Source-sink Ratio Research Articles

Effects of retained node numbers on berry maturity and yield components of cane-pruned Sauvignon blanc

Cane pruning is used in most New Zealand Sauvignon blanc vineyards to manage yield, vine balance (relationship between vegetative growth and fruit growth) and fruit primary and secondary metabolites. The source–sink ratio (TLA/FM—total leaf area to fruit mass or ELA/FM—exposed leaf area to fruit mass), the fruit mass to pruning mass (FM/PM), the fruit mass to cane mass (FM/CM) and fruit composition provide an assessment of the vine performance and balance. The interpretation of these metrics (i.e., TLA/FM, ELA/FM, FM/PM, FM/CM) requires their comparison with known optimal ranges specific to cultivars, locations and growing conditions. More often, such context- and cultivar-specific optimal ranges do not exist, thus warranting research to investigate them. To understand the influence of retained node numbers on the vegetative and fruit development of Sauvignon blanc, grapevines were pruned across three vineyard sites (two in Marlborough—Site 1 and 2, and one in Waipara—Site 3) over two growing seasons, retaining 10, 20, 30, 40 and 50 nodes on one to four canes (each cane carrying ten nodes, with 50-node vines carrying on average 12.5 nodes on each of the four canes). The accumulation of soluble solids (TSS) generally increased at lower node numbers and vine yields, reflecting an increase in ELA/FM, with 50-node vines having the least TSS concentration at harvest. The average berry mass, titrable acidity (TA) and pH were unaffected by node numbers over the two seasons. A low source–sink ratio induced by high node numbers not only reduced the vine capacity to ripen the current crop but also reduced the following season’s bunch number per shoot (from 1.8 to 1.6 bunches per shoot; p < 0.05), average bunch mass (from 82.0 ± 6 g to 67.7 ± 3 g; p < 0.01) and bunch mass per shoot (from 153.5 ± 15 g to 106.7 ± 9 g; p < 0.05). When compared to 50-node vines, 10-node vines had a two-fold increase in the average cane mass (from 30.1 ± 3.9 g to 69.2 ± 8.7 g; p < 0.001) and average old cane mass (from 82.4 ± 6.9 g to 163.8 ± 21 g; p < 0.001). The ELA/FM and TLA/FM required for optimal TSS accumulation were 0.75 m2 kg-1 and 2.0 m2 kg-1, respectively, across all sites. A source–sink ratio above these values resulted in high average cane mass and average old cane mass (an indication of excess vigour), while lower values indicated reduced vigour and slowed TSS accumulation. This research provides useful optimal ranges to compare and interpret vine balance metrics measured at those sites.

PostBP: A Python library to analyze outputs from wildfire growth models

Wildfire is an important natural disturbance agent in Canadian forests, but it has also caused significant economic damage nationwide. Spatial fire growth models have emerged as important tools for representing wildfire dynamics across diverse landscapes, enabling the mapping of key wildfire hazard metrics such as location-specific burn probabilities or likelihoods of fire ignition. While these summary metrics have gained popularity, they often fall short in capturing the directional spread of wildfires and their potential spread distances. The metrics depicting the directional spread of wildfire can be derived from raw outputs generated with fire growth models, such as the perimeters and ignition locations of individual fires, but extracting this information requires complex data processing. To address this data gap, we present PostBP, an open-source Python package designed for post-processing the raw outputs of fire growth models — the ignition locations and perimeters of individual fires simulated over multiple stochastic iterations — into a matrix of fire spread likelihoods between all pairs of forest patches in a landscape. The PostBP also generates several other summary outputs, such as the source-sink ratio and the fire spread rose diagram. We provide an overview of PostBP's capabilities and demonstrate its practical application to a forested landscape.•Wildfire growth models generate large amounts of outputs, which are hard to summarize for practical decision-making.•The PostBP package calculates the summary metrics characterizing the directional spread of wildfires.•The fire risk summaries generated with PostBP can support the assessments of wildfire risk and mitigation measures.

