Sink Ratio Research Articles

Grain yield, milling and breadmaking quality responses to foliar diseases in old and modern Argentinean wheat cultivars

Foliar diseases limit yield and modify the quality of the bread wheat. Due to genetic improvement reduced source:sink ratio, it is possible to speculate that the diseases infections penalize yield more in modern than in old cultivars, affecting differentially quality commercial and milling properties. The objective of this work was to analyze the changes in yield and quality of bread wheat due to the presence of foliar diseases in old and modern bread wheat cultivars artificially inoculated with Puccinia triticina, compared to a control plots protected with fungicide. Foliar diseases penalized yield due to reductions in the number of grains in all cultivars. Protein in grain-flour, wet-dry gluten and sedimentation were reduced when Pyrenophora tritici-repentis was the main pathogen, while Puccinia triticina only reduced the protein content in grain. Modern cultivars shower greater decreased proteins in grain-flour and gluten than old cultivars, probably associated with higher yield and lower source:sink ratio respect to the old cultivars. The changes in dough rheology and breadmaking quality, as a consequence of foliar diseases, were not as marked or as consistent as observed on milling quality, and the magnitude and direction of those effects were not as clear as those observed in milling quality.

Kernel weight responses to the photothermal environment in maize dent × flint and flint × flint hybrids

AbstractMaize (Zea mays L.) grain yield is assumed to be source limited during the flowering period but sink limited during grain growth; however, environmental restrictions during active grain filling may strongly affect final kernel weight (KW). In this study, we evaluated the effect of natural changes in photothermal conditions during lag phase (LP) and effective grain‐filling period (EGFP) on KW, its physiological determinants, and the post‐flowering source–sink relationships of flint and semident germplasm. F1 hybrids of flint × flint and dent × flint background were tested during four seasons (Y1, Y2, Y3, and Y4). Across years, the highest KW (286 mg) was obtained under the maximum photothermal quotients during LP (PTQLP = 1.18 MJ m−2 °C−1) and EGFP (PTQEGFP = 1.07 MJ m−2 °C−1) of Y2, whereas the smallest KW (252 mg) and source–sink ratio during grain filling was obtained under the lowest PTQEGFP (.79 MJ m−2 °C−1) of Y3. Supra‐optimum temperatures during LP of Y3 negatively affected potential KW determination, and hence kernel growth rate (P < .001) as a result of reduced assimilate availability per kernel. Hybrids dent × flint exhibited higher grain yield, kernel number, and plant growth around flowering than flint × flint throughout evaluated seasons but had reduced source–sink relationship during grain filling (P < .05) and increased KW sensitivity (P < .001) to changes in the photothermal conditions. Results emphasized the importance of the photothermal environment during grain filling on KW determination (particularly for seasons with great photothermal imbalance between filling subphases) as well as the dependency of KW responses on the genetic background.

Papaya (Carica papaya L.) Phenology under Different Agronomic Conditions in the Subtropics

European consumers have perceived that papaya fruits produced in subtropical areas (the Canary Islands and Mediterranean regions) do not have the desired quality at certain periods of the year. Thus, the development of technical and management strategies to optimize the yield and the quality of the fruit requires crop phenology studies. Meteorological variables (air temperature, relative humidity, and photosynthetically active radiation) and morphological characteristics (plant height, leaf emission rate, and leaf area) were recorded throughout the crop cycle. All the leaves and fruits were labeled in their anthesis week to calculate the source–sink ratio and to study the development and quality of the fruits. Data were collected in three commercial orchards representing two different types of systems, greenhouse and screenhouse, and two different regions: two plastic cover greenhouses located in the south (SP) and in the north (NP) of Tenerife, and one 40-mesh net screenhouse in the north of the island (NN). The selection of these cultivation systems and locations was made deliberately, so that the ambient variables within these crop protection structures were different throughout the cultivation cycle in order to better fit the model construction. The results suggested that in order to maintain good fruit quality, better environmental control is necessary inside the greenhouses and the screenhouse. Monitoring variables such as the growing degree days, the photosynthetically active radiation, and the number of fruits per plant leaf area ratio provided useful information for papaya production management in the Canary Islands and other subtropical areas, allowing farmers to predict harvest and fruit quality.

