Nitrogen Use Efficiency Traits Research Articles

Breeding progress of nitrogen use efficiency of cereal crops, winter oilseed rape and peas in long-term variety trials.

Grain yield and NUE increased over time while nitrogen yield did not drop significantly despite reduced nitrogen input. Selection for grain and nitrogen yield is equivalent to selection for NUE. Breeding and registration of improved varieties with high yield, processing quality, disease resistance and nitrogen use efficiency (NUE) are of utmost importance for sustainable crop production to minimize adverse environmental impact and contribute to food security. Based on long-term variety trials of cereals, winter oilseed rape and grain peas tested across a wide range of environmental conditions in Germany, we quantified long-term breeding progress for NUE and related traits. We estimated the genotypic, environmental and genotype-by-environment interaction variation and correlation between traits and derived heritability coefficients. Nitrogen fertilizer application was considerably reduced between 1995 and 2021 in the range of 5.4% for winter wheat and 28.9% for spring wheat while for spring barley it was increased by 20.9%. Despite the apparent nitrogen reduction for most crops, grain yield (GYLD) and nitrogen accumulation in grain (NYLD) was increased or did not significantly decrease. NUE for GYLD increased significantly for all crops between 12.8% and 35.2% and for NYLD between 8% and 20.7%. We further showed that the genotypic rank of varieties for GYLD and NYLD was about equivalent to the genotypic rank of the corresponding traits of NUE, if all varieties in a trial were treated with the same nitrogen rate. Heritability of nitrogen yield was about the same as that of grain yield, suggesting that nitrogen yield should be considered as an additional criterion for variety testing to increase NUE and reduce negative environmental impact.

Genome-wide dissection and haplotype analysis identified candidate loci for nitrogen use efficiency under drought conditions in winter wheat.

Climate change causes extreme conditions like prolonged drought, which results in yield reductions due to its effects on nutrient balances such as nitrogen uptake and utilization by plants. Nitrogen (N) is a crucial nutrient element for plant growth and productivity. Understanding the mechanistic basis of nitrogen use efficiency (NUE) under drought conditions is essential to improve wheat (Triticum aestivum L.) yield. Here, we evaluated the genetic variation of NUE-related traits and photosynthesis response in a diversity panel of 200 wheat genotypes under drought and nitrogen stress conditions to uncover the inherent genetic variation and identify quantitative trait loci (QTLs) underlying these traits. The results revealed significant genetic variations among the genotypes in response to drought stress and nitrogen deprivation. Drought impacted plant performance more than N deprivation due to its effect on water and nutrient uptake. GWAS identified a total of 27 QTLs with a significant main effect on the drought-related traits, while 10 QTLs were strongly associated with the NUE traits. Haplotype analysis revealed two different haplotype blocks within the associated region on chromosomes 1B and 5A. The two haplotypes showed contrasting effects on N uptake and use efficiency traits. The in silico and transcript analyses implicated candidate gene coding for cold shock protein. This gene was the most highly expressed gene under several stress conditions, including drought stress. Upon validation, these QTLs on 1B and 5A could be used as a diagnostic marker for NUE and drought tolerance screening in wheat.

Nitrogen transport and assimilation in tea plant (Camellia sinensis): a review.

Nitrogen is one of the most important nutrients for tea plants, as it contributes significantly to tea yield and serves as the component of amino acids, which in turn affects the quality of tea produced. To achieve higher yields, excessive amounts of N fertilizers mainly in the form of urea have been applied in tea plantations where N fertilizer is prone to convert to nitrate and be lost by leaching in the acid soils. This usually results in elevated costs and environmental pollution. A comprehensive understanding of N metabolism in tea plants and the underlying mechanisms is necessary to identify the key regulators, characterize the functional phenotypes, and finally improve nitrogen use efficiency (NUE). Tea plants absorb and utilize ammonium as the preferred N source, thus a large amount of nitrate remains activated in soils. The improvement of nitrate utilization by tea plants is going to be an alternative aspect for NUE with great potentiality. In the process of N assimilation, nitrate is reduced to ammonium and subsequently derived to the GS-GOGAT pathway, involving the participation of nitrate reductase (NR), nitrite reductase (NiR), glutamine synthetase (GS), glutamate synthase (GOGAT), and glutamate dehydrogenase (GDH). Additionally, theanine, a unique amino acid responsible for umami taste, is biosynthesized by the catalysis of theanine synthetase (TS). In this review, we summarize what is known about the regulation and functioning of the enzymes and transporters implicated in N acquisition and metabolism in tea plants and the current methods for assessing NUE in this species. The challenges and prospects to expand our knowledge on N metabolism and related molecular mechanisms in tea plants which could be a model for woody perennial plant used for vegetative harvest are also discussed to provide the theoretical basis for future research to assess NUE traits more precisely among the vast germplasm resources, thus achieving NUE improvement.