Evaluation of source–sink manipulation through defoliation treatments in promising bread wheat lines under optimal irrigation and rainfed conditions

The source–sink (S-S) ratio during the grain-filling period is crucial for wheat crop yield. The aim of this study was to investigate the relative sensitivity of grain yield in response to treatments of S-S ratio changes to determine the extent of S-S limitation during grain filling in modern wheat genotypes. The S-S manipulation treatments included four levels: check (CH), removal of flag leaf (RFL), removal of all leaves (RAL), and removal of the upper half of the spikes (RHS). The results showed significant differences between genotypes (pb< 0.001%) in all traits. Drought stress decreased grain weight per spike (GWS) (g) and grain yield (GY) (kg/ha) by 18% and 25%, respectively. The average reduction in GWS under irrigation and rainfed conditions was 8.25% and 6.71% for RFL and 12.25% and 11.15% for RAL, respectively. By RFL and RAL, increasing the remobilization from the stem and spike straw helped to reduce the effects of source limitation. Also, by RHS, the reduction in photosynthetic materials production in both conditions was only equivalent to 38% and 29% of the expected values, respectively, which shows the presence of strong sinks in vegetative organs (stem and spike) compared to grains. Vegetative organs seem to have a larger sink for the uptake of photosynthetic materials than grains when the source–sink ratio increases. However, high-yield genotypes showed more severe source limitation, while low-yield genotypes showed more relative sink limitation. Overall, to increase the yield potential in high-yielding genotypes, photosynthetic sources and sinks in low-yielding genotypes should be improved.

Response of carbon fixation, allocation, and growth to source-sink manipulation by defoliation in vegetative citrus trees.

Source-sink balance in plants determines carbon distribution, and altering it can impact carbon fixation, transport, and allocation. We aimed to investigate the effect of altered source-sink ratios on carbon fixation, transport, and distribution in 'Valencia' sweet orange (Citrus x sinensis) by various defoliation treatments (0%, 33%, 66%, and 83% leaf removal). Gas exchange parameters were measured on 0 and 10 days after defoliation using A/Ci response curves, and leaf export was measured two days after defoliation using radioisotope tracer techniques. Greater defoliation increased the maximum rate of carboxylation (Vcmax), electron transport rate (J1200), and triose-phosphate utilization rate (TPU). Leaf export was unaffected by defoliation but increased in leaves closer to the shoot apex. Basipetal translocation velocity in the trunk remained unaltered, indicating that more photosynthates remained in the shoot rather than being transported directly to the root sink. Defoliated plants initiated more new flush shoots but accumulated less shoot biomass per plant after 8 weeks. Carbon allocation to fine roots was smaller in defoliated plants, suggesting defoliation led to retention of carbohydrates in aboveground organs such as the trunk and other shoots from previous growing cycles. In conclusion, the low source-sink ratio increased carbon fixation without impacting individual leaf export in citrus. The results suggest that intermediate sinks such as the aboveground perennial organs play a role in mediating the translocation velocity. Further research is necessary to better understand the dynamics of source-sink regulation in citrus trees.

The critical period for yield and grain protein determination in quinoa (Chenopodium quinoa Willd.)

Context or problemDespite its global significance as a highly nutritious food, the critical period for grain yield and grain protein determination of quinoa has not yet been identified. Objective or research questionThis study aimed to determine the critical period of grain number, yield, and grain protein of quinoa in contrasting environments of South America. MethodsFive experiments were conducted in contrasting South American environments, including Argentina, Chile, Ecuador, and Peru, from latitudes 4°S to 39°S, and between 19 and 2165 m.a.s.l. Treatments consisted of the factorial combination of two quinoa cultivars (except in Peru, where only one genotype was used) and 4–9 shading treatments (50–85% shade) applied over 10–20 days throughout the crop cycle, depending on the site and the length of the crop cycle. We evaluated how GY, its components, and grain protein responded to the reduction of the source-sink ratio at different phenological stages. ResultsYield of unstressed controls varied from 2.2 t ha−1 in Lima to 9.8 t ha−1 recorded in Valdivia. The grain protein concentration ranged between 12.6% in Lima and 16.8% in Loja. The most sensitive yield-determining period was between –26 and 445 °Cd from flowering across genotypes and environments. Grain protein concentration increased by up to 19% when the source of assimilates was reduced after anthesis; however, this was insufficient to compensate for the protein yield that was affected by the reduction in grain yield due to shading. ConclusionsThe critical period for quinoa grain yield was determined throughout the flowering and grain-filling stages across genotypes and environments, mainly due to a decrease in both grain number and above-ground biomass. Implications or significanceIdentifying the critical period provides a useful target for breeding and management strategies to increase the quinoa crop yield.

