Genotypic Variation In Response Research Articles

Differential response of maize genotypes to low and normal nitrogen supply at seedling stage

High nitrogen (N) efficiency crop genotypes utilize resources rationally and reduce N losses. To evaluate the extent of genotypic variation in response to N supply, twenty-four maize genotypes were grown in Soilrite (peat mass, vermiculite and pearlite mix) supplied with low N level (2mM) or normal N level (25mM) in Hoagland solution. At 21 DAS the average shoot height (SH), leaf area (LA), stem dry weight (SDW), leaf dry weight (LDW), above ground dry weight (ADW), root dry weight (RDW) and total plant dry weight (PDW) were 38.1, 257.5, 67.3, 121.5, 96.9, 49.4, 76.9 and 140.6% higher respectively in seedlings exposed to normal N treatment than those grown under low N level. The shoot N content (SNC), root N content (RNC), above ground N accumulation (ANA), root N (RNA) and total plant N accumulation (PNA) were found to be 1.79, 2.23, 3.51, 3.30 and 3.44-fold increased at normal N supply over low N. Coefficients of variation (CV) varied greatly and ranged from 10.9-37.8 and 9.4-36.7 under low-N and normal-N treatment, respectively. LA, SDW, LDW, ADW, TDW, SNC, RNC, ANA, RNA and TNA showed significant positive correlation both under low N and normal N regime (p< 0.05). SDW, LDW, ADW, PDW, SNC, RNC, ANA, RNA and PNA were significantly correlated and had high CVs reflecting the difference of N in different maize genotypes and these parameters were selected for calculation of N efficiency comprehensive index. According to the N efficiency comprehensive index scatter map under low and normal N conditions, genotypes HKI-164-D4, HKI-325-17 AN, HKI-1332, DTL-3, DTL-2, DHM-117 and DTL-1 were efficient under both low and normal-N conditions and genotypes DTL-10, SNJ-2011-96, PSRJ-13099, NSJ-211 and Z59-17were inefficient under both low and normal-N conditions

Assessing phosphorus efficiency and tolerance in maize genotypes with contrasting root systems at the early growth stage using the semi‐hydroponic phenotyping system

AbstractBackgroundDevelopment of an evaluation tool to determine genotypic variation in phosphorus (P) utilization efficiency is essential to ensure crop productivity and farmers’ income under low P environments.AimsThis study aimed to develop an evaluation tool to determine genotypic variation in low‐P tolerance and P use efficiency under low P environments.MethodsRoot response and P efficiency traits in 20 maize genotypes with contrasting root systems were assessed 32 days after transplanting into the semi‐hydroponic root phenotyping system under low P (10 µM) or optimal P (200 µM) supply.ResultsCompared to optimal P, low P supply increased root‐to‐shoot biomass ratio by 48.7% (shoot dry weight decreased by 20.0% and root dry weight increased by 20.6%). Low P supply increased total root length by 17.8% but decreased primary root depth, with no significant change in lateral root number across all genotypes. Low P stress enhanced P utilization efficiency. Based on genotypic variation and correlations among the 17 measured plant traits in response to low P stress, nine traits were converted to low‐P tolerance coefficients (LPTC), compressed by principal component analysis. The three principal component scores were extracted for hierarchical cluster analysis and classified the 20 genotypes into three groups with different P efficiency, including two P‐efficient genotypes and nine P‐inefficient genotypes.ConclusionsThe study demonstrated genotypic variation in response to low P stress. The P‐efficient genotypes with higher LPTC values better adapted to low P environments by adjusting root architecture and re‐distributing P and biomass in plant organs. The systematic cluster analysis using selected traits and their LPTC values can be used as an evaluation tool in assessing P efficiency among the genotypes.

Genotypic variation in the tolerance to moderate cadmium toxicity among 20 maize genotypes with contrasting root systems.

