Genetic and physiological characterization of traits related to salinity tolerance in an advanced backcross population of wheat

In large areas of the world wheat production is highly affected by soil salinity. Increasing the genetic variability of currently used wheat varieties is an efficient approach to overcome production losses and prevent food insecurity. Synthetic hexaploid wheat is widely regarded as donor of favorable exotic alleles with respect to tolerance against biotic and abiotic stress factors such as salinity stress. The objective of the present study was to identify genomic regions, which contribute to salinity tolerance at various growth stages in wheat. Therefore, the 151 advanced backcross lines (AB-lines) of the winter wheat population “Z86” (BC2F3:7), containing introgressions of the synthetic hexaploid wheat Syn86L in the background of the German elite cultivar Zentos, were employed in this study. Salt stress experiments were conducted at germination and seedling stage as well as under field conditions with natural salinization in Uzbekistan in three consecutive years. At various growth stages, the AB-lines of the Z86 population and their parents were differently affected by salt stress. At the same molar concentration of salts, the impact of sodium sulfate (Na2SO4) on plants growth was higher than of sodium chloride (NaCl). Notably, for most studied parameters the recurrent elite parent Zentos was performing better than the synthetic parent Syn86, the donor of exotic alleles. In respect to root and shoot length Syn86 surpassed the elite cultivar. In this study, several non-destructive sensor technologies were used which allow accurate and continuous monitoring of morpho-physiological parameters of plants exposed to salinity stress. These data present the first report of a dual-mode microwave resonator which was allowing accurate estimation of water content as well as the ionic conductivity in leaves of mono- and dicotyledonous plants. Additionally, measurement of the photosynthetic rate of plants exposed to salt shock revealed highly significant genotype by treatment interaction effect 20 minutes after initiation of salt stress, where Zentos was performing better than Syn86. In order to detect genomic regions associated with the measured traits under salinity stress the Z86 population was genotyped using the iSelect 90K chip. After data cleaning 11,050 polymorphic SNP marker remained which were applied for quantitative trait loci analysis (QTL) for the 48 studied traits. Using SAS 9.4 the multi-locus approach incorporated in the hierarchical QTL model was able to reduce the number of false-positive putative QTL and hence endorsed the power of detected true QTL. In summary, 116 QTL main effects (including QTL with epistatic effects) and 165 QTL for marker by treatment interaction (including QTL with epistatic by treatment interaction) were detected. One of the major QTL showing pleiotropic effects, among them on shoot dry weight under salinity stress, was found on the short arm of chromosome 7D at 29.97 cM. In-silico analysis of the QTL chromosome region revealed a gene coding for TaGSTu3, an enzyme belonging to the tau-class of the glutathione S-transferase family (GST). GSTs are well known for their role in detoxification of reactive oxygen species (ROS) in plants, which is highly increased under salinity stress. Gene expression analysis at three time-points during the seedling stage (10, 16 and 30 days after salt application) revealed higher expression of TaGSTu3 in Zentos under salinity stress and decreased expression in the comparing parent Syn86. This is the first report of atau-class GST found to contribute significantly to salinity tolerance in wheat. The present study successfully identified QTL from elite cultivar Zentos as well as from the donor germplasm Syn86.The detected favorable alleles introgressed in the AB-lines of the Z86 population can be directly employed in breeding programs via marker-assisted selection for efficiently breeding cultivars with improved salinity tolerance and desired agronomic traits.Genetische und physiologische Charakterisierung von Merkmalen im Bezug auf Salztoleranz in einer Rückkreuzungspopulation von Weizen Die Versalzung der Böden beeinträchtigt in weiten Teilen der Welt die Weizenproduktion. Zum Ausgleich von hohen Ertragseinbussen, bzw. zur Sicherung der Ernährung der