Exploring the responses of crop photosynthesis to CO2 elevation at the molecular, physiological, and morphological levels toward increasing crop production

Exploring the impact of elevated CO2 on photosynthesis is vital for understanding plant responses to climate change. In C3 plants, elevated CO2 concentrations generally enhance CO2 assimilation by increasing chloroplast CO2 concentration. However, the underlying mechanisms are complex since photosynthesis involves multiple physiological processes operating at different time scales and varying among plant species. In this review, we focused on the responses of key photosynthetic processes in crop, including CO2 diffusion conductances such as stomatal conductance (gs), mesophyll conductance (gm), photochemical reactions, the Calvin-Benson cycle, and related metabolic pathways. Short-term exposure to elevated CO2 often decreases gs and gm while increasing the electron transport rate. However, long-term exposure to elevated CO2 can decrease photosynthetic capacity due to coordinated downregulation of multiple processes, particularly when the sink‒source ratio declines. To enhance plant productivity under elevated CO2, it is crucial to maintain or enhance sink activity and understand the CO2 response mechanisms at the molecular, physiological, and morphological levels. This review provides an update on the short- and long-term responses of gs, gm, electron transport system, and carbon assimilation metabolism to elevated CO2. Furthermore, it offers a perspective on improving crop production in the future with elevated CO2 levels.

Yield and quality traits of wheat and rapeseed in response to source-sink ratio and heat stress in post-flowering

The probability of occurrence of high temperatures and cloudiness events increases during the post-flowering period of temperate crops in the southern cone of South America. Several studies have evaluated the effect of high temperature or shading on wheat and rapeseed, but little is known about the impact of the combined effect of both stresses on the yield and grain quality of these crops during the post-flowering phase. This study aims to analyze the sensitivity and stability of wheat and rapeseed grain yield and quality in response to shading, high temperature and the combined stresses during post-flowering in two contrasting environments. Field experiments were carried out using the same wheat and rapeseed genotypes in environments with high (Valdivia, Chile) and medium (Buenos Aires, Argentina) yield potential. The treatments consisted of i) control, ii) shading stress, iii) heat stress and iv) combined shading and heat stress during the central hours of day. Portable chambers were placed on the plots at 7–10 days from anthesis in wheat and 14 days from the beginning of flowering in rapeseed, throughout 10 days. Grain yield was significantly reduced for the combined stress in wheat (−46%) and rapeseed (−39%) in Buenos Aires, but there were no differences between treatments in any crop in Valdivia. Combined stress in rapeseed produced a trade-off between grain number (−40%) and grain thousand weight (+43%) in Valdivia, while grain thousand weight was penalized (−25%) in Buenos Aires. For wheat there were no differences in grain protein in both locations, while for rapeseed protein increased due to the combined stress in Buenos Aires (+15%), no effects were recorded for grain oil in either location. Our results showed a high stability of grain weight in rapeseed to single and combined environmental stresses, with better environmental conditions during grain filling.

Do mutations modifying the leaf area (nr3) and the number of potential seeds (dfc) influence photosynthetic gas exchange characteristics in common buckwheat Fagopyrum esculentum Moench?

Contemporary buckwheat breeding in Russia is based mainly on a Mendelian mutation det. Some additional mutations are being considered for inclusion in buckwheat breeding programs. Among them are the nr3 (narrow leaf 3) and dfc (determinate floret cluster). We evaluated the effects of the mutations on both the characteristics of photosynthetic gas exchange and the number of seeds per plant. The nr3 reduces the leaf surface area by 1.4 times. The mutant plants show some compensatory increase in photosynthesis rate, which, however, is not enough to reach the level of the source ability as in the wild type since the number of seeds per plant is significantly decreased. The possibility of using this mutation in buckwheat breeding depends on the accumulation of modifiers that increase either leaf size or photosynthesis rate. The reduced number of flowers of the dfs mutation is compensated by an increase in flower fertility, and the number of seeds per plant does not change compared to the wild type. It explains the absence of differences between the dfs and wild type in terms of the photosynthesis rate. This experiment did not reveal any problems for using the dfc mutation in breeding. In general, the results of the work support the photosynthesis rate in buckwheat is regulated based on the source-sink ratio.