Cadmium (Cd) contamination in farmland is a serious environmental and safety issue affecting plant growth, crop productivity, and human health. This study aimed to investigate genotypic variation in root morphology and Cd accumulations under moderate Cd stress among diverse maize genotypes. Twenty maize genotypes with contrasting root systems were assessed for Cd tolerance 39 days after transplanting (V6, six-leaf stage) under 20 μmol L-1 CdCl2 using a semi-hydroponic phenotyping platform in a glasshouse. Cadmium stress significantly inhibited plant growth across all genotypes. Genotypic variation in response to Cd toxicity was apparent: shoot dry weight varied from 0.13 (genotype NS2020) to 0.35 g plant-1 (Dongke301) with deductions up to 63% compared with non-Cd treatment (CK). Root dry weightof 20 genotypes ranged from 0.06 (NS2020) to 0.18 g plant-1 (Dongke301) with a deduction up to 56%. Root length ranged from 2.21 (NS590b) to 9.22 m (Dongke301) with a maximal decline of 76%. Cadmium-treated genotypes generally had thicker roots and average diameter increased by 34% compared with CK. Genotypes had up to 3.25 and 3.50 times differences in shoot and root Cd concentrations, respectively. Principal component and cluster analyses assigned the 20 genotypes into Cd-tolerant (five genotypes) and Cd-sensitive (15 genotypes) groups. Maize genotypes varied significantly in response to moderate Cd stress. Cadmium-tolerant genotypes optimized root morphology and Cd accumulation and distribution. This study could assist in the selection and breeding of new cultivars with improved adaptation to Cd-contaminated soil for food and feed or land remediation purposes. © 2022 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Multivariate characterization of biochemical and physiological attributes of quinoa (Chenopodium quinoa Willd.) genotypes exposed to nickel stress: implications for phytoremediation.

Nickel (Ni) is an essential element for plants; however, excessive uptake of Ni causes phytotoxicity in plants. The phytotoxic effects of Ni onthe growth of quinoa and the underlaying mechanisms for Ni tolerance and phytoremediation are unknown. Hence, the present study investigated Ni tolerance and accumulation potential of two quinoa genotypes (Puno and Vikinga). Both genotypes were exposed to Ni (0, 100, 200, 300, and 400μM) in half-strength Hoagland nutrient solution for three weeks. Results revealed that shoot and root lengths, biomass, stomatal conductance, and chlorophyll contents were decreased with the increase of Ni concentration. Excessive uptake of Ni resulted in the limited uptake of K by root and its translocation to shoot. Ni caused oxidative stress in plants by overproduction of H2O2 leading to lipid peroxidation of cell membranes. Genotype Puno showed greater tolerance to Ni than Vikinga based on tolerance index, lower bioconcentration factor, and translocation factor. Greater tolerance of Puno was mainly attributed to improved physiological responses and amelioration of oxidative stress by induction of antioxidant enzymes such as peroxidase (POD), catalase (CAT), superoxide dismutase (SOD), and ascorbate peroxidase (APX). It was revealed through multivariate analysis that Ni had strong negative correlations with growth and physiological attributes and positive associations with oxidative stress attributes. The study demonstrated genotypic variation in response to varying Ni concentrations and Puno performed better than Vikinga for phytostabilization of Ni-contaminated soils.

Genotypic variation in response to drought stress is associated with biochemical and transcriptional regulation of ureides metabolism in common bean (Phaseolus vulgaris L.)

Ureidic legumes such as common bean (Phaseoulus valgaris L.) plants export nitrogen from the nodules to shoots and leaves as ureides during symbiotic biological nitrogen fixation. Common bean gene encoding allantoinase (allantoin amidohydrolase, EC 3.5.2.5), is a key enzyme that catalyses the hydrolysis of allantoin to allantoic acid. It plays a role in ureide generation for export and ureide catabolism to generate a nitrogen source in sinks tissues. As such, one of the adaptive mechanisms of plants to drought stress, is associated with ureides accumulation. To identify genetic variation of common bean in response to drought stress, changes in the expression of ALLANTONAISE (PvALN) gene and ureides content were examined in the leaf tissues of the three common bean genotypes (CAL96, DAB514 and DAB541) and one tepary bean genotype (Phaseolus acutifolius A.Gray). Amongst all the genotypes, the suggested drought susceptibility in DAB514 common bean genotype, was probably attributed to a repressed PvALN expression rate which were corroborated by an impaired ureides levels, and reduced plant growth. On contrary, drought stress induced an upregulated relative expression of PvALN coupled with an increase in allantoin and allantoate in DAB541 common bean genotype. In addition, the sustained plant growth in CAL96 was probably attributed to a steady amount of allantoin synthesized under drought stress. Taken together, DAB541 and CAL96 common bean genotypes are the promising genotypes with an induced upregulated transcriptional control of catabolism and/or biosynthesis of ureides, hence potential genotypes for selection and introduction under Botswana semi-arid conditions.

