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Faba bean (Vicia faba L.) is an important component of cropping systems in cool, arid environments. However, no review has specifically focused on the quantitative sensitivity of physiological processes in faba bean to low temperature and water deficits. The objective of this review was to examine published functional relationships between physiological activity and these environmental variables. Among faba bean genotypes, temperature generally resulted in a consistent linear response in plant ontogeny and leaf area development. By contrast, nitrogen fixation exhibited a sharp threshold response to temperature such that at temperatures below ~13.5–15°C faba bean had virtually no nitrogen fixation activity. This inability to fix nitrogen under cool temperatures is likely to be a major weakness for faba bean in cool-season production systems. Water deficit also had a large impact on the physiology of faba bean. Ontogeny was generally shortened when plants were subjected to drought, resulting in major yield decreases. Genotypic differences within faba bean have been identified for initiation of partial stomata closure at high soil-water content, resulting in possible soil-water conservation in the field. Also, differences among genotypes have been identified in the sensitivity of nitrogen fixation activity to water deficits. Finally, collectively the reviewed functional relationships have been applied to simulation analysis of the geospatial impact of irrigation regimes and of sowing date for faba bean production. These geospatial studies offered insights on options to improve faba bean management.

Water and nitrogen (N) are the major limitations for maximizing crop yield. However, there has been no detailed examination of these limitations on fresh kernel yield in sweet corn (Zea mays L.). A...

Symbiotic nitrogen-fixation of soybean (Glycine max [Merr.] L) commonly decreases in response to soil drying in advance of other plant processes. While a few soybean lines express nitrogen-fixation drought tolerance, breeding for genetic variation is hampered by laborious phenotyping procedures. The objective of this research was to explore the potential of an initial screen for nitrogen-fixation drought-tolerant genotypes based on a possible relationship with xylem-vessel diameter. The hypothesis was that nitrogen-fixation drought tolerance might result from fewer, large-diameter xylem vessels in the stem that are vulnerable to disrupted flow as water deficit develops. The disrupted flow could cause nitrogen products to accumulate in nodules resulting in negative feedback on nitrogen-fixation rate. The proposed screen involved exposing de-rooted shoots to a suspension containing microspheres (45-53 μm diameter) and recording the decrease in transpiration rate as a result of microsphere xylem-blockage. Two soybean populations were tested. One population was progeny derived from mating of two parents with high and low nitrogen-fixation drought sensitivity. A high correlation (R2 = 0.68; P

Faba bean (Vicia faba L.) is a useful grain legume for production in Mediterranean climates due to its consumption as food for humans and feed for animals, and its ability to symbiotically fix atmospheric nitrogen. Currently, in Morocco a substantial fraction of faba bean is sown under a rainfed management scheme in which the crop is sown after about a 15-day delay following the first rains after the dry season. The 15-day delay allows weed seeds to germinate and be killed during land tillage prior to sowing of faba bean. However, the 15-day delay shortens the growing season and may negatively impact seed yield. Two alternate sowing date criteria were simulated for faba bean sowing date in Morocco as approaches to increase production. In addition to the 15-day delay management by farmers, sowing was simulated to occur immediately following accumulation of 10 mm or 25 mm of water in the soil. A geospatial analysis was undertaken using the SSM-faba bean model to simulate production on a 1° × 1° grid across Morocco. Eighty three locations were each simulated for 30 growing seasons of weather input. The simulation results for the 25-mm sowing date criteria resulted in decreased geographical area in which faba bean could be grown while the 10-mm sowing date criteria resulted in an expanded geographical area for faba bean production. The average yield based only on seasons in which sowing was achieved, was fairly stable among the sowing-date criteria. The probability of yield increase of the 10-mm sowing date criterion as compared to the 15-day delay sowing was greater than 50% in much of the area found suitable for faba bean production. Assuming an acceptable method for weed control for the 10-mm sowing date criterion, this alternate management could expand faba bean production in Morocco as compared to the current practice of a 15-delay in sowing date.

Low rainfall limits crop yield, particularly for maize (Zea mays L.) in southern Africa. Consequently, there is a need to identify genetic sources of specific drought-related traits that can contri...