Bevölkerung, könnte eine zunehmende genetische Variabilität von aktuell genutzten Weizensorten einen effizienten Lösungsansatz bieten. Synthetischer hexaploider Weizen wird als Quelle von nützlichen exotischen Allelen im Hinblick auf Toleranzen gegenüber biotischen und abiotischen Stressfaktoren, wie etwa Salzstress angesehen. Ziel der vorliegenden Arbeit war die Lokalisation von genomischen Regionen, die zur Salztoleranz von Weizen in verschiedenen Entwicklungsstadien beitragen. Dazu wurden 151 AB-Linien (Advanced Backcross) der Winterweizenpopulation "Z86" (BC2F3:7) untersucht, welche vorteilhafte Gene des synthetischen hexaploiden Weizens Syn86L im Hintergrund der deutschen Eliteweizensorte Zentos beinhaltet. Experimente unter Salzstress wurden sowohl im Keimungs- und Jungpflanzenstadium, als auch unter natürlichen Bedingungen in Usbekistan in drei aufeinanderfolgenden Jahren auf Feldern mit hoher Salinität durchgeführt. Die AB-Linien als auch ihre Eltern waren zu unterschiedlichen Entwicklungsstadien verschieden stark vom Salzstress betroffen. Bei Natriumsulfat (Na2SO4) führte die gleiche molare Salzkonzentration zu einer stärkeren Schädigung der Pflanzen als bei Natriumchlorid (NaCl). Bei den meisten untersuchten Parametern schnitt der rekurrente Eliteelter Zentos besser ab als der synthetische Elter Syn86. Nur im Hinblick auf Wurzel- und Sprosslänge übertraf Syn86 den Kulturweizen. Für dieses Projekt kamen verschiedene nicht-invasive Sensortechnologien zum Einsatz, welche ein akkurates und kontinuierliches Beobachten der morphophysiologischen Parameter bei den gestreßten Pflanzen erlaubten. Im Rahmen dieser Arbeit wurde ein Dual-Mode Mikrowellensensor präsentiert, der zerstörungsfrei sowohl den Wassergehalt, als auch die Ionenleitfähigkeit von mono- und dikotylen Pflanzen erfasst. Außerdem wurden in dieser Arbeit erstmalig Daten von Weizenpflanzen präsentiert, die einem plötzlichen Salzschock zugeführt wurden. Hierbei konnte festgestellt werden, dass genotypisch signifikante Unterschiede 20 Minuten nach der Initiation von Salzstress feststellbar waren, wobei Zentos höhere Photosyntheseraten aufzuweisen hatte als Syn86. Um genomische Regionen zu detektieren, die mit den untersuchten Merkmalen unter Salzstress assoziieren, wurde die Z86-Population mit dem iSelect 90K Chip genotypisiert. Die nach der Datenreinigung verbliebenen 11.050 polymorphen Single-Nucleotide Polymorphism (SNP) Marker wurden im Rahmen der Quantitative Trait Loci (QTL) Analyse für die 48 untersuchten Merkmale verwendet. Durch Verwendung von SAS (Version 9.4) wurde das Multi-Locus-Verfahren in das hierarchische QTL-Model eingebunden, um die Zahl der Falsch-positiven QTL zu reduzieren und dadurch die Aussagekraft der echten QTL zu verstärken. Hierbei wurden insgesamt 116 QTL für Haupteffekte (inklusive QTL mit epistatischen Effekten) und 165 QTL für die Interaktion mit der Behandlung (inklusive QTL mit epistatischen Effekten in Interaktion mit der Behandlung) detektiert. Ein bedeutendes QTL mit pleiotropischen Effekten (u.a. für das Sprosstrockengewicht unter Salzstress) wurde auf dem kurzen Arm des Chromosoms 7D mit der Position 29,87 cM gefunden. In-silico-Analyse der QTL-Region des Chromosoms ergab ein Gen, das für TaGSTu3, ein Enzym der tau-Klasse aus der Familie Glutathion-S-Transferasen (GST), kodiert. Die GSTs sind bekannt für ihre Rolle bei der Detoxifikation von reaktiven Sauerstoffspezies (ROS) in Pflanzen, die unter Salzstress vermehrt produziert werden. Die Gen-Expressions-Analysen an drei Zeitpunkten (10, 16 und 30 Tage nach der Applikation von Salzstress) des Jungpflanzenstadiums von Weizenpflanzen zeigte eine höhere Expression von TaGSTu3 in Zentos im Vergleich zu Syn86, bei der die Expression von TaGSTu3 unter Stressbedingungen sank. In dieser Arbeit wurde erstmalig der signifikante Beitrag der GST aus der tau-Klasse zur Salztoleranz von Weizen nachgewiesen. Die vorliegende Studie hat erfolgreich QTL identifiziert, wobei die günstigen Allele sowohl von der Eliteweizensorte Zentos als auch von dem synthetischen Weizen Syn86 stammen. Die detektierten nützlichen und exotischen Allele, die in den AB-Linien der Z86-Population vorhanden sind, können direkt in Züchtungsprogrammen über Marker-Aßisted Selection eingebunden werden. Dadurch kann zur effizienteren Züchtung von Sorten mit salztoleranten als auch weiteren bevorzugten agromischen Merkmalen beigetragen werden