Identification and characterization of high-yielding, short-duration rice genotypes for tropical Asia.

Previous efforts to increase the yield of tropical rice (Oryza sativa L.) have focused on medium‐duration varieties. However, there is increasing demand for high‐yielding short‐duration varieties that can adapt to intensified cropping systems and climate change. Our goal was to identify physiological traits associated with high yield in elite short‐duration genotypes suitable for tropical Asia. We conducted field experiments in five consecutive growing seasons at the International Rice Research Institute, the Philippines. We selected genotypes in the first two seasons, then performed a detailed characterization of the most promising genotypes in the following three seasons. Of the 50 advanced‐generation genotypes, three had consistently high yield and early maturity, with yields 11 to 38% higher than that of ‘IRRI104’ (‘IR50404‐57‐2‐2‐3’), a short‐duration variety that is widely grown in Southeast Asia. These genotypes were 20 to 32 cm taller than IRRI104. We found that for grain growth, low source capacity, defined as stem nonstructural carbohydrates at heading plus biomass accumulation after heading, was the major factor for the low yield of IRRI104. Although sink capacity (spikelets m−2 × grain weight) in the promising genotypes was comparable to that of IRRI104, they had a 25 to 53% higher source–sink ratio (source capacity/sink capacity) than IRRI104, which was attributed to larger leaf area and greater biomass accumulation during the grain‐filling stage. This result suggests that slight changes in plant development to promote height combined with increased leaf area around heading would improve the yield of short‐duration rice varieties in tropical Asia.

What are the differences in yield formation among two cucumber (Cucumis sativus L.) cultivars and their F1 hybrid?

To elucidate the mechanisms underlying the differences in yield formation among two parents (P1 and P2) and their F1 hybrid of cucumber, biomass production and whole source–sink dynamics were analyzed using a functional–structural plant model (FSPM) that simulates both the number and size of individual organs. Observations of plant development and organ biomass were recorded throughout the growth periods of the plants. The GreenLab Model was used to analyze the differences in fruit setting, organ expansion, biomass production and biomass allocation. The source–sink parameters were estimated from the experimental measurements. Moreover, a particle swarm optimization algorithm (PSO) was applied to analyze whether the fruit setting is related to the source–sink ratio. The results showed that the internal source–sink ratio increased in the vegetative stage and reached a peak until the first fruit setting. The high yield of hybrid F1 is the compound result of both fruit setting and the internal source–sink ratio. The optimization results also revealed that the incremental changes in fruit weight result from the increases in sink strength and proportion of plant biomass allocation for fruits. The model-aided analysis revealed that heterosis is a result of a delicate compromise between fruit setting and fruit sink strength. The organ-level model may provide a computational approach to define the target of breeding by combination with a genetic model.