Just behind wheat and rice, maize is the third most important grain crop in the world, grown in many agricultural areas. In Mozambique, rainfall is declining, posing serious threats to national food sovereignty and security, particularly in southern regions of the country. Despite this fact, few research studies have been conducted on the performance of Mozambique´s maize germplasm under drought stress conditions. A randomized design combining eight maize genotypes (six traditional Mozambican genotypes: LVA34, TCDE, G234, D456C, MABC, C123; and two commercial cultivars from DuPont Pioneer: P0023 and P9838) and three water regimes (control (irrigated), stress and recovery) was used to characterize the maize resilience to water deficit. The photochemical performance was accessed by rapid chlorophyll fluorescence induction curves (JIP-test). The use of Performance Index based dendrogram analysis allowed to explain genotypes behavior on the different experimental sets (control, drought stress and recovery). G234 and C123 presented the best performance with the lowest mortality rates, showing a better ability to cope with drought stress when compared to other genotypes from Mozambique and to the commercial cultivars from DuPont Pioneer.

Faba bean (Vicia faba L.) is an important traditional pulse crop in many parts of Asia and the Mediterranean region. However, water deficit and temperature, two of the key variables associated with...

Nitrogen fixation and nodule permeability to O 2 diffusion are decreased by drought stress. Since γ-aminobutyric acid (GABA) synthesis is rapidly stimulated by a variety of stress conditions including hypoxia, it was hypothesized that decreased O 2 availability in nodules stimulates glutamate decarboxylase (GAD) activity (EC 4.1.1.15), thereby resulting in GABA accumulation. First, the amino acid composition of xylem sap was determined in plants subjected to soil water deficits. While the xylem sap concentration of several amino acids increased when the plant was subjected to a water deficit, the greatest increase was in GABA. GABA accumulation was examined in response to stress induced by hypoxia or the addition of polyethylene glycol (PEG) to the nutrient solution. The exposure of soybean nodules to hypoxia for 6 h enhanced the GABA concentration by 6-fold, but there was no change in GABA concentration in response to the PEG treatment. No major changes in the in vitro GAD activity were measured in nodule cytosol or bacteroids. The present data do not support the hypothesis that decreased nodule O 2 permeability and a resulting O 2 deprivation inside nodules may stimulate in vitro GAD activity and thus GABA accumulation. However, the data could indicate a possible effect of hypoxia and drought stress on the in vivo activity of GAD.

Water-deficit conditions limit increasing crop yield around the world. In order to improve crop yield it has been proposed to decrease water use early in the season so more water will be available ...

Maintenance and recovery of the canopy area when drought stress is relieved may be critical for maintaining high productivity. In this study, experiments were conducted in controlled environments t...

As the risk of drought attributable to climate change increases, the development of high-yielding, drought-adapted cultivars will be critical for minimizing yield losses in crops like soybean (Glyc...

Symbiotic nitrogen-fixation activity of grain legumes commonly does not exhibit tolerance to soil drying, including in peanut (Arachis hypogaea L.). Since the demand for nitrogen of peanut is large...

Increasing the photosynthesis rate of plants has been recently revitalized as an approach for increasing grain crop yields and solving world food crises. The idea that photosynthesis is the key to increasing grain crop yields is not new. Considerable research in the 1970s and 1980s showed that carbon input was not limiting for crop growth and yield. Instead, the availability and uptake of water and nutrients were found to be critical for increasing grain yield, and that conclusion still applies today. In this Opinion article, nitrogen limitation is given particular attention because of its quantitative linkage with vegetative and reproductive growth and its essential role as a quantitative component of seeds.

Crop yield requires leaf area to intercept solar radiation and to undertake photosynthesis, both of which depend on nitrogen (N) accumulation. Further, the amount of accumulated plant N at ...

The beginning of the ‘Arab Spring’ in 2011, a regional revolution which started in the Tunisian city of Sidi Bouzid in late 2010, occurred in part as a result of drought-triggered high wheat prices, which in the past led to ‘bread riots’ across several Middle East and North Africa (MENA) nations. Here we present, for the first time, an analysis of possible amelioration of wheat yield loss and greater stability in bread supply resulting from the incorporation of putative drought-tolerant traits into wheat cultivars grown in Tunisia. To this end, we used a simulation crop modeling approach using SSM-Wheat to evaluate yield loss or gain resulting from three types of water-saving traits that have been recently identified in wheat. These consisted in partial stomatal closure at high soil water content, overall decrease in transpiration rate (TR), and partial stomatal closure under elevated vapor pressure deficit (VPD). To capture large gradients in seasonal precipitation across wheat growing areas over a small country such as Tunisia, a grid pattern of 29 × 29 km was established as a basis for the geospatial simulation. Surprisingly, the simulation reflected opposite strategies in terms of water use (water-saving vs aggressive water use). The highest yield gain (30%) resulting from water-saving modification was found to occur in the food-insecure region of Sidi Bouzid. Traits enabling aggressive water use were found to be generally favorable across Tunisia, with one trait leading to up to 80% and 40% increases in yield and its stability in the food-challenged south of the country. However, major yield penalties were found to occur if water-saving traits were to be deployed in the ‘wrong’ region. Those findings could be used as a blueprint to navigate complex trait × environment interactions and to better inform local breeding and management programs to improve wheat yield and it stability in Tunisia and the MENA region in general.

