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Atmospheric nitrogen fixation as a result of the symbiosis between bacteria and legume species, can result in major advantages in providing host plants with organic nitrogen. The objective of the present study was to evaluate the physiological potential during early seedling development for initiation of nodulation and nitrogen fixation activity of four grain legumes species: soybean [Glycine max (L.)], cowpea [Vigna unguiculate (L.) Walp], common bean [Phaseolus vulgaris (L.)], and peanut [Arachis hypogaea (L.)]. Seedlings were grown on a hydroponic solution so that nodule development could be readily observed until about 3 weeks after germination. Nodules developed in all cases. Acetylene reduction activity (ARA) by soybean and cowpea was also found early in seedling development. In contrast, peanut and common bean showed little or no development of ARA during seedling development. The results provided insight into differences in physiological potential among grain legumes in establishing symbio...

Drought is one of the most important environmental factors that limit crop production. It has been hypothesized that a limited-transpiration trait under high vapor pressure deficit (VPD) is a mechanism for water conservation leading to yield increase under water-deficit conditions, The first research objective was to compare expression of limited-transpiration (TRlim) in lentil (Lens culinaris Medik.) observed by whole-plant measurements in controlled environments and under natural conditions outdoors during a high VPD period. Seventeen lentil genotypes were studied. All genotypes showed a linear increase with increasing VPD under natural conditions. Differences were observed among genotypes in their expression of TRE, with increasing VPD in the controlled environment. Almost all genotypes showed a VPD breakpoint at approximately 3.4 kPa. A simulation analysis was conducted across South Asia to identify where, how often, and how much this trait in lentil would benefit farmers with four different VPD breakpoint scenarios (VPD breakpoint at 3.4, 2.2, 1.1 kPa, and VPD-insensitive). Results showed that the limited-transpiration trait at a low simulated threshold (1.1 kPa) can result in improved lentil performance in drought-prone environments and that the impact of the trait on lentil productivity varies with geography and environment. The largest average yield increase was simulated for drought-prone environments (250 g m(-2)). Outcomes from this simulation study provide insights into the plausible role of the limited-transpiration trait under high VPD in future lentil genetic improvement and implies that a search for germplasm with a breakpoint as low as 1.1 kPa needs to be made.

Soybean [Glycine max (L.) Merr.] genotype PI 471938 expresses a slow-wilting phenotype in the field, and the progeny of this genotype have shown to have high yield under water deficit conditions. However, the physiological basis for the slow-wilting trait in PI 471938 remains unclear, and failure to understand the causal mechanism may limit future breeding efforts. This study investigated three primary hypotheses for trait expression that could explain slow-wilting trait in PI 471938: (1) a low osmotic potential in the leaves allowing greater water retention, (2) high elastic modulus of leaves resulting in delayed development of wilting, and (3) high hydraulic conductance allowing rapid water redistribution in the plants. Experiments included three other soybean genotypes as references for the results obtained with PI 471938. Surprisingly, the results for PI 471938 did not prove to be unique as compared to the other three tested genotypes for any of the three hypotheses. These negative results ind...

Limitations in water availability for irrigation due to drought and water-use regulations necessitate accurate approaches to estimate water use. An energy balance approach is commonly used that is inherently empirical and requires an ill-defined coefficient. An alternative is to use a relationship based on vapor pressure deficit (VPD) and plant growth to predict plant transpiration rate. This study was undertaken to evaluate these approaches for tall fescue (Festuca arundinacea Schreb.). Experiments examined differences in water loss of tall fescue plants when grown in three temperatures with varying vapor pressure deficit (VPD), and with treatments of low nutrition and of growth regulator trinexapac-ethyl, which depressed growth. Within a temperature, the low-nutrition and growth-regulator treatments greatly affected clipping mass, however water loss remained similar. In hydroponic experiments, treatments altering clipping mass did not necessarily change total plant growth. Hence, a challenge to using whole-plant growth for estimating transpiration of this grass is to accurately determine growth only from clipping data. Transpiration was positively correlated with VPD, especially within each temperature, but there were indications that the higher temperature treatments caused decreased plant control over transpiration. The instability of physiological control over transpiration highlights the potential limitations of both equations in estimating transpiration rates.

Drought can be a critical limitation on peanut yield. A physiological trait that may help to ameliorate drought is limited transpiration (TRlim), defined as a limitation on further increases in transpiration rate (TR) under high vapour pressure deficit (VPD) conditions. The advantage of the TRlim trait is that it allows plant water conservation to increase soil water availability for use during late-season drought. While this trait has been identified in peanut, there is no information of how readily the trait may be transfer to progeny lines. The objective of this study was to obtain preliminary information on the expression of the TRlim trait in two peanut progeny populations. One population was runner type of 88 RILs derived from the mating of Tifrunner × NC 3033. The second set was selected for the virginia-type phenotype of large pods obtained from mating of PI 585005 (ICGV 86015) and N0808olJCT, both of which expressed the TRlim trait. A two-tier screen was applied to both populations. The initial screen was based on exposure of de-rooted shoots to silver ions. Fifteen runner type and 12 virginia type were selected for direct measures of transpiration response to varying VPD. The results from each of the two populations showed that an effective expression of the TRlim trait occurred in about 30% of the progeny in each population. While these results do not offer a definitive index of inheritance, they do indicate that there appears to be a strong possibility of transferring the TRlim trait to progeny genotypes.

