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Agronomy, Volume 9, Issue 9 (September 2019)

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Open AccessArticle
A Novel Compost for Rice Cultivation Developed by Rice Industrial By-Products to Serve Circular Economy
Agronomy 2019, 9(9), 553; https://doi.org/10.3390/agronomy9090553 (registering DOI) - 15 Sep 2019
Abstract
Rice is the major staple crop worldwide, whereas fertilization practices include mainly the application of synthetic fertilizers. A novel compost was developed using 74% of rice industrial by-products (rice bran and husks) and tested in rice cultivation in Greece’s main rice producing area. [...] Read more.
Rice is the major staple crop worldwide, whereas fertilization practices include mainly the application of synthetic fertilizers. A novel compost was developed using 74% of rice industrial by-products (rice bran and husks) and tested in rice cultivation in Greece’s main rice producing area. Field experimentation was conducted in two consecutive growing seasons (2017 and 2018) and comprised six fertilization treatments, including four compost rates (C1: 80, C2: 160, C3: 320 kg ha−1 of nitrogen all in split application, C4: 160 kg ha−1 of nitrogen in single application), a conventional treatment, as well as an untreated control. A total of 21 morpho-physiological and quality traits were evaluated during the experimentation. The results indicated that rice plants in all compost treatments had greater height (8%–64%) and biomass (32%–113%) compared to the untreated control. In most cases, chlorophyll content index (CCI) and quantum yield (QY) were similar or higher in C3 compared to the conventional treatment. C2 and C3 exhibited similar or greater yields, 7.5–8.7 Mg ha−1 in 2017 and 6.3–6.9 Mg ha−1 in 2018, whereas the conventional treatment resulted in 7.3 Mg ha−1 and 6.8 Mg ha−1 in the two years, respectively. No differences were observed in most quality traits that affect the rice commodity. The current study reveals that in sustainable farming systems based on circular economy, such as organic ones, the application of the proposed compost at the rate of 6 Mg ha−1 can be considered sufficient for the rice crop nutrient requirements. Full article
(This article belongs to the Special Issue Transfer of Waste to Resource in Agriculture)
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Open AccessFeature PaperReview
The Effect of Chromosome Structure upon Meiotic Homologous and Homoeologous Recombinations in Triticeae
Agronomy 2019, 9(9), 552; https://doi.org/10.3390/agronomy9090552 (registering DOI) - 14 Sep 2019
Viewed by 80
Abstract
The tribe Triticeae contains about 500 diploid and polyploid taxa, among which are important crops, such as wheat, barley and rye. The phylogenetic relationships, genome compo-sition and chromosomal architecture, were already reported in the pioneer genetic studies on these species, given their implications [...] Read more.
The tribe Triticeae contains about 500 diploid and polyploid taxa, among which are important crops, such as wheat, barley and rye. The phylogenetic relationships, genome compo-sition and chromosomal architecture, were already reported in the pioneer genetic studies on these species, given their implications in breeding-related programs. Hexaploid wheat, driven by its high capacity to develop cytogenetic stocks, has always been at the forefront of these studies. Cytogenetic stocks have been widely used in the identification of homoeologous relationships between the chromosomes of wheat and related species, which has provided valuable information on genome evolution with implications in the transfer of useful agronomical traits into crops. Meiotic recombination is non-randomly distributed in the Triticeae species, and crossovers are formed in the distal half of the chromosomes. Also of interest for crops improvement is the possibility of being able to modulate the intraspecific and interspecific recombination landscape to increase its frequency in crossover-poor regions. Structural changes may help in this task. In fact, chromosome truncation increases the recombination frequency in the adjacent intercalary region. However, structural changes also have a negative effect upon recombination. Gross chromosome rearrangements produced in the evolution usually suppress meiotic recombination between non-syntenic homoeologs. Thus, the chromosome structural organization of related genomes is of great interest in designing strategies of the introgression of useful genes into crops. Full article
(This article belongs to the Special Issue Chromosome Manipulation for Plant Breeding Purposes)
Open AccessArticle
A New Approach to Farm Biodiversity Assessment
Agronomy 2019, 9(9), 551; https://doi.org/10.3390/agronomy9090551 (registering DOI) - 14 Sep 2019
Viewed by 115
Abstract
A reduction in biodiversity due to farming operations has been broadly reported. As a solution, policy makers in the European Union have introduced several programs in recent years to enhance biodiversity on farms but these have met with only limited success. One of [...] Read more.
A reduction in biodiversity due to farming operations has been broadly reported. As a solution, policy makers in the European Union have introduced several programs in recent years to enhance biodiversity on farms but these have met with only limited success. One of the main reasons for this lack of success is that the experience, knowledge and attitudes of farmers are not taken into account when biodiversity conservation programs are formulated. Farmers’ opinions must be taken into consideration in the creation of future programs, which should also include an assessment by the farmers of the value of the nature of their farms. In this study, farmers were asked to express their opinion on the attractiveness of their farm in relation to pollinators, game, birds, amphibians, reptiles, rodents and non-crop (wild) plants. Data were then analysed using a novel method in which each farm was assigned to one of four categories. High nature-value farms contained more natural features in the landscape, such as individual trees or ponds. Socio-economic factors, such as gender, also influenced the farm assessments; female farmers were more critical compared to their male counterparts. The establishment of field margins or watercourse by the farmers significantly increased the possibility that the farm would be classified as attractive. Full article
(This article belongs to the Section Farming Sustainability)
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Open AccessArticle
Physiological and Molecular Osmotic Stress Responses in Three Durum Wheat (Triticum Turgidum ssp Durum) Genotypes
Agronomy 2019, 9(9), 550; https://doi.org/10.3390/agronomy9090550 (registering DOI) - 13 Sep 2019
Viewed by 127
Abstract
This study aims to investigate the activities and expression of enzymes of primary metabolism and relate these data with the growth performance of three different durum wheat genotypes (Maali; YT13; and ON66) under osmotic stress. Growth traits—including plant height, dry weight (DW) and [...] Read more.