Two maize (Zea mays L.) lines had previously been developed, one for expression in leaves of high osmotic adjustment (HOA) and the other for low osmotic adjustment (LOA). In field, these lines diff...

Premise of the study In many cases, the functioning of a biological system cannot be correctly understood if its physical anatomy is incorrectly described. Accurate knowledge of the anatomy of soybean [Glycine max (L.) Merril] nodules and its connection with the root vasculature is important for understanding its function in supplying the plant with nitrogenous compounds. Previous two-dimensional anatomical observations of soybean nodules led to the assumption that vascular bundles terminate within the cortex of the nodule and that a single vascular bundle connects the nodule to the root. We wanted to see whether these anatomical assumptions would be verified by digitally reconstructing soybean nodules in three dimensions. Methods Nodules were dehydrated, embedded in paraffin, and cut into 15 μm thick sections. Over 200 serial sections were stained with safranin and fast green, and then photographed using light microscopy. Images were digitally cleared, aligned, and assembled into a three-dimensional (3D) volume using the Adobe program After Effects. Key results In many cases, vascular bundles had a continuous connection around the nodules. The 3D reconstruction also revealed a dual vascular connection originating in the nodule and leading to the root in 22 of the 24 nodules. Of the 22 dual connections, 11 maintained two separate vascular bundles into the root with independent connections to the root vasculature. Conclusions A more robust and complex anatomical pathway for vascular transport between nodules and root xylem in soybean plants is indicated by these observations and will contribute to a better understanding of the symbiotic relationship between soybean plants and nitrogen-fixing bacteria within the nodules.

Water deficits are the major limitation in increasing crop yields in many regions of the world. Various plant traits that might result in yield increases in water-limited environments have been discussed for decades. Conservative use of soil water is an important breeding strategy in drought-prone environments that can be achieved by traits based on partial stomatal closure under specific environmental conditions to limit transpiration rate (TR). The focus of this review is on a specific trait for conservative soil water that results in partial stomatal closure that can be supported by a plant. This limit on TR is expressed in terms of the atmospheric vapour pressure deficit (VPD) at which partial stomatal closure occurs. The review provides the physiological background of partial stomatal closure under elevated VPD. Simulation studies that analyse the potential benefits of this trait are also discussed. Finally, we provide a review of the various research that has been made in the identification of genetic variability of this trait in major crops.

International audience; The genus Vigna (Fabaceae) is an agriculturally important taxon, which includes several crop species such as cowpea (Vigna unguiculata L), mung bean (Vigna radiata) and azuki bean (Vigna angularis). Most studies have focused on cowpea (Vigna unguiculata (L.) as a drought‐resistant crop, although insights on the mechanisms that confer this species the ability to grow in dry environment are still not fully resolved. The diversity of this rich genus has been overlooked in many physiological studies. This study explores the physiological mechanisms of response to soil drying (N2 fixation, transpiration rate and changes in C and N allocation) across three species of the Vigna genus: Vigna radiata, Vigna unguiculata, Vigna vexillata (tuber cowpea). A significant variability among the studied Vigna accessions was found for the threshold in decline of N2 fixation with soil drying. Less variability was observed in the transpiration threshold. Through the analysis of leaf traits variation under well‐watered and water‐deficit conditions, we were able to relate the variability in N2 fixation and transpiration response to C/N metabolism modifications resulting in different allocation of carbon and nitrogen to leaves under water deficit.