Effect of the Systemic Neonicotinoid Insecticide Dinotefuran on Leaf-level Photosynthesis in Loblolly Pine (Pinus taeda)

ABSTRACT Bark beetles (Coleoptera: Curculionidae: Scolytinae) are a common pest in loblolly pine (Pinus taeda L.) plantations, and climate intensification threatens to increase the range of bark beetle infestation and vulnerability of loblolly pine. New insecticides and management options are needed to maintain loblolly pine plantation productivity, mitigating increased bark beetle risk. The systemic neonicotinoid insecticide dinotefuran (Safari 20SG systemic insecticide, Valent USA, LLC), is utilized by nursery managers to protect loblolly pine from bark beetles, but there is little published literature on the insecticide’s potential phytotoxicity. The objective of this study was to evaluate the effect of dinotefuran on the leaf-level photosynthesis of three loblolly pine genotypes. Dinotefuran was applied to lower tree boles, and photosynthetic measurements occurred two months later. Dinotefuran did not significantly impact leaf-level gross photosynthesis (Pgmax), light-saturated net photosynthesis (Pnet) or dark respiration (Rd); nor was there any significant genotypic variation in responses. Dinotefuran appears to be a promising insecticide for bark beetle prevention without risk of foliar toxicity.

Biofortification of Diverse Basmati Rice Cultivars with Iodine, Selenium, and Zinc by Individual and Cocktail Spray of Micronutrients

Given that an effective combined foliar application of iodine (I), selenium (Se), and zinc (Zn) would be farmer friendly, compared to a separate spray of each micronutrient, for the simultaneous biofortification of grain crops, we compared effectiveness of foliar-applied potassium iodate (KIO3, 0.05%), sodium selenate (Na2SeO4, 0.0024%), and zinc sulfate (ZnSO4∙7H2O, 0.5%), separately and in their combination (as cocktail) for the micronutrient biofortification of four Basmati cultivars of rice (Oryza sativa L.). Foliar-applied, each micronutrient or their cocktail did not affect rice grain yield, but grain yield varied significantly among rice cultivars. Irrespective of foliar treatments, the brown rice of cv. Super Basmati and cv. Kisan Basmati had substantially higher concentration of micronutrients than cv. Basmati-515 and cv. Chenab Basmati. With foliar-applied KIO3, alone or in cocktail, the I concentration in brown rice increased from 12 to 186 µg kg−1. The average I concentration in brown rice with foliar-applied KIO3 or cocktail was 126 μg kg−1 in cv. Basmati-515, 160 μg kg−1 in cv. Chenab Basmati, 153 μg kg−1 in cv. Kisan Basmati, and 306 μg kg−1 in cv. Super Basmati. Selenium concentration in brown rice increased from 54 to 760 µg kg−1, with foliar-applied Na2SeO4 individually and in cocktail, respectively. The inherent Zn concentration in rice cultivars ranged between 14 and 19 mg kg−1 and increased by 5–6 mg Zn per kg grains by foliar application of ZnSO4∙7H2O and cocktail. The results also showed the existence of genotypic variation in response to foliar spray of micronutrients and demonstrated that a foliar-applied cocktail of I, Se, and Zn could be an effective strategy for the simultaneous biofortification of rice grains with these micronutrients to address the hidden hunger problem in human populations.