Background Drought stress is a major limiting factor of soybean [Glycine max (L.) Merr.] production around the world. Soybean plants can ameliorate this stress with improved water-saving, sustained N2 fixation during water deficits, and/or limited leaf hydraulic conductance. In this study, carbon isotope composition (δ13C), which can relate to variation in water-saving capability, was measured. Additionally, nitrogen isotope composition (δ15N) and nitrogen concentration that relate to nitrogen fixation were evaluated. Decrease in transpiration rate (DTR) of de-rooted soybean shoots in a silver nitrate (AgNO3) solution compared to deionized water under high vapor pressure deficit (VPD) conditions was used as a surrogate measurement for limited leaf hydraulic conductance. A panel of over 200 genetically diverse soybean accessions genotyped with the SoySNP50K iSelect BeadChips was evaluated for the carbon and nitrogen related traits in two field environments (Athens, GA in 2015 and 2016) and for transpiration response to AgNO3 in a growth chamber. A multiple loci linear mixed model was implemented in FarmCPU to perform genome-wide association analyses for these traits. Results Thirty two, 23, 26, and nine loci for δ13C, δ15N, nitrogen concentration, and transpiration response to AgNO3, respectively, were significantly associated with these traits. Candidate genes that relate to drought stress tolerance enhancement or response were identified near certain loci that could be targets for improving and understanding these traits. Soybean accessions with favorable breeding values were also identified. Low correlations were observed between many of the traits and the genetic loci associated with each trait were largely unique, indicating that these drought tolerance related traits are governed by different genetic loci. Conclusions The genomic regions and germplasm identified in this study can be used by breeders to understand the genetic architecture for these traits and to improve soybean drought tolerance. Phenotyping resources needed, trait heritability, and relationship to the target environment should be considered before deciding which of these traits to ultimately employ in a specific breeding program. Potential marker-assisted selection efforts could focus on loci which explain the greatest amount of phenotypic variation for each trait, but may be challenging due to the quantitative nature of these traits.

Correction de la notice https://prodinra.inra.fr/record/471516 ; 10.1007/s13593-019-0570-6; International audience; Historically, the agronomic focus of crop mineral nutrition has yielded responses to individual elements (N, P, K...) to determine the economically optimum fertilization rates. This prognostic approach required several parameters for crops, climates, and soils that are often estimated with large uncertainty leading to over-fertilization and environmental problems in some systems (e.g., maize in China), and under-fertilization and soil mining in other systems (e.g., wheat in Australia). In this review, an alternative approach is developed for reducing the uncertainty intrinsically linked to this prognostic approach. Our approach is based on four propositions: (1) the evidence of an allometry between the metabolic shoot mass (scaling with leaf area) and the structural shoot mass (supporting and vascular tissues) within plants that allows the formulation of critical N dilution curves and the determination of the Nitrogen Nutrition Index (NNI) for estimating the N nutrition status of field crops; (2) the co-regulation of crop N uptake dynamics by both soil N supply and crop N demand in relation with its growth capacity that allows a better, more generalizable estimation of timing and rate of fertilizer; (3) a better understanding of the effects of genotype-environment-management interactions on N use efficiency in cropping systems reducing then drastically uncertainties linked to the classical prognostic approach for N fertilization; (4) as P and K also relate allometrically with biomass, P and K concentrations can be directly related to N concentration for the formulation of a multi-element diagnosis of crop nutrition. Here, we develop the theoretical background supporting these four propositions and outline implications for both fertilization management and crop phenotyping.

International audience; AbstractHistorically, the agronomic focus of crop mineral nutrition has yielded responses to individual elements (N, P, K…) to determine the economically optimum fertilization rates. This “prognostic” approach required several parameters for crops, climates, and soils that are often estimated with large uncertainty leading to over-fertilization and environmental problems in some systems (e.g., maize in China), and under-fertilization and soil mining in other systems (e.g., wheat in Australia).In this review, an alternative approach is developed for reducing the uncertainty intrinsically linked to this prognostic approach. Our approach is based on four propositions: (1) the evidence of an allometry between the metabolic shoot mass (scaling with leaf area) and the structural shoot mass (supporting and vascular tissues) within plants that allows the formulation of critical N dilution curves and the determination of the Nitrogen Nutrition Index (NNI) for estimating the N nutrition status of field crops; (2) the co-regulation of crop N uptake dynamics by both soil N supply and crop N demand in relation with its growth capacity that allows a better, more generalizable estimation of timing and rate of fertilizer; (3) a better understanding of the effects of genotype–environment–management interactions on N use efficiency in cropping systems reducing then drastically uncertainties linked to the classical prognostic approach for N fertilization; (4) as P and K also relate allometrically with biomass, P and K concentrations can be directly related to N concentration for the formulation of a multi-element diagnosis of crop nutrition. Here, we develop the theoretical background supporting these four propositions and outline implications for both fertilization management and crop phenotyping.