CONTEXT Faba bean is a crucial component of Mediterranean food systems. However, the crop is somewhat underrepresented in the major crop models and usage of these models requires substantial calibration with data that might not be available. The Simple Simulation Model (SSM) is a simple, non-calibrated and physiology-based model that has the advantage of having a reduced number of parameters that can all be measured or inferred from simple experiments. OBJECTIVE We aimed to parameterize and assess the capacity of the SSM to simulate faba bean phenology, dry matter accumulation, nitrogen accumulation and final yield and to explore the impact of supplemental irrigation on crop production. MATERIALS & METHODS Model simulations were compared to observations collected over 30 experimental situations in Morocco, Tunisia, and Lebanon. SSM was then used to explore water restrictive irrigation scenarios, allowing two irrigation events after flowering, with a total irrigation dose of 50 mm, in the Middle East and in North Africa (MENA). RESULTS AND CONCLUSIONS The prediction error on final total above ground dry matter was satisfactory and the dynamics of dry matter and nitrogen accumulation in plant organs matched the observations. This study showed that 50 mm irrigation can be sufficient to substantially improve faba bean production sustainability in MENA. In the driest areas (below 200 mm in-season rainfall), 50 mm irrigation could reduce the risk of low crops by up to 34% and increase yield sufficiently to meet average farm household needs. In more humid areas of the region, 50 mm irrigation could improve faba bean yield by up to 1 t/ha compared to an average yield of 3.5 t/ha. Simulation outputs showed that deficit irrigation could improve N soil balance and soil health in the mid- to long-term. The analysis of the simulation results can be used to advise farmers on best adapted irrigation dates without additional in situ measurement. SIGNIFICANCE This study revealed that non-calibrated models such as SSM can simulate yield and dry matter accumulation with a predictive capacity similar to calibrated tools making it suitable for addressing a known gap in irrigation management for Mediterranean food systems. In the MENA region, relative small amounts of irrigation (50 mm) can substantially reduce production risk, and so increase security for farmers, and improve faba bean productivity and sustainability.

International audience; Vapor pressure deficit (VPD) is one of the critical variables that drives evapotranspiration, and is of fundamental importance in crop physiology and modeling in the face of climate change. Unfortunately, direct records of atmospheric moisture are rarely available at short temporal scales, e.g. hourly, and country or regional scales. Most models use approximations to estimate daily transpiration-weighted VPD. Tanner and Sinclair (1983) suggested an approach to calculate weighted daily VPD as a fraction (0.75) of the difference between daily maximum and minimum vapor pressure based on estimates calculated from daily maximum and minimum temperatures, respectively. A test of the Tanner-Sinclair suggestion is reported by obtaining daily weighted VPD from hourly measurements of humidity and temperature. The objective of this study was to assess the fractional value to obtained daily weighted VPD estimations. This study was based on ten years of hourly weather data collected at thirty five stations across the wide diversity of environments that exist in France.Highlights:• Weighted daily vapor pressure deficit (VPD) needed to calculate crop transpiration.• Weighted VPD proposed to be 0.75 of daily maximum VPD (Frac).• Weighted VPD assessed across the divergent climates in France.• For most climates in the Summer and Fall, Frac was in the range of 0.7–0.8.• Higher Frac values were obtained in Winter months and in sea-influenced climates.

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Assessing the food availability and food security of countries is a critical exercise in which crop simulation models are essential. Application of crop models has been limited often to estimate yield per unit area of one or a few important field crops, whereas what is really required is the total national production of diverse crops including forages, vegetables and fruit trees that compete for limited resources of land and water. In this study a simple crop model (SSM-iCrop2; Simple Simulation Models) was set up for an entire country using a bottom-up approach such that it provides representative estimates of potential yield and other crop properties at provincial level as influenced by climate, soil, management and cultivar. The information is then used to calculate total plant production at province and country levels, as influenced by available land and water resources and by the efficiency of utilizing the resources using the concepts relative yield gap and irrigation efficiency. Iran was used as a case study to develop the modeling framework and illustrative outputs. Development of the framework resulted in accumulation of large bodies of valuable geospatial information and statistics across disciplines that are critical for analysis of plant production at a country level. The framework allows different scenarios of national plant production to be evaluated. This includes assessing the possibility of increasing national plant production via intensification, optimizing water allocation across plant species at province and country levels by changing the cropping pattern, and assessing and prioritizing possible ways of adapting a country's agriculture to limited land and water resources and climate change.

International audience; Physiological and management modifications to increase crop yields require an appreciation of the impact of these changes on a geospatial basis. It is quite possible that the yield response to any modification may vary from positive in one location to negative in another location. Therefore, tools to undertake geospatial analysis are required to assess the overall impact. It is argued that mechanistic models based on the physics and physiology of plant development, growth, and yield formation are required for such tasks. Several criteria in selecting model tools are discussed. First, models that need to be "calibrated" are not suited for geospatial assessments because the calibration processes causes the model to be an empirical representation of the calibration data and limited to the calibration environment. Extreme caution is needed to extrapolate model use beyond the domain of calibration, since geospatial analysis requires the model to be run for a range of geographical locations over a number of growing seasons. Second, to readily understand the output from simulations across space and time, models needs to be compact and transparent so output that seems inconsistent or not intuitively obvious can be tracked to the critical features in the model. Models with a smaller number of parameters are likely to be more transparent. Finally, it is necessary that the robustness of the model has been tested against a range of environmental conditions. In this paper, we discuss the example of the Simple Simulation Model (SSM) as an option that meets these criteria.