Triose phosphate utilization in leaves is modulated by whole-plant sink-source ratios and nitrogen budgets in rice.

Triose phosphate utilization (TPU) is a biochemical process indicating carbon sink-source (im)balance within leaves. When TPU limits leaf photosynthesis, photorespiration-associated amino acid exports probably provide an additional carbon outlet and increase leaf CO2 uptake. However, whether TPU is modulated by whole-plant sink-source relations and nitrogen (N) budgets remains unclear. We address this question by model analyses of gas-exchange data measured on leaves at three growth stages of rice plants grown at two N levels. Sink-source ratio was manipulated by panicle pruning, by using yellower-leaf variant genotypes, and by measuring photosynthesis on adaxial and abaxial leaf sides. Across all these treatments, higher leaf N content resulted in the occurrence of TPU limitation at lower intercellular CO2 concentrations. Photorespiration-associated amino acid export was greater in high-N leaves, but was smaller in yellower-leaf genotypes, panicle-pruned plants, and for abaxial measurement. The feedback inhibition of panicle pruning on rates of TPU was not always observed, presumably because panicle pruning blocked N remobilization from leaves to grains and the increased leaf N content masked feedback inhibition. The leaf-level TPU limitation was thus modulated by whole-plant sink-source relations and N budgets during rice grain filling, suggesting a close link between within-leaf and whole-plant sink limitations.

Effect of high temperature during the late seed filling period on green stem disorder in soybean

ContextGreen stem disorder (GSD) in soybeans is a condition wherein delayed leaf and stem maturation at harvest negatively affects harvest efficiency and seed quality. Biotic and abiotic stresses promote GSD, which is mediated by sink limitations at the flowering and pod setting stages. Previous studies have suggested that high-temperature stress promotes GSD. However, the critical growth period and its mechanisms have not yet been elucidated. ObjectiveThe present study investigated the relationship between temperature and GSD severity in growth chambers and fields. MethodsThe study was conducted in two parts. First, the effects of high temperature on GSD (30/25 ℃, day/night) at different growth stages were analyzed in growth chambers. Second, field experiments were conducted to verify the relationship between temperature during the late seed-filling period and GSD severity. Three near-isogenic lines (NILs) with different combinations of maturation genes, E1, E2, and E3, were cultivated on three sowing dates (June, July, and August) for two years. ResultsHigh temperatures in the late seed-filling period significantly promoted GSD severity, whereas high temperatures in the early seed-filling period had no effect on GSD. Sink size did not decrease with high-temperature treatments. The field experiment in 2019 also revealed a positive correlation between GSD severity and mean temperature during the late seed-filling period, whereas mean temperature before the seed-filling period showed no correlation with GSD. Temperatures during the late seed-filling period accounted for GSD suppression in the late-maturation genotype and late sowing dates, whereas the early maturation genotype had an unknown mechanism to promote GSD. On the other hand, in the field experiment in 2020, ratio of source ability to sink size became lower than in 2019 because of higher solar radiation during sowing to R1 period increased sink size. As a result, in 2020, the effect of temperature relatively low compared to the effect of source-sink ratio. ConclusionThe findings indicate that high temperatures during the late seed-filling period promoted GSD. Sink limitations were not the cause of the phenomena. Annual variation of GSD occurrences could be explained by considering effects of both temperature and solar radiation in the specific growth stage. The late seed-filling period corresponds to autumn during the soybean cropping season. Therefore, the phenomena revealed in this study could be responsible for the GSD occurrences promoted by global warming in soybean fields. ImplicationsThis study facilitates selecting appropriate soybean cropping seasons and cultivars for each area to avoid GSD occurrence.

Interactive effect of branch source-sink ratio and leaf aging on photosynthesis in pistachio.