Evaluating landscape-scale wildfire exposure in northwestern Iran

We implemented a fine-scale fire modeling approach to assess wildfire exposure in the highly valued resources and assets (HVRAs) of Ardabil Province (18,000 km2), northwestern Iran. For this purpose, we used the minimum travel time algorithm and simulated 60,000 wildfires under wildfire season most frequent weather scenarios. Wildfire exposure was analyzed on different vegetation types and municipalities using burn probability (BP), conditional flame length (CFL), and fire size (FS) modeling outputs. Also, we obtained the fire potential index (FPI) and source–sink ratio metrics to assess wildfire transmission across the study area. The BP ranged from 0.0003 to 0.013 (mean = 0.0008) and varied substantially among and within the HVRAs of the study area. While the lowest BP values located in broadleaf forests, the highest BP values concentrated on flashy fuel areas, including cereal crops, mountain meadows, and grazed pastures. The average CFL was 0.3 m, with the highest values peaking in cereal crops and wooded pastures located on slopes. FS ranged from about 1–1700 ha, with an average value of 225 ha. Fires ignited in the northern part of the study area resulted in the most significant FS values, due to the large contiguous patches of high fuel loads. High FPI values were associated with large fire ignition areas and anthropic fire occurrence hotspots in the northern and southern parts of the study area. Cereal crops and grazed pastures behaved as relevant wildfire sources of fires exposing rural communities. The results of this study may help support the development of an improved wildfire risk management policy in the study area. The methods from this study could be replicated in neighboring areas and other cultural landscapes of the Middle East, where wildfires pose a threat to human assets and natural values.

Biophysical model of coral population connectivity in the Arabian/Persian Gulf.

The coral reef ecosystems of the Arabian/Persian Gulf (the Gulf) are facing profound pressure from climate change (extreme temperatures) and anthropogenic (land-use and population-related) stressors. Increasing degradation at local and regional scales has already resulted in widespread coral cover reduction. Connectivity, the transport and exchange of larvae among geographically separated populations, plays an essential role in recovery and maintenance of biodiversity and resilience of coral reef populations. Here, an oceanographic model in 3-D high-resolution was used to simulate particle dispersion of "virtual larvae." We investigated the potential physical connectivity of coral reefs among different regions in the Gulf. Simulations reveal that basin-scale circulation is responsible for broader spatial dispersion of the larvae in the central region of the Gulf, and tidally-driven currents characterized the more localized connectivity pattern in regions along the shores in the Gulf's southern part. Results suggest predominant self-recruitment of reefs with highest source and sink ratios along the Bahrain and western Qatar coasts, followed by the south eastern Qatar and continental Abu Dhabi coast. The central sector of the Gulf is suggested as recruitment source in a stepping-stone dynamics. Recruitment intensity declined moving away from the Straits of Hormuz. Connectivity varied in models assuming passive versus active mode of larvae movement. This suggests that larval behaviour needs to be taken into consideration when establishing dispersion models, and establishing conservation strategies for these vulnerable ecosystems.

Soil nutrients and lowered source:sink ratio mitigate effects of mild but not of extreme drought in trees

Little is known about environmental factors that mitigate or intensify drought effects on tree functioning. We hypothesized that higher nutrient availability and manipulations of the source:sink ratio can partially compensate negative drought effects when drought is not too severe, whilst too extreme drought can inhibit carbon and nutrient uptake and allocation irrespective of nutrient availability or the plant source:sink balance. We exposed three year-old Pinus sylvestris saplings during two subsequent years to drought using four different water supply regimes (from no drought to extreme drought) and released drought thereafter. Trees were exposed to two soil nutrient regimes. In addition, partial and full needle removal was performed. We assessed biomass, leaf gas exchange and tissue non-structural carbohydrates (NSCs). Extreme drought reduced stomatal conductance, photosynthesis, biomass and NSC, whereas intermediate drought levels only slightly affected biomass and NSC. Defoliation stimulated photosynthesis and fertilization increased growth and root biomass fraction, but mainly in the two intermediate drought levels. Only extreme drought pushed P. sylvestris trees to mortality. We conclude that tree mortality under severe drought periods will not be mitigated, but that the effects of low intensity drought stress could be compensated by increased nutrient availability and decreased source:sink ratio.

Fruit and Leaf Response to Different Source-Sink Ratios in Apple, at the Scale of the Fruit-Bearing Branch.

