Aerial canopy temperature differences between fast‐ and slow‐wilting soya bean genotypes

Drought stress limits crop growth and yield in soya bean (Glycine max [L.] Merr.), but there are relatively few tools available to assess the ability of different genotypes to tolerate drought. Aerial infrared image analysis was evaluated as a potential tool for identifying drought tolerance in soya bean. Drought effects were evaluated from late vegetative to mid‐reproductive stages of soya bean development in an experiment with ten genotypes including five slow‐ and five fast‐wilting genotypes that were from a population derived from Benning×PI416937. There were two deficit irrigation levels for 2 years and one deficit irrigation level for the third year along with a fully irrigated control level. When the canopy was completely closed, relative canopy temperature was determined using an infrared camera taken from an aerial platform 50–75 m above the experiment. As water availability decreased, the relative canopy temperature generally increased. Moreover, slow‐wilting soya bean genotypes generally had lower canopy temperature compared to fast‐wilting genotypes, and grain yield was generally positively associated with cool canopy temperatures. The results indicate that the determination of canopy temperature is a promising tool for rapid characterization of drought‐related traits in soya bean.     

Estimation of phenotypic variability in symbiotic nitrogen fixation ability of common bean under drought stress using 15N natural abundance in grain

Common bean (Phaseolus vulgaris L.) is the most important food legume, cultivated by small farmers and is usually exposed to unfavorable conditions with minimum use of inputs. Drought and low soil fertility, especially phosphorus and nitrogen (N) deficiencies, are major limitations to bean yield in smallholder systems. Beans can derive part of their required N from the atmosphere through symbiotic nitrogen fixation (SNF). Drought stress severely limits SNF ability of plants. The main objectives of this study were to: (i) test and validate the use of ¹⁵N natural abundance in grain to quantify phenotypic differences in SNF ability for its implementation in breeding programs of common bean with bush growth habit aiming to improve SNF, and (ii) quantify phenotypic differences in SNF under drought to identify superior genotypes that could serve as parents. Field studies were conducted at CIAT-Palmira, Colombia using a set of 36 bean genotypes belonging to the Middle American gene pool for evaluation in two seasons with two levels of water supply (irrigated and drought stress). We used ¹⁵N natural abundance method to compare SNF ability estimated from shoot tissue sampled at mid-pod filling growth stage vs. grain tissue sampled at harvest. Our results showed positive and significant correlation between nitrogen derived from the atmosphere (%Ndfa) estimated using shoot tissue at mid-pod filling and %Ndfa estimated using grain tissue at harvest. Both methods showed phenotypic variability in SNF ability under both drought and irrigated conditions and a significant reduction in SNF ability was observed under drought stress. We suggest that the method of estimating Ndfa using grain tissue (Ndfa-G) could be applied in bean breeding programs to improve SNF ability. Using this method of Ndfa-G, we identified four bean lines (RCB 593, SEA 15, NCB 226 and BFS 29) that combine greater SNF ability with greater grain yield under drought stress and these could serve as potential parents to further improve SNF ability of common bean.     

Old and New Cultivars of Soya Bean (Glycine max L.) Subjected to Soil Drying Differ in Abscisic Acid Accumulation,Water Relations Characteristics and Yield

Two old (Huangsedadou and Longxixiaohuangpi (LX)) and two new (Jindou 19 (JD) and Zhonghuang 30 (ZH)) soya bean (Glycine max (L.) Merr.) cultivars were used to investigate the influence of soil drying on the abscisic acid (ABA) accumulation in leaves, stomatal conductance (g_s), leaf water relations, osmotic adjustment (OA), leaf desiccation tolerance, yield and yield components. The greater ABA accumulation was induced by soil drying, which also inducing g_s decreased at higher soil water contents (SWC) and leaf relative water content (RWC) significantly decreased at lower SWC in the new soya bean cultivars than in the old soya bean cultivars. The soil water threshold between the value at which stomata began to close and the RWC began to decrease was significantly broader in the new cultivars than in the old cultivars. The new cultivars had significantly higher OA and lower lethal leaf water potential than old cultivars when the soil dried. The old cultivars had greater biomass, but lower grain yield than the new cultivars in well‐watered, moderate stress and severe stress conditions. Thus with soil drying, the new soya bean cultivars demonstrated greater adaptation to drought by inducing greater ABA accumulation, stomatal closure at higher SWC, enhanced OA and better water relations, associated with increased leaf desiccation tolerance, greater water use efficiency and higher yield.     