Tolerance of Pima and Upland cotton to trifloxysulfuron (Envoke) herbicide under field conditions

Trifloxysulfuron (Envoke) is an acetolactate synthase-inhibitor herbicide and can be used to control many broadleaf weeds and nutsedges in cotton production. However, there is a lack of information on genotypic variation in response to the herbicide. In this field study, 60 Pima (Gossypium barbadense L.) lines, 122 Upland (G. hirsutum L.) lines, and 9 Upland × Pima segregating populations were divided into five tests (18A, 18B, 18G, 18RB, and 18HQ) to evaluate trifloxysulfuron tolerance at the 7-true leaf stage (42 days after planting) under the same field conditions in 2018. Across the five tests, Pima cotton genotypes tested in this study did not show any visual crop injury based on percentage of plants with chlorosis at 6 days after treatment (DAT), indicating consistent and high levels of trifloxysulfuron tolerance. However, the response to trifloxysulfuron within Upland cotton is highly variable. While Upland cotton is overall more sensitive to trifloxysulfuron with crop injury up to 80% than Pima cotton, 19 lines had injury below 5% including one line with no visual injury, and 19 lines had injury between 5% and 10%. In test 18HQ with 15 transgenic Upland cultivars and 17 non-transgenic Upland lines, the analysis of variance detected a significant genotypic difference. The broad-sense heritability estimates for trifloxysulfuron tolerance based on crop injury at 6 DAT was 0.555, suggesting that trifloxysulfuron tolerance in Upland cotton is moderately heritable. This study represents the first report that Pima cotton and many Upland cotton lines are highly tolerant to trifloxysulfuron with no or little crop injury.

Climate Change Impacts on Cacao: Genotypic Variation in Responses of Mature Cacao to Elevated CO2 and Water Deficit

Climate change poses a significant threat to agricultural production in the tropics, yet relatively little research has been carried out to understand its impact on mature tropical tree crops. This research aims to understand the genotypic variation in growth and photosynthesis in mature cacao trees in response to elevated CO2 and water deficit. Six genotypes were grown under greenhouse conditions at ambient (ca. 437 ppm) and elevated CO2 (ca. 724 ppm) and under well-watered and water deficit conditions for 23 months. Leaf- and canopy-level photosynthesis, water-use efficiency, and vegetative growth increased significantly in response to elevated CO2. Water deficit had a significant negative effect on many photosynthetic parameters and significantly reduced biomass production. The negative effect of water deficit on quantum efficiency was alleviated by elevated CO2. Genotypic variation was observed in several parameters including stomatal conductance, stomatal density and index, quantum efficiency, and biomass production, indicating the potential to develop more climate-change-resilient genotypes that can cope with predicted future climate change conditions. Elevated CO2 reduced some of the negative effects of water deficit through changes in water-use efficiency and light utilisation and reduced the negative impact of water deficit on biomass accumulation, but this was genotype-specific.

Dissecting the Genotypic Variation of Growth Responses to Far-Red Radiation in Tomato.

The recent development of light-emitting diodes (LEDs) and their application in modern horticulture stimulated studies demonstrating that additional far-red (FR) radiation (700–800 nm) increases plant dry mass. This effect of FR has been explained by improved photosynthesis and/or plant architecture. However, the genotypic variation in this response is largely unknown. Here, we aim to explore and explain the genotypic variation in growth responses to additional FR. We expected the genotypic variation in the responses of plant dry mass to additional FR. Further, we hypothesized that a significant improvement of both net assimilation rate (NAR) and leaf area ratio (LAR) is responsible for a strong dry mass increase under additional FR, while some genotypes respond only marginally or even negatively in NAR or LAR under FR, thus resulting in a weak FR effect on plant dry mass. To test these hypotheses, we grew 33 different tomato genotypes for 21 days with 0, 25, or 100 μmol m–2 s–1 of FR added to a common white + red LED background lighting of 150 μmol m–2 s–1. Genotypes responded similarly with respect to plant height, stem dry mass, and shoot:root ratio; i.e., they all increased with increasing FR. However, the response of total plant dry mass varied among genotypes. We categorized the genotypes into three groups (strongly, moderately, and weakly responding groups) based on their relative response in total plant dry mass to FR. Growth component analysis revealed that the strongly responding genotypes increased strongly in NAR rather than LAR. The weakly responding genotypes, however, showed a substantial increase in LAR but not NAR. The increase in LAR was due to the increase in specific leaf area. Leaf mass fraction, which is the other component of LAR, decreased with FR and did not differ between groups. In conclusion, tomato genotypes that increased strongly in NAR in response to FR were able to achieve a more substantial increase in dry mass than did other genotypes. This is the first study to explain the differences in growth responses of a large number of tomato genotypes toward FR in their light environment.

