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The GRAS transcription factors play an indispensable role in plant growth and responses to environmental stresses. The GRAS gene family has extensively been explored in various plant species; however, the comprehensive investigation of GRAS genes in white lupin remains insufficient. In this study, bioinformatics analysis of white lupin genome revealed 51 LaGRAS genes distributed into 10 distinct phylogenetic clades. Gene structure analyses revealed that LaGRAS proteins were considerably conserved among the same subfamilies. Notably, 25 segmental duplications and a single tandem duplication showed that segmental duplication was the major driving force for the expansion of GRAS genes in white lupin. Moreover, LaGRAS genes exhibited preferential expression in young cluster root and mature cluster roots and may play key roles in nutrient acquisition, particularly phosphorus (P). To validate this, RT‐qPCR analysis of white lupin plants grown under +P (normal P) and −P (P deficiency) conditions elucidated significant differences in the transcript level of GRAS genes. Among them, LaGRAS38 and LaGRAS39 were identified as potential candidates with induced expression in MCR under −P. Additionally, white lupin transgenic hairy root overexpressing OE‐LaGRAS38 and OE‐LaGRAS39 showed increased root growth, and P concentration in root and leaf compared to those with empty vector control, suggesting their role in P acquisition. We believe this comprehensive analysis of GRAS members in white lupin is a first step in exploring their role in the regulation of root growth, tissue development, and ultimately improving P use efficiency in legume crops under natural environments. [ABSTRACT FROM AUTHOR]

Manganese is an essential nutrient and plays key roles in photosynthetic processes, including in NAD‐malic enzyme (NAD‐ME)‐type C4 plants as an activator of NAD‐ME. However, little is known about the Mn requirements of switchgrass (Panicum virgatum L.). To study Mn requirements for optimum growth and biomass production, a lowland ('Alamo') and an upland ('Cave‐in‐Rock') switchgrass ecotype were grown with either washed sand, vermiculite, or perlite and fertilized with nutrient solutions ranging in [Mn] from 0 to 200 μM. In the perlite experiment, pearl millet [Pennisetum glaucum (L.) R. Br. 'KGraze'] was also grown. Shoot [Mn] was highly responsive to increasing Mn in the nutrient solution. When grown in washed sand and vermiculite, tissue [Mn] remained above those normally considered deficient, even in the 0 μM Mn treatment, and no Mn treatment effects on biomass production were found. In perlite, end‐of‐season shoot [Mn] were <5 mg kg−1 in all entries when no Mn was supplied, and a decrease in biomass production compared with 10–25 μM Mn treatments was observed for Alamo and KGraze, but not for Cave‐in‐Rock. Relative chlorophyll contents of switchgrass were lower in the 0 μM Mn treatment than in other treatments late in the season, but in KGraze, they were low early in the season and increased throughout the season, resulting in less pronounced (but still significant) differences at late stages. Overall, results indicated that switchgrass and pearl millet respond differently to low Mn availability and that even low levels of shoot tissue [Mn] allow switchgrass to maintain biomass production. [ABSTRACT FROM AUTHOR]

Little is known about the availability of residual fertilizer-N and cotton (Gossypium spp.) residue-N to subsequent crops. This study determined the effects of two soil types and N fertilization rates on the recovery of residual 15N-fertilizer and 15N from labeled cotton residue in the soil and plants of subsequent cotton crops. Microplots in the San Joaquin Valley, California, on a Panoche day loam [fine-loamy, mixed (calcareous), thermic Typic Terriorthents] and a Waseo sandy loam (coarse-loamy, mixed, nonacid, thermic Typic Torriorthents) were used to trace the fate of 15N from labeled aboveground cotton residue separately from the 15N in roots and soil. Total 15N-fertilizer recovery in the second year after application averaged 5.8% for Acala (G. hirsutum L.) and 2.9% for Pima (G. barbadense L.) cotton. In the third year after application, total 15N-fertilizer recovered by Acala averaged 2.0% on the clay loam soil and 3.3% on the sandy loam. Most of this recovered 15N-fertilizer was cycled through soil pools and roots and only small amounts originated from labeled aboveground residue. Virtually all of the 15N applied in the form of labeled aboveground residue and recovered in the soil was found in the top 0.3 m. The 15N-fertilizer which cycled through belowground pools was found mainly in the top 0.6 m of the soil. Recovery of residual 15N-fertilizer appears to contribute little to total cotton N uptake in the second and third crop after application. [ABSTRACT FROM AUTHOR]