Evaluation of three sets of advanced backcrosses of eggplant with wild relatives from different gene pools under low N fertilization conditions.

The development of new cultivars with improved nitrogen use efficiency (NUE) is key for implementing sustainable agriculture practices. Crop wild relatives (CWRs) provide valuable genetic resources for breeding programs aimed at achieving this goal. In this study, three eggplant (Solanum melongena) accessions together with their advanced backcrosses (ABs; BC3 to BC5 generations) were evaluated for 22 morpho-agronomic, physiological, and NUE traits under low nitrogen (LN) fertilization conditions. The ABs were developed with introgressions from the wild relatives Solanum insanum, Solanum dasyphyllum, and Solanum elaeagnifolium. The AB population comprised a total of 25, 59, and 59 genotypes, respectively, with overall donor wild relative genome coverage percentages of 58.8%, 46.3%, and 99.2%. The three S. melongena recurrent parents were also evaluated under control (normal) N fertilization. Reduction of N fertilization in the parents resulted in decreased chlorophyll content-related traits, aerial biomass, stem diameter, and yield and increased NUE, nitrogen uptake efficiency (NUpE), and nitrogen utilization efficiency (NUtE). However, the decrease in yield was moderate, ranging between 62.6% and 72.6%. A high phenotypic variation was observed within each of the three sets of ABs under LN conditions, with some individuals displaying improved transgressive characteristics over the recurrent parents. Using the single primer enrichment technology 5k probes platform for high-throughput genotyping, we observed a variable but high degree of recurrent parent genome recovery in the ABs attributable to the lines recombination, allowing the successful identification of 16 quantitative trait loci (QTL). Different allelic effects were observed for the introgressed QTL alleles. Several candidate genes were identified in the QTL regions associated with plant growth, yield, fruit size, and NUE-related parameters. Our results show that eggplant materials with introgressions from CWRs can result in a dramatic impact in eggplant breeding for a more sustainable agriculture.

Mining natural genetic variations for nitrogen use efficiency utilizing nested synthetic hexaploid wheat introgression libraries

Wheat is grown on more than 240 million hectares globally, more than any other commercial crop. Variation for nitrogen-use efficiency (NUE) in wheat germplasm is very important as efficiency of nitrogen fertilizers use can have significant effect on overall consumption of N. In the present study we used nested synthetic hexaploid wheat introgression libraries to detect genetic variation associated with NUE and related traits. The libraries were genotyped with 9474 SNP markers and used for genome-wide association mapping. Significant phenotypic variation was observed for all measured and derived traits. We detected 10 Quantitative trait locus (QTL) and 19 marker-trait associations (MTAs) possibly involved in improving NUE. Of these, 5 QTL and 8 MTAs detected under nitrogen-limited conditions have potential for use in breeding to increase nitrogen-deficiency tolerance. Nitrate transporter genes collocated with detected MTAs showed significant changes in expression of TaNRT2 genes in response to N-starvation and N-recovery. The identified promising breeding lines with stable yield, better NUE and acceptable protein content may constitute an important genetic resource in improving NUE of modern wheat varieties.