Soya Bean (Glycine max L. Merr.) Genotype Response to Early-season Flooding: II. Aboveground Growth and Biomass

Soya bean is often grown in regions prone to periodic flooding, thus selecting cultivars that maintain production under waterlogged conditions is desirable. An experiment involving flooded soya beans was planted in southern Florida to examine (1) stem and leaf growth; (2) morphological adaptations; and (3) the relationship between early‐season and late‐season flood tolerance in flooded soya beans. Eleven soya bean genotypes previously defined as tolerant or sensitive to flooding were subjected to three treatments at 21 days after sowing (DAS): (1) no flood, (2) 2‐week flood and (3) 4‐week flood. All plants were harvested 49 DAS. Flooded plants exhibited lower stem dry weights but greater partitioning to the stem. Non‐flood treatments had greater leaf dry weight, leaf area and partitioning to leaves than flooded plants. There were positive correlations of genotype stem dry weight and leaf dry weight to early‐season flood tolerance but stem partitioning was negatively correlated with early‐season flood tolerance. Genotypic rankings of early‐season flood tolerance in this study were not correlated with earlier studies basing flood tolerance on seed yield. Our study highlights the range of soya bean morphological adaptations in response to flood. However, our results indicate that early‐season screening may not be an accurate predictor of soya bean genotypic response to late‐season flood.     

Variability of N2-fixation in common bean (Phaseolus vulgaris L.) under P deficiency is related to P use efficiency

Common bean often faces P deficiency in soils where it is generally grown. Such a deficiency is a major limitation to grain yield improvement, especially when common bean relies on N2 fixation. Screening for symbiotic N2 fixation (SNF) under P deficiency (72 μmol P plant-1 week-1) was performed in a glasshouse with 220 lines originating from the Andean and Meso-American gene pools. Large variability in shoot dry weight and SNF under P deficiency was found. SNF tolerance to P deficiency was mostly found among late flowering type IV lines, with the exception of three early flowering type III lines. The SNF tolerance to P deficiency was correlated with: (i) low nodule P concentration in all the growth types, and (ii) intense and early nodulation for type IV lines, or (iii) large root dry weight and high nodule nitrogenase for type III lines. Large genotypic variability for nitrogen use efficiency, i.e. biomass per N concentration was also found. However, the ratio plant N per plant P concentration was the most discriminating. We concluded that this later ratio, which is almost similar to plant N-fixed per plant P concentration, in glasshouse hydroponics culture might be: (i) an estimate of the P use efficiency for SNF, (ii) a consequence of low P concentration in plant organs, especially nodules, and (iii) a determinant of genotypic variability of SNF tolerance to P deficiency. This revised version was published online in July 2006 with corrections to the Cover Date.     

Physiological and Molecular Characterization of Faba bean (Vicia faba L.) Genotypes for Adaptation to Drought Stress

Faba bean (Vicia faba L.) is one of the most important and drought sensitive grain legumes. Drought stress is thus one of major constraints in global faba bean production. In this study, twenty local and exotic faba bean genotypes were characterized on physiological and molecular basis. Seeds of faba bean genotypes (six per pot) were sown in poly venyl chloride pots. After seedling emergence, soil moisture was maintained at 100%, 50% and 25% of field capacity designated as well watered, moderate drought and severe drought, respectively. Drought stress significantly influenced the leaf area, leaf temperature, stomatal conductance, relative leaf water contents, grain yield and water‐use efficiency. Faba bean genotypes also differed for the leaf area, leaf temperature, relative leaf water contents, grain yield and water‐use efficiency. Faba bean genotypes Kamline and L.4 were better equipped to curtail water loss, maintain tissue water status, produce stable grain yield and had better water‐use efficiency under mild and severe drought stress, and may be used in breeding programmes. Amplified fragment length polymorphism markers showed high potential in detecting polymorphism and estimating genetic diversity among faba bean genotypes. Unweighted pair group method with arithmetic mean cluster analysis of the genotypes illustrated considerable association between molecular diversity, genetic background and geographic origin. In crux, high polymorphic rate and polymorphism information content values, together with the low genetic similarity observed among tested genotypes suggests a high level of heterogeneity, which may be used in breeding programmes to assemble different drought tolerance mechanisms in one genotype.     