This study aims to investigate the activities and expression of enzymes of primary metabolism and relate these data with the growth performance of three different durum wheat genotypes (Maali; YT13; and ON66) under osmotic stress. Growth traits—including plant height, dry weight (DW) and relative water content (RWC)—were measured to classify genotypes depending on their tolerance to stress. Several enzymes were investigated: Ascorbate peroxidase (APX), Glutamine Synthetase (GS), Glutamine dehydrogenase (GDH), Glutamate synthase (GOGAT), Glucose 6-phosphate dehydrogenase (G6PDH), and Phosphoenolpyruvate Carboxylase (PEPC). The expression of the cytosolic and plastidic glutamine synthetase (TaGS1 and TaGS2), high affinity nitrate transporters (TaNRT2.3) and Glutamate dehydrogenase (TaGDH) were also detected by qRT-PCR. The results indicated different growth performances among genotypes, indicating Maali and YT13 as tolerant genotypes and ON66 as a drought-susceptible variety. Data showed a decrease in PEPC and increase in APX activities under osmotic stress; a slight decrease in GS activity was observed, together with an increase in G6PDH in all genotypes; GS and NRT2 expressions changed in a similar pattern in the different genotypes. Interestingly, Maali and YT13 showed higher transcript abundance for GDH under stress compared to ON66, suggesting the implication of GDH in protective phenomena upon osmotic stress. Full article
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Open AccessArticle
Freeze-Thaw Induced Gully Erosion: A Long-Term High-Resolution Analysis
Agronomy 2019, 9(9), 549; https://doi.org/10.3390/agronomy9090549 (registering DOI) - 13 Sep 2019
Viewed by 117
Abstract
Gullies are significant contributors of sediment to streams in the southeastern USA. This study investigated gully erosion in the clay-rich soils of east Tennessee under a humid subtropical climate. The aims of this study were to (1) estimate long-term erosion rates for different [...] Read more.
Gullies are significant contributors of sediment to streams in the southeastern USA. This study investigated gully erosion in the clay-rich soils of east Tennessee under a humid subtropical climate. The aims of this study were to (1) estimate long-term erosion rates for different gully geomorphic settings, (2) compare patterns of erosion for the different settings, and (3) model the response of gully erosion to freeze-thaw events. Erosion was measured weekly from June 2012 to August 2018 using 105 erosion pins distributed in gully channels, interfluves, and sidewalls. Erosion rates were estimated from average slopes of lines of best fit of pin lengths versus time. Maximum and minimum temperature was calculated daily using an on-site weather station and freeze-thaw events were identified. Gully erosion was modeled using antecedent freeze-thaw activity for the three geomorphic settings. Long-term erosion rates in channels, interfluves, and sidewalls were 2.5 mm/year, 20 mm/year, and 21 mm/year, respectively; however, week-by-week erosion was statistically different between the three settings, indicating different erosive drivers. Models of erosion with lagged freeze-thaw variables explained up to 34.8% of the variability in erosion variables; sidewall erosion was most highly related to freeze-thaw activity. Freeze-thaw in prior weeks was an important variable in all erosion models. Full article
(This article belongs to the Special Issue Surface Runoff and Soil Erosion under Various Climate Conditions)
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Open AccessCommunication
Effects of Sewage Sludge Amendments on the Growth and Physiology of Sweet Basil
Agronomy 2019, 9(9), 548; https://doi.org/10.3390/agronomy9090548 (registering DOI) - 13 Sep 2019
Viewed by 141
Abstract
Currently, wastewater treatment plants produce large amounts of sewage sludge. Due to the rich content of organic matter and minerals, sewage sludge can be used as soil amendments for eroded soils. The aim of this work was to assess sewage sludge (SS) in [...] Read more.
Currently, wastewater treatment plants produce large amounts of sewage sludge. Due to the rich content of organic matter and minerals, sewage sludge can be used as soil amendments for eroded soils. The aim of this work was to assess sewage sludge (SS) in combination with an eroded soil (ES) collected from the North Eastern Romania as growth substrate for sweet basil, and their effect on basil growth and physiology. The experiment was conducted in a greenhouse under controlled environment conditions. The tested substrates were: (1) eroded soil, ES; (2) mixture of eroded soil (15%) + sewage sludge, ES + SS (85%); and (3) sewage sludge, SS (100%). Three types of parameters were studied: morphological traits, physiological, and biochemical parameters. The maximum quantum yield of Photosystem II Fv/Fm was reduced in basil leaves grown on eroded soil (0.80) and was close to the normal value in ES + SS (0.83). Chlorophyll a and the carotenoids content were higher for plants grown on SS and significantly higher for those grown in ES + SS compared with the one of plants grown on ES. The fresh biomass yield and height of basil increased with 44% and 34.5% under ES + SS over ES. Total phenolic content was higher in plants grown on ES (7.34 mg/g dry weight Gallic acid equivalent), which also led to an increased antioxidant activity (44.4%) evaluated by the DPPH (2,2-diphenyl-1-picrylhydrazyl) method. Fourier-Transform Infrared (FT-IR) (4000–400 cm−1) spectra of basil did not show significant qualitative differences among the plants from different treatments. The results of this study demonstrated that SS application led to the improvement of the basil morpho-physiological parameters, allowing the growth of basil on ES + SS. Full article
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Open AccessArticle
Optimization of Herbicide Use: Study on Spreading and Evaporation Characteristics of Glyphosate-Organic Silicone Mixture Droplets on Weed Leaves
Agronomy 2019, 9(9), 547; https://doi.org/10.3390/agronomy9090547 - 12 Sep 2019
Viewed by 170
Abstract
Herbicide deposition rate can be affected by the leaf surface features of weeds and have a significant impact on the overall efficacy. In this paper, an orthogonal experiment was conducted to investigate the differences of droplet evaporation and spreading characteristics corresponding to weed [...] Read more.