The production of peanut (Arachis hypogaea L.) in warm environments and on sandy soils makes the crop vulnerable to soil drying in nearly every cropping season. Several traits are being explored to overcome yield decreases resulting from the inevitable water deficits that develop in the soil. In this review, two traits: (1) an early limitation on transpiration rate (TR) as the soil dries, and (2) limitation on maximum TR (TRlim) under high vapor pressure deficit (VPD) in peanut will be discussed. Both of these traits result in water conservation by limiting plant transpiration rates and are potential reasons for genetic variation in Transpiration Efficiency (TE). The basis for transpiration response to soil water deficits and high VPD at the tissue and whole plant levels appears to be leaf and root hydraulic properties. A contributing factor in determining hydraulic limitations is water transport through membranes via aquaporins (AQP). Overall, both of the two traits result in phenotypes with an ability to conserve water especially under late-season drought events. While large genetic variability in these traits has been observed in peanut, breeding efforts are still required to exploit these promising traits in commercial cultivars. This review focuses on the traits in peanut that allow identification of tolerant genotypes with potential yield increase in water-limited environments. A recent progress in molecular marker technology has made it possible to measure polymorphism in peanut and to identify molecular markers or quantitative trait loci (QTL) linked to TE and its surrogate traits despite its low levels of molecular polymorphism and complex polyploid genome. We also reviewed some of these QTLs and their potential application for molecular breeding in peanut under water-limited environments.

Historically, wheat yields in drought-prone Australian environments have been consistently increasing for over a century. There is currently an agreement that approximately half of that increase is attributable to breeding programmes, but their physiological basis remains poorly documented. In this investigation, we hypothesized that limited whole-plant transpiration rate (TR) under high atmospheric vapour pressure deficit (VPD) could result in advantageous water conservation and crop yield increase under south Australian conditions. Therefore, TR response to VPD was measured in the 0.9–3.2 kPa range for a group of 23 wheat cultivars that were released from 1890 to 2008. Consistent with a water-conservation hypothesis, all genotypes displayed a VPD break point (BP) in TR with increasing VPD such that TR was limited at VPD above a BP of about 2 kPa. The BP and slope of TR with increasing VPD above the break point were correlated with the year of release, although the changes were in different directions. Such changes in these transpiration parameters were independent of plant leaf area and only marginally correlated with Zadok's stages. These results indicated that selection over 120 years by breeders for yield increase unconsciously resulted in genotype selection for the expression of the limited-TR trait.

To avoid dehydration and drought stress, plants must balance transpirational water loss with water transport capacity to replenish water in the leaves. Therefore, changes in hydraulic conductivity (Ktotal) of the soil-plant system during soil drying may be critical in determining transpiration rates. There has, however, been little study of the changes in Ktotal with respect to decreasing volumetric soil water content. In this study, Ktotal was measured on pot-grown soybean (Glycine max (Merr.) L.) plants subjected to controlled soil drying across 2 weeks. These results showed that once soil dried to a point when there was a decrease in transpiration rate, there was a coincident decrease in Ktotal. Further, losses in soil water resulted in further decreases in Ktotal and transpiration rate. These results showed that the commonly observed pattern of decrease in transpiration rate with decreases in volumetric soil water content is intimately linked to system Ktotal.

The recovery capacity of physiological activity after rewatering is a fundamental trait in assessing crop productivity after periods of drought. The objective of this study was to document the rapidity of recovery of both transpiration rate (TR) and nitrogen fixation (NF) activity by soybean (Glycine max (Merr.) L.) plants after being subjected to defined soil water deficits. Recovery was studied for ten genotypes: two parent genotypes (PI 471938, which expressed nitrogen fixation tolerant to water deficit, and Hutcheson, which expresses nitrogen fixation sensitivity to water deficit), and eight progeny genotypes derived from the mating of these parents. This divergence in response to drought of parents and progeny lines potentially offered divergence in rate of recovery from drought stress. Four experiments were conducted in a greenhouse with three different levels of severity in drought treatments. The recovery even under severe drought was generally rapid: TR recovered in 2–3 d and NF recovered...

Soybean genotype PI 416937 has previously been found to have low leaf hydraulic conductivity, which was hypothesized to be the basis for limited transpiration (TR lim ) rates under high vapor pressure deficit. Previous studies with de-rooted shoots showed there was a consistency in the expression of TR lim and plant response to exposure to silver, an aquaporin (AQP) inhibitor. However, it is not clear what confounding influence treatments with metal AQP inhibitors may have on AQP transcript expression. This study was undertaken to extend the observations of response to silver and zinc using intact plants. In a comparison of four genotypes, intact plants of PI 416937 were uniquely insensitive to exposure to silver and of PI 471938 were uniquely insensitive to zinc. RNA abundance of eight AQPs was measured after treatment with the AQP inhibitors. There were differences in the abundance of RNA among genotypes. There was a general trend of less change in abundance in PI 416937 following silver treatment in contrast to increased abundance in the other genotypes. This result would be consistent with little or no response in transpiration rate in the intact plants of PI 416937 following silver treatment. Following zinc treatment, there was a rapid increase in RNA abundance in PI 471938 in comparison to the other genotypes. However, the changes in AQP abundance following treatment with metal inhibitors indicates the likely interaction of direct response of AQP to metals and alternation of expression of AQP transcripts. These results indicate that the results from treatment with metal inhibitors should likely be considered only as preliminary screens from which genotypes need to be tested directly for the TR lim trait.