Crop models are essential in undertaking large scale estimation of crop production of diverse crop species, especially in assessing food availability and climate change impacts. In this study, an existing model (SSM, Simple Simulation Models) was adapted to simulate a large number of plant species including orchard species and perennial forages. Simplification of some methods employed in the original model was necessary to deal with limited data availability for some of the plant species to be simulated. The model requires limited, readily available input information. The simulations account for plant phenology, leaf area development and senescence, dry matter accumulation, yield formation, and soil water balance in a daily time step. Parameterization of the model for new crops/cultivars is easy and straight-forward. The resultant model (SSM-iCrop2) was parameterized and tested for more than 30 crop species of Iran using numerous field experiments. Tests showed the model was robust in the predictions of crop yield and water use. Root mean square of error as percentage of observed mean for yield was 18% for grain field crops, 14% for non-grain crops 14% for vegetables and 28% for fruit trees.

Pressures on water availability for irrigation of turfgrasses continue in many parts of the United States as climate and weather patterns shift and populations increase. It is essential to understand underlying factors controlling water loss to more precisely predict irrigation requirements and develop new strategies for improving effective use of water. In this study, we investigate two key components of potential water loss from a bentgrass (Agrostis stolonifera L.) system that have not previously been examined in detail: 1) water loss in darkness, and 2) water loss through evaporation directly from the soil. The experiments were conducted in controlled environment chambers with intact cores from the field. An automated gravimetric system and soil moisture probes allowed precise measurements of water loss over ranges of vapor pressure deficits (VPD). The gravimetric and soil probe results indicated that substantial evapotranspiration occurred in darkness, at rates 40 to 60% of that in the light across VPDs. Simulations using field weather data from dry and humid environments indicated nighttime water loss rates would be expected to be 30 to 40% of that in the light. Using cores treated with a fast-acting, desiccating herbicide that eliminated transpiration but kept core resistances intact, evaporation directly from the soil surface was estimated to account for 40% of total water loss in the light and 60 to 70% in the dark. The results, collectively, indicated that water loss in darkness must be separately accounted for to accurately estimate daily evapotranspiration totals and irrigation requirements. Furthermore, because of the very high potential for evaporative water loss in the light and dark, efforts to improve water use efficiencies in the turfgrass system should include strategies that regulate both transpiration by the plant and evaporation from the soil surface.

Water is a critical limitation of crop yield in Middle East environments. Cereal production is limited to the winter months when rains occur. Options to increase the effective use of the available water to increase yield could be of direct benefit. This simulation study was undertaken for four locations in Syria that encompassed the wetter climate for wheat production in the north and the drier climate for barley production in the middle and south. Simulations were done for four sowing dates along with either the absence or presence of mulch on the soil surface. These simulations showed that sowing in early November for both barley and wheat resulted in the highest average yields among the simulated sowing dates. Surprisingly, the retention of straw mulch on the soil surface had only a small impact on yield. In most cases, yield increases were fairly modest in the range of about 4 to 9%. Since management practices to retain straw mulch in place in the field are challenging in the Syrian environment, these simulations do not indicate priority be given to developing this management practice solely for water retention.

Symbiotic N2 fixation research thus far has been primarily focused on selection of bacteria. However, little progress in impacting crop yields has resulted from this approach. Bacteria introduced in field soils rarely compete well with indigenous bacteria, including mutated lines selected for high nitrogen fixation capacity. Consequently, introduction of 'elite' bacteria in fields commonly does not result in crop yield increase. This review highlights that the primary regulation of N2 fixation is a result of response of integrated physiological activity at the plant level. Nitrogen feedback from the host plant plays an important role in regulating the N2 fixation rate. Rapid sequestration of fixed nitrogen by the plant is especially important for high N2 fixation activity. In addition, water cycling in the plant between the shoot and nodules plays a key role in sustaining high N2 fixation activity. Therefore, attention in selecting the host-plant genotype is suggested to be the next step to increasing N2 fixation activity of grain legumes.

Peanut (Arachis Hypogeae L.) is commonly grown on sandy soil and in environments with intermittent rainfall, both of which can lead to soil water-deficit. Limited transpiration (LT) under elevated ...