Physiological and Yield Responses of Faba bean (Vicia faba L.) to Drought Stress in Managed and Open Field Environments

Water scarcity is threatening the sustainability of global food grain production systems. Devising management strategies and identification of crop species and genotypes are direly required to meet the global food demands with limited supply. This study, consisted of two independent experiments, was conducted to compare faba bean (Vicia faba L.) genotypes Giza Blanka, Goff‐1, Hassawi‐1, Hassawi‐2 and Gazira‐2 in terms of physiological attributes and yield under water‐limited environments. In first experiment, conducted in a growth chamber, osmotic stress of ?0.78, ?0.96, ?1.19 and ?1.65 MPa was induced using polyethylene glycol for 4 weeks. In second experiment, conducted in open field for two consecutive growing seasons, water deficit treatments were applied 3 weeks after sowing. In this experiment, irrigation was applied when an amount of evaporated water from the ‘class A pan’ evaporation reached 50 mm (well watered), 100 mm (moderate drought) and 150 mm (severe drought). Water deficit, applied in terms of osmotic stress or drought, reduced the root and shoot length, related leaf water contents, total chlorophyll contents and efficiency of photosystem‐II, plant height, grain yield and related attributes in faba bean; increased the leaf free proline, leaf soluble proteins and malondialdehyde contents, and triggered the maturity in tested faba bean genotypes. However, substantial genetic variation was observed in the tested genotypes in this regard. For instance, root length of genotypes Giza Blanka and Hassawi‐2 decreased gradually, whereas it was increased in genotypes Goff‐1, Hassawi‐1 and Gazira‐2 with increase in the level of osmotic stress. Genotypes Gazira‐2 and Hassawi‐2 had better relative leaf water contents, leaf free proline and soluble proteins under water deficit conditions; however, these were minimum in genotype Giza Blanka. Better accumulation of leaf free proline, soluble proteins, and maintenance of chlorophyll contents, tissue water, efficiency of photosystem‐II and grain weight in water‐limited conditions helped some genotypes like Hassawi‐2 to yield better. Future breeding programs for developing new faba bean genotypes for water‐limited environments may consider these traits.     

Understanding physiological and morphological traits contributing to drought tolerance in barley

Drought stress is a major limiting factor for crop production in the arid and semi‐arid regions. Here, we screened eighty barley (Hordeum vulgare L.) genotypes collected from different geographical locations contrasting in drought stress tolerance and quantified a range of physiological and agronomical indices in glasshouse trails. The experiment was conducted in large soil tanks subjected to drought treatment of eighty barley genotypes at three‐leaf stage and gradually brought to severe drought by withholding irrigation for 30 days under glasshouse conditions. Also, root length of the same genotypes was measured from stress‐affected plants growing hydroponically. Drought tolerance was scored 30 days after the drought stress commenced based on the degree of the leaf wilting, fresh and dry biomass and relative water content. These characteristics were related to stomatal conductance, stomatal density, residual transpiration and leaf sap Na, K, Cl contents measured in control (irrigated) plants. Responses to drought stress differed significantly among the genotypes. The overall drought tolerance was significantly correlated with relative water content, stomatal conductance and leaf Na⁺ and K⁺ contents. No significant correlations between drought tolerance and root length of 6‐day‐old seedling, stomatal density, residual transpiration and leaf sap Cl^? content were found. Taking together, these results suggest that drought‐tolerant genotypes have lower stomatal conductance, and lower water content, Na⁺, K⁺ and Cl^? contents in their tissue under control conditions than the drought‐sensitive ones. These traits make them more resilient to the forthcoming drought stress.     