Genotypic variation in response to extreme events may facilitate kelp adaptation under future climates

Marine heatwaves (MHWs) have caused declines in many kelp forests globally. Although the ecological effects of these climatic extremes have been well examined, studies on the role of genotypic variation in underpinning population responses under pressures are lacking. Understanding how kelps respond to different warming profiles and, in particular, intraspecific variation in responses is necessary to confidently anticipate the future of kelp forests, yet this remains a critical knowledge gap for most species. This study examined the responses of early life stages of 9 different genotypes of the Australian kelp Ecklonia radiata to different MHW profiles, where cumulative heat intensity was kept constant: control treatment (constant 19°C), heat spikes (fluctuating 19-23°C), low intensity MHW (ramp up 23°C) and high intensity MHW (ramp up 27°C). Overall, we found significant declines in E. radiata gametophyte performance in all MHW treatments and delays in sporophyte recruitment during MHW exposure. We also found significant genotype by environment (G×E) interactions, suggesting tolerance to acute thermal stress is influenced by genetic variation. Our results showed that offspring from different genotypes within the same population respond differently to MHWs, indicating that some genotypes are susceptible to MHWs while others are more resistant. While the effects on standing genetic variation and subsequent susceptibility to other stressors are unknown, our findings suggest that in addition to immediate impacts on marine organisms, natural genotypic variation in response to thermal anomalies may facilitate the gradual evolution of populations with increased thermal tolerance under future climates.

Genome-Wide Association Studies Reveal Genomic Regions Associated With the Response of Wheat (Triticum aestivum L.) to Mycorrhizae Under Drought Stress Conditions.

In the majority of wheat growing areas worldwide, the incidence of drought stress has increased significantly resulting in a negative impact on plant development and grain yield. Arbuscular mycorrhizal symbiosis is known to improve drought stress tolerance of wheat. However, quantitative trait loci (QTL) involved in the response to drought stress conditions in the presence of mycorrhizae are largely unknown. Therefore, a diverse set consisting of 94 bread wheat genotypes was phenotyped under drought stress and well watered conditions in the presence and absence of mycorrhizae. Grain yield and yield components, drought stress related traits as well as response to mycorrhizae were assessed. In parallel, wheat accessions were genotyped by using the 90k iSelect chip, resulting in a set of 15511 polymorphic and mapped SNP markers, which were used for genome-wide association studies (GWAS). In general, drought stress tolerance of wheat was significantly increased in the presence of mycorrhizae compared to drought stress tolerance in the absence of mycorrhizae. However, genotypes differed in their response to mycorrhizae under drought stress conditions. Several QTL regions on different chromosomes were detected associated with grain yield and yield components under drought stress conditions. Furthermore, two genome regions on chromosomes 3D and 7D were found to be significantly associated with the response to mycorrhizae under drought stress conditions. Overall, the results reveal that inoculation of wheat with mycorrhizal fungi significantly improves drought stress tolerance and that QTL regions associated with the response to mycorrhizae under drought stress conditions exist in wheat. Further research is necessary to validate detected QTL regions. However, this study may be the starting point for the identification of candidate genes associated with drought stress tolerance and response to mycorrhizae under drought stress conditions. Maybe in future, these initial results will help to contribute to use mycorrhizal fungi effectively in agriculture and combine new approaches i.e., use of genotypic variation in response to mycorrhizae under drought stress conditions with existing drought tolerance breeding programs to develop new drought stress tolerant genotypes.