Herbicide deposition rate can be affected by the leaf surface features of weeds and have a significant impact on the overall efficacy. In this paper, an orthogonal experiment was conducted to investigate the differences of droplet evaporation and spreading characteristics corresponding to weed leaf surface with hairy, waxy and rough (ridged) structures. Three weed species—Descurainia sophia, Lepidium lotifolium, and Lolium temulentumwere included in the study, representing these three leaf structures respectively. Glyphosate sprays with organic silicone surfactant in different concentrations were composed for the test. Single droplets with two diameters of 0.05 μL and 0.1 μL were deposited on the leaves to evaluate the evaporation and spreading characteristics. A digital camera was used and the evaporation duration and the maximum droplet coverage images could be captured and extracted from the recorded videos. The Image Processing Toolbox in Matlab was applied to segment the images for droplet and leaf background and the binary images’ pixel numbers were counted for coverage area calculation. The results revealed that the evaporation duration was reduced with the increase of the organic silicone concentration, while the spread area was expanded. The droplet spread more widely and evaporated faster on D. sophia leaves than on the leaves with L. lotifolium and L. temulentum surfaces. The spreading area and evaporation duration varied much faster on L. lotifolium leaves than on the leaves of other weed species. The droplet sizes affected spreading more significantly on L. temulentum leaf surface, as the spreading procedure of small size droplets was restrained by the groove structure. The results of this study would benefit the consideration of the farmers when selecting the proper nozzle code and the determining of the surfactant mixture in order to optimize the use of herbicides like glyphosate. Full article
(This article belongs to the Special Issue Weed Management & New Approaches)
Open AccessArticle
Regulation of Spraying 6-BA in the Late Jointing Stage on the Fertile Floret Development and Grain Setting in Winter Wheat
Agronomy 2019, 9(9), 546; https://doi.org/10.3390/agronomy9090546 - 12 Sep 2019
Viewed by 107
Abstract
Wheat yield is largely determined by the grains per spike, which in turn is related to the fertile floret development prior to anthesis. The aim of this study was to assess the physiological mechanism of exogenous 6-benzylaminopurine (6-BA) on fertile floret development and [...] Read more.
Wheat yield is largely determined by the grains per spike, which in turn is related to the fertile floret development prior to anthesis. The aim of this study was to assess the physiological mechanism of exogenous 6-benzylaminopurine (6-BA) on fertile floret development and grain setting characteristics by foliar application in winter wheat. Field experiments were conducted during the 2016–2017 and 2017–2018 growing seasons in China. Two foliar spraying applications with water (S0) and 6-BA (S1) were applied to a large-spike variety (V1) and a multiple-spike variety (V2) 25 days after jointing. At anthesis, spike dry weight and soluble sugar, sucrose, auxin, and cytokinin were all positively correlated with the number of fertile florets and grains per spike. During the abortion stage of fertile florets, 6-BA application compared to the control reduced the auxin content, increased the cytokinin content and spike dry matter and transported more soluble sugar and sucrose from the non-spike organs to the spike. Exogenous 6-BA application increased the number of fertile florets (~1.84 to ~2.50) and number of grains (~2.83 to ~3.51) by primarily suppressing the number of degenerated and aborted florets. The results provide important evidence that 6-BA application has a positive effect on floret fertility and grain setting, which lead to a further increase in grain yield. Full article
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Open AccessArticle
Effect of Salinity Stress and Microbial Inoculations on Glomalin Production and Plant Growth Parameters of Snap Bean (Phaseolus vulgaris)
Agronomy 2019, 9(9), 545; https://doi.org/10.3390/agronomy9090545 - 12 Sep 2019
Viewed by 156
Abstract
Salinity is a major abiotic stress that can adversely affect plant growth, yield, other physiological parameters, and soil health. Salinity stress on biomass production of salt-sensitive crops, like snap bean (Phaseolus vulgaris), is a serious problem, and specifically in South Florida, [...] Read more.