Tree source-sink ratio has a predominant and complex impact on tree performance and can affect multiple physiological processes including vegetative and reproductive growth, water and nutrient use, photosynthesis, and productivity. In this study, we manipulated the branch level source-sink ratio by reduction of photosynthetic activity (partial branch defoliation) or thinning branch fruit load early in the growing season (after fruit set) in pistachio (Pistacia vera) trees. We then characterized the leaf photosynthetic light response curves through leaf aging. In addition, we determined changes in leaf non-structural carbohydrates (NSC) and nitrogen (N) concentrations. In leaves with high source-sink ratios, there was a gradual decrease in maximum net photosynthetic rate (ANmax) over the growing season, while in branches with low source-sink ratios, there was a sharp decline in ANmax in the first two weeks of August. Branches with high-sink showed an up-regulation (increase) in photosynthesis toward the end of July (at 1,500 growing degree days) during the period of rapid kernel growth rate and increased sink strength, with ANmax being about 7 μmol m-1 s-1 higher than in branches with low-sink. In August, low source-sink ratios precipitated leaf senescence, resulting in a drastic ANmax decline, from 25 to 8 μmol m-1 s-1 (70% drop in two weeks). This reduction was associated with the accumulation of NSC in the leaves from 20 to 30 mg g-1. The mechanisms of ANmax reduction differ between the two treatments. Lower photosynthetic rates of 8-10 μmol m-1 s-1 late in the season were associated with lower N levels in high-sink branches, suggesting N remobilization to the kernels. Lower photosynthesis late in the season was associated with lower respiration rates in low-source branches, indicating prioritization of assimilates to storage. These results can facilitate the adaptation of management practices to tree crop load changes in alternate bearing species.

Crop/Plant Modeling Supports Plant Breeding: II. Guidance of Functional Plant Phenotyping for Trait Discovery.

Observable morphological traits are widely employed in plant phenotyping for breeding use, which are often the external phenotypes driven by a chain of functional actions in plants. Identifying and phenotyping inherently functional traits for crop improvement toward high yields or adaptation to harsh environments remains a major challenge. Prediction of whole-plant performance in functional-structural plant models (FSPMs) is driven by plant growth algorithms based on organ scale wrapped up with micro-environments. In particular, the models are flexible for scaling down or up through specific functions at the organ nexus, allowing the prediction of crop system behaviors from the genome to the field. As such, by virtue of FSPMs, model parameters that determine organogenesis, development, biomass production, allocation, and morphogenesis from a molecular to the whole plant level can be profiled systematically and made readily available for phenotyping. FSPMs can provide rich functional traits representing biological regulatory mechanisms at various scales in a dynamic system, e.g., Rubisco carboxylation rate, mesophyll conductance, specific leaf nitrogen, radiation use efficiency, and source-sink ratio apart from morphological traits. High-throughput phenotyping such traits is also discussed, which provides an unprecedented opportunity to evolve FSPMs. This will accelerate the co-evolution of FSPMs and plant phenomics, and thus improving breeding efficiency. To expand the great promise of FSPMs in crop science, FSPMs still need more effort in multiscale, mechanistic, reproductive organ, and root system modeling. In summary, this study demonstrates that FSPMs are invaluable tools in guiding functional trait phenotyping at various scales and can thus provide abundant functional targets for phenotyping toward crop improvement.

Alternative Approaches to Chemical Thinning for Regulating Crop Load and Alternate Bearing in Apple

In the past, chemical thinning dominated in fruit orchards. This paper for the special issue outlines alternatives to chemical thinning for crop load management (CLM) and its effect on fruit size, firmness, sugar, starch, and weight, indicating ripeness and fruit quality, yield, and alternate bearing. A total of 450 apple trees (Malus domestica Borkh., cv. ‘Roter Boskoop’; six years old) on M9 rootstock were used at the Klein-Altendorf experimental station (50° N) of the University of Bonn, Germany. As the first alternatives, trees were mechanically blossom-thinned at the balloon stage (BBCH 59) with a rotor speed of 320 rpm or 380 rpm at 5 km/h tractor speed or were chemically thinned at the full bloom stage (BBCH 65) with ammonium thiosulfate (ATS), ethephon (ETH), and/or 6-benzyladenine (BA) at 10–12 mm fruit size (BBCH 71) after applying ATS/ETH. Flower clusters and/or cluster leaves (source) were manually removed to determine the optimum sink-source ratio to achieve different ratios of fruitlets (sink) relative to the leaves (source) at fruit set (BBCH 67–69). Un-thinned, adjacent trees served as the control. The majority of CLM methods improved fruit size and weight. Removing cluster leaves at fruit set increased fruit size and weight of the remaining fruit, which has not been observed before. The most effective treatment for fruit size and weight and return bloom was the 75% flower cluster and complete cluster leaf removal. Removal of more than 50% of flower clusters successfully improved return bloom, indicative of alternate bearing. The mechanical blossom thinning had a positive effect on fruit size and weight with a return bloom similar to that of removal of 50% flower clusters.