Temperature and vapor pressure deficit (VPD) are two important environmental factors influencing stomatal conductance and transpiration. A limited transpiration rate (TRlim) trait expressed under high VPD has been shown to offer an approach to increase crop yield in water-limited areas. The benefit of the TRlim trait is that it lowers the effective VPD under which plants lose water and so conserves soil water to support crop growth for use during drought periods later in the growing season. Previous studies at moderate temperatures (32 degrees C and lower) identified 12 maize (Zea mays L.) hybrids that express the TRlim trait. A critical question is whether the TRlim trait is also expressed by these hybrids under temperatures up to 38 degrees C, which are relevant in environments where maize may be grown. Five hybrids failed to express the TRlim trait at 38 degrees C but seven hybrids had sustained expression of the trait at 38 degrees C. The loss of expression of the TRlim response in the five hybrids was found to occur in the very narrow range of temperature increase from 36 to 38 degrees C. The genetic differences in water use among these maize hybrids could be useful in selecting hybrids that are especially well adapted for temperature conditions in a targeted production area.

One plant trait that has been developed in several crop species to increase the effectiveness in water use through the cropping season is limited-transpiration under elevated atmospheric vapor pressure deficit (VPD). This trait allows water conservation early in the season so that there is more soil water available late in the season for sustained physiological activity during seed development. In sweet corn (Zea mays L. saccharata), where the quality of the kernels is important, this trait could prove to be especially beneficial. The background objective of this study was to explore 16 sweet corn cultivars for expression of the limited-transpiration trait. It was found at 32 °C that 13 of the 16 cultivars expressed the trait. It was found in a subset of eight of these cultivars, however, only half retained the limited-transpiration trait at 38 °C. The additional objectives were to explore the hypotheses that expression of the limited-transpiration trait was related to plant hydraulic conductance, and to the abundance of silver-sensitive aquaporins in the leaves. In cultivars that lost expression of the limited-transpiration trait at 38 °C there were large increases in plant hydraulic conductance at 38 °C as compared to 32 °C. Abundance of silver-sensitive aquaporins was related to the transpiration rate under low VPD conditions. That is, those cultivars with more abundant silver-sensitive aquaporins had greater transpiration rates as a result of greater stomatal conductance. These results showed that while expression of the limited-transpiration trait in sweet corn at 32 °C was common, differences in expression of the trait at 38 °C were observed due to differences in plant hydraulic conductance and stomatal conductance.

Virtually no information exists on the response of sweet corn (Zea mays L. saccharata) to nitrogen fertility and irrigation treatments in terms of leaf nitrogen accumulation and the consequent impact on leaf CO2 assimilation rate and on crop growth as measured as radiation use efficiency (RUE). A two-year field experiment was undertaken in which a sweet corn cultivar was subjected to all combinations of five nitrogen fertility and three irrigation treatments. Leaf photosynthesis measurements were made at stages of 7–9 leaves, tasseling, silking, blistering, and milking. Leaf nitrogen per unit area was also measured at these five stages plus two additional stages before and after the five core measurements. Total nitrogen and plant mass was accumulated at the seven stages to track total nitrogen accumulation and to calculate RUE. The overall patterns in the measured variables were similar to those reported for field maize. However, leaf nitrogen per unit area for sweet corn under optimum conditions was greater than reported for field maize. The higher leaf nitrogen per unit area in sweet corn did not, however, result in greater leaf photosynthesis rates and RUE than reported for field maize. The results of these unique observations on sweet corn indicate the possibility of greater nitrogen storage in sweet corn leaves that is not directly linked with photosynthesis and carbon accumulation.

In wheat, night-time transpiration rate (TRN) could amount to 14–55% of daytime transpiration rate (TR), depending on the cultivar and environment. Recent evidence suggests that TRN is much less responsive to soil drying than daytime TR, and that such ‘wasteful’ water losses would increase the impact of drought on yields. In contrast, other evidence indicates that pre-dawn, circadian increases in TRN may enable enhanced radiation use efficiency, resulting in increased productivity under water deficit. Until now, there have been no attempts to evaluate these seemingly conflicting hypotheses in terms of their impact on yields in any crop. Here, using the Mediterranean environment of Tunisia as a case study, we undertook a simulation modelling approach using SSM-Wheat to evaluate yield outcomes resulting from these TRN trait modifications. TRN represented 15% of daytime TR-generated yield penalties of up to 20%, and these worsened when TRN was not sensitive to soil drying TR. For the same TRN level (15%), simulating a predawn increase in TRN alleviated yield penalties, leading to yield gains of up to 25%. Overall, this work suggests that decreasing TRN but increasing pre-dawn circadian control would be a viable breeding target to increase drought tolerance in a Mediterranean environment.