Salinity is a major abiotic stress that can adversely affect plant growth, yield, other physiological parameters, and soil health. Salinity stress on biomass production of salt-sensitive crops, like snap bean (Phaseolus vulgaris), is a serious problem, and specifically in South Florida, USA, where saline soils can be found in major agricultural lands. Research studies focused on the ‘snap bean–Rhizobium–arbuscular mycorrhizal fungi (AMF)’ relationship under salinity stress are limited, and fewer studies have evaluated how this tripartite symbiosis affects glomalin production (GRSP), a glycoprotein released by AMF. A shade house experiment was conducted to elucidate the effects of three microbial inoculations (IC = inoculation control; IT1 = AMF and IT2 = AMF + Rhizobium) on three salinity treatments (SC = salinity control 0.6 dS m−1, S1 = 1.0 dS m−1, and S2 = 2.0 dS m−1) on snap bean growth and yield. Our results indicate that S2 reduced 20% bean biomass production, 11% plant height, 13% root weight, and 23% AMF root colonization. However, microbial inoculations increased 26% bean yield over different salinity treatments. Maximum salinity stress (S2) increased 6% and 18% GRSP production than S1 and SC, respectively, indicating the relative advantage of abiotic stress on AMF’s role in soil. Dual inoculation (IT2) demonstrated a beneficial role on all physiological parameters, biomass production, and GRSP synthesis compared to single inoculation (IT1) treatment with all three salinity levels. Full article
(This article belongs to the Special Issue Rhizobium–Legume Symbiosis)
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Open AccessArticle
Killing Weed Seeds with Exhaust Gas from a Combine Harvester
Agronomy 2019, 9(9), 544; https://doi.org/10.3390/agronomy9090544 - 12 Sep 2019
Viewed by 149
Abstract
We investigated if hot exhaust gas from a combine harvester could be used to reduce germination or kill weed seeds during the harvesting process. During the threshing and cleaning process in the combine, weed seeds and chaff are separated from the crop grains. [...] Read more.
We investigated if hot exhaust gas from a combine harvester could be used to reduce germination or kill weed seeds during the harvesting process. During the threshing and cleaning process in the combine, weed seeds and chaff are separated from the crop grains. After this separation, weed and crop seeds not collected can be exposed to exhaust gas before seeds are returned to the field. Seeds of some common weed species (Alopecurus myosuroides, Centaurea cyanus, Geranium pusillum, Lapsana communis, Lolium perenne, Rumex crispus, Spergula arvensis, and Tripleurospermum inodorum) were treated with exhaust gas at temperatures of 75 °C or 85 °C, 110 °C, and 140 °C for 2, 4, and 6 s, respectively. Afterwards, the seeds were germinated for 16 days. We found that 75 °C and 85 °C were insufficient to significantly reduce germination of the seeds after three durations. Some seeds were still able to germinate after 4 s exposure of 110 °C. An exposure of 140 °C for 4 and 6 s repressed germination of all species. We conclude that there is potential to develop combine harvesters that exploit the exhaust gas to either kill or reduce the ability of weed seeds to germinate before seeds are returned to the field. Full article
(This article belongs to the Special Issue Weed Management & New Approaches)
Open AccessArticle
Applications of Fungal Strains with Keratin-Degrading and Plant Growth Promoting Characteristics
Agronomy 2019, 9(9), 543; https://doi.org/10.3390/agronomy9090543 - 12 Sep 2019
Viewed by 96
Abstract
Protein hydrolysates (PHs) are organic non-microbial biostimulants having beneficial effects on plants. The study was designed to assess the effects on plants by the applications of PHs obtained from Trichoderma isolates grown on keratin wastes. Trichoderma isolates were characterized for indole-3-acetic acid and [...] Read more.
Protein hydrolysates (PHs) are organic non-microbial biostimulants having beneficial effects on plants. The study was designed to assess the effects on plants by the applications of PHs obtained from Trichoderma isolates grown on keratin wastes. Trichoderma isolates were characterized for indole-3-acetic acid and siderophores production, activity of lytic enzymes, phosphorous solubilization and inhibition of pathogens growth, using qualitative specific tests. Fungal isolates were cultured on a medium with keratin wastes (wool and feathers) to obtain PHs. Fungal PHs were tested in vivo for plant biostimulant action, as follows: (i) seeds germination test; (ii) activation of plant proton pump; (iii) evaluation of effect on tomato seedling growth. PHs from T. asperellum cultured on feathers medium reached the highest values for all parameters recorded (plant height and diameter, number of leaves and branches), with the exception of those for plant biomass, which were maximum for the wool medium. The metabolites released by keratin degradation under the activity of selected T. asperellum isolate improved crop health and productivity. The use of PHs can be a reasonable solution for the environmental pollution of by-products from the food chain, as well as for the replacement of chemical fertilizers with microbial formulations to stimulate plant growth. Full article
(This article belongs to the Section Soil and Plant Nutrition)
Open AccessReview
Potential Benefits and Risks for Soil Health Derived From the Use of Organic Amendments in Agriculture
Agronomy 2019, 9(9), 542; https://doi.org/10.3390/agronomy9090542 - 12 Sep 2019
Viewed by 99
Abstract
The use of organic amendments in agriculture is a common practice due to their potential to increase crop productivity and enhance soil health. Indeed, organic amendments of different origin and composition (e.g., animal slurry, manure, compost, sewage sludge, etc.) can supply valuable nutrients [...] Read more.