Physiological and Agronomic Mechanisms Involved in ‘Source–Sink’ Relationship in the High-Yield Population of Weak-Gluten Wheat

In order to provide a theoretical basis and technical approach for the construction and regulation of medium- and high-yield population cultivation practice of wheat after rice, agronomic and physiological characteristics in medium-high yielding populations were investigated by setting different basic seedlings and cutting leaves and ears with isotope tracing method in week-gluten wheat (Ningmai 29). The results showed that the medium-high yield (yield above 7500 kg/km2) group could be achieved at medium densities (150 × 104/hm2 and 225 × 104/hm2), whose populations own suitable number of spikes, higher grain number per spike and thousand-grain weight (the larger and stronger ‘sink’). Meanwhile, these two medium-high yielding populations had higher leaf area index and suitable light-transmission rate after anthesis; thus, the leaf net photosynthetic rate after anthesis was higher, and the capacity of carbon assimilates was stronger. From the 15N test, it can be seen that the relationship between individuals in the medium-high yielding population (medium-density) is more harmonious, and the plant had higher nitrogen utilization efficiency. More nitrogen is concentrated in the spike at maturity. The results of the 13C pot trials showed that the top-three functional leaves had a higher capacity for source-production, which was also the main source of post-flowering assimilates. Increasing their area to improve the ‘source–sink’ ratio would help coordinate the ‘source–sink’ relationship in the group with a stronger ‘sink’. The main technical approach is to increase the area and duration of the upper-three functional leaves after anthesis on the basis of a larger sink, thus ensuring a higher source–sink ratio and a harmonious ‘source–sink’ relationship after flowering.

Post-veraison increase in source-sink ratio via manipulation of sink availability gradually reduces leaf functionality in grapevine (cv. Pinot noir)

The vegetative-reproductive balance is critical in determining grapevine quality and productivity. Many agricultural practices (bunch thinning, defoliation, green pruning) can modify the source-sink relationships leading to altered vineyard efficiency and berry quality. Field experiments aimed at understanding how a decrease in sink availability influences leaf physiology of the reproductive shoot. In Pinot noir trained to guyot, control shoots were compared to shoots subjected to basal girdling (G), bunch removal (BR) or a combination of both treatments (G + BR). Morpho-physiological traits including leaf water status, gas-exchange, leaf temperature, chlorophyll fluorescence, leaf starch and soluble sugars, petiole and leaf dry weight were collected at different time of the day and over several days to evaluate the dynamics of leaf functionality following treatments application. The gradual reduction in sink availability induced significant reductions in leaf gas-exchange and PSII efficiency from the second day after the treatments’ application. Nonetheless, while reductions in photosynthetic capacity and increases in leaf temperature associated with a compromised stomatal physiology were present in the G + BR shoots, no differences were observed between bunch removal and control treatments. Girdling and G + BR showed a significant reduction in leaf chlorophyll a and b as well as carotenoids content when compared to control shoots. The increase in the source-sink ratio subsequently produced a marked increase in leaf starch, hexoses and sucrose accompanied by a reduction in the specific leaf area while the girdling did not affect the weight and brix degree of the bunches. This work shows how the progressive reduction in sink availability compromises leaf physiological functionality putatively owing to a reduction in assimilates translocation capacity from the leaf and hence starch storage and accumulation. However, limited effects were observed for shoots in which only the bunch was removed suggesting that assimilates allocation to other vegetative and/or reproductive sinks can maintain leaf functionality even in days characterized by unfavourable environmental conditions. • Sink availability greatly influences source dynamics • Reducing sink availability in grapevine resulted in higher diurnal susceptibility of the leaf to environmental stresses such as high VPD and air temperature • Source-sink relationships can indirectly govern water status via stomatal regulation of transpiration • Source-sink dynamics should be considered as a potential mechanism to exploit for reducing the impact of climate change in grapevine.