A better understanding of plant nitrogen (N) dynamics in modern varieties of Acala (Gossypium hirsutum L.) and Pima (G. barbadense L.) cotton grown with prevailing management practices may help in the design of N management strategies that optimize N utilization and lint yields. The response of Acala cotton to different N fertility levels was evaluated on a Panoche clay loam (fine-loamy, mixed (calcareous), thermic Typic Torriorthents) and on a Wasco sandy loam (coarse-loamy, mixed, nonacid, thermic Typic Torriorthents). Nitrogen treatments of 56, 112, 168, and 224 kg N ha-1 and check plots were established in 1998, 1999, and 2000. Plant shoots were collected and fractionated into different components at several growth stages for determination of N concentration. Both Acala and Pima tissue N concentrations were strongly affected by developmental stage and N treatment. Acala tissue N concentrations differed significantly between soil types. Maximum N uptake rates of both Pima and Acala occurred between early square and early bloom. Physiological N use efficiency averaged 11.4 kg lint kg-1 plant N for Acala grown on the Panoche clay loam and 9.4 kg kg-1 on the Wasco sandy loam, and 13.2 kg kg-1 for Pima grown on Panoche clay loam. Leaf N concentration as an in-season indicator of N status and estimates of seasonal soil N mineralization potential may be useful in optimizing cotton N management. [ABSTRACT FROM AUTHOR]

SummaryAtmospheric CO2 concentration ([CO2]) and temperature are likely to increase in the future and may change plant growth and composition characteristics. Rhizoma peanut (Arachis glabrata Benth.) and bahiagrass (Paspalum notatum Flügge) were grown on a natural field soil in temperature-gradient greenhouses to evaluate the effects of elevated [CO2] and temperature on tissue composition and digestibility during the establishment year. Carbon dioxide levels were maintained at 365 (ambient) and 640 μL CO2 L–1 air. The temperature-gradient greenhouses were regulated to obtain air temperature sectors of 0.2, 1.5, 2.9, and 4.5 °C above ambient. Samples were taken of previously undefoliated herbage at 57, 86, 121, 148, and 217 days after planting and entire plots were harvested at 218 days after planting. Elevated [CO2] increased total nonstructural carbohydrate concentration in rhizoma peanut leaves by almost 50%. Rhizoma peanut leaf N concentration was 6% lower at elevated than at ambient [CO2]. The N concentration in new rhizomes of rhizoma peanut was increased by high [CO2], while the N concentration in bahiagrass was not affected by temperature or [CO2]. No effects of [CO2] and temperature were found on neutral detergent fibre in rhizoma peanut leaves or stems; however, elevated [CO2] increased neutral detergent fibre in bahiagrass leaves. Only at season end was in vitro organic matter digestion of rhizoma peanut higher at ambient (623 g kg–1) than at elevated [CO2] (609 g kg–1). Elevated [CO2] had a greater effect on tissue composition of rhizoma peanut than of bahiagrass. These data suggest that elevated temperature and CO2-induced changes in chemical composition of forage species adapted to humid subtropics will be relatively small, particularly for C4 species. [ABSTRACT FROM AUTHOR]

AbstractConcerns about climatic change have stimulated interest in the response of plants to increasing CO2 concentration ([CO2]), temperature, and their possible interactions. The purpose of this study was to determine the effects of elevated [CO2] and air temperature on photosynthesis, development, and biomass production of rhizoma peanut (Arachis glabrata Benth.) and bahiagrass (Paspalum notatum Flügge) during the establishment year. Forages were grown in four temperature-gradient greenhouses on a natural Grossarenic Paleudult soil profile at temperatures of 0.2, 1.5, 2.9, and 4.5 °C above ambient, and at [CO2] of 365 and 640 μL CO2 L–1 air. Elevated [CO2] accelerated establishment and ground cover of both species. Leaf and canopy photosynthesis of both species increased at elevated [CO2], with greater increases in rhizoma peanut than bahiagrass. Averaged across five sampling dates, total biomass production of rhizoma peanut and bahiagrass responded to elevated [CO2] with a 52 and 9% increase, respectively. Increasing temperature enhanced biomass production of bahiagrass but not rhizoma peanut. Forage yield at the end of the growing season in CO2-enriched treatments was increased over that in ambient [CO2] treatments (385 vs. 318 g m–2 for rhizoma peanut and 376 vs. 321 g m–2 for bahiagrass). Overall, the enhancement of rhizoma peanut under elevated [CO2] was greater than that of bahiagrass; however, bahiagrass responded more positively to increasing temperature. [ABSTRACT FROM AUTHOR]