Apple fruit growth is the result of several factors: inherent demand (relative sink strength) of the fruit (defined by the demands for cell division and expansion growth, etc.), carbon assimilation by the source leaves (source strength), and the resulting allocation to the organ in question. It is thus a complex process involving source–sink interactions. In the present study, we designed an experimental system in which parts of fruit-bearing branches of two apple cultivars (“Fuji” and “Ariane”) were isolated from the rest of the tree by girdling and then subjected to specific pruning and fruit removal treatments to create a wide range of global (branch-level) source–sink ratios. We monitored not only fruit kinetics but also photosynthesis as a response to light in leaves of the three different shoot types (i.e., the rosette, the bourse, and the vegetative shoots) to 1) study the impact of source–sink distance on carbon partitioning between fruits within the same branch and 2) to investigate the impact of source/sink ratio on fruit growth and leaf photosynthetic activity. Our results indicate 1) no significant differences among lateral fruits belonging to different ranks, and this independent of source availability; 2) that a modification of the source/sink ratio seems to be compensated by an alteration of the photosynthetic rate of leaves, with stronger and weaker values obtained for lower and higher ratios, respectively. Moreover, our results seem to suggest that two growing sinks together will upregulate photosynthesis rate more strongly than one growing sink does on its own, and this with the same leaf area per fruit. These results are discussed, and some hypotheses are put forward to explain them.

Differential source–sink manipulation affects leaf carbohydrate and photosynthesis of early- and late-harvest nectarine varieties

Source–sink balance is a major determinant of carbon partitioning within plants. Thinning is an agronomic practice that consists of changing the ratio between leaves and fruits, the source and sink plant organs, respectively. Decreasing the fruit load on a peach tree is supposed to lead to an increase in fruit size and sometimes in soluble solid content in the remaining fruit. However, this response would change in early and late harvest peach varieties when considering the reduction in sink organs and decrease in photosynthetic process. The aim of this work was to study the effects of source–sink balance on physiological and metabolic parameters of two nectarine varieties with different fruit time development and harvest. Differential thinning was concurrently performed in trees of both varieties. Fruit development kinetics in addition to physiological parameters, such as chlorophyll fluorescence, gas-exchange, and leaf sugar composition, were determined over two harvest seasons. The decrease in photosynthetic rate in thinned trees was associated with stomata limitation and transitory sugar accumulation in leaves with sorbitol as the most abundant sugar. On the other hand, most photochemical processes remained constant in leaves of both varieties regardless of the thinning treatment. We suggest that increasing the source–sink ratio via thinning treatment leads to transient soluble sugar accumulation in the leaves and indicates an imbalance in drain capacity resulting in reduced photosynthesis and stomatal closure. In these nectarine varieties, thinning led to lower net photosynthesis but had no significant impact on final fruit size. Fruit thinning also allowed the development of other sink organs (such as vegetative suckers) and probably occurred as an acclimation process in order to maintain source–sink balance within the tree.

Electron balancing under different sink conditions reveals positive effects on photon efficiency and metabolic activity of Synechocystis sp. PCC 6803

BackgroundCyanobacteria are ideal model organisms to exploit photosynthetically derived electrons or fixed carbon for the biotechnological synthesis of high value compounds and energy carriers. Much effort is spent on the rational design of heterologous pathways to produce value-added chemicals. Much less focus is drawn on the basic physiological responses and potentials of phototrophs to deal with natural or artificial electron and carbon sinks. However, an understanding of how electron sinks influence or regulate cellular physiology is essential for the efficient application of phototrophic organisms in an industrial setting, i.e., to achieve high productivities and product yields.ResultsThe physiological responses of the cyanobacterium Synechocystis sp. PCC 6803 to electron sink variation were investigated in a systematic and quantitative manner. A variation in electron demand was achieved by providing two N sources with different degrees of reduction. By additionally varying light and CO2 availabilities, steady state conditions with strongly differing source–sink ratios were established. Balancing absorbed photons and electrons used for different metabolic processes revealed physiological responses to sink/source ratio variation. Surprisingly, an additional electron sink under light and thus energy limitation was found not to hamper growth, but was compensated by improved photosynthetic efficiency and activity. In the absence of carbon and light limitation, an increase in electron demand even stimulated carbon assimilation and growth.ConclusionThe metabolism of Synechocystis sp. PCC 6803 is highly flexible regarding the compensation of additional electron demands. Under light limitation, photosynthesis obviously does not necessarily run at its maximal capacity, possibly for the sake of robustness. Increased electron demands can even boost photosynthetic activity and growth.