Genotype-by-Environment Interaction for Quantitative Trait Loci Affecting Nitrogen Use Efficiency and Associated Traits in Potato

Deciphering the genetic basis of complex traits like nitrogen use efficiency (NUE) requires understanding the genotype-by-environment (G × E) interaction and linking physiological functions and agronomic traits to DNA markers. Multi-environment experiments were conducted in different environments representing low and high nitrogen levels combined with rain-fed and irrigation production conditions at three different locations in Ethiopia: Debre-Tabor, Injibara and Koga, in 2013 and 2015. The objectives of the study were to determine the G × E interaction and stability of genotypes for NUE of potato and to identify markers associated with NUE and NUE-related agronomic and physiological traits in potato under these diverse environments. Data were analyzed using GenStat, and genotype plus the genotype and environment (GGE) biplot model; the marker-trait associations were discovered using the R-software package GWASpoly. The analysis of variance that included location and production system had estimates for genotype variance (σ2g) that were low compared with the estimates for environment variance (σ2e) and genotype-by-environment interaction variance (σ2ge) for most measured traits at both N levels. The GGE analysis identified two mega-environments that coincided with the two production systems. The high N level environments both at Debre-Tabor and Injibara, and the low N environment at Koga, respectively, were the most suitable environments for discriminating the potato cultivars and being representative test environments for NUE evaluation in the rain-fed mega-environment and irrigation mega-environment. A total of 77 marker trait associations were identified for NUE and NUE-related agronomic and physiological traits. Multi-trait genomic regions that harbored significant marker-trait associations for NUE and NUE-related traits were found on chromosomes III, V and VI. The effect of production season was greater than the effect of N levels on QTL × environment interaction for most NUE-related traits.

Epistatic QTLsPlay a Major Role in Nitrogen Use Efficiency and Its Component Traits in Indian Spring Wheat

Nitrogen use efficiency (NUE) in wheat may significantly reduce the excessive use of N fertilizers. However, being a quantitative trait, understanding its genetic basis is required for efficient wheat breeding. The present study was carried out to dissect the complex trait through the mapping of quantitative trait locus (QTLs) related to NUE component traits in Indian wheat. A linkage map was constructed using F2 population derived from two parents contrasting for nitrogen-responsive traits using simple sequence repeat (SSR) markers. Phenotyping for root dry weight, N uptake and utilization were carried out under a high nitrogen environment. Twenty-seven main effect QTLs for eight traits and 26 interaction QTLs for three traits were detected. The main effect QTLs explained a significant amount of phenotypic variance up to the extent of 11.18%. The QTLs were also found to have significant epistatic interactions governed by both additive and non-additive gene action. In particular, chromosome 2A harbours QTLs for many traits viz. SDW, RDW, TDW, R:S, %N, NUtE, and NUpE, including epistasis and interaction QTLs that were flanked by markers Xwmc728-Xwmc473 and Xwmc779-Xgwm249. Taken together, the genomic regions on 2A, 4A, and 7A were found to contain QTLs for a majority of the studied NUE traits that can be potentially exploited in future wheat breeding programmes.

Genetics of nitrogen use efficiency and its component traits under nitrogen-rich environment in wheat (Triticum aestivum)

Minimizing the footprints of overuse of nitrogen (N) on the ecosystem is the need of an hour. There is little information on the genetic inheritance of NUE and its component traits. The present study was therefore designed to study the genetic behaviour of NUE traits under abundant N supply. Diallel analysis of 21 F1 along with 7 parents was carried out for NUE traits, viz. shoot dry weight (SDW), root dry weight (RDW), maximum root length (MRL), N% in shoot, gram N in shoot (gN) and nitrogen use efficiency (NUE) under high N in hydroponic condition. Analysis of variance revealed significance for both general combining ability (GCA) and specific combining ability (SCA) for all NUE traits indicating the importance of both additive and non-additive gene action for these traits. Baker's ratio revealed a preponderance of additive genes over non-additive for SDW, RDW and MRLsuggesting thereby effectivity of selection for SDW, RDW, gN, and MRL in the early segregating generation of high GCA lines can improve NUE under high N. Crosses with high SCA effects for SDW, RDW, gN and N% were from the parent combination of high × low GCA effects, whereas for MRL, low × low GCA parents resulted in crosses with high SCA effect indicating the dispersal of favourable alleles in the different parents. Our study indicates the feasibility of improvement of NUE through direct selection for the component traits under N rich environment.