SUMMARY: Global warming, climate change, and industrial pollution are altering our environment subjecting plants, microbiomes, and ecosystems to an increasing number and complexity of abiotic stress conditions, concurrently or sequentially. These conditions, termed, "multifactorial stress combination" (MFSC), can cause a significant decline in plant growth and survival. However, the impacts of MFSC on reproductive tissues and yield of major crop plants are largely unknown. We subjected soybean (Glycine max) plants to a MFSC of up to five different stresses (water deficit, salinity, low phosphate, acidity, and cadmium), in an increasing level of complexity, and conducted integrative transcriptomic‐phenotypic analysis of their reproductive and vegetative tissues. We reveal that MFSC has a negative cumulative effect on soybean yield, that each set of MFSC condition elicits a unique transcriptomic response (that is different between flowers and leaves), and that selected genes expressed in leaves or flowers of soybean are linked to the effects of MFSC on different vegetative, physiological, and/or reproductive parameters. Our study identified networks and pathways associated with reactive oxygen species, ascorbic acid and aldarate, and iron/copper signaling/metabolism as promising targets for future biotechnological efforts to augment the resilience of reproductive tissues of major crop plants to MFSC. In addition, we provide unique phenotypic and transcriptomic datasets for dissecting the mechanistic effects of MFSC on the vegetative, physiological, and reproductive processes of a crop plant. [ABSTRACT FROM AUTHOR]

Summary: Climate change‐driven extreme weather events, combined with increasing temperatures, harsh soil conditions, low water availability and quality, and the introduction of many man‐made pollutants, pose a unique challenge to plants. Although our knowledge of the response of plants to each of these individual conditions is vast, we know very little about how a combination of many of these factors, occurring simultaneously, that is multifactorial stress combination, impacts plants.Seedlings of wild‐type and different mutants of Arabidopsis thaliana plants were subjected to a multifactorial stress combination of six different stresses, each applied at a low level, and their survival, physiological and molecular responses determined.Our findings reveal that, while each of the different stresses, applied individually, had a negligible effect on plant growth and survival, the accumulated impact of multifactorial stress combination on plants was detrimental. We further show that the response of plants to multifactorial stress combination is unique and that specific pathways and processes play a critical role in the acclimation of plants to multifactorial stress combination.Taken together our findings reveal that further polluting our environment could result in higher complexities of multifactorial stress combinations that in turn could drive a critical decline in plant growth and survival. [ABSTRACT FROM AUTHOR]

A combination of drought and heat stress, occurring at the vegetative or reproductive growth phase of many different crops can have a devastating impact on yield. In soybean (Glycine max), a considerable effort has been made to develop genotypes with enhanced yield production under conditions of drought or heat stress. However, how these genotypes perform in terms of growth, physiological responses, and most importantly seed production, under conditions of drought and heat combination is mostly unknown. Here, we studied the impact of water deficit and heat stress combination on the physiology, seed production, and yield per plant of two soybean genotypes, Magellan and Plant Introduction (PI) 548313, that differ in their reproductive responses to heat stress. Our findings reveal that although PI 548313 produced more seeds than Magellan under conditions of heat stress, under conditions of water deficit, and heat stress combination its seed production decreased. Because the number of flowers and pollen germination of PI 548313 remained high under heat or water deficit and heat combination, the reduced seed production exhibited by PI 548313 under the stress combination could be a result of processes that occur at the stigma, ovaries and/or other parts of the flower following pollen germination. [ABSTRACT FROM AUTHOR]

SUMMARY: Global warming and climate change are driving an alarming increase in the frequency and intensity of extreme climate events, such as droughts, heat waves, and their combination, inflicting heavy losses to agricultural production. Recent studies revealed that the transcriptomic responses of different crops to water deficit (WD) or heat stress (HS) are very different from that to a combination of WD + HS. In addition, it was found that the effects of WD, HS, and WD + HS are significantly more devastating when these stresses occur during the reproductive growth phase of crops, compared to vegetative growth. As the molecular responses of different reproductive and vegetative tissues of plants to WD, HS, or WD + HS could be different from each other and these differences could impact many current and future attempts to enhance the resilience of crops to climate change through breeding and/or engineering, we conducted a transcriptomic analysis of different soybean (Glycine max) tissues to WD, HS, and WD + HS. Here we present a reference transcriptomic dataset that includes the response of soybean leaf, pod, anther, stigma, ovary, and sepal to WD, HS, and WD + HS conditions. Mining this dataset for the expression pattern of different stress response transcripts revealed that each tissue had a unique transcriptomic response to each of the different stress conditions. This finding is important as it suggests that enhancing the overall resilience of crops to climate change could require a coordinated approach that simultaneously alters the expression of different groups of transcripts in different tissues in a stress‐specific manner. [ABSTRACT FROM AUTHOR]