Response of the Hydrological Cycle in Asian Monsoon Systems to Global Warming Through the Lens of Water Vapor Wave Activity Analysis

AbstractThe column integrated water vapor (CWV)‐based local wave activity (LWA) is adapted to examine the response of the hydrological cycle and extremes of the Asian summer monsoon in CMIP5 simulations under the RCP8.5 forcing scenario. A tight linear relationship between CWV LWA ( ) and its sink ( , which measures the intensity of the local hydrological cycle and extremes, affords a simple scaling framework for the hydrological cycle intensity in terms of the contributions from (i) ratio of moisture participating in the hydrological cycle, (ii) stirring length scale, (iii) background moisture gradient, and (iv) hydrological cycling rate. Future CWV LWA over the broad Asian monsoon region shows a large increase (~35%), attributable largely to the increase of the background moisture. The scaling analysis reveals a distinct mix of the contributing factors for the increase in between East Asian and Indian monsoon regions, despite both experiencing sizable increase of .

Estimating the upper and lower limits of kernel weight under different water regimes in hybrid maize seed production

In hybrid maize (Zea mays L.) seed production, both the kernel quality and the germination rate, which are positively related to kernel weight (KW), are very important. Water deficit can change the source–sink ratio (SSR) and thus affects KW. To create a water-saving irrigation program that facilitates the production of high-quality seed, it is necessary to properly model the KW–water relationship. Irrigation experiments were conducted in 2014 and 2015 in an arid region of Northwest China to investigate the effects of deficit irrigation on maize plant biomass and yield; and pollination experiments were conducted in 2016 to obtain a wide range of SSR and KW data. Analysis of the results showed that water deficit at the vegetative or flowering stages reduced post-flowering biomass gain (PBG) and kernel number (KN), thus significantly affecting SSR. At the grain-filling stage it reduced PBG but had no significant effect on KN, thus reducing SSR. Only the treatment of no irrigation in the grain-filling stage in 2015 significantly reduced KW. The Jensen model can accurately simulate the relationship between PBG and relative evapotranspiration at each growth stage. The water sensitivity index of PBG in the vegetative, flowering, grain-filling and ripening stages were respectively 0.48, 0.48, 0.97, and 0.16. Based on the experimental data of 2016, the hyperbolic upper (UpKW) and lower (LowKW) limit equations were created for KW as a function of SSR using boundary analysis. UpKW and LowKW increased as SSR increased, but the difference between UpKW and LowKW first increased and then decreased as SSR increased. When SSR was 0, UpKW was 178.39 mg and LowKW was 155.56 mg. When SSR is not less than 867.23 mg kernel−1, UpKW and LowKW are both 326.97 mg, which is the potential KW. Combined with the KN–water model, the models developed in this study can be used to develop a water-saving and irrigation program that produces high-quality seed.

Maize Grain Weight Sensitivity to Source–Sink Manipulations under a Wide Range of Field Conditions

Physiological causes for grain weight determination in maize (Zea mays L.) are not clear. Source–sink relationships during grain filling modulate grain weight, and there are controversies regarding the degree of source limitation that may exist during grain filling. We aimed to analyze likely causes of the responsiveness of maize grain weight to defoliation and degraining treatments imposed 15 d after silking, quantifying the responsiveness of grain weight to these source–sink manipulations in a large number of field conditions (52 background conditions in which source–sink manipulations were imposed). Grain weight was largely unresponsive to increases in source availability but was diminished by defoliations in six out of seven experiments. Interestingly, grain weight reductions due to defoliation were not hierarchical (grains from different positions along the ear responded similarly) and were not worsened by imposing a simultaneous heat stress. Heat affected the grain growth capacity directly, and indirect effects (through reducing source strength due to accelerated senescence) were not evident. The penalty imposed by heat was neither increased by defoliation nor diminished by degraining, and the reduction in grain weight was similar for grains with different potential size. Our study reinforced the concept that maize yield is limited by the sink strength during grain filling, even when grain weight may respond to reductions in the grain filling source–sink ratio.