Slow canopy wilting (SW) is a water conservation trait controlled by quantitative trait loci (QTLs) in late maturity group soybeans [Glycine max (L.) Merr.]. Recently, two exotic (landraces) plant introductions (PI 567690 and PI 567731) were identified as new SW lines in early maturity groups. Here, we show that the two PIs share the same water conservation strategy of limited maximum transpiration rates as PI 416937. However, in contrast to PI 416937, the transpiration rates of these PIs were sensitive to an aquaporin inhibitor, indicating an independence between limited maximum transpiration and the lack of silver-sensitive aquaporins. Yield tests of selected recombinant inbred lines from two elite/exotic crosses provide direct evidence to support the benefit of SW in drought tolerance. Four SW QTLs mapped in a Pana×PI 567690 cross at multiple environments were found to be co-located with previous reports. Moreover, two new SW QTLs were mapped on chromosomes 6 and 10 from a Magellan×PI 567731 cross. These two QTLs explain the observed relatively large contributions of 20-30% and were confirmed in a near-isogenic background. These findings demonstrate the importance of SW in yield protection under drought and provide genetic resources for improving drought tolerance in early maturity group soybeans.

The phenomenological expression showing crop yield to be directly dependent on crop transpiration use efficiency (TE) has encourage continued focus on TE as a viable approach to increasing crop yields. The difficulty in the phenomenological perspective is that research tends not to match with the underlying mechanistic variables defining TE. Experimental evidence and the mechanistic derivation of TE by Tanner and Sinclair show that the common focus on increasing the intrinsic ratio of leaf CO2 / H2O exchange has limited opportunities for improvement. On the other hand, the derivation showed that daily vapor pressure deficit (VPD) weighted for the daily cycle of transpiration rate has a large, direct impact on TE. However, VPD is often viewed as an environmental variable although daily weighted VPD can be under plant control as a result of partial stomatal closure during the midday. Such partial stomatal closure results in decreased weighted VPD and transpiration rate, there can be substantial conservation of soil water. The conserved soil water allows sustained physiological activity during subsequent periods of developing water deficits, which can be especially beneficial during reproductive development. The shift in the temporal dynamics of water use by water conservations traits has been shown in simulation studies to result in substantial yield increases. It is suggested from this analysis that effective water use through the growing season is more important for increasing crop yield than attempts focused on improving the static, intrinsic TE ratio.

In plants, aquaporins (AQP) occur in multiple isoforms in both plasmalemma and tonoplast membranes resulting in regulation of water flow in and out of cells, and ultimately, water transfer through a series of cells in leaves and roots. Consequently, it is not surprising that physiological and molecular studies have identified AQPs as playing key roles in regulating hydraulic conductance in roots and leaves. As a result, the activity of AQPs influences a range of physiological processes including phloem loading, xylem water exit, stomatal aperture and gas exchange. The influence of AQPs on hydraulic conductance in plants is particularly important in regulating plant transpiration rate, particularly under conditions of developing soil water-deficit stress and elevated atmospheric vapor pressure deficit (VPD). In this review, we examine the impact of AQP activity and hydraulic conductance on crop water use and the identification of genotypes that express soil water conservation as a result of these traits. An important outcome of this research has been the identification and commercialization of cultivars of peanut (Arachis hypogaea L.), maize (Zea mays L.), and soybean (Glycine max (Merr) L.) for dry land production systems.

International audience; Nitrogen (N) accumulation in legumes is one of the main determinants of crop yield. Although N accumulation from symbiotic nitrogen fixation or N absorption from the soil has been widely investigated, there is no clear consensus on timing of the beginning of N accumulation and the termination of N accumulation and the physiological events that may be associated with these two events. The analyses conducted in this study aimed at identifying the determinant of N accumulation in two grain legume species. Nitrogen accumulation dynamics and mass accumulation and development stages were recorded in the field for several genotypes of common bean (Phaseolus vulgaris) and faba bean (Vicia faba) under different growing conditions. This study showed that during the vegetative stages, N accumulation rate was correlated with mass accumulation rate. However, the maximum accumulation of N did not correspond to the time of the maximum mass accumulation. In fact, for both species, N accumulation was found to persist in seed growth. This challenges a common hypothesis that seed growth causes a decrease in N accumulation because of a shift of the photosynthate supply to support the seed growth. Even more surprising was the shift of the active accumulation of N in faba bean to late in the growing season as compared with common bean. N accumulation by faba bean only was initiated at high rates very late in vegetative growth and persisted at high rates well into seed fill.

Yield loss due to water deficit is ubiquitous in maize (Zea mays L.) production environments in the United States. The impact of water deficits on yield depends on the cropping system management and physiological characteristics of the hybrid. Genotypic diversity among maize hybrids in the transpiration response to vapor pressure deficit (VPD) indicates that a limited-transpiration trait may contribute to improved drought tolerance and yield in maize. By limiting transpiration at VPD above a VPD threshold, this trait can increase both daily transpiration efficiency and water availability for lateseason use. Reduced water use, however, may compromise yield potential. The complexity associated with genotype X environment X management interactions can be explored in a quantitative assessment using a simulation model. A simulation study was conducted to assess the likely effect of genotypic variation in limited-transpiration rate on yield performance of maize at a regional scale in the United States. We demonstrated that the limited-transpiration trait can result in improved maize performance in drought-prone environments and that the impact of the trait on maize productivity varies with geography, environment type, expression of the trait, and plant density. The largest average yield increase was simulated for drought-prone environments (135 g m(-2)), while a small yield penalty was simulated for environments where water was not limiting (-33 g m(-2)). Outcomes from this simulation study help interpret the ubiquitous nature of variation for the limited-transpiration trait in maize germplasm and provide insights into the plausible role of the trait in past and future maize genetic improvement.

