruit set.

POSTHARVEST DISEASE: EFFECTS OF THE PHYSIOLOGICAL AGE OF BANANAS (MUSA SPP.) ON THEIR SUSCEPTIBILITY TO WOUND ANTHRACNOSE DUE TO COLLETOTRICHUM MUSAE

ISHS IV International Symposium on Banana: International Conference on Banana and Plantain in Africa: Harnessing International Partnerships to Increase Research Impact POSTHARVEST DISEASE: EFFECTS OF THE PHYSIOLOGICAL AGE OF BANANAS (MUSA SPP.) ON THEIR SUSCEPTIBILITY TO WOUND ANTHRACNOSE DUE TO COLLETOTRICHUM MUSAE

Characterization of the interactions between architecture and source-sink relationships in winter oilseed rape (Brassica napus) using the GreenLab model.

This study aimed to characterize the interaction between architecture and source-sink relationships in winter oilseed rape (WOSR): do the costs of ramification compromise the source-sink ratio during seed filling? The GreenLab model is a good candidate to address this question because it has been already used to describe interactions between source-sink relationships and architecture for other species. However, its adaptation to WOSR is a challenge because of the complexity of its developmental scheme, especially during the reproductive phase. Equations were added in GreenLab to compute expansion delays for ramification, flowering of each axis and photosynthesis of pods including the energetic cost of oil synthesis. Experimental field data were used to estimate morphological parameters while source-sink parameters of the model were estimated by adjustment of model outputs to the data. Ecophysiological outputs were used to assess the sources/sink relationships during the whole growth cycle. First results indicated that, at the plant scale, the model correctly simulates the dynamics of organ growth. However, at the organ scale, errors were observed that could be explained either by secondary growth that was not incorporated or by uncertainties in morphological parameters (durations of expansion and life). Ecophysiological outputs highlighted the dramatic negative impact of ramification on the source-sink ratio, as well as the decrease in this ratio during seed filling despite pod envelope photosynthesis that allowed significant biomass production to be maintained. This work is a promising first step in the construction of a structure-function model for a plant as complex as WOSR. Once tested for other environments and/or genotypes, the model can be used for studies on WOSR architectural plasticity.