Reducing Nitrogen Input in Barley Crops While Maintaining Yields Using an Engineered Biostimulant Derived From Ascophyllum nodosum to Enhance Nitrogen Use Efficiency.

Intensive agricultural production utilizes large amounts of nitrogen (N) mineral fertilizers that are applied to the soil to secure high crop yields. Unfortunately, up to 65% of this N fertilizer is not taken up by crops and is lost to the environment. To compensate these issues, growers usually apply more fertilizer than crops actually need, contributing significantly to N pollution and to GHG emissions. In order to combat the need for such large N inputs, a better understanding of nitrogen use efficiency (NUE) and agronomic solutions that increase NUE within crops is required. The application of biostimulants derived from extracts of the brown seaweed Ascophyllum nodosum has long been accepted by growers as a sustainable crop production input. However, little is known on how Ascophyllum nodosum extracts (ANEs) can influence mechanisms of N uptake and assimilation in crops to allow reduced N application. In this work, a significant increase in nitrate accumulation in Arabidopsis thaliana 6 days after applying the novel proprietary biostimulant PSI-362 was observed. Follow-up studies in barley crops revealed that PSI-362 increases NUE by 29.85–60.26% under 75% N input in multi-year field trials. When PSI-362 was incorporated as a coating to the granular N fertilizer calcium ammonium nitrate and applied to barley crop, a coordinated stimulation of N uptake and assimilation markers was observed. A key indicator of biostimulant performance was increased nitrate content in barley shoot tissue 22 days after N fertilizer application (+17.9–72.2%), that was associated with gene upregulation of root nitrate transporters (NRT1.1, NRT2.1, and NRT1.5). Simultaneously, PSI-362 coated fertilizer enhanced nitrate reductase and glutamine synthase activities, while higher content of free amino acids, soluble protein and photosynthetic pigments was measured. These biological changes at stem elongation stage were later translated into enhanced NUE traits in harvested grain. Overall, our results support the agronomic use of this engineered ANE that allowed a reduction in N fertilizer usage while maintaining or increasing crop yield. The data suggests that it can be part of the solution for the successful implementation of mitigation policies for water quality and GHG emissions from N fertilizer usage.

Nitrogen Use Efficiency in Sorghum: Exploring Native Variability for Traits Under Variable N-Regimes.

Exploring the natural genetic variability and its exploitation for improved Nitrogen Use Efficiency (NUE) in sorghum is one of the primary goals in the modern crop improvement programs. The integrated strategies include high-throughput phenotyping, next generation sequencing (NGS)-based genotyping technologies, and a priori selected candidate gene studies that help understand the detailed physiological and molecular mechanisms underpinning this complex trait. A set of sixty diverse sorghum genotypes was evaluated for different vegetative, reproductive, and yield traits related to NUE in the field (under three N regimes) for two seasons. Significant variations for different yield and related traits under 0 and 50% N confirmed the availability of native genetic variability in sorghum under low N regimes. Sorghum genotypes with distinct genetic background had interestingly similar NUE associated traits. The Genotyping-By-Sequencing based SNPs (>89 K) were used to study the population structure, and phylogenetic groupings identified three distinct groups. The information of grain N and stalk N content of the individuals covered on the phylogenetic groups indicated randomness in the distribution for adaptation under variable N regimes. This study identified promising sorghum genotypes with consistent performance under varying environments, with buffer capacity for yield under low N conditions. We also report better performing genotypes for varied production use—grain, stover, and dual-purpose sorghum having differential adaptation response to NUE traits. Expression profiling of NUE associated genes in shoot and root tissues of contrasting lines (PVK801 and HDW703) grown in varying N conditions revealed interesting outcomes. Root tissues of contrasting lines exhibited differential expression profiles for transporter genes [ammonium transporter (SbAMT), nitrate transporters (SbNRT)]; primary assimilatory (glutamine synthetase (SbGS), glutamate synthase (SbGOGAT[NADH], SbGOGAT[Fd]), assimilatory genes [nitrite reductase (SbNiR[NADH]3)]; and amino acid biosynthesis associated gene [glutamate dehydrogenase (SbGDH)]. Identification and expression profiling of contrasting sorghum genotypes in varying N dosages will provide new information to understand the response of NUE genes toward adaptation to the differential N regimes in sorghum. High NUE genotypes identified from this study could be potential candidates for in-depth molecular analysis and contribute toward the development of N efficient sorghum cultivars.