International audience; Lentil (Lens culinaris Medik.) is a major crop highly valued in the food and nutritional security of millions of people, as well as a rotation crop. Lentil is grown in areas facing many environmental constraints from low moisture availability and high temperatures to winter cold at high elevations. The use of an appropriate and robust crop model can off er mechanistic bases for exploring and extrapolating the impact of a given plant trait or crop management across a range of environments. First, we used the generic SSM-Legumes model to develop a simple and transparent lentil model. The SSM-Legumes model had a robust predictive capability to assess variation in the phenological development and yield of lentil in three locations in the Middle East (Lebanon and Syria) with large differences in rainfall. The agreement between simulated and observed days to flowering or maturity and yield showed the robustness of the model in predicting lentil growth and yield. Second, we incorporated into SSM-legumes a submodel allowing a more realistic accounting of crop survival at very low soil water content, resulting in more realistic predictions of lentil growth and yield. Third, we used the model to test the potential for increasing lentil yields by the retention of crop residue on the soil surface to decrease soil evaporation. Our results showed yield increases of up to 25% in all three locations from the retention of previous crop residues.

A limited-transpiration (TR lim ) trait has been identified in many crop species, including sorghum ( Sorghum bicolor (L.) Moench), that results in restricted transpiration rate under high vapor pressure deficits (VPD). The benefit of TR lim is that under high midday-VPD conditions crop water loss is limited so that there is water conservation and positions the crop to better withstand later-season drought. Previous studies performed at 31 °C found that TR lim was commonly expressed among sorghum genotypes. It was also found that those lines with low VPD breakpoints for expression of the TR lim trait exhibited insensitivity in transpiration rate to being fed silver ions. However, it is uncertain how applicable these previous results obtained at 31 °C might be at higher temperature that may exist at midday in regions where sorghum is commonly grown. The current study tested for the expression of TR lim at 37 °C in 16 sorghum genotypes previously found to express the trait at the lower temperature. Only three of the genotypes sustained expression of TR lim at 37 °C. These results indicate that for environments where temperature may commonly reach or exceed 37 °C, sorghum genotypes have been favored that acclimate to the high temperature by losing the TR lim trait. In conditions in which very high temperatures threaten crop heat stress, those genotypes that lose the TR lim trait at high temperature may be more desirable since increasing transpiration rates at these temperatures can result in leaf cooling. The silver test failed to discriminate genotypes for expression of the TR lim trait at high temperature.

Increased urban demand for landscape irrigation, as well as interest in promoting water-use efficient species by municipalities, water purveyors, and homeowners associations emphasize the need for comparative data on consumptive water use by warm-season lawn grasses. The objective of this study was to quantify actual evapotranspiration (ETa) and to develop crop coefficients (Kc) for four warm-season turfgrass species, namely ‘Tifway’ bermudagrass (Cynodon dactylon (L.) Pers. x Cynodon transvaalensis Burtt-Davy), ‘Empire’ zoysiagrass (Zoysia japonica Steud.), ‘Floratam’ St. Augustinegrass [Stenotaphrum secundatum (Walter) Kuntze], and ‘Argentine’ bahiagrass (Paspalum notatum Flugge). Crop coefficients were derived by dividing ETa (measured directly from lysimeter weight change over 24 to 72-h periods) by reference evapotranspiration (ETo) calculated from the ASCE–EWRI Standardized Method using onsite weather station data. Data were collected over three seasons from non-stressed, well-watered turf. For 17 of the 30 measurement periods, Kc did not differ among the 4 species, and on 24 of 30 periods zoysiagrass, bermudagrass, and St. Augustinegrass Kc did not differ from one another. A trend toward elevated Kc was observed in bahiagrass in years 2 and 3, particularly during early spring measurement periods. Kc values for all species fluctuated across seasons and years, peaking to ∼0.8 during active growth periods when vapor pressure deficit and solar radiation were greatest, and declining to ∼0.3 in late fall and winter. Root growth differences among the species appeared to have a stronger relationship to ET rates than did shoot growth rate. Results demonstrated that the commonly recommended warm-season turf coefficient of 0.6, while approximating overall average annual ETa, under-predicted ETa during active growth periods and over-predicted ETa during late fall and winter periods, when turf was slowly growing or quiescent. The results indicate seasonal refinement of Kc values may be needed to more effectively meet consumptive water use requirements of warm-season turfgrasses.