The use of organic amendments in agriculture is a common practice due to their potential to increase crop productivity and enhance soil health. Indeed, organic amendments of different origin and composition (e.g., animal slurry, manure, compost, sewage sludge, etc.) can supply valuable nutrients to the soil, as well as increase its organic matter content, with concomitant benefits for soil health. However, the application of organic amendments to agricultural soil entails a variety of risks for environmental and human health. Organic amendments often contain a range of pollutants, including heavy metals, persistent organic pollutants, potential human pathogens, and emerging pollutants. Regarding emerging pollutants, the presence of antibiotic residues, antibiotic-resistant bacteria, and antibiotic-resistance genes in agricultural amendments is currently a matter of much concern, due to the concomitant risks for human health. Similarly, currently, the introduction of microplastics to agricultural soil, via the application of organic amendments (mainly, sewage sludge), is a topic of much relevance, owing to its magnitude and potential adverse effects for environmental health. There is, currently, much interest in the development of efficient strategies to mitigate the risks associated to the application of organic amendments to agricultural soil, while benefiting from their numerous advantages. Full article
(This article belongs to the Special Issue Soil Health in Agroecosystems)
Open AccessArticle
The Current Stage of Greening Vegetation in Selected Wine-Regions of South Moravian Region (Czech Republic)
Agronomy 2019, 9(9), 541; https://doi.org/10.3390/agronomy9090541 - 12 Sep 2019
Viewed by 87
Abstract
Viticulture, as a large part of the agriculture sector of the South Moravian Region, represents significant erosion-prone land use in which soils face various agronomic issues, such as poor organic carbon levels, erosion, and fertility loss. Service crops providing a so-called ecosystem service [...] Read more.
Viticulture, as a large part of the agriculture sector of the South Moravian Region, represents significant erosion-prone land use in which soils face various agronomic issues, such as poor organic carbon levels, erosion, and fertility loss. Service crops providing a so-called ecosystem service can reduce erosion and runoff, regulate pests and weeds and increase soil organic matter and fertility. However, these crops may generate some disservices, such as water and nutrient competition; and thus, it is important for winegrowers to find applicable options for service crops depending on local soil, climate conditions, and the expected service. Inter-row management in the South Moravian Region varies from bare soils to grass cover to different types of cover with herbaceous (flowering) species. A total of 113 vineyard sites were evaluated during the years 2016 and 2017. This study presents the actual state of inter-row management in vineyards and comparison within six wine-growing regions. A two-year evaluation shows significant differences in prevalent greening management between regions. Bare soil in vineyards, the most erosion-prone vineyard floor management, appear from 10% (e.g., Bzenec, Valtice) to 19% (e.g., Mikulov, V. Bílovice) of vineyard area within evaluated regions. Bare soil management is mostly used in new plantations to reduce water and nutrient competition; however, the erosion and the runoff rates are generally higher on this variant compared to other types of cover crop management, especially on slopes. Although, alternate greening is the most used type occurring from 50% to 74% of vineyards area in five of the six selected regions, the type of inter-row vegetation differs considerably. While in Bzenec and Mikulov there is a higher appearance of herbaceous cover with native species in later succession stages, in Velké Bílovice and Valtice grass cover and commercial plant mixtures are more frequent. Knowledge current stage can be useful for planning new plantation or anti-erosion measures. Full article
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Open AccessArticle
Evaluation of Mobile Heat Treatment System for Treating In-Field HLB-Affected Trees by Analyzing Survival Rate of Surrogate Bacteria
Agronomy 2019, 9(9), 540; https://doi.org/10.3390/agronomy9090540 - 12 Sep 2019
Viewed by 161
Abstract
Huanglongbing (HLB or citrus greening) is a disease caused by an insect-transmitted bacterial pathogen Candidatus Liberibacter asiaticus (CLas). Thermotherapy has been successfully used by others to reduce the population of CLas bacteria in HLB-affected citrus trees under greenhouse studies. Thermotherapy is [...] Read more.
Huanglongbing (HLB or citrus greening) is a disease caused by an insect-transmitted bacterial pathogen Candidatus Liberibacter asiaticus (CLas). Thermotherapy has been successfully used by others to reduce the population of CLas bacteria in HLB-affected citrus trees under greenhouse studies. Thermotherapy is the application of heat as a strategy to reduce the adverse economic impact of certain pests and diseases. CLas is a fastidious, non-cultivable organism. The high variance in CLas titers in canopy samples together with this lack of cultivability makes it impossible to use classical bacteriological techniques to measure the viability either before or after treatments. Therefore, we used the survival rates of a surrogate bacterium, Klebsiella oxytoca, in order to evaluate the effectiveness of a mobile thermotherapy delivery system developed for in-field treatment of HLB-affected trees. K. oxytoca is a Gram-negative, rod-shaped bacterium that was originally isolated from soil and has been used in the development of industrial applications related to ethanol fuel production. It served as a biologically-based sensor of temperature stress (biosensor) in this study. Thermocouples and biosensor packets (plastic cups with suspended small snap-top tubes) containing the K. oxytoca were attached to an HLB-affected citrus tree and their canopy locations mapped. The mobile thermotherapy treatment hood covered the canopy of the HLB-affected tree. Then, steam and hot water were injected through nozzles inside of the hood to increase the temperature of the tree canopy. A standard temperature–time combination of 54 °C for 90 s was chosen based on preliminary studies where heat treatment parameters caused a significant reduction in CLas populations without inflicting permanent damage to the tree. The survival ratio of the K. oxytoca in the biosensor packets was found to range from complete elimination to 5% with treatments of 250 s and a maximum temperature of 54 °C. Full article
(This article belongs to the Special Issue Precision Agriculture)
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Open AccessArticle
Stacking Agricultural Management Tactics to Promote Improvements in Soil Structure and Microbial Activities
Agronomy 2019, 9(9), 539; https://doi.org/10.3390/agronomy9090539 - 12 Sep 2019
Viewed by 98
Abstract
Linking agricultural management tactics to quantifiable changes in soil health-related properties is a key objective for increasing adoption of the most favorable management practices. We used two long-term, no-till cropping studies to illustrate the variable patterns of response of soil structure indices and [...] Read more.