Closing the global ozone yield gap: Quantification and cobenefits for multistress tolerance.

Increasing both crop productivity and the tolerance of crops to abiotic and biotic stresses is a major challenge for global food security in our rapidly changing climate. For the first time, we show how the spatial variation and severity of tropospheric ozone effects on yield compare with effects of other stresses on a global scale, and discuss mitigating actions against the negative effects of ozone. We show that the sensitivity to ozone declines in the order soybean>wheat>maize>rice, with genotypic variation in response being most pronounced for soybean and rice. Based on stomatal uptake, we estimate that ozone (mean of 2010-2012) reduces global yield annually by 12.4%, 7.1%, 4.4% and 6.1% for soybean, wheat, rice and maize, respectively (the "ozone yield gaps"), adding up to 227Tg of lost yield. Our modelling shows that the highest ozone-induced production losses for soybean are in North and South America whilst for wheat they are in India and China, for rice in parts of India, Bangladesh, China and Indonesia, and for maize in China and the United States. Crucially, we also show that the same areas are often also at risk of high losses from pests and diseases, heat stress and to a lesser extent aridity and nutrient stress. In a solution-focussed analysis of these results, we provide a crop ideotype with tolerance of multiple stresses (including ozone) and describe how ozone effects could be included in crop breeding programmes. We also discuss altered crop management approaches that could be applied to reduce ozone impacts in the shorter term. Given the severity of ozone effects on staple food crops in areas of the world that are also challenged by other stresses, we recommend increased attention to the benefits that could be gained from addressing the ozone yield gap.

Physiological mechanisms underpinning tolerance to high temperature stress during reproductive phase in mungbean (Vigna radiata (L.) Wilczek)

This study investigated the physiological factors underlying genotypic variation in response to high temperature and the role of acclimation prior to high temperature stress, in mungbean genotypes, selected based on their sensitivity to high temperature. The genotypes were subjected to three temperature regimes during the reproductive phase, i.e. normal (28 °C/24 °C, CON), acclimation temperature (35 °C/28 °C, Ac-HT) before transferring to high temperature (45 °C/30 °C), and direct exposure of non-acclimated plants to high temperature (45 °C/30 °C, NAc-HT). Environmentally controlled growth chambers were used to provide the required temperature regimes. The plants were maintained at fully watered conditions throughout the growing cycle. The average shoot biomass (including root) was reduced by 9% and 41%, and the grain yield by 31% and 50%, in the acclimated (Ac-HT) and non-acclimated (NAc-HT) treatments, respectively, compared to CON. The mean root weight in the NAc-HT treatment was reduced by 32%, while the mean root weight in Ac-HT treatment was comparable to CON, although there was genotypic variation with in the treatments. The mean root weight in the tolerant group was 48%, 180% and 130% greater than susceptible group, in CON, Ac-HT and NAc-HT treatments, respectively. There was significant variation among genotypes for root weight. A positive relationship (r2 = 0.54**) between root and shoot weight indicated that plants with larger root weight also produced higher shoot biomass. The high temperature tolerant genotypes responded to acclimation treatment by promoting root growth while such enhanced root growth was not observed in susceptible genotypes. The study suggested that acclimation treatment followed by high temperature could be used as a technique to identify genotypes with ability to adapt to high temperature stress conditions.