There is debate over determining the appropriate model complexity to simulate crop development, growth, and yield. An approach that is sometimes suggested is to compare the performance of models using common datasets for ability to reproduce specific sets of observations. However, this narrow-focused approach overlooks the critical heuristic aspects in using models to explore and understand the behavior of cropping systems at the process level. We argue that the key criteria of model evaluation are both transparency and overall robustness. While model robustness (often mislabeled as “validation”) is sometimes presented at some level, model transparency has normally been ignored in model comparison studies. The objective of this paper is to examine the transparency and robustness of four wheat (Triticum aestivum L.) models that are markedly different in detail: CropSyst and SSM as simpler models and APSIM and DSSAT as more complex models. Data for development, growth and yield of the crop were collected from a wide range of environmental and growth conditions in the Grogan region of Iran. Models parameterization was done according to the guidelines for each model and then model testing and comparison were performed using different datasets. The two simpler models were found to be more robust than the complex models; across all the evaluated crop variables, the coefficient of variation in yield prediction was lower for SSM (8.2%) and CropSyst (14.3%) than APSIM (15.0%) and DSSAT (18.5%). Transparency of the models was mainly gauged by the number of input parameters needed by the models. Simulations using APSIM (292 parameters) and DSSAT (211 parameters) required the definition of about fourfold more parameters than CropSyst (50 parameters) and SSM (55 parameters). The simulation results showed no significant relationship between model performance and parameter number; the lack of transparency sacrificed in complexity was not rewarded by increased robustness in the output.

Summary Genotypic differences were found in decrease of leaf expansion with exposure to high vapour pressure deficit. Changes in leaf expansion were associated with down-regulation of expansin and extensin genes., Vapour pressure deficit (VPD) is considered an important environmental factor that might affect leaf expansion and transpiration rate (TR) in plants. Two slow-wilting soybean (Glycine max (L.) Merr.) genotypes PI 416937 and PI 471938 along with commercial cultivar Hutcheson were subjected to low (1.2–1.6 kPa) and high VPD (2.8–3 kPa) environments to study their leaf expansion and TR over five days. Among the three genotypes, PI 416937 had the lowest increase in its TR (34%) at high VPD compared with low VPD and the greatest decrease in leaf area (31%). In contrast, Hutcheson had the highest increase in TR (87%) under high VPD and the lowest decrease in leaf expansion rate (18%). Expansin and extensin genes were isolated in PI 416937 to determine if changes in leaf expansion were associated with changes at the molecular level. The four studied genes were all suppressed after five days in the high VPD environment.

A plant trait to minimize the impact of drought on crop yield is limited-transpiration rate (TR) under high ambient vapor pressure deficit (VPD) so that soil water is conserved to sustain grain fill. Variation among maize (Zea mays L) hybrids has been identified for the existence of the limited-TR trait at high atmospheric VPD, and the VPD at which TR becomes limited. Further, it has been shown that the TR limitation at high VPD is related to plant hydraulic conductance, which may be due to differences in aquaporin expression. This paper reports studies to relate the TR response of 21 maize hybrids to treatment of leaves and intact plants with cycloheximide (CHX) and four aquaporin inhibitors: silver (AgNO3), gold (HAuCl4), zinc (ZnCl2), and mercury (HgCl2). There was no discrimination among hybrids based on treatment with Hg or CHX. Segregation between hybrids for response to increasing VPD corresponded with differences in leaf response to Ag and Au treatment and intact plant response to Zn. The highest correlation (r = 0.90) between VPD breakpoint and TR response to inhibitor was with Ag treatment of leaves. These results indicate that Ag may be an effective initial screen for expression of the limited-TR trait under high VPD. (C) 2014 Elsevier B.V. All rights reserved.

Lentil (Lens culinaris Medikus) is one of the most important annual food legumes that plays an important role in the food and nutritional security of millions in the world. Lentil is mainly grown under rainfed environments, where drought is one of the most challenging abiotic stresses that negatively impacts lentil production in the arid and semi-arid areas. Therefore, development of drought-adapted cultivars is one of the major objectives of national and international lentil breeding programs. The goal of this review is to provide a report on the current status of traits of lentil that might result in yield increases in water-limited environments and identify opportunities for research on other traits. Lately, traits that are either related to developmental plasticity and/or altered rooting and shoot characteristics have received considerable attention in the efforts to increase lentil yield in water-limited environments. However, two traits that have recently been proven to be especially useful in other legumes are still missing in lentil drought research: early partial stomatal closure under soil drying, and limited-transpiration under high atmospheric vapor pressure deficit. This review provides suggestions for further exploitation of these two soil–water-conservation traits in lentil.

The soil volumetric water content at which partial stomatal closure is initiated with soil drying is a critical variable in comparing the sensitivity of plants to water-deficit conditions. Those plants that initiate stomatal closure at higher soil water contents result in soil water conservation, which allows water use to be spread over more days resulting in sustained crop physiological activity during the ongoing development of water deficit. The threshold for the initiation of the partial stomatal closure appears to be fairly stable for individual genotypes when referenced against soil water contents, defined as fraction transpirable soil water (FTSW). Although early partial closure of stomata is associated with decreased photosynthetic capacity, simulations have shown that the overall benefit of sustained physiological activity with developing drought as a result of this trait is generally expected to allow yield increase.

The driving force of transpiration rate is the gradient in vapor pressure between the dry atmosphere and the wet interior of leaves, commonly referred to as the vapor pressure deficit (VPD). The other key variable is the resistance to vapor diffusion from the leaves attributed to the aperture of the stomata pores. Partial stomatal closure at modest VPD results in limited-transpiration rate and, hence, conservative use of water. The conservative use of water allows more water to be available to sustain physiological activity later in the growing species. However, in many crop species, the limited-transpiration rate is not commonly expressed in commercial genotypes. Only recently have specific genotypes been identified that express the trait, and these genotypes are now being exploited in breeding programs. These breeding efforts have led to commercial cultivars in maize and soybean resulting in increased yields under dry land conditions.