Application of a plane-stratified emission model to predict the effects of vegetation in passive microwave radiometry

This paper reports the application to vegetation canopies of a coherent model for the propagation of electromagnetic radiation through a stratified medium. The resulting multi-layer vegetation model is plausibly realistic in that it recognises the dielectric permittivity of the vegetation matter, the mixing of the dielectric permittivities for vegetation and air within the canopy and, in simplified terms, the overall vertical distribution of dielectric permittivity and temperature through the canopy. Any sharp changes in the dielectric profile of the canopy resulted in interference effects manifested as oscillations in the microwave brightness temperature as a function of canopy height or look angle. However, when Gaussian broadening of the top and bottom of the canopy (reflecting the natural variability between plants) was included within the model, these oscillations were eliminated. The model parameters required to specify the dielectric profile within the canopy, particularly the parameters that quantify the dielectric mixing between vegetation and air in the canopy, are not usually available in typical field experiments. Thus, the feasibility of specifying these parameters using an advanced single-criterion, multiple-parameter optimisation technique was investigated by automatically minimizing the difference between the modelled and measured brightness temperatures. The results imply that the mixing parameters can be so determined but only if other parameters that specify vegetation dry matter and water content are measured independently. The new model was then applied to investigate the sensitivity of microwave emission to specific vegetation parameters.</p> <p style='line-height: 20px;'><b>Keywords: </b>passive microwave, soil moisture, vegetation, SMOS, retrieva

Physiological response of Kentucky bluegrass under salinity stress

Salinity is a major abiotic stress in plant agriculture which reduces seed germination, vegetative growth, and flowering, and limits crop productivity world-wide. Salinity causes water deficit, ion toxicity, and nutrient deficiency in plants, which can result in cellular damage, growth reduction, and even death. Kentucky bluegrass (Poa pratensis L.) is the most widely used cool-season species in cool-arid climates; however it has relatively poor salt-tolerance. Thus the development of Kentucky bluegrass genotypes with increased salt tolerance is of interest to turf breeders. One impediment to selection towards this goal is finding an efficient and accurate method to evaluate the salt tolerance. The objective of this study was to examine physiological responses to salt stress and to evaluate the genetic diversity among the accessions used in the research. Salt-tolerant accessions PI371768 (768) and PI440603 (603) and salt-sensitive varieties Midnight and Baron were exposed to four levels of salinity imposed by irrigating with salt solutions of 0 dS m-1 (control), 6 dS m-1, 12 dS m-1, and 18 dS m-1 or 24 dS m-1. Soil salinity was measured using Acclima Digital TDT sensors and grass response to the stress was measured using turf quality ratings, stomatal conductance, leaf water potential and electrolyte leakage. In general, turfgrass quality, stomatal conductance, and leaf water potential decreased while electrolyte leakage increased under salinity stress. Midnight and Baron exhibited greater changes in these measurements, indicating more sensitivity compared to 768 and 603. The 6 dS m-1 treatment had little effect on the salt-tolerant accessions. Salt tolerance of 603 and 768 was confirmed and likewise, salt sensitivity of Baron and Midnight was confirmed. The genetic similarity of all cultivars used in this study was very high. All of the evaluation measurements were highly correlated, with water potential and electrolyte leakage being the most reliable and accurate methods due to the low standard deviations. Due to more repeatable methods and less user error, electrolyte leakage and turfgrass quality are recommended methods for screening salt tolerance of turfgrasses