Rice Transcriptome Analysis Reveals Nitrogen Starvation Modulates Differential Alternative Splicing and Transcript Usage in Various Metabolism-Related Genes.

Nitrogen (N) is crucial for plant growth and development; however, excessive use of N fertilizers cause many problems including environmental damage, degradation of soil fertility, and high cost to the farmers. Therefore, immediate implementation is required to develop N efficient crop varieties. Rice being low nitrogen use efficiency (NUE) and a high demand staple food across the world has become a favorite crop to study the NUE trait. In the current study, we used the publicly available transcriptome data generated from the root and shoot tissues of two rice genotypes IR-64 and Nagina-22 (N-22) under optimum N supply (N+) and chronic N-starvation (N−). A stringent pipeline was applied to detect differentially expressed genes (DEGs), alternatively spliced (DAS) genes, differentially expressed transcripts (DETs) and differential transcript usage (DTU) transcripts in both the varieties and tissues under N+ and N− conditions. The DAS genes and DTU transcripts identified in the study were found to be involved in several metabolic and biosynthesis processes. We suggest alternative splicing (AS) plays an important role in fine-tuning the regulation of metabolic pathways related genes in genotype, tissue, and condition-dependent manner. The current study will help in understanding the transcriptional dynamics of NUE traits in the future.

Nitrogen Use Efficiency in Durum Wheat Under Different Nitrogen and Water Regimes in the Mediterranean Basin.

Improving nitrogen use efficiency (NUE) represents one of the main goals to reduce N input in maximizing crop yield for sustainable agriculture. A NUE key strategy is the exploitation of genetic variation in available germplasm together with the understanding of molecular mechanisms governing this complex trait. Thus, NUE, its components, nitrogen uptake efficiency (NUpE) and nitrogen utilization efficiency (NUtE), and NUE-related traits heritability were evaluated in ancient (Cappelli, Capeiti, Russello, and Mazzancoio) and modern (Messapia, Tiziana, Svevo, and Normanno) wheat genotypes for tackling nitrogen (N) and/or water limitation in both growth chamber and field experiments. Our results exhibited a reduction of NUE, NUpE, and NUtE under water and combined (nitrogen + water) stress in all the genotypes, as expected. The contribution of genetic variability on phenotypic variation was significant for NUtE, harvest index, post-anthesis nitrogen uptake (PANU), and biomass production traits. Moreover, the stress tolerance indexes, calculated and bi-plotted for N and water stresses, exhibited two distinct clusters for many traits as then confirmed by principal component analysis. Although modern varieties showed higher crop yield and NUE under conventional N and water regimes, ancient varieties exhibited best performances to cope with both stresses, mainly under water limitation. Finally, the usage index, which takes into account total biomass increase, underlined that old genotypes were less affected by both stresses during crop cycle. In particular, these genotypes showed the best performances for NUE and its components under both stresses at stem elongation and milk ripening as shown also by PANU. In addition, at these stages, nitrate and ammonium transporter gene expressions in the root were performed, showing the highest activity in ancient varieties. In conclusion, the identification of NUE traits during a specific crop cycle stage, under both N and water limitation, will help in the breeding of more resilient varieties in Mediterranean sustainable agriculture by reducing N supply.

Timing and Splitting of Nitrogen Application to Increase Tef (Eragrostic Tef (Zucc.) Trotter) Yield and Nitrogen Use Efficiency at Central Highlands of Ethiopia