A Simple Drought‐Sensitive Model for Leaf : Stem Partitioning of Wheat

We investigated the leaf : stem partitioning of winter wheat (Triticum aestivum L. varieties ‘Dekan’ and ‘Batis’) with and without drought influence. Irrigated and drought‐stressed winter wheat, grown in a rainout shelter in 2009/10 and 2013/14, were sampled during shoot elongation phase at the experimental Farm Hohenschulen located in Northern Germany. The data set contains leaf (DM_L) and stem dry masses (DM_S), as well as measured water contents for several soil layers. A reduced relative dry matter allocation to leaves was observed under drought stress. Our results clearly show that, if simulated leaf : stem partitioning is not sensitive to drought, this will cause a positive bias in simulated leaf and a negative bias in simulated stem dry matter under water‐limited conditions. This is in accordance with previous studies which revealed that crop simulators often overestimate the impact of drought on light‐use efficiency, whereas the consequences on leaf area development are underestimated. However, the drought stress‐induced shift in leaf : stem partitioning is yet not considered by most common wheat crop simulators. Our aim was to fill the gap in simulation of drought stress implications on leaf area development. A simple allometric model for leaf : stem partitioning () was parameterized. Starting from the allometric leaf : stem relationship observed under optimum water supply, a correction term was introduced, which allows to adapt the partitioning to drought stress conditions. The lg‐transformed root‐weighted soil water potential in the rooting zone (lgψ_root, lg(hPa)), calculated as a function of measured water contents and simulated root distribution, was used as a drought stress indicator. The linear correction term assumes an increase of the stem fraction, proportional to the difference between lgψ_root and a drought stress threshold (pF_crit, lg(hPa)). The analysis revealed that the shift in allometric partitioning towards stem fraction starts with lgψ_root greater than 1.92 [lg(hPa)]. The slope of the relative increase of dry matter allocated to the stem fraction was determined with 0.26 [lg(hPa)^?1]. Both parameters of the correction term were found to be highly significant. Implications for crop modelling are discussed.     

Drought Priming at Vegetative Growth Stage Enhances Nitrogen‐Use Efficiency Under Post‐Anthesis Drought and Heat Stress in Wheat

To study the effects of early drought priming at 5th‐leaf stage on grain yield and nitrogen‐use efficiency in wheat (Triticum aestivum L.) under post‐anthesis drought and heat stress, wheat plants were first exposed to moderate drought stress (drought priming; that is, the leaf water potential reached ca. ?0.9 MP a) at the 5th‐leaf stage for 11 days, and leaf water relations and gas exchange rates, grain yield and yield components, and agronomic nitrogen‐use efficiency (ANUE ) of the primed and non‐primed plants under post‐anthesis drought and heat stress were investigated. Compared with the non‐primed plants, the drought‐primed plants possessed higher leaf water potential and chlorophyll content, and consequently a higher photosynthetic rate during post‐anthesis drought and heat stress. Drought priming also resulted in higher grain yield and ANUE in wheat under post‐anthesis drought and heat stress. Drought priming at vegetative stage improves carbon assimilation and ANUE under post‐anthesis drought and heat stress and their combination in wheat, which might be used as a field management tool to enhance stress tolerance of wheat crops to multiple abiotic stresses in a future drier and warmer climate.     

Relationship between Biomass Production and Nitrogen Fixation under Drought-Stress Conditions in Peanut Genotypes with Different Levels of Drought Resistance

The relationship between biomass production and N₂ fixation under drought‐stress conditions in peanut genotypes with different levels of drought resistance is not well understood. The objective of this study was to determine the effect of drought on biomass production and N₂ fixation by evaluating the relative values of these two traits under well watered and water‐stress conditions. Twelve peanut genotypes were tested under field conditions in the dry seasons of 2003/2004 and 2004/2005 in north‐east Thailand. A split‐plot design with four replications was used. Main‐plot treatments were three water regimes [field capacity (FC), 2/3 available soil water (AW) and 1/3 AW], and sub‐plot treatments were 12 peanut lines. Data were recorded on biomass production and N₂ fixation under well watered and water‐stress conditions. Genotypic variations in biomass production and N₂ fixation were found at all water regimes. Biomass production and N₂ fixation decreased with increasing levels of drought stress. Genotypes did not significantly differ in reductions for biomass production, but did differ for reductions in N₂ fixation. High biomass production under both mild and severe drought‐stress conditions was due largely to high potential biomass production under well‐watered conditions and, to a lesser extent, the ability to maintain high biomass production under drought‐stress conditions. High N₂ fixation under drought stress also was due largely to high N₂ fixation under well‐watered conditions with significant but lower contributions from the ability to maintain high nitrogen fixation under drought stress. N₂ fixation at FC was not correlated with the reduction in N₂ fixation at 2/3 AW and 1/3 AW. Positive relationships between N₂ fixed and biomass production of the tested peanut genotypes were found at both levels of drought stress, and the relationship was stronger the more severe the drought stress. These results suggested that the ability to maintain high N₂ fixation under drought stress could aid peanut genotypes in maintaining high yield under water‐limited conditions.     