Study of the Soil Water Movement in Irrigated Agriculture

In irrigated agriculture, the study of the various ways water infiltrates into the soils is necessary. In this respect, soil hydraulic properties, such as soil moisture retention curve, diffusivity, and hydraulic conductivity functions, play a crucial role, as they control the infiltration process and the soil water and solute movement. This Special Issue presents the recent developments in the various aspects of soil water movement in irrigated agriculture through a number of research topics that tackle one or more of the following challenges: irrigation systems and one-, two-, and three-dimensional soil water movement; one-, two-, and three-dimensional infiltration analysis from a disc infiltrometer; dielectric devices for monitoring soil water content and methods for assessment of soil water pressure head; soil hydraulic properties and their temporal and spatial variability under the irrigation situations; saturated–unsaturated flow model in irrigated soils; soil water redistribution and the role of hysteresis; soil water movement and drainage in irrigated agriculture; salt accumulation, soil salinization, and soil salinity assessment; effect of salts on hydraulic conductivity; and soil conditioners and mulches that change the upper soil hydraulic properties and their effect on soil water movement

Rice response to simultaneous biotic and abiotic stresses

With the predicted climate change and an ever-growing population there is increasing pressure to develop crop plants with improved stress responses, increased yield and high nutritive value. We have explored transcriptomic changes in the leaves and roots of rice plants (Oryza sativa japonica cv Nipponbare) in response to drought and the root-knot nematode Meloidogyne graminicola. A glasshouse model was developed to mimic conditions experienced by rice plants in the field. The plant responses under simultaneous biotic and abiotic stress were dominated by the drought element accompanied by a unique set of genes that were only responsive to the simultaneous stress. Highlighted within this group were novel members of stress-responsive gene families for example cytochrome P450, wall-associated kinases, lipid transfer proteinlike proteins and new candidate genes that may play important roles in the response of rice to multiple stresses. The genes that were differentially regulated between the multiple and the drought stress treatment were explored using loss-of-function mutants. The loss-of-function mutant for peroxidase precursor gene (per) showed improved growth and yield compared to the wildtype Nipponbare plants. The experiments conducted in growth rooms were validated in a field study. Both Nipponbare rice plants, and the popular lowland indica rice cv IR64 were grown under prolonged vegetative drought stress accompanied by cyst nematode or root-knot nematode infection. Reduction of phytate, an anti-nutrient, has been adopted as a major strategy to improve the nutritional value of crop plants. Nematode susceptibility of low phytate Arabidopsis plants was studied to determine the effect of reduced phytate content on the plant’s defence response. The study has provided insight into the genome-wide transcriptional changes in rice under a combined biotic and abiotic stress. It has led to better understanding of the stress responses in plants that will be advantageous in developing crop varieties with improved yield and nutritive value

Root adaptive responses of tall fescue (Festuca arundinacea) growing in sand treated with petroleum hydrocarbon contamination