Stand establishment and early growth are important for successful cotton (Gossypium hirstum L.) production, but in comparison with other crops, cotton seedlings develop slowly after emergence. The objectives of this study were to compare and contrast early vigor of diverse cotton genotypes under greenhouse and field conditions. A total of 144 genotypes were grown in a greenhouse and destructively sampled 34 d after planting (DAP). A range of seedling characteristics including areas and weights of the cotyledons and first, second, and third leaves were determined, and leaf weight ratio, specific leaf area, and leaf area ratio were calculated. Of the 144 genotypes that were grown in the greenhouse, a subset of 40 were selected and planted in the field where plant characteristics were assessed at 17, 27, 35, and 48 DAP. Genotypes differed in shoot and stem dry weights, as well as cotyledon, first, second, and third leaf, and total leaf area, as well as dry weight. A positive correlation of seed weight and rapid early growth as indicated by shoot biomass was observed at 34 DAP in the greenhouse through 48 DAP in the field. Shoot biomass of field‐grown plants sampled at 17, 27, 35, and 48 DAP was positively correlated with the size of the cotyledons and the first leaf measured at 17 DAP, as well as with the seed weight. Further characterization of high‐ and low‐seedling‐vigor genotypes identified in this study may provide insights into the physiological and genetic mechanisms associated with early vigor of cotton. [ABSTRACT FROM AUTHOR]

Low productivity and nutritive value of cool-season perennial forages, such as tall fescue [Schedonorus arundinaceus (Schreb.) Dumort.] during summer necessitates the identification of warm-season forages that improve nutritive value and yield of cool-season-based forage systems. A fast-growing, warm-season tropical legume sunn hemp (Crotalaria juncea L.) has the potential to accomplish this. Our objectives were to evaluate herbage accumulation and nutritive value (crude protein [CP], in vitro true digestibility [IVTD], neutral detergent fiber [NDF], acid detergent fiber [ADF], and NDF digestibility [NDFD, 48 h]) of sunn hemp harvested 35, 45, and 55 d after planting (DAP) at 10- and 15-cm heights and to determine regrowth potential when harvested 20 d after each initial harvest over two consecutive years. Sunn hemp herbage accumulation averaged 1.9 and 3.1 Mg ha-1 at 45 and 55 DAP, respectively. Herbage accumulation of initial harvest increased linearly from 35 to 45 to 55 DAP by 119 and 57%, respectively. Herbage accumulation of regrowth after the 35 DAP initial harvest was 262 and 303% greater than the 45 and 55 DAP initial harvests, respectively. Cutting height did not affect (P > 0.05) any variables. The greatest CP (154 g kg-1 dry matter) was observed at 35 DAP and decreased linearly with DAP. Both NDF (P < 0.01) and ADF (P = 0.01) concentrations increased linearly with DAP for both initial and regrowth harvests. The IVTD of initial and regrowth harvests averaged 794 and 624 g kg-1 dry matter, respectively. Forage NDFD for initial and regrowth harvests averaged 487 and 392 g kg-1 NDF, respectively. Nutritive value and herbage accumulation of sunn hemp can be optimized by initially harvesting between 35 and 45 DAP, and leaving at least 10 cm of residue to allow for regrowth. [ABSTRACT FROM AUTHOR]

Switchgrass, a potential biofuel crop, is a genetically diverse species with phenotypic plasticity enabling it to grow in a range of environments. Two primary divergent ecotypes, uplands and lowlands, exhibit trait combinations representative of acquisitive and conservative growth allocation strategies, respectively. Whether these ecotypes respond differently to various types of environmental drivers remains unclear but is crucial to understanding how switchgrass varieties will respond to climate change. We grew two upland, two lowland, and two intermediate/hybrid cultivars of switchgrass at three sites along a latitudinal gradient in the central United States. Over a 4‐year period, we measured plant functional traits and biomass yields and evaluated genotype‐by‐environment (G × E) interaction effects by analyzing switchgrass responses to soil and climate variables. We found substantial evidence of G × E interactions on biomass yield, primarily due to deviations in the response of the southern lowland cultivar Alamo, which produced more biomass in hotter and drier environments relative to other cultivars. While lowland cultivars had the highest potential for yield, their yields were more variable year‐to‐year compared to other cultivars, suggesting greater sensitivity to environmental perturbations. Models comparing soil and climate principal components as explanatory variables revealed soil properties, especially nutrients, to be most effective at predicting switchgrass biomass yield. Also, positive correlations between biomass yield and conservative plant traits, such as high stem mass and tiller height, became stronger at lower latitudes where the climate is hotter and drier, regardless of ecotype. Lowland cultivars, however, showed a greater predisposition to exhibit these conservative traits. These results suggest switchgrass trait allocation trade‐offs that prioritize aboveground biomass production are more tightly associated in hot, dry environments and that lowland cultivars may exhibit a more specialized strategy relative to other cultivars. Altogether, this research provides essential knowledge for improving the viability of switchgrass as a biofuel crop. [ABSTRACT FROM AUTHOR]