Linking agricultural management tactics to quantifiable changes in soil health-related properties is a key objective for increasing adoption of the most favorable management practices. We used two long-term, no-till cropping studies to illustrate the variable patterns of response of soil structure indices and microbial activity to additional management tactics, including crop rotational diversity, residue management and cover cropping. We found that observable effects of management tactics on soil properties were often dependent on the current crop phase sampled, even though the treatments were well-established. In some cases, a single additional management tactic produced a response, two tactics each produced a response and sometimes there were interactions between tactics. However, importantly, we never observed a negative effect for any of the response variables when stacking soil health building practices in no-till cropping systems. The collective results from the two field studies illustrate that soil health improvements with stacking management tactics are not always simply additive and are affected by temporal relationships inherent to the treatments. We conclude that the implementation of multiple positive management tactics increases the likelihood that improvements in soil properties can be documented with one or more of the proxy measures for soil health. Full article
(This article belongs to the Special Issue Soil Health in Agroecosystems)
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Open AccessArticle
Planting Locations with Higher Temperature Produce More Bioactive Compounds and Antioxidant Capacities of Wheat
Agronomy 2019, 9(9), 538; https://doi.org/10.3390/agronomy9090538 - 11 Sep 2019
Viewed by 173
Abstract
Bioactive compounds such as phenols and phytic acid in wheat contribute to antioxidant capacities. (1) Background: Prior studies drew a general conclusion that the environment affected bioactive compounds greatly, but how the single environmental factor affects these characteristics remains unclear. (2) Methods: We [...] Read more.
Bioactive compounds such as phenols and phytic acid in wheat contribute to antioxidant capacities. (1) Background: Prior studies drew a general conclusion that the environment affected bioactive compounds greatly, but how the single environmental factor affects these characteristics remains unclear. (2) Methods: We conducted that twenty-eight winter wheat genotypes were grown in replicated trials at seven locations in China for two consecutive years and subdivided the environmental factor into five soil factors and six meteorological factors to evaluate the impact on the antioxidant capabilities and bioactive compounds contents of wheat grains by using principal component analysis (PCA). RT-PCR was used to identify gene expression of bioactive compounds under different conditions. (3) Results: Temperature affects bioactive compounds contents and antioxidant capacities greatly in wheat grains. Accumulation time, daylight length, and daily maximum temperature showed a high correlation with bioactive compounds contents and antioxidant capacities, especially in the vegetative growth phase. The gene TaMIPs related to phytic acid and TaPAL1, TaC3H1, TaC4H, Ta4CL1, and TaCOMT1 related to total phenolics had higher gene expression level with larger temperature differences in wheat grains. (4) Conclusions: The planting locations with higher temperatures and longer daylight length could produce higher contents of bioactive compounds and antioxidant capacities and the cooler temperatures of a planting location might produce wheat grains with lower phytic acid contents in wheat grains. Full article
Open AccessArticle
Influence of Zeolite and Phosphorus Applications on Water Use, P Uptake and Yield in Rice under Different Irrigation Managements
Agronomy 2019, 9(9), 537; https://doi.org/10.3390/agronomy9090537 - 11 Sep 2019
Viewed by 184
Abstract
Phosphorus (P) deficiency often occurs in paddy fields due to its high fixation, and low solubility and mobility in soils, especially under water stress. Available soil P and plant P uptake could be improved through the application of zeolite. However, little is known [...] Read more.
Phosphorus (P) deficiency often occurs in paddy fields due to its high fixation, and low solubility and mobility in soils, especially under water stress. Available soil P and plant P uptake could be improved through the application of zeolite. However, little is known about the impact of zeolite on P uptake in rice under water stress. A two-year lysimetric experiment using a split-split plot design investigated the effects of zeolite (0 or 15 t ha−1) and P (0 or 60 kg ha−1) applications on water use, P uptake, and grain yield in rice under two irrigation management systems (continuous flooding irrigation (CF) and improved alternate wetting and drying irrigation (IAWD)). Both irrigation systems produced equivalent effective panicles and grain yield. Compared with CF, IAWD reduced water use and aboveground P uptake and improved water-use efficiency (WUE) in rice. The applications of zeolite or P alone increased grain yield, WUE, soil available P, and stem, leaf, and panicle P concentration, and aboveground P uptake, but had no significant effect on water use. The enhanced grain yield induced by zeolite was related to the increase in aboveground P uptake. The zeolite application enhanced NH4+–N retention in the topsoil and prevented NO3–N from leaching into deeper soil layers. Moreover, Zeolite made lower rates of P fertilizer possible in paddy fields, with benefits for remaining P supplies and mitigating pollution due to excessive P. These results suggest that the combined application of zeolite and P under improved AWD regime reduced water use, improved P uptake and grain yield in rice, and alleviated environment risk. Full article
(This article belongs to the Special Issue Increasing Agricultural Water Productivity in a Changing Environment)
Open AccessFeature PaperCommunication
Relationships between Rootstock-Scion Combinations and Growing Regions on Watermelon Fruit Quality
Agronomy 2019, 9(9), 536; https://doi.org/10.3390/agronomy9090536 - 11 Sep 2019
Viewed by 92
Abstract
Grafting of vegetable plants is done primarily to reduce the potential for damage caused by soil-borne diseases. Most of the watermelons (Citrullus) grown in the Mediterranean Basin, including in Israel, are grafted, mainly on interspecific hybrid pumpkin (Cucurbita) rootstocks. [...] Read more.