Fruit, mesocarp, and endocarp responses to crop load and to different estimates of source: sink ratio in olive (cv. Arauco) at final harvest

Abstract The annual fluctuations in olive crop load due to alternate bearing and other factors often lead to large differences in fruit size and oil content between years at harvest. A better understanding of how fruit parameters respond to the different leaf: fruit (i.e., source: sink) ratios that occur with contrasting crop loads would provide important information for crop management. Thus, the primary objectives of this study conducted with the cv. Arauco in three growing seasons were to: 1) determine the weight and size responses of the fruit and its main tissues, mesocarp (pulp) and endocarp (pit), to crop load; and 2) obtain relationships between different estimates of the source: sink ratio versus various fruit and oil parameters. Fruit thinning was performed by hand on uniform trees with high initial crop loads four weeks after full bloom the first season to obtain different crop loads at harvest. The thinning percentages the first season were 24%, 48% and 87%, along with an unthinned control. The same trees were then monitored the following two seasons without any further thinning. Fruit were sampled at harvest each season to determine fruit and tissue weights and diameters, oil weight per fruit, and oil concentration (%). Fruit weight was reduced 30–40% by high crop loads in each growing season with the mesocarp being much more affected than the endocarp. Oil weight per fruit (−50%) showed a somewhat greater reduction than fruit weight to crop load due to both fruit diameters and fruit oil concentration being decreased at high crop loads. Fruit and tissue weights and oil weight per fruit all displayed bilinear functions versus source: sink ratio when the source was expressed as canopy volume (a surrogate for leaf area) and sink on both a fruit number and glucose equivalent (GE) basis. Source limited fruit growth at both medium and high crop loads due to limited photoassimilate availability based on the bilinear functions, and the slope of the endocarp response to source: sink ratio was 15 times less than that of the mesocarp when expressed on a GE basis. A quantitative comparison with previously published studies indicated that maximum fruit weight appears to be obtained in olive between 1–2 m2 of leaf area per kg of GE. The bilinear relationships of source: sink ratio versus fruit weight observed in this study could contribute to crop modelling, and further research concerning how and when the mesocarp and endocarp respond to crop load is needed to aid crop management in obtaining sufficient fruit size and quality for table olive cultivars.

Effects of soil type on vineyard performance and berry composition in the Río de la Plata Coast (Uruguay)

<p style="text-align: justify;"><strong>Aims:</strong> Vineyards in Uruguay are concentrated over soils formed from Quaternary sediments; however, in recent years vineyard surface over soils formed from metamorphic rocks has increased. In this context, this study assessed the relationships between soil physical properties and grapevine vegetative development, yield and berry composition, in order to understand how vine response is affected and characterize the viticultural production potential for different regions. </p><p style="text-align: justify;"><strong>Methods and results:</strong> The work was conducted from 2011 to 2014 in non-irrigated Tannat commercial vineyards located in the Río de la Plata coastal region. Roots were studied by excavating trial pits and soils were described. For each vintage, the Dryness index was estimated and pre-dawn leaf water potential was measured. Vine response (vigor, yield and berry composition) was determined for each vineyard. Three soil texture classes over two types of parent rock were observed. Vineyards on soils formed over metamorphic rocks, coarse-textured and with lower depth and water availability, had lower yield, lower vegetative development and higher concentration of compounds associated with berry quality. In contrast, vineyards on soils formed over Quaternary sediments or over metamorphic rock but with greater water availability showed the inverse response.</p><p style="text-align: justify;"><strong>Conclusion:</strong> The amount of available water in the root zone significantly affected plant growth, yield, bunch rot and berry composition.</p><p style="text-align: justify;"><strong>Significance and impact of the study:</strong> According to edaphic conditions, it is possible to optimize grapevine production within the sub-region of Río de la Plata coast by balancing the source:sink ratio for each soil through vineyard management.</p>

Does the pre-flowering period determine the potential grain weight of sunflower?