Plant function arises from a complex network of structural and physiological traits. Explicit representation of these traits, as well as their connections with other biophysical processes, is required to advance our understanding of plant‐soil‐climate interactions. We used the Terrestrial Regional Ecosystem Exchange Simulator (TREES) to evaluate physiological trait networks in maize. Net primary productivity (NPP) and grain yield were simulated across five contrasting climate scenarios. Simulations achieving high NPP and grain yield in high precipitation environments featured trait networks conferring high water use strategies: deep roots, high stomatal conductance at low water potential ("risky" stomatal regulation), high xylem hydraulic conductivity and high maximal leaf area index. In contrast, high NPP and grain yield was achieved in dry environments with low late‐season precipitation via water conserving trait networks: deep roots, high embolism resistance and low stomatal conductance at low leaf water potential ("conservative" stomatal regulation). We suggest that our approach, which allows for the simultaneous evaluation of physiological traits, soil characteristics and their interactions (i.e., networks), has potential to improve our understanding of crop performance in different environments. In contrast, evaluating single traits in isolation of other coordinated traits does not appear to be an effective strategy for predicting plant performance. Our process‐based model uncovered two beneficial but contrasting trait networks for maize which can be understood by their integrated effect on water use/conservation. Modification of multiple, physiologically aligned, traits were required to bring about meaningful improvements in NPP and yield. [ABSTRACT FROM AUTHOR]

Summary: Heat waves occurring during droughts can have a devastating impact on yield, especially if they happen during the flowering and seed set stages of the crop cycle. Global warming and climate change are driving an alarming increase in the frequency and intensity of combined drought and heat stress episodes, critically threatening global food security.Because high temperature is detrimental to reproductive processes, essential for plant yield, we measured the inner temperature, transpiration, sepal stomatal aperture, hormone concentrations and transcriptomic response of closed soybean flowers developing on plants subjected to a combination of drought and heat stress.Here, we report that, during a combination of drought and heat stress, soybean plants prioritize transpiration through flowers over transpiration through leaves by opening their flower stomata, while keeping their leaf stomata closed. This acclimation strategy, termed 'differential transpiration', lowers flower inner temperature by about 2–3°C, protecting reproductive processes at the expense of vegetative tissues.Manipulating stomatal regulation, stomatal size and/or stomatal density of flowers could serve as a viable strategy to enhance the yield of different crops and mitigate some of the current and future impacts of global warming and climate change on agriculture. [ABSTRACT FROM AUTHOR]

Nitrogen (N) limitation reduces leaf growth and photosynthetic rates of maize ( Zea mays), and constrains photosynthate translocation to developing ears. Additionally, the period from about 1 week before to 2 weeks after silking is critical for establishing the reproductive sink capacity necessary to attain maximum yield. To investigate the influence of carbohydrate availability in plants of differing N status, a greenhouse study was performed in which exogenous sucrose (Suc) was infused around the time of silking into maize stems grown under different N regimes. N deficiency significantly reduced leaf area, leaf longevity, leaf chlorophyll content and photosynthetic rate. High N-delayed leaf senescence, particularly of the six uppermost leaves, compared to the other two N treatments. While N application increased ear leaf soluble protein concentration, it did not influence glucose and suc concentrations. Interestingly, ear leaf starch concentration decreased with increasing N application. Infusion of exogenous suc tended to increase non-structural carbohydrate concentrations in the developing ears of all N treatments at silking and 6 days after silking. However, leaf photosynthetic rates were not affected by suc infusion, and suc infusion failed to increase grain yield in any N treatment. The lack of an effect of suc infusion on ear growth and the high ear leaf starch concentration of N-deficient maize, suggest that yield reduction under N deficiency may not be due to insufficient photosynthate availability to the developing ear during silking, and that yield reduction under N deficiency may be determined at an earlier growth stage. [ABSTRACT FROM AUTHOR]

Recently, sweet sorghum [Sorghum bicolor (L) Moench] has garnered renewed attention as a promising feedstock for ethanol production. A byproduct of this is bagasse, which is sweet sorghum stalks remaining after juice extraction. It is possible that sweet sorghum bagasse could provide a source of livestock feed and that its nutritive value could be increased by ammoniation. Ammoniation refers to the treatment of lowquality forages with NH3 to improve crude protein concentration, digestibility, and animal intake. The main objective of this study was to evaluate sweet sorghum bagasse as a livestock feed and determine the effect of ammoniation on in vitro true digestibility (IVTD) and crude protein (CP) of sweet sorghum bagasse. In vitro true digestibility and CP were determined on bagasse of 12 sweet sorghum cultivars grown in three environments and treated with and without anhydrous NH3 (39.0 g kg-1). Across environments, ammoniation increased bagasse IVTD from a mean of 731 g kg-1 dry matter (DM) to a mean of 750 g kg-1 DM, but IVTD of bagasse from only two of three environments was increased. Crude protein averaged 117 g kg-1 DM for ammoniated samples compared to 26 g kg-1 DM for nontreated samples. Ammoniation increased CP in every cultivar and in every environment. Sweet sorghum bagasse IVTD and CP characteristics combined with large yields indicate that this byproduct could serve as livestock feed and merits further investigation. [ABSTRACT FROM AUTHOR]