Grafting of vegetable plants is done primarily to reduce the potential for damage caused by soil-borne diseases. Most of the watermelons (Citrullus) grown in the Mediterranean Basin, including in Israel, are grafted, mainly on interspecific hybrid pumpkin (Cucurbita) rootstocks. Biblical law (Leviticus 19:19) does not allow intergeneric grafting, so in recent years, great efforts have been made in Israel to find or breed watermelon rootstocks. Both interspecific and intergeneric grafting can have negative or positive effects on fruit yield and quality after harvest. The inconsistencies in fruit quality and shelf-life parameters can be attributed to differences in production environments. However, many farmers are grafting and planting the same rootstock-scion combination all over the country, regardless of local soil, water, and climactic conditions. We studied the effect of similar rootstock-scion combinations on watermelon yield and fruit quality in three regions of Israel differing in soil type and altitude. Fruit-quality parameters were evaluated after 4 days at 21 °C (local marketing simulation). Fruit quality was significantly affected, mainly by the growing region, based on factorial analysis, but also by rootstock-scion combination, regardless of rootstock vigor. Therefore, the best rootstock-scion combination needs to be found and adopted for each growing region. Grafting was essential for watermelon crop survival in contaminated soils and improved both plant performance and postharvest fruit quality, but was not a factor in non-contaminated soils. Full article
Open AccessArticle
Sorghum as a Novel Crop for Central Europe: Using a Broad Diversity Set to Dissect Temperate-Adaptation
Agronomy 2019, 9(9), 535; https://doi.org/10.3390/agronomy9090535 - 11 Sep 2019
Viewed by 120
Abstract
Sorghum (Sorghum bicolor L. Moench) is a promising novel crop for Central Europe. However, enhancements in cold tolerance and early maturity are essential for a successful adaptation to cooler climates. We scored a broad sorghum diversity set (n = 338) for [...] Read more.
Sorghum (Sorghum bicolor L. Moench) is a promising novel crop for Central Europe. However, enhancements in cold tolerance and early maturity are essential for a successful adaptation to cooler climates. We scored a broad sorghum diversity set (n = 338) for early chilling tolerance, high-latitude adaptation, and bioenergy related agronomical traits in multi-environment trials. Our results show a high phenotypic variation and medium to high heritabilities for most traits, indicating that a robust breeding progress is feasible. Several public accessions with a good adaptation to cooler climates were identified, which can serve as valuable base material for sorghum breeding in temperate areas. Genome-wide association studies reveal a polygenic (quantitative) character for most of the traits, confirming previous studies. Hence, for practical breeding, it will be difficult to conduct efficient marker-assisted selection for temperate-adaptation traits in genetically diverse material. Full article
(This article belongs to the Section Crop Breeding and Genetics)
Open AccessArticle
Is Cattle Manure Application with Plastic-Film Mulch a Good Choice for Potato Production?
Agronomy 2019, 9(9), 534; https://doi.org/10.3390/agronomy9090534 - 11 Sep 2019
Viewed by 167
Abstract
Using manure in potato production has been considered for its potential environmentally friendly effects. Two years of field experiments were conducted to evaluate the effects of different kinds of fertilizer and soil surface treatments on potato growth. Experimental treatments consisted of three soil [...] Read more.
Using manure in potato production has been considered for its potential environmentally friendly effects. Two years of field experiments were conducted to evaluate the effects of different kinds of fertilizer and soil surface treatments on potato growth. Experimental treatments consisted of three soil surface treatments, including black plastic-film mulch (BM), transparent film-plastic mulch (TM), and non-mulched (NM) treatment, and two fertilizer treatments, including inorganic fertilizer (IF), and cattle manure (CM). The results showed that low environmental temperatures at early growth stages harmed potato growth. The more suitable hydrothermal environment under BM treatment induced 9–67%, 1–223%, 15–30%, −1–11% and 18–34% greater plant height, leaf area index (LAI), tuber yield, crop evapotranspiration (ETc) and water use efficiency (WUE), respectively, than NM and TM treatments. Plastic-film mulch increased soil carbon dioxide concentration, especially for the TM treatment. With low soil nitrogen content during the whole growth stage, and high soil carbon dioxide concentration during sprout and seedling stages, the CM treatment reduced plant height, LAI, tuber yields, ETc and WUE by 27–155%, 2–96%, 6–23%, 2–6% and 8–25%, respectively. These results suggest that inorganic fertilizer with black plastic-film mulch is still the best choice for potato production, and further studies are needed to identify the best level of cattle manure used under black plastic-film mulch. Full article
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Open AccessArticle
Effects of Light, Temperature, and Soil Depth on the Germination and Emergence of Conyza canadensis (L.) Cronq.
Agronomy 2019, 9(9), 533; https://doi.org/10.3390/agronomy9090533 - 11 Sep 2019
Viewed by 139
Abstract
Understanding the dynamics of invasive species under global climate change requires knowledge about the effects of environmental factors on germination and emergence. We considered Conyza canadensis (L.) Cronq., an invasive species that is quickly invading Southern European agricultural systems, and performed germination assays [...] Read more.