Phytoremediation is a green technique used to restore polluted sites through plant-initiated biochemical processes. Its effectiveness, however, depends on the successful establishment of plants in the contaminated soil. Soils that are contaminated with polycyclic aromatic hydrocarbons (PAHs), especially low molecular weight, mobile PAHs such as naphthalene pose a significant challenge to this. Plant roots growing in these soils exhibit changes to their structure, physiology and growth patterns. Tall fescue (Festuca arundinacea) roots grown in sand contaminated with either petroleum crude oil (10.8g total extractable hydrocarbons kg-1 sand dw) or naphthalene (0.8g kg-1 sand dw) exhibited a temporary inhibition in elongation with accelerated lateral growth (p<0.01), whilst also showing a deviation from the normal root orientation responses to gravity. Scanning electron micrographs (SEM) revealed that the stele in the contaminated roots was located much further away from the root epidermis, because the cortex was larger (p<0.001) due to the cells being more isodiametric in shape. Once past the initial acclimatisation period of 2.5-3.0 months, no visual differences were observed between control and treated plants, but the root ultrastructural modifications persisted. The fluorescent hydrophobic probe „Nile red‟ was applied to the epidermis of a living root to mimic and visualise the uptake of naphthalene into the root through the transpiration stream. The root sections were also stained with 0.1% (w/v) berberine hemisulphate in order to stain Casparian bands. Overlaying images obtained with the use of Texas red HYQ filter (wavelength 589-615nm) and UV illumination (wavelength 345-458nm) revealed the presence of passage cells in the endodermis and uptake of Nile red into protoxylem vessels beyond the endodermis of control roots. On the other hand, the path of Nile red was blocked at the endodermis of naphthalene- treated roots. The cell walls in the endodermis of naphthalene-treated roots were prominently thickened (p<0.001) and lacked passage cells. The treated roots also possessed a well-formed exodermis (p<0.01). The results suggest that the well-formed endodermis lacking passage cells, the well-formed exodermis as well as the increased cortex zone provided an effective barrier to the flux of hydrophobic xenobiotics towards the inner core of the roots, if previously exposed to the contaminants. The SEM images of naphthalene-treated as well as crude oil-treated roots showed partial collapse in the cortex zone, presumably due to water stress, but the treated plants withstood drought stress better than the control plants. The underlying physiological changes responsible for the adaptive responses of tall fescue to the exposure to naphthalene contamination were studied through metabolic profiling of plant roots and shoots. The results indicated synergistic interactions between sugars or sugar- like compounds and phenolic compounds may assist to create an integrated redox system and contribute to stress tolerance in naphthalene-treated tall fescue. The signal for a compound speculated to be indole acetic acid (IAA) was either subdued or absent in the tissues of naphthalene-treated tall fescue, suggesting the existence of a detoxification mechanism/ defence pathway in the treated plants. The ultra-structural and molecular modifications, resulting from PAH stress enabled tall fescue to resist tougher challenges

Ag-IoT for crop and environment monitoring: Past, present, and future

CONTEXT: Automated monitoring of the soil-plant-atmospheric continuum at a high spatiotemporal resolution is a key to transform the labor-intensive, experience-based decision making to an automatic, data-driven approach in agricultural production. Growers could make better management decisions by leveraging the real-time field data while researchers could utilize these data to answer key scientific questions. Traditionally, data collection in agricultural fields, which largely relies on human labor, can only generate limited numbers of data points with low resolution and accuracy. During the last two decades, crop monitoring has drastically evolved with the advancement of modern sensing technologies. Most importantly, the introduction of IoT (Internet of Things) into crop, soil, and microclimate sensing has transformed crop monitoring into a quantitative and data-driven work from a qualitative and experience-based task. OBJECTIVE: Ag-IoT systems enable a data pipeline for modern agriculture that includes data collection, transmission, storage, visualization, analysis, and decision-making. This review serves as a technical guide for Ag-IoT system design and development for crop, soil, and microclimate monitoring. METHODS: It highlighted Ag-IoT platforms presented in 115 academic publications between 2011 and 2021 worldwide. These publications were analyzed based on the types of sensors and actuators used, main control boards, types of farming, crops observed, communication technologies and protocols, power supplies, and energy storage used in Ag-IoT platforms