Grain weight (GW) is an important component of grain yield and quality of sunflower and the improvement of this trait has been proposed as an aim for breeding of this crop. There is strong evidence suggesting the pre-flowering period as key to determining GW in different crops; however, the key traits and mechanisms controlling GW during this phase are still largely unknown in sunflower. This study conducted a detailed survey of how the pre-flowering period determines grain growth dynamics by assessing the early developmental process during the growth of reproductive organs and the sensitivity of GW, grain number (GN) and grain oil concentration to different source–sink manipulations immediately before flowering. Two experiments were carried out under field conditions in two growing seasons. In Exp. 1 two sunflower oilseed hybrids contrasting in GW (Alybro and SG) were sown at the Experimental Station of the Universidad Austral de Chile in Valdivia (39°47′S, 73°14′W), Chile. In Exp. 2, the same hybrids plus a confectionery genotype (RHA) were evaluated in the Experimental Station where two source–sink treatments were performed: a control (without manipulation) and a shading treatment starting 16days previous to anthesis, i.e. during the R2-R5 period. Crop development, average and individual GW, GN and oil concentration of grains were assessed at harvest. Also, flower and grain traits and their dynamics were measured from early reproductive stage (ovary at R3) to harvest in different grain positions from the capitulum (e.g., fresh and dry weight and dimensions of grains, pericarp and embryo and grain oil concentration). GW was significantly affected by genotype and shading treatments imposed at pre-anthesis, but no statistical effect of the lower source–sink ratio was found on GN. Contrary to GW, grain oil of oilseed genotypes was highly conservative under the source–sink reduction in our study. Positive associations were found between final GW and: ovary weight at R3, at anthesis (R5), ovary growth rate, grain dimensions and water content. Final GW also showed a linear association with ovary growth rate. This study is the first to evaluate the ovary weight from the early development stage and the ovary growth rate during the pre-anthesis period in sunflower and the effect of source reduction at pre-anthesis on grain oil concentration, supporting the importance of the maternal tissues on the setting of potential and actual GW in sunflower.

Low source-sink ratio reduces reserve starch in grapevine woody canes and modulates sugar transport and metabolism at transcriptional and enzyme activity levels.

Severe leaf removal decreases storage starch and sucrose in grapevine cv. Cabernet Sauvignon fruiting cuttings and modulates the activity of key enzymes and the expression of sugar transporter genes. Leaf removal is an agricultural practice that has been shown to modify vineyard efficiency and grape and wine composition. In this study, we took advantage of the ability to precisely control the number of leaves to fruits in Cabernet Sauvignon fruiting cuttings to study the effect of source-sink ratios (2 (2L), 6 (6L) and 12 (12) leaves per cluster) on starch metabolism and accumulation. Starch concentration was significantly higher in canes from 6L (42.13±1.44mggDW-1) and 12L (43.50±2.85mggDW-1) than in 2L (22.72±3.10mggDW-1) plants. Moreover, carbon limitation promoted a transcriptional adjustment of genes involved in starch metabolism in grapevine woody tissues, including a decrease in the expression of the plastidic glucose-6-phosphate translocator, VvGPT1. Contrarily, the transcript levels of the gene coding the catalytic subunit VvAGPB1 of the VvAGPase complex were higher in canes from 2L plants than in 6L and 12L, which positively correlated with the biochemical activity of this enzyme. Sucrose concentration increased in canes from 2L to 6L and 12L plants, and the amount of total phenolics followed the same trend. Expression studies showed that VvSusy transcripts decreased in canes from 2L to 6L and 12L plants, which correlated with the biochemical activity of insoluble invertase, while the expression of the sugar transporters VvSUC11 and VvSUC12, together with VvSPS1, which codes an enzyme involved in sucrose synthesis, increased. Thus, sucrose seems to control starch accumulation through the adjustment of the cane sink strength.