Nitrogen supplied by N2 fixation to soybean [Glycine max (L.) Merr.] may not be sufficient to maximize yield. Field studies were conducted in 2002, 2003, and 2004 on Sharkey clay soil (very-fine, smectitic, thermic Chromic Epiaquert) at Stoneville, MS (33°26′ N lat). The objective was to determine the effect of high rates of N applied as a replacement for N2 fixation in nonirrigated and irrigated environments. Eight cultivars ranging from Maturity Group II to IV were planted on 17 Apr. 2002, 2 Apr. 2003, and 25 Mar. 2004. Not all cultivars were evaluated in all 3 yr. Glyphosate herbicide was used in all 3 yr and a non-glyphosate herbicide treatment was applied in 2002. Cultivars grown in 2003 were also evaluated under an application of 21.3 kg ha-1 of Mn. All cultivar, herbicide, and Mn treatments were evaluated in irrigated and nonirrigated environments with fertilizer N (PlusN treatment) or without fertilizer N (ZeroN treatment). In the PlusN treatment, granular NH4NO3 was surface applied at soybean emergence at rates of 290 kg ha-1 in 2002, 310 kg ha-1 in 2003, and 360 kg ha-1 in 2004. When analyzed over all management practices (years, cultivars, herbicide, and Mn treatments), the PlusN treatment resulted in significantly decreased ureide concentration (57.2 and 53.5% reduction) and significantly increased biomass accumulation (14.1 and 16.7%), N accumulation (12.8 and 28.1%), and seed yield (7.7 and 15.5%) for the irrigated and nonirrigated environments, respectively. The majority of the yield increase in each environment resulted from increased number of seed (9.5% irrigated and 16.2% nonirrigated). These results confirm the sensitivity of N2 fixation to drought and indicate that N2 fixation may limit yield of soybean grown in both irrigated and nonirrigated environments of the midsouthern USA, and that N2 fixation deficiencies occur before the beginning of processes that determine number of seed. [ABSTRACT FROM AUTHOR]

Background: Carbon (C) and nitrogen (N) assimilate availability and their ratios are crucial for maize grain production and N‐use efficiency. Aim: Our aim was to give a mechanistic understanding of yield formation regulated by assimilate C:N balance during both early ear development and rapid grain filling. Methods: Maize was grown under field conditions with 0, 200, and 300 kg N ha−1 (referred to as N0, N200, and N300, respectively). Ear growth, grain yield, and dynamics of total C and N accumulation in ear leaves, cobs, and developing kernels (apical and basal proportions separated from the longitudinally middle of ear) were investigated, as well as the non‐structural carbohydrates and free amino acids. Results: Compared to N‐sufficient plants, low‐N plants contained 16% to 70% less N and 8% to 50% less C in the developing kernels, causing 43% to 52% yield losses, which indicated that low‐N kernels received less amino acid per unit sugar from the maternal plants. This was supported by lower concentrations of the main N transport molecules (glutamine and asparagine) in ear leaves at silking and 21 days after silking (DAS) coupled with the larger amounts of C accumulated as starch under N deficient compared to adequate N supply. Nitrogen treatment did not influence the concentrations of total free amino acids and soluble protein in the cob, neither at silking nor 21 DAS, but it did influence cob free amino acid composition. Compared to the adequate N supply, low‐N plants contained 75% and 57% less glutamine and asparagine in apical kernels at silking, as well as 36% and 31% less in basal kernels. Free amino acid concentrations in both cob and kernels were less responsive to N treatments at 21 DAS than at silking, especially in the basal ear halves. Conclusion: Maize grain production under low‐N environment can be more attributed to the balance in assimilate composition, particularly the amino acid profile, than the C‐assimilate availability for ear growth and development. [ABSTRACT FROM AUTHOR]

Episodes of prolonged drought coupled with heat waves (i.e. drought and heat combination) can have a devastating impact on agricultural production and crop yield. It is therefore not surprising that improving tolerance to drought and heat combination has been a major goal for breeders and biotech companies. Although much is known about the physiological and molecular responses of vegetative tissues to a combination of drought and heat stress, less is known about the impact of this stress combination on yield and different yield components. Here, we used a meta‐analysis approach to synthesize results from over 120 published case studies of crop responses to combined drought and heat stress. Our findings reveal that drought and heat stress combination significantly impacts yield by decreasing harvest index, shortening the life cycle of crops, and altering seed number, size and composition. Furthermore, these impacts are more severe when the stress combination is applied during the reproductive stage of plants. We further identify differences in how legumes and cereals respond to the stress combination and reveal that utilizing C3 or C4 metabolism may not provide an advantage to plants during stress combinations. Taken together our study highlights a need to focus future studies, as well as breeding efforts, on crop responses to drought and heat combination at the reproductive stage of different crop species. [ABSTRACT FROM AUTHOR]