ABSTRACT A field experiment was conducted for three consecutive years (2017 to 2019) to determine the appropriate time of nitrogen (N) fertilizer application during the crop growth cycle for increased tef productivity and nitrogen use efficiency (NUE) at central highlands of Ethiopia. A split-plot experimental design was used with two varieties and eight timings of N application at different growth stages. The results showed that variety and time of N application had a significant effect on growth parameters, NUE traits, yield, and yield components of tef at both locations. Kora variety gave higher growth parameters of tef at both locations and higher yield at Ude. Regarding time of N application, the highest yield was obtained when N was applied 50% at planting +25% at tillering + 12.5% at flag leaf +12.5% at heading, though not significantly different from other split applications at Ude. Split application increased grain yield and NUE traits as compared to full N application at once. However, at Minjar, split application didn’t show any significant difference of grain yield and NUE traits with that of full application. Partial budget analysis at Ude also showed that N application of 50% at planting +25% at tillering + 12.5% at flag leaf +12.5% at heading gave the highest net benefit and MRR. Therefore, four times (50% at planting +25% at tillering + 12.5% at flag leaf +12.5% at heading of split N fertilizer application can be recommended for higher economic yield and NUE of tef at Ude area, but split application is not advantageous at Minjar area.

Genotypic Variation in Nitrogen Use-Efficiency Traits of 28 Tobacco Genotypes

Knowing the nitrogen use efficiency (NUE) of crops is crucial to minimize environmental pollution, although NUE is rarely provided for numerous genotypes in the tobacco (Nicotiana tabacum L.) crop. Through the growth of contrasting genotypes in nutritive solutions, we aimed to characterize five NUE components of 28 genotypes and to classify them according to their efficiency and responsiveness to nitrogen (N) availability. On average, physiological N use efficiency, N harvest index, and N uptake efficiency decreased by 16%, 4%, and 57%, respectively, under N-deficient conditions, while N utilization efficiency decreased by 43% at adequate N supply. The relative efficiency of N use varied from 35% to 59% among genotypes. All genotypes of the Virginia and Maryland varietal groups were efficient, and those of the Burley, Comum, and Dark groups were inefficient, while the responsiveness varied among genotypes within varietal groups, except for Maryland genotypes. Our findings are helpful in indicating genotypes with distinguished efficiency and responsiveness to N supply, which can be further chosen according to soil N level or affordability to N fertilizers worldwide in tobacco crops. In a general framework, this can lead to a more sustainable use of N and can support tobacco breeding programs for NUE.

Identification of QTLs Associated with Nitrogen Use Efficiency and Related Traits in a Diploid Potato Population

Developing N use efficient potato varieties requires exploring the genetic basis of nitrogen use efficiency (NUE) and associated agronomic and physiological traits. In order to identify QTLs for NUE and NUE-related traits, and to determine the relationships between the traits and QTLs in potato, a diploid potato mapping population (CxE) was evaluated in the field in Ethiopia under low and high N fertilizer levels. QTL detection was performed using interval mapping and multiple QTL mapping (MQM). A total of 52 putative QTLs were identified for ten traits, of which 28 QTLs were detected under low N availability while the remaining 24 QTLs were detected under high N conditions. Several QTLs were location and N level specific, suggesting the presence of QTL x environment interaction. A region on linkage group V (21-38 cM) accumulated the largest number of QTLs. This region coincides with the earliness locus encoded by the CDF1 gene, suggesting that earliness has a profound influence on NUE. A putative second QTL region on linkage group V located 20 cM from the earliness locus (38-56 cM) and a region on linkage group IV (60-72 cM) might be useful other regions to focus on, for NUE improvement in potato. To verify the stability of the identified QTLs and to use these for the detection of possible candidate genes, further multi-environment trials with larger population size may be required.

Identification of quantitative trait loci associated with nitrogen use efficiency in winter wheat.