Soya Bean (Glycine max L. Merr.) Genotype Response to Early-season Flooding: I. Root and Nodule Development

Soya bean is often grown in regions subject to periodic flooding, with the rooting zone most affected by flooding due to its proximity to the source of stress. Our objectives were to examine the effects of flooding soya bean on its primary roots, adventitious roots and root nodules, and to determine relationships between root morphological changes and early‐season flood tolerance. The experiment was conducted in Belle Glade, FL with 11 soya bean genotypes subjected to (i) no flood, (ii) 2‐week flood 21–35 days after sowing (DAS) or (iii) 4‐week flood 21–49 DAS. All plants were harvested 49 DAS. Flooding reduced soya bean primary root weight, length and volume across genotypes. Adventitious root length and volume were greater in the 4‐week than the 2‐week flood. Soya bean nodule dry weight was threefold higher in the non‐flooded treatments. Genotypic differences in root development and tolerance to flooding were noted, with early‐season flood tolerance correlated with primary root dry weight, length and surface area, and adventitious root dry weight. However, there was no correlation between this study's early‐season root development and late‐season flood tolerance based on seed yield from previous studies. Our results indicate that full season trials may be necessary to identify flood‐tolerant soya bean germplasm.     

Fungal Endophytes Enhance Agronomically Important Traits in Severely Drought‐Stressed Barley

Crops often face severe and damaging local drought events, and in some regions, these episodes are predicted to become more frequent due to climate change. Some micro‐organisms have been shown to improve drought tolerance and improve yield in crop plants. Here, we show that fungal root endophytes isolated from a wild barley species (Hordeum murinum subsp. murinum) induced significant improvements in agronomic traits for a severely drought‐stressed barley cultivar grown in a controlled environment, including number of tillers, grain yield and shoot biomass. Five endophyte strains were tested, and the trait that showed the greatest significant difference in the drought‐stressed plants was the number of tillers, where all of the endophyte treatments induced a greater number of tillers per plant. However, except in one case, the mean dry root weight for all plants was greater in the control plants, indicating preferential allocation of resources to aboveground parts in the endophyte treatments. Results were not consistent across all endophyte treatments, with some endophytes performing much better than others. As these growth studies were conducted using soil‐based compost, the results may translate to the field and suggest that some of these endophytes have potential as barley inoculants in arid growing conditions.     

How does water and salt stress affect the germination and initial growth of Brazilian soya bean cultivars?

The effects of water and salt stress on rate of germination and seedling growth were investigated under laboratory conditions in 46 soya bean genotypes from Central-West region of Brazil to verify how these stresses may limit crop establishment during the initial growth stage and also to identify the most tolerant genotypes to drought and salinity. Mild water and salt stresses were imposed by seed exposure to –0.20 MPa iso-osmotic solutions with polyethylene glycol—PEG 6000 (119.57 g/L) or NaCl (2.357 g/L) for 12 days at 25°C. The germination percentage, seedling length and seedling dry matter were measured, and then, salt or drought tolerance indexes were calculated. The “NS 5909 RG,” “NS 7000 IPRO,” “NS 7338IPRO,” “FPS Solimões RR,” “NS 5151 IPRO,” “SYN 13610 IPRO,” “LG 60177 IPRO,” “NS 6909 IPRO” and “BMX Desafio RR” were identified as the most drought-tolerant genotypes, whereas under salinity conditions, the genotypes “5D 615 RR,” “BMX Desafio RR,” “5D 6215 IPRO” and “BMX Ponta IPRO” were identified as tolerant. The “BMX Desafio RR” is the genotype most adapted to both stress conditions and, therefore, should be used under conditions of water shortage and excess salt in the soil at sowing time.     

QTL mapping for six ear leaf architecture traits under water‐stressed and well‐watered conditions in maize (Zea mays L.)