Summary: Local adaptation is an important process in plant evolution, which can be impacted by differential pathogen pressures along environmental gradients. However, the degree to which pathogen resistance loci vary in effect across space and time is incompletely described.To understand how the genetic architecture of resistance varies across time and geographic space, we quantified rust (Puccinia spp.) severity in switchgrass (Panicum virgatum) plantings at eight locations across the central USA for 3 yr and conducted quantitative trait locus (QTL) mapping for rust progression.We mapped several variable QTLs, but two large‐effect QTLs which we have named Prr1 and Prr2 were consistently associated with rust severity in multiple sites and years, particularly in northern sites. By contrast, there were numerous small‐effect QTLs at southern sites, indicating a genotype‐by‐environment interaction in rust resistance loci. Interestingly, Prr1 and Prr2 had a strong epistatic interaction, which also varied in the strength and direction of effect across space.Our results suggest that abiotic factors covarying with latitude interact with the genetic loci underlying plant resistance to control rust infection severity. Furthermore, our results indicate that segregating genetic variation in epistatically interacting loci may play a key role in determining response to infection across geographic space. See also the Commentary on this article by Catalán & Vogel, 227: 1587–1590. [ABSTRACT FROM AUTHOR]

Accurate assessment of crop water uptake (WU) and water use efficiency (WUE) is not easy under field conditions. Carbon isotope discrimination (Δ13C) has been used as a surrogate of WUE to examine crop yield responses to drought and its relationship with WU and WUE. A 2‐yr study was conducted (i) to characterize genotypic variation in Δ13C, grain yield, and other physiological parameters in common bean (Phaseolus vulgaris L.) parental lines, and (ii) to examine the relationships between grain Δ13C, shoot Δ13C, and grain yield under well‐watered and terminal drought stress conditions. All measured plant traits were strongly influenced by water availability, and genotypic differences in grain yield, shoot Δ13C, and grain Δ13C were found in both watered and terminal drought stress environments. The parental lines were classified into two drought adaptation groups, drought resistant and drought sensitive, based on a yield drought index. High yields under drought conditions were related to (i) greater water uptake, as indicated by high Δ13C in genotypes previously shown to have deeper roots (e.g., SEA 5 and BAT 477), and (ii) increased WUE, denoted by lower Δ13C and greater pod harvest index (PHI) (e.g., SER 16). Coupling of Δ13C measurements with measured yield and yield components analyses, such as PHI, provided an avenue to distinguish different physiological traits among drought resistant genotypes underlying adaptation to water deficit stress. [ABSTRACT FROM AUTHOR]

In comparison with other annual crops, cotton (Gossypium hirsutum L.) seedlings develop slowly after emergence. More rapid seedling development can provide advantages in limiting disease, insect, and weed impacts on cotton seedlings. Information on the mechanisms determining early vigor in cotton is limited. Therefore, three genotypes previously identified to differ in seedling vigor and one commercial cultivar were selected for detailed characterization of early growth in greenhouse and field conditions. Growing environment and genotype effects were significant for many of the measured traits. Environmental conditions prevailing in field and greenhouse conditions differentially affected seedling growth, including cotyledon biomass, root weight ratio (RWR), net assimilation rate (NAR), and specific leaf area (SLA). Genotypic differences were found in one or both environments for cotyledon area, area of the first leaf, total leaf area, and leaf, stem, root, and total biomass. Leaf weight ratio (LWR), stem weight ratio (SWR), RWR, LAR, and SLA differed among genotypes at most stages, but this was not the case for relative growth rate and NAR. The high‐vigor genotype generally had longer roots, larger cotyledons, greater cotyledon, stem, and total biomass, and greater SWR and RWR than the low‐vigor genotype. The low‐vigor genotype had the greatest LAR, SLA, and LWR among the four genotypes. Results obtained in this study suggest that factors such as the efficiency of photoassimilate conversion into biomass, energy density of the biomass, root carbon exudation, and/or photosynthetic rates differ between the low‐vigor and high‐vigor genotypes. [ABSTRACT FROM AUTHOR]

Water deficit stress is a major factor limiting soybean [Glycine max (L.) Merr.] yield. High water use efficiency (WUE) offers a means to potentially ameliorate drought impact, but increased WUE is often associated with a reduction in transpiration (T) and an accompanied reduction in photosynthesis. This interdependence of T and photosynthesis is a major constraint in selection for high WUE by breeding programs. Measurement of genetic variability in WUE and T through carbon isotope ratio (δ13C) and oxygen isotope ratio (δ18O), respectively, could be important in identifying genotypes with high WUE that also have relatively high T and thus higher rates of biomass production. This study's objective was to identify genomic regions associated with δ13C and δ18O. A diverse collection of 373 soybean genotypes was grown in four field environments and whole-plant samples collected at early reproductive growth were characterized for δ13C and δ18O. After quality assessment, 31,260 polymorphic single-nucleotide polymorphism (SNP) markers with a minor allele frequency ⩾5% were used for association analysis. Genome-wide association analysis identified 54 environment-specific SNPs associated with δ13C and 47 SNPs associated with δ18O. These SNP markers tagged 46 putative loci for δ13C and 21 putative loci for δ18O and may represent an important resource for pyramiding favorable alleles for drought tolerance and identifying genotypes with high WUE. [ABSTRACT FROM AUTHOR]