Turfgrass and Climate Change

Core Ideas Climate change will affect temperature and precipitation patterns. Increasing temperatures will cause a shift in turfgrass species to more northen climates. Variation among varieties of turfgrass provide opportunity to increase climate resilience. Climate change will increase abiotic and biotic stresses on turfgrass. Climate change is occurring and is impacting biological systems through increased temperatures, more variable precipitation, and increased CO2 in the atmosphere. These effects have been documented for agricultural species, primarily grain crops, pasture and rangeland species. The extension of these relationships to turfgrass has been limited; however, these plants are an important part of our ecosystems and preservation of these plantings adds to social value and ecosystem services. Turfgrasses can be divided into cool‐season and warm‐season species and the projected changes in maximum air temperatures, along with increased root zone temperatures may promote a Northward migration of warm‐season turfgrasses. Increased spring precipitation and more variable summer precipitation coupled with more intense precipitation events are projected to occur requiring enhanced management of soil water. Turfgrass management to ensure adequate root zone soil water, and the selection of varieties or species with greater drought tolerance in the warmer regions will be necessary to preserve turfgrass plantings. Increases in CO2 benefits turfgrass growth and positively affects water use efficiency, which decreases the potential effects of a more variable precipitation regime because of impacts on soil water use. Genotypic variation in response to soil water deficits provides a foundation for screening turfgrass species to adapt to climatic stresses. Changes in temperature and precipitation variation will increase the potential for abiotic and biotic stresses on turfgrasses. Turfgrass management will require increased attention to increased abiotic and biotic stresses.

栽植密度を用いた大気CO_2上昇下で高い生産性を示すコムギ品種の選抜方法 : 過去50年間に北海道で育成された秋播性コムギの疎植適応における品種間差異(平成27年度年次講演会一般公演)

栽植密度を用いた大気CO_2上昇下で高い生産性を示すコムギ品種の選抜方法 : 過去50年間に北海道で育成された秋播性コムギの疎植適応における品種間差異(平成27年度年次講演会一般公演)

Leaf and canopy scale drivers of genotypic variation in soybean response to elevated carbon dioxide concentration.

The atmospheric [CO2 ] in which crops grow today is greater than at any point in their domestication history and represents an opportunity for positive effects on seed yield that can counteract the negative effects of greater heat and drought this century. In order to maximize yields under future atmospheric [CO2 ], we need to identify and study crop cultivars that respond most favorably to elevated [CO2 ] and understand the mechanisms contributing to their responsiveness. Soybean (Glycine max Merr.) is a widely grown oilseed crop and shows genetic variation in response to elevated [CO2 ]. However, few studies have studied the physiological basis for this variation. Here, we examined canopy light interception, photosynthesis, respiration and radiation use efficiency along with yield and yield parameters in two cultivars of soybean (Loda and HS93-4118) previously reported to have similar seed yield at ambient [CO2 ], but contrasting responses to elevated [CO2 ]. Seed yield increased by 26% at elevated [CO2 ] (600μmol/mol) in the responsive cultivar Loda, but only by 11% in HS93-4118. Canopy light interception and leaf area index were greater in HS93-4118 in ambient [CO2 ], but increased more in response to elevated [CO2 ] in Loda. Radiation use efficiency and harvest index were also greater in Loda than HS93-4118 at both ambient and elevated [CO2 ]. Daily C assimilation was greater at elevated [CO2 ] in both cultivars, while stomatal conductance was lower. Electron transport capacity was also greater in Loda than HS93-4118, but there was no difference in the response of photosynthetic traits to elevated [CO2 ] in the two cultivars. Overall, this greater understanding of leaf- and canopy-level photosynthetic traits provides a strong conceptual basis for modeling genotypic variation in response to elevated [CO2 ].

Effect of post-sowing nitrogen management on co-limitation of nitrogen and water in canola and mustard