The Effect of Partial Defoliation on Quality Characteristics of Vitis vinifera L. cv. Cabernet Sauvignon Grapes 1. Sugars, Acids and pH

The effect was studied of partial defoliation (33% and 66%) on the sugar and acid accumulation and pH in grapes of Vitis vinifera L. cv. Cabernet Sauvignon. Although the total soluble sugar (TSS) in grapes of partially defoliated vines was significantly higher than that of non-defoliated vines in some cases, no significant differences were generally found. No significant differences in total titratable acidity (TT A) were found between treatments. The timing of defoliation had no effect on TSS in grapes, whereas TT A tended to be higher the earlier partial defoliation was commenced. In general, 33 % and 66% defoliated vines respectively produced approximately 33 % and 200% more TSS and TT A in the fruit per cm2 leaf area than non-defoliated vines. No significant differences between defoliation treatments were found on a per gram dry berry mass or per berry basis for glucose and fructose or tartaric and malic acid. However, 66% defoliated vines had significantly less soluble solids in berries per shoot, which was probably caused by a lower total berry mass per shoot. Although no significant differences in sugar composition could be found between defoliation treatments, tartaric acid levels tended to be higher and malic acid levels lower as a result of partial defoliation. Partial defoliation had no effect on the accumulation patterns of sugars and acids. Glucose dominated in berries at veraison, with fructose dominating at ripeness. The highest total tartaric and malic acid concentrations occurred at pea size. Malic acid content decreased rapidly from veraison, whereas the decrease in tartaric acid was not pronounced. Must pH was not affected by partial defoliation. The results seem to suggest that the general metabolism of vines was favourably changed by partial defoliation, mainly in terms of a more favourable source: sink ratio, more efficient photosynthesis, and an improved canopy microclimate.

Kernel δ18O reflects changes in apical dominance and plant transpiration in tropical maize

AbstractModification of source–sink ratios in tropical maize through detasseling is an ancestral agronomical practice used for increasing yields under stressful conditions. However, the mechanisms behind such effect are not well understood given the difficulties to determine physiological processes such as photosynthesis and whole‐plant transpiration in the field. We have tested the potential ability of kernel δ18O to assess differences in grain yield (GY) through changes in plant transpiration caused by the modification of water availability and source–sink modification treatments, (including removal of the tassel and different numbers of leaves) in three tropical maize hybrids differing in drought tolerance. Drought‐tolerant genotypes displayed higher yields and lower kernel δ18O values than the drought‐susceptible genotype under both well‐watered (WW) and water‐stressed (WS) conditions. Detasseling caused a positive increase in GY under well‐watered (up to 8%) and water‐deficit conditions (up to 36%). Reduction in leaf area (source) through defoliation treatments caused a large impact on GY showing a trade‐off between maintaining a photosynthetic versus transpiring leaf area. Thus, while a reasonable reduction in leaf area significantly improved plant water availability (as shown by lower kernel δ18O values) and consequently GY under water deficit (up to 40%), it caused a maximum reduction of 25% in GY under well‐watered conditions. Variations in GY were significantly (p < .05) correlated with changes in δ18O under both well‐watered (r = −.67) and WS conditions (r = .75 and .82). Our results also reinforce the utility of δ18O measured in mature kernels as a powerful ecophysiological tool for assessing genotypic differences in apical dominance, transpiration and yield under both WW and WS conditions in tropical maize.