Maize (Zea mays L.) grain yield is considered to be highly associated with carbohydrate dynamics in leaves and developing ears during the critical period bracketing silking. Carbohydrate changes are sensitive to variation in nitrogen (N) availability, yet a comprehensive analysis of the N effect on various carbohydrate concentrations around silking remains elusive. A 2-yr field study was conducted to investigate grain yield, N uptake, ear dry matter and carbohydrate concentrations in ear-leaves and whole ears (prior to silking) and kernels (after silking) of maize grown with 0, 150, and 300 kg N ha-1. Greater N availability increased maize shoot dry matter and N content at silking and physiological maturity, as well as grain yield. While N had little effect on ear-leaf glucose concentration, sucrose concentration increased but starch concentration decreased with increasing N, regardless of sampling time. Prior to silking, glucose and fructose concentrations in the developing ear responded positively to increasing N availability, but sucrose and starch concentrations declined. In growing kernels shortly after silking, glucose and fructose concentrations in N fertilized treatments were significantly lower than those in the zero-N treatment. In contrast, a significant increase in kernel starch concentration was found in response to 300 kg N ha-1. These observations point to an important role of the carbohydrate composition of unpollinated ears prior to silking with regard to kernel set and post-silking kernel starch accumulation, and thus final crop yield. [ABSTRACT FROM AUTHOR]

Planting date is one of the main factors affecting soybean (Glycine max [L.] Merr.) yield. Environmental conditions in the US Midsouth allow for planting dates from late March through early July, and maturity groups (MGs) ranging from 3 to 6. However, the complexity of interactions among planting date, MG, and the environment makes the selection of an optimum MG cultivar difficult. A regional 3-yr study, conducted at eight locations with latitudes ranging from 30.6 to 38.9°N, planting dates ranging from late March to early July, and MGs 3 to 6, was used to examine the relationship between relative yield and planting day. The data indicated that yield was dependent on the location and MG choice. There was a quadratic response of relative yield to planting day in six out of the eight locations studied for MG 3 cultivars, and in five locations for MG 4 cultivars. On the other hand, MG 5 and 6 cultivars were more likely to have a negative linear relationship, with a quadratic response in only two of the eight locations. Optimum planting dates that maximized yield were dependent on the location and MG combination and ranged from 22 March to 17 May. Delaying planting dates from mid May to early June reduced yields by 0.09 to 1.69% per day, with the rate of decline greatest at the southern-most locations. Overall, MG 4 cultivars maximized yield or were not statistically different from the highest yielding MG at most locations and planting dates. [ABSTRACT FROM AUTHOR]

Bioactive compounds that are produced by select rice cultivars have the potential to control barnyardgrass, a major rice yield-limiting factor. In this study, the Vietnamese rice cultivars, OM 3536, OM 4498 and OM 5930, were selected and their inhibitory activity on cress, lettuce, canola and barnyardgrass was evaluated by using donor-receiver bioassays. These bioassays revealed that OM 3536 and OM 5930 exerted the greatest inhibitory activity, with an average growth inhibition of 57.2% on the roots and shoots of barnyardgrass. A bioassay-guided approach was used to identify the allelopathic fractions from OM 5930 and was coupled with reverse-phase chromatography in order to isolate several growth-inhibitory fractions. The effective dose of the aqueous methanol extract of the rice plants that was required for 50% inhibition ( ID50) of the shoot and root growth of the four test plant species, as determined by a logistic regression analysis, averaged 0.091 and 0.062 g mL−1 for OM 5930 and 0.112 and 0.072 g mL−1 for OM 3536, respectively. The ID50 of the barnyardgrass roots and shoots in the assays, as determined by a logistic regression analysis, was 0.044 and 0.149 g mL−1 for OM 3536 and 0.052 and 0.114 g mL−1 for OM 5930, respectively. A growth-inhibitory fraction in the aqueous methanol extract of OM 5930 was isolated and the inhibitory activity on lettuce seedlings was determined. At a concentration of 100 p.p.m., this growth-inhibitor inhibited lettuce root growth by up to 80.2%, compared to the control plants. These findings demonstrate that the dried plant tissues of Vietnamese rice cultivars could contain bioactive compounds that strongly inhibit plant growth. [ABSTRACT FROM AUTHOR]