Rain-fed wheat and barley are key crops in the Middle-East. A slight improvement in the effective use of water and in grain yield could greatly improve lives of subsistence farmers. This study aimed to evaluate the relative merits of wheat and barley in this region by simulating yields across 404 uniformly spread locations across 30 growing seasons. The results emphasized the primary importance of sowing date in each location. In comparison to wheat, barley generally was capable of rapid progress through its development stages allowing it to avoid deleterious late-season droughts and to have greater yields in low rainfall regions. A large part of Middle-East appeared unsuited for rain-fed production of these two grain species if seasonal yield variability is a concern.

The Penman energy balance equation has become a common approach to estimating the evaporation of plant canopies. Unfortunately, implementation of the energy balance equation requires various assumptions and empiricisms, including “crop coefficients”, so that in practice the Penman equation is used as a framework in which to apply empirical approximations. These limitations are reviewed in this paper. An alternative to the energy balance approach suggested by Penman was a “sink strength” model in which the gradient in vapor pressure was considered the prime driver of plant water loss. In this paper, the sink strength model is developed for determining plant canopy transpiration based on explicitly defined properties of the plants. The key variables are the carbon assimilation pathway of photosynthesis and the biochemical composition of the plant material being synthesized. These two parameters define the transpiration efficiency coefficient and radiation use efficiency that are required in the calculation of transpiration. Also, it is necessary to define a weighted vapor pressure gradient for transpiration when making estimates of the amount of transpiration on a daily basis. The derived expression of the sink strength model was used to compare predicted transpiration with measured values of four turf grass species measured over three years. A close linear correlation was observed for all grasses ( P

In the context of climate change, producing the same amount of food with less water has become a challenge all over the world. This is also true for the Lingot bean production in the area of Castelnaudary of southwest France where market competition with imported bean has made it crucial to achieve high yields to maintain production in the area. The use of an appropriate and robust crop model can help to identify crop management solutions to face such issues. We used SSM-legumes, a crop model generic to legume species, as well as field observations recorded over five years on eight farms of the Castelnaudary area to assess the effect of different irrigation scenarios on bean yield and water consumption. First, it was demonstrated that the SSM-legumes model is robust in simulating the development and growth of Lingot bean in non-stressed or moderately stressed conditions of this region regarding water and nutrient availability. Then, the use of the model to compare irrigation scenarios provided guidance on how to improve irrigation management for Lingot bean production. These results showed that farmers could achieve slightly higher yields with less water by basing irrigation decisions on the water content of the soil.

A limited-transpiration trait has been proposed for sorghum (Sorghum bicolor L.) as a desirable trait for water-deficit environments so that water conservation early in the growing season allows greater water availability during the latter stages of crop growth. This study was undertaken to explore if chemical inhibitors—mercury, silver, gold, zinc, cylcoheximide—could be used to screen for the limited-transpiration trait. Inhibitors were fed either to detached leaves or to the root systems of intact plants, and changes in transpiration rates were recorded. Only treatment with silver resulted in discrimination among genotypes. Those genotypes that most strongly expressed the limited-transpiration trait were less sensitive to being fed silver than those that either had weaker expressions of the limited-transpiration trait or did not express the trait. The results with leaves indicated the silver test could be effective as a negative screen for sorghum genotypes that potentially express the limited-transpir...

Limited transpiration rate (TR) under high vapor pressure deficit (VPD) conditions has been proposed as a desirable trait for crop yield improvement. The limited-TR trait has been identified in several single-cross maize hybrids, and among these hybrids, a range in the VPD breakpoint for limited TR was identified. It was hypothesized that the variation in the VPD breakpoint was due to differences in hydraulic conductance in their roots or leaves, or both. Therefore, the objective of this study was to compare relative hydraulic conductance in the roots and leaves across the maize hybrids expressing the VPD breakpoint. It was found that the VPD of the breakpoint was correlated with each of three indices of hydraulic conductance. That is, low VPD breakpoint was associated with low hydraulic conductance in both leaves and roots indicating a common, underlying limiting mechanism in these two tissues. It was hypothesized that expression of similar aquaporin populations influencing hydraulic flow across membranes in the roots and leaves may account for the consistency in results across the indices of hydraulic conductance.

Peanut (Arachis hypogaea L.) is an important legume that is often grown in drought-prone areas. Low epidermal conductance (EC) may delay the dehydration of leaves and improve plant survival of severe water-deficit stress. No reports of genetic variation for EC in peanut have been found in the literature. Therefore, the main objective of this study was to document genetic variation for EC among 21 peanut (Arachis spp.) genotypes in two greenhouse experiments and a field experiment. The effects of water-deficit stress on EC and the association between EC and stomata density (SD) were also investigated. Tests for an influence of water-deficit stress on EC were inconclusive. Comparison of EC and SD among genotypes failed to show any significant correlations in the various test environments. However, genetic variation for EC in peanut was found in both greenhouse experiments, with genotypes TMV 2, PI 298639, and VA 98R having very low EC. In the field, genotype SPT 06-07 was found to have low EC. These results indicate that selection of genotypes with low EC is a viable approach in identifying peanut genotypes with improved capacity to survive severe soil water deficits.