Maintaining winter wheat (Triticum aestivum L.) productivity with more efficient nitrogen (N) management will enable growers to increase profitability and reduce the negative environmental impacts associated with nitrogen loss. Wheat breeders would therefore benefit greatly from the identification and application of genetic markers associated with nitrogen use efficiency (NUE). To investigate the genetics underlying N response, two bi-parental mapping populations were developed and grown in four site-seasons under low and high N rates. The populations were derived from a cross between previously identified high NUE parents (VA05W-151 and VA09W-52) and a shared common low NUE parent, ‘Yorktown.’ The Yorktown × VA05W-151 population was comprised of 136 recombinant inbred lines while the Yorktown × VA09W-52 population was comprised of 138 doubled haploids. Phenotypic data was collected on parental lines and their progeny for 11 N-related traits and genotypes were sequenced using a genotyping-by-sequencing platform to detect more than 3,100 high quality single nucleotide polymorphisms in each population. A total of 130 quantitative trait loci (QTL) were detected on 20 chromosomes, six of which were associated with NUE and N-related traits in multiple testing environments. Two of the six QTL for NUE were associated with known photoperiod (Ppd-D1 on chromosome 2D) and disease resistance (FHB-4A) genes, two were reported in previous investigations, and one QTL, QNue.151-1D, was novel. The NUE QTL on 1D, 6A, 7A, and 7D had LOD scores ranging from 2.63 to 8.33 and explained up to 18.1% of the phenotypic variation. The QTL identified in this study have potential for marker-assisted breeding for NUE traits in soft red winter wheat.

Physiological Basis of Heterosis for Nitrogen Use Efficiency of Maize

Efficient use of nitrogen inputs for concurrent improvements in grain yield and nitrogen use efficiency (NUE) has been recognized as a viable strategy for sustainable agriculture development. Yet, there is little research on the possible physiological basis of maize hybrid heterosis for NUE and measurable traits that are corresponding to the NUE heterosis. A field study was conducted for two years to evaluate the heterosis for NUE and determine the relationship between NUE and its physiological components. Two commercial hybrids, ‘Xianyu335’ and ‘Zhengdan958’, and their parental inbred lines, were grown at 0 (0 N) and 150 kg N ha−1 (150 N), in a randomized complete block design with four replications each year. Compared to their parental lines, both hybrids displayed a significant heterosis, up to 466%, for NUE. N internal efficiency (NIE) accounted for 52% of the variation in heterosis for NUE, while there was generally negligible heterosis for nitrogen recovery efficiency (NRE). Heterosis for NIE and thereby for NUE in maize was ascribed to (i) an earlier establishment of pre-anthesis source for N accumulation, which phenotypically exhibited as a faster leaf appearance rate with higher maximum LAI and photosynthetic nitrogen use efficiency; (ii) a larger amount of N being remobilized from the vegetative tissues, especially from leaves, during the grain filling. Phenotypically, there was notably a rapid reduction in post-anthesis specific weights of leaf and stalk, but with maintained functionally stay-green ear leaves; and (iii) a higher productive efficiency per unit grain N, which was characterized by a reduced grain N concentration and enhanced sink strength.

Temporal Dynamics and the Contribution of Plant Organs in a Phenotypically Diverse Population of High-Yielding Winter Wheat: Evaluating Concepts for Disentangling Yield Formation and Nitrogen Use Efficiency.

Enhancing crop nitrogen use efficiency (NUE) is a key requirement for both economic and ecological reasons. Consequently, the genotypic potential for NUE in winter wheat (Triticum aestivum L.) requires further exploitation. Emerging plant phenomic techniques may provide knowledge about traits contributing to grain N uptake (GNup) and grain yield (GY). However, the understanding of beneficial strategies concerning the temporal dynamics of NUE and GY formation and the role of plant organs is still scarce especially under high-yielding European conditions—particularly to discriminate interesting lines in the breeding process. Thus, screening for potentially useful NUE traits in terms of variation, stability, and contribution to target traits will be an essential prerequisite for the development of efficient phenotyping strategies. Therefore, 46 NUE and yield formation traits were assessed in a population of 75 breeding lines over 3 years from 2015 to 2017 in southern Germany, including dry matter (DM), N concentration, and N uptake at anthesis and maturity, both at the aboveground-plant and plant organ levels. Significant genotype and genotypexenvironment effects were observed for all traits. While GY was more related to post-anthesis assimilation, also DM translocation contributed substantially to GY by 31–44%. At maturity, total aboveground DM as opposed to harvest index predominantly determined GY. NUE for GY was better described by N uptake efficiency than by N utilization efficiency. GNup was greatly influenced by variation in GY, but not in grain N concentration, and by total N uptake and not the N harvest index. Post-anthesis N uptake highly depended on the year and was low in comparison to N translocation. However, post-anthesis N uptake was always correlated with GNup, suggesting the need to also consider stay-green strategies under temperate growing conditions. While anthesis traits were only moderately descriptive, GY will be enhanced by increasing total biomass and the N uptake efficiency. Similarly, targeting total N uptake, particularly at post-anthesis, seems to be a rewarding strategy to boost GNup. Thus, high-throughput phenotyping should be targeted rather toward detecting traits related to DM and N acquisition than to the internal allocation and rather to post-anthesis than to anthesis traits.