Strip Tillage Improves Grain Yield and Nitrogen Efficiency in Wheat under a Rice–Wheat System in China

To characterize the adaptability of strip tillage for wheat production in a rice–wheat rotation system in China, a two-year experiment was conducted. Three methods of tillage and sowing were designed, including broadcast and drill sowing following full tillage (TS1 and TS2) as well as drill sowing following strip tillage (TS3), under two planting densities. Compared to TS2, TS1 only increased seedling tiller number (by 17%–54%) at the beginning of the over-wintering stage, while TS3 improved tiller number, leaf area, and shoot weight (by 17%–39%, 14%–15%, and 19%–27%, respectively), achieving individual seedlings with improved growth vigor. An increased planting density (300 vs. 225 plants m−2) significantly promoted culms, leaf area, and shoot weight per m2 seedlings (by 8%–14%, 7%–23%, and 11%–19%, respectively) under TS3, improving seedling growth quality. The present results indicate that vigorous seedling growth promoted the potential and synergy of the source and sink (maximum leaf area, grains per m2, and sink–source ratio), thereby increasing grain yield. Furthermore, TS3 promoted nitrogen (N) uptake (by 7%–9%) compared with TS1 and TS2. The present study highlights the good adaptability and applicability of strip tillage for the environmentally conscious and efficient production of wheat in rice–wheat rotation systems.

Quantifying source-sink relationships of drip-fertigated potato under various water and potassium supplies

Water and fertilizer supply can affect the processes of assimilate production (source) and assimilate accumulation (sink), thereby causing differences in potato yield. However, little is known about the coupling effects of irrigation amount and potassium rate on potato tuber yield and its potential source-sink relationships. The objective of this study was to quantify how water and potassium supplies affected the source-sink relationships of drip-fertigated potato after tuber emergence. A two-year field experiment was conducted during the potato growing seasons of 2019 and 2020, with three irrigation levels (W1: 60% ET c , W2: 80% ET c and W3: 100% ET c , where ET c is the crop water requirements) and four potassium rates (K0: 0 kg ha -1 , K1: 135 kg ha -1 , K2: 270 kg ha -1 and K3: 405 kg ha -1 ). The results showed that compared with K0, the treatments viz ., K1, K2 and K3 increased average tuber yield by 1.3%, 17.3% and 15.5% in 2019 and 10.7%, 24.0% and 19.3% in 2020, respectively. However, compared with W3, the treatments viz ., W1 and W2 reduced the average tuber yield by 8.0% and 12.9% in 2019 and 8.9% and 14.7% in 2020, respectively. The beta sigmoid growth function well fitted the relationship of source capacity and sink capacity. The source capacity and source activity increased with the increase of potassium rate under W2 and W3 in 2019 and under W3 in 2020, while the sink capacity and sink activity first increased and then declined with the increasing potassium rate. Increasing water and potassium supply generally increased the vegetative growth and tuber growth time. The tuber growth rate first increased and then decreased with the increase of potassium rate, while it increased with the increasing irrigation amount. The sink-source ratio decreased with the increase of potassium rate, but there was no significant difference between K1 and K2, and the sink-source ratio under K3 was significantly lower than that in the other potassium treatments. It was concluded that potato was in source-sink balance under K1 and K2, but not under K3. The quantitative approach produced parameters that characterized the differences of source and sink capacity in response to various water and potassium supplies. Sufficient irrigation (W3) with moderate potassium application (K2) increased potato yield mainly by maintaining its source-sink balance. • A model approach was proposed to quantify source-sink relationships of potato under various water and potassium supplies. • The mechanism analysis of yield difference from various water and potassium supplies was conducted by source-sink balance. • Source-sink capacity was affected by different water and potassium management practices. • The sink-source ratio was not significantly different between 135 and 270 kg ha -1 , indicating the source-sink balance. • Various water and potassium application amounts influenced plant potassium absorption and tuber yield.

Kitagenki, a high-yielding rice variety, exhibits a high yield potential under optimum crop management practices