Morphological traits for ear leaf are determinant traits influencing plant architecture and drought tolerance in maize. However, the genetic controls of ear leaf architecture traits remain poorly understood under drought stress. Here, we identified 100 quantitative trait loci (QTLs) for leaf angle, leaf orientation value, leaf length, leaf width, leaf size and leaf shape value of ear leaf across four populations under drought‐stressed and unstressed conditions, which explained 0.71%–20.62% of phenotypic variation in single watering condition. Forty‐five of the 100 QTLs were identified under water‐stressed conditions, and 29 stable QTLs (sQTLs) were identified under water‐stressed conditions, which could be useful for the genetic improvement of maize drought tolerance via QTL pyramiding. We further integrated 27 independent QTL studies in a meta‐analysis to identify 21 meta‐QTLs (mQTLs). Then, 24 candidate genes controlling leaf architecture traits coincided with 20 corresponding mQTLs. Thus, new/valuable information on quantitative traits has shed some light on the molecular mechanisms responsible for leaf architecture traits affected by watering conditions. Furthermore, alleles for leaf architecture traits provide useful targets for marker‐assisted selection to generate high‐yielding maize varieties.     

Drought and heat stress reduce yield and alter carbon rhizodeposition of different wheat genotypes

Drought and high temperature are major environmental stress factors threatening wheat production during grain filling stage resulting in substantial yield losses. Four wheat genotypes (Suntop, IAW2013, Scout and 249) were planted under two temperature levels (25 and 30°C) and two water levels (15% and 25% soil moisture content). Wheat yield, leaf δ¹³C, plant rhizodeposition, shoot biomass and root traits were examined. Low moisture (drought stress) and high temperature (heat stress) decreased the grain yield of all wheat genotypes, in particular 249, while combined drought and temperature stresses had the most pronounced negative effect on plant biomass and grain yield. Decreasing soil water availability decreased the allocation of plant‐derived C to soil organic carbon (SOC) and to microbial biomass through rhizodeposition. Leaf δ¹³C decreased with increased yield, suggesting that higher yielding genotypes were less water stressed and allocated less C to SOC and microbial biomass through rhizodeposition. Wheat genotypes with lower root/shoot ratios and thinner roots were more efficient at assimilating C to the grain, while genotypes with higher root/shoot ratios and thicker roots allocated more C belowground through rhizodeposition at the expense of producing higher yield. Therefore, improving these traits for enhanced C allocation to wheat grain under variable environmental conditions needs to be considered.     

Evaluating the role of seed priming in improving drought tolerance of pigmented and non‐pigmented rice

This study was conducted to evaluate the influence of seed priming on drought tolerance of pigmented and non‐pigmented rice. Seeds of pigmented (cv. Heug Jinju Byeo) and non‐pigmented (cv. Anjoong) rice were soaked in water (hydropriming) or solution of CaCl₂ (osmopriming). Seeds were sown in soil‐filled pots retained at 70 (well‐watered) and 35% (drought) water‐holding capacity. Drought stress caused erratic and poor stand establishment and decreased the growth of both rice types. More decrease in plant height and leaf area under drought stress was noted in pigmented rice, whereas decrease in root length and seedling dry weight, under drought, was more obvious in non‐pigmented rice. Pigmented rice maintained more tissue water and photosynthesis and had more polyphenols, flavonoids and antioxidant activity than non‐pigmented rice. Seed priming was effective in improving stand establishment, growth, polyphenols, flavonoids and antioxidant activity; however, extent of improvement was more in pigmented rice under drought. In conclusion, drought caused erratic germination and suppressed plant growth in both rice types. However, pigmented rice had better drought tolerance owing to uniform emergence, and better physiological and morphological plasticity. Seed priming was quite helpful in improving the performance of both rice types under drought and well‐watered conditions.     

Late‐season photosynthetic rate and senescence were associated with grain yield in winter wheat of diverse origins