Genetic Diversity of Potato Cultivars for Nitrogen Use Efficiency Under Contrasting Nitrogen Regimes

Developing cultivars that use nitrogen more efficiently is a sustainable strategy for reducing nitrogen use in crop production. To assess the genetic diversity for nitrogen use efficiency (NUE) and related traits in potato, a total of 97 (88 for the Western-European market and 9 Ethiopian) cultivars were evaluated at two nitrogen levels (40 kg/ha and 120 kg/ha) for 24 quantitative traits in Debre-Tabor and Injibara (Ethiopia) in the 2013 main rainy season (June to September). Highly significant variation was found among genotypes for almost all measured traits. Plant height, NUE, tuber yield, and yield-related traits and model parameters for canopy development (maximum canopy covers area under the canopy curve) were significantly affected by N levels across locations. Dutch cultivars had more rapid initial canopy development and matured earlier than the Ethiopian cultivars at both N levels and locations. A hierarchical cluster analysis grouped the cultivars in 9 and 11 genetically distinct classes at low and high N, respectively. The genetic component accounted for a large portion of the phenotypic variation for plant height, tuber number per plant, average tuber weight, and NUE under both N regimes, as indicated by a high heritability. Strong phenotypic correlations were observed between NUE and tuber number per plant, days to maturity, tuber dry matter %, maximum canopy cover, and area under the canopy curve under both low and high N conditions. The result is indicative to set the best parental line selection criteria for crossing purpose and utilize the cultivars for further potato NUE breeding programmes.

Identification of QTLS for NH4+ and NO3- use efficiency under water stress and non-stress conditions and expression analysis of glutamine synthetase and nitrate reductase in rice (Oryza Sativa L.)

Nitrogen (N) is one of the most critical inputs and the current average nitrogen use efficiency (NUE) in the rice field is approximately 33%, poorest among cereals. Predominant form of N in aerobic soils is nitrate (NO3-) while ammonium (NH4+) exists in anaerobic soils. Development of cultivars with improved NH4+ or NO3- use efficiency by harnessing inherent significant variability for NUE can be an important approach. Considering these facts, the present study was established with one hundred twenty two and selected thirty two recombinant inbred lines (RILs) of two indica genotypes, Danteshwari × Dagad deshi under three nitrogen forms and three environments. The trend analysis of NH4+-N and NO3--N dynamics revealed that NH4+-N concentration persisted more under anaerobic condition and NO3--N concentration under aerobic conditions. Three way-ANOVA showed high level of significance for variance components (G, N, E) and their interactions effects (GXN, GXE, NXE, EXNXG) for yield and NUE and their component traits. Mean performance of genotypes depicted higher values for agronomically important traits i.e. yield and NUE under NH4+ as compared to NO3--N and N0. The phenotypic and genotypic data was statistically analyzed for QTLs identification for yield and NUE traits. A total of 58 QTLs conferring the corresponding five traits were detected under three N forms and two environments. We also investigated the different members of AMT (Ammonium transporters), NRT (Nitrate transporters), GS (Glutamine Synthetase) and GOGAT (Glutamate Synthase) genes, involved in NUE and analyzed the expression pattern of each gene using gene-specific primer in young rice seedlings. Collectively, OsGln1;1, OsGln1;2, OsGln1;3, OsGln2, OsGlt1 and OsGlt2 manifested different and reciprocal responses to nitrate and ammonium supply. The activity of enzymes NR, NiR, GS and GOGAT was significantly affected by NH4+and NO3- treatment. These results assist us to identify NH4+ and NO3- responsive cultivars which could be used for cultivation and/or used as parent’s in future breeding program to produce better nitrogen use efficiency varieties under water stress and non-stress conditions.