In the Hokkaido region of Japan, a new japonica-type high-yielding rice variety (HYV), Kitagenki, demonstrated higher grain yield than the early developed japonica-type HYVs; however, its yield potential is unknown. Therefore, a four-year (2015–2018) field study was conducted to elucidate the (1) yield potential of Kitagenki, (2) effect of early and late nitrogen (N) applications on the grain yield of Kitagenki, and (3) effect of early N application and planting density on the grain yield of Kitagenki. Experiment 1 consisted of three early N (10.5 N: basal 10.5 g N m−2, 16.5 N: basal 16.5 g N m−2, and 10.5 N + T1: basal 10.5 g N m−2 with topdressing of 6 g N m−2 at the panicle formation stage) combined with two late N (− T2: no topdressing at the full-heading stage, and + T2: topdressing of 6 g N m−2 at the full-heading stage) applications. Experiment 2 consisted of two early N (10.5 N and 16.5 N) applications combined with two planting densities (standard planting: 22.8–23.0 hill m−2 and sparse planting: 11.4–11.5 hill m−2). The yield potential of Kitagenki was approximately 1200 g m−2 of gross hulled grain, which is the highest yield recorded among japonica-type HYVs cultivated in Japan. In experiment 1, the grain yield of Kitagenki was improved by both early N (16.5 N, 10.5 N + T1 > 10.5 N) and late N (+ T2 > − T2) applications owing to the improved sink capacity and source ability. We suggest 10.5 N + T1 + T2 and 16.5 N + T2 as the optimum combination of early and late N applications to stably maximize the grain yield of KG. In experiment 2, the grain yield of KG was significantly improved by early N (16.5 N > 10.5 N) application but not significantly by planting density. In 16.5 N, sparse planting tended to produce a higher grain yield by lowering the lodging scores and increasing the source-sink ratio compared to those obtained with standard planting. Therefore, we suggest 16.5 N sparse planting as the optimum combination of early N application and planting density to stably maximize the grain yield of Kitagenki.

Response of Source-Sink Characteristics and Rice Quality to High Natural Field Temperature During Reproductive Stage in Irrigated Rice System.

Global warming greatly affects the development of rice at different growth stages, thereby deteriorating rice quality. However, the effect of high natural field temperature during reproductive stages on rice quality is unclear. Thus, grain filling dynamics, source-sink characteristics and quality-related traits were compared between two contrasting natural field temperature conditions namely normal (low temperature) (LRT) and hot (high temperature) growth season (HRT) during reproductive stage. Compared with LRT, HRT significantly increased chalky grain rate (about 1.6–3.1%), chalkiness level (about 4.7–22.4%), protein content (about 0.93–1.07%), pasting temperature, setback, and consistence, and decreased total starch content (about 4.6–6.2%). Moreover, HRT significantly reduced the leaf area index (LAI, about 0.54–1.11 m2 m–2), specific leaf weight (SLW, about 1.27–1.44 mg cm–2) and source-sink ratio (leaf-sink ratio and/or stem-sink ratio), shortened the active grain filling period by 3.1–3.2 days, and reduced the rations of dry matter translocation to grain (RDMs). In conclusion, we suggested that significant reduction in assimilate translocation after flowering, resulting in the reduced active grain-filling duration and the poor rice quality (high chalkiness and the poor eating and cooking quality), modulated by source-sink characteristics in response to high natural field temperature during reproductive stage. These results enriched the study of high temperature-stressed rice and served as an important reference for selecting high-quality, heat-tolerant varieties and protecting rice quality under high-temperature conditions.

Genetic differences as estimators of osmotic adjustment and source-sink balance in grapevine hybrid elites

This study deals with the best responses of a diverse collection of grapevine genotypes to osmotic stress associated with source-sink balance responses given by an estimator such as leaf area to fruit ratio. ‘Centennial Seedless’, a drought tolerant cultivar, was selected as control. The cultivars, ‘Victoria’ and ‘Argessis’, were chosen as a repetition from previous research dealing with pollen grain test, two years ago. Ten genotypes were hybrid elites in first and second hybrid generations. Three cultivars ‘Victoria’, ‘Centennial Seedless’, and ‘Argessis’ were grown under field conditions in containers, and in the soil under greenhouse conditions. Significant differences were found between genotypes for both responses to osmotic stress and source-sink balance. ‘Centennial Seedless’ and ‘BP9’ hybrid showed the best responses of induced osmotic adjustment; results confirmed the compensatory potassium uptake theory. ‘Victoria’ and ‘Argessis’ had almost the same average values as ‘Centennial Seedless’ osmotic estimator for induced osmotic adjustment. ‘Victoria’ and ‘HR7’ hybrid showed an increase in osmotic stress in the cell, after application of polyethylene glycol solutions without potassium cation and a lower source-sink ratio, which could be associated with higher photosynthesis rates. No correlations were identified between the mechanisms expressed by the analyzed estimators, indicating that they are activated and functional separately from each other, sometimes only compensatory.