There is a lack of studies that have investigated grain yield, its components and photosynthesis in late stages of wheat growth, giving us insufficient understanding of how these factors interact to contribute to yield during this period. As a result, three field experiments were carried out examining 20 winter wheat genotypes of diverse origins under irrigated, terminal drought and dryland conditions in the southern Idaho. Our objective was to evaluate the interaction between post‐anthesis physiological traits, especially leaf‐level photosynthetic capacity, senescence and yield components on grain yield in different moisture regimes. Genotype differences were found in leaf‐level photosynthesis and senescence, canopy temperature depression, grain yield and yield components in each water regime. Grain yield was closely associated with traits related to grain numbers. In all three moisture regimes, positive correlations were observed between grain yield and photosynthesis that were dependent on the timing or physiological growth stage of the photosynthetic measurement: highly significant correlations were found in the mid‐ and late grain filling stages, but no correlations at anthesis. Consistent with these findings, flag leaf senescence at the late grain filling stage was negatively correlated with grain yield and photosynthetic rate (under terminal drought and dryland conditions). These findings provided evidence that grain yield was sink‐limited until the final stages of growth, at which time sustained photosynthesis and delayed senescence were critical in filling grain. Because the trends were consistent in moisture sufficient and deficient conditions, the results suggest that late‐season photosynthesis and delayed leaf senescence are driven by the size of the reproductive carbon sink, which was largely governed by factors affecting grain numbers.     

Selection of wheat genotypes for biomass allocation to improve drought tolerance and carbon sequestration into soils

The biomass allocation pattern of plants to shoots and roots is a key in the cycle of elements such as carbon, water and nutrients with, for instance, the greatest allocations to roots fostering the transfer of atmospheric carbon to soils through photosynthesis. Several studies have investigated the root to shoot ratio (R:S) biomass of existing crops but variation within a crop species constitutes an important information gap for selecting genotypes aiming for increasing soil carbon stocks for climate change mitigation and food security. The objectives of this study were to evaluate agronomic performance and quantify biomass production and allocation between roots and shoots, in response to different soil water levels to select promising genotypes for breeding. Field and greenhouse experiments were carried out using 100 genotypes including wheat and Triticale under drought‐stressed and non‐stressed conditions. The experiments were set‐up using a 10 × 10 alpha lattice design with two replications under water stress and non‐stress conditions. The following phenotypic traits were collected: number of days to heading (DTH), number of productive tillers per plant (NPT), plant height (PH), days to maturity (DTM), spike length (SL), kernels per spike (KPS), thousand kernel weight (TKW), root biomass (RB), shoot biomass (SB), root to shoot ratio (R:S) and grain yield (GY). There was significant (p < 0.05) variation for grain yield and biomass production because of genotypic variation. The highest grain yield of 247.3 g/m² was recorded in the genotype LM52 and the least was in genotype Sossognon with 30 g/m². Shoot biomass ranged from 830 g/m² (genotype Arenza) to 437 g/m² (LM57), whilst root biomass ranged between 603 g/m² for Triticale and 140 g/m² for LM15 across testing sites and water regimes. Triticale also recorded the highest R:S of 1.2, whilst the least was 0.30 for wheat genotype LM18. Overall, drought stress reduced total biomass production by 35% and R:S by 14%. Genotypic variation existed for all measured traits useful for improving drought tolerance, whilst the calculated R:S values can improve accuracy in estimating C sequestration potential of wheat. Wheat genotypes LM26, LM47, BW140, LM70, LM48, BW152, LM75, BW162, LM71 and BW141 were selected for further development based on their high total biomass production, grain yield potential and genetic diversity under drought stress.     

Comparison of Salt and Drought‐Stress Effects on Maize Growth and Yield Formation with Regard to Acid Invertase Activity in the Kernels

The long‐term effects of salt stress (11 dS m^?1) and drought stress (35 % WHC) were investigated for two maize genotypes, focusing on the relation between metabolic changes around the time of pollination and the impact on yield determinants at maturity. The relatively salt‐resistant hybrid Pioneer 3906 and the relatively drought‐resistant hybrid Fabregas were compared. The experiments were conducted in large plastic containers in a vegetation hall in two consecutive years (2011 and 2012). Plant height and leaf area were significantly reduced under both stress conditions. The transpiration rate was only slightly reduced under drought stress; but under salt stress, a significant reduction occurred 40–53 days after sowing. As a significant increase in sucrose concentrations was observed in the salt‐treated maize kernels 2 days after pollination, the availability of assimilates was not limiting and the plants could afford to save water by reduced stomatal opening. Although under both stress conditions the soluble acid invertase activity was reduced 2 days after pollination, concomitantly, an increase in hexose concentrations was observed. Thus, in these experiments, the delivery of hexoses by acid invertase activity did not limit kernel development. Differences in grain yield at maturity between salt and drought stress were most likely caused by salt‐specific effects (Na⁺ toxicity), Fabregas being more affected than Pioneer 3906.