In rainfed Mediterranean environments crop yields are limited by nitrogen (N) and water. The concept of water and N co-limitation has been used to describe how these competing resources are allocated during growth, it has been proposed that growth is optimum when water and N are equally limiting. All the published work so far on water and N co-limitation has been done in cereals using single applications of fixed amounts of N. However, delayed and split applications of N at key phenological growth stages can improve N use efficiency and alter the severity of N and water stress during the growth of the crop. The aim of the work reported here was to assess water and N co-limitation in the indeterminate crops canola (Brassica napus) and mustard (B. juncea) under different post-sowing N treatments. Four field experiments were conducted over three years with different cultivars of canola and mustard, under different water regimes, and grown with three N rates (0, 100 and 200kgNha−1 as granular urea) applied at different phenological growth stages. The results suggested that yield gaps (Yg; the difference between actual and attainable yield) increased as total stress from water and N (TWN) and the maximum of the two stresses (MWN) increased and declined as the degree of water-N co-limitation increased, whether based on total stress (CTWN) or maximum stress (CMWN). However, seasonal and genotypic variation in the Yg reduction and improvement in water use efficiency (WUE) with the degree of co-limitation were observed for CTWN. Application of N improved the CTWN without having the effect of split N application timing. No relationship was found between N use efficiency for seed yield (NUESY) of canola and mustard and co-limitation indices, which may be due to low N uptake efficiency during the pre-flowering period and low physiological efficiency during the post – flowering period. This study provides the first empirical evidence that yield of canola and mustard is co-limited by water and N under post-sowing N application with seasonal and genotypic variation in response to CTWN. Future studies need to focus on the interaction of pre and post-flowering water and N stresses and their effect on CTWN in devising crop management tools for this environment.

Genotypic variations in ion homeostasis, photochemical efficiency and antioxidant capacity adjustment to salinity in cotton (Gossypium hirsutum L.)

ABSTRACTTo determine the genotypic variation in response to salt (NaCl) stress in cotton (Gossypium hirsutum L.) seedlings, potassium (K+) and sodium (Na+) homeostasis, photochemical energy utility, reactive oxygen metabolism and the activity of antioxidant enzymes were comparatively analyzed in three cotton cultivars (CCRI 49, CCRI 35 and Z 51504) under salt constraint. The results showed that NaCl treatment significantly inhibited biomass accumulation, and the extent of inhibition was highest in CCRI 49 and lowest in Z 51504. Salinity caused an ion imbalance in plants but ion homeostasis was less pronounced in Z 51504, as it accumulated more K+ and less Na+. Experiments of salt shock treatment were tested using a non-invasive micro-test (NMT) system, which also revealed that Z 51504 had lower Na+ influx and better K+ retention. Salinity increased excess-energy dissipation [non-photochemical quenching (qN) and photorespiration rate (PR)], but depressed photochemical efficiency such as photosynthesis rate (Pn), quenching (qP), photochemical quantum yield of photosystem (ΦPSII) and electron transport rate (ETR). As a result, more electrons were driven to other sinks, for example decreasing ETR/Pn and increasing the O2− generation rate. However, the superior tolerance of Z 51504 had a better balance of photochemical energy under salt conditions, displayed higher photochemical efficiency and excess-energy dissipation. Furthermore, the antioxidant enzyme activities were also affected by salt stress and less effectively removed reactive oxygen species. The antioxidant enzyme activities of Z 51504 were higher than those of CCRI 49 and CCRI 35, which resulted in lower levels of reactive oxygen species (ROS) and mitigated the salt-induced membrane lipid peroxidation. The overall results indicated that more effective retention of ions, photochemical energy utility and ROS-removing capability were probably the main reasons for the stronger salt tolerance in Z 51504.

Genotypic variation in response to salinity in a new sexual germplasm of Cenchrus ciliaris L.

As part of a breeding program for new salt-tolerant sexual genotypes of Cenchrus ciliaris L., here we evaluated the salt-stress response of two new sexual hybrids, obtained by controlled crosses, at seedling and germination stages. A seedling hydroponic experiment with 300 mM NaCl was performed and physiological variables and growth components were evaluated. While salt-treated sexual material did not show a decrease in productivity with respect to control plants, a differential response in some physiological characteristics was observed. Sexual hybrid 1-9-1 did not suffer oxidative damage and its proline content did not differ from that of control treatment. By contrast, sexual hybrid 1-7-11 suffered oxidative damage and accumulated proline, maintaining its growth under saline stress. At the germination stage, sexual hybrid 1-9-1 presented the highest Germination Rate Index at the maximum NaCl concentration assayed, suggesting an ecological advantage in this genotype. These new sexual resources are promising maternal parental with differential response to salt and could be incorporated in a breeding program of C. ciliaris in the search of new genotypes tolerant to salinity.