Understanding the dynamics of invasive species under global climate change requires knowledge about the effects of environmental factors on germination and emergence. We considered Conyza canadensis (L.) Cronq., an invasive species that is quickly invading Southern European agricultural systems, and performed germination assays in growth chambers at eight constant temperatures with alternating light (2.5, 5, 10, 15, 20, 25, 30, and 40 °C, with 12 h/12 h—light/dark), three alternating temperatures in alternating light (12/18, 17/23, and 22/28 °C, with 12 h/12 h—light/dark) and three fixed temperatures (15, 20, and 25 °C) in complete darkness. Furthermore, emergence assays were performed in pots considering four depths (0, 2.5, 5, and 10 mm), three temperatures with alternating light (15, 20, and 25 °C) and un-treated or pre-treated seeds (water imbibition and light for two days). C. canadensis was able to germinate in a wide range of temperatures (from 5–10 °C to 30 °C). The highest germination capacity was observed at 15 °C (light/dark); no differences were observed at 17/23 and 22/28 °C with respect to 20 and 25 °C (light/dark), while germinations were significantly reduced at 12/18 °C. The lowest germination time was observed at 25 °C (light/dark) and it was significantly increased at 12/18 °C and in darkness. The highest emergence was from 0 mm depth; pre-treatment significantly increased the emergence from 2.5 mm and 5 mm depth, but not from 10 mm depth. Modeling germination rates as a function of temperature allowed us to determine Tb = 6.8 °C (base temperature) and Tc = 35.8 °C (ceiling temperature). In light of these results, the potential for C. canadensis to spread into new environments and possible new management methods are discussed. Full article
(This article belongs to the Section Weed Science and Weed Management)
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Open AccessArticle
Does Harvesting Affect the Spatio-Temporal Signature of Pests and Natural Enemies in Alfalfa Fields?
Agronomy 2019, 9(9), 532; https://doi.org/10.3390/agronomy9090532 - 11 Sep 2019
Viewed by 115
Abstract
Determining the spatio-temporal distribution and association of pests and natural enemies would be useful for implementing biological control of pests and could also be used in site-specific pest management. In this study, the spatio-temporal distribution and association of aphids, plant bugs, and natural [...] Read more.
Determining the spatio-temporal distribution and association of pests and natural enemies would be useful for implementing biological control of pests and could also be used in site-specific pest management. In this study, the spatio-temporal distribution and association of aphids, plant bugs, and natural enemies were assessed in alfalfa fields using geo-statistics and spatial analysis by distance indices (SADIE). Additionally, the effect of alfalfa hay-harvesting on the spatial and temporal distribution of these insects was investigated for the first time. Geostatistical analysis indicated that the degree of dependence (DD) was ≥75% for 11 out of 39, 9 out of 35, 3 out of 12, 10 out of 29, and 2 out of 20 datasets for pea aphid Acyrthosiphon pisum, spotted alfalfa aphid Therioaphis maculata, cowpea aphid Aphis craccivora, alfalfa plant bug Adelphocoris lineolatus, and tarnished plant bug Lygus rugulipennis, respectively. The results also indicated that DD was ≥75% in 7 out of 45, 18 out of 45, and 3 out of 20 datasets for Coccinella septempunctata, Hippodamia variegata, and Pterostichus melanarius, respectively. Harvesting decreased the aggregation of the ladybirds, which resulted in a decrease in the index of aggregation. The geo-statistics results were confirmed by SADIE in 75% of datasets. These results can be used in biological control and site-specific management of aphids and plant bugs in alfalfa fields. Full article
(This article belongs to the Special Issue Information Technologies for Precision Plant and Crop Protection)
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Open AccessArticle
Impact of Biochar on Physicochemical Properties of Haplic Luvisol Soil under Different Land Use: A Plot Experiment
Agronomy 2019, 9(9), 531; https://doi.org/10.3390/agronomy9090531 - 11 Sep 2019
Viewed by 154
Abstract
There is limited information regarding the effect of biochar (BioC) on improving the fertility of degraded soils (fallow and grassland), particularly with respect to changes with time. The objective of the study was to evaluate, in a three-year field experiment, the influence of [...] Read more.
There is limited information regarding the effect of biochar (BioC) on improving the fertility of degraded soils (fallow and grassland), particularly with respect to changes with time. The objective of the study was to evaluate, in a three-year field experiment, the influence of BioC on the physicochemical properties of Haplic Luvisol. BioC, obtained via wood waste pyrolysis at 650 °C, was applied to the soil of subplots under fallow and grassland at rates of 0, 1, 2, and 3 kg·m−2. Soil samples were collected eight times, from 2013 to 2015. Physicochemical characterization was performed for soil and BioC by analyzing density, pH, surface charge, as well as ash and organic carbon content. BioC’s influence on the physicochemical properties of degraded soils was determined by analyzing the changes in pH, specific surface area, radius, and volume of the micropore. The addition of BioC affected analyzed soils to varying degrees. In the case of the fallow, a positive effect on changes in these parameters was observed, particularly at the highest biochar dose and for the last year of the experiment. However, for the grassland, in most cases we observed the opposite trend—for example, pH and specific surface area values decreased with increasing biochar dose. We believe that it is necessary to examine how BioC affects sorption properties of organic matter of fallow and grassland soils, as well as the BioC’s influence on humic acids of these soils as a function on BioC dose and function of time. Full article
(This article belongs to the Special Issue Interaction of Biochar on Organic Waste Composting)
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Open AccessArticle
Enhancing Zinc Accumulation and Bioavailability in Wheat Grains by Integrated Zinc and Pesticide Application
Agronomy 2019, 9(9), 530; https://doi.org/10.3390/agronomy9090530 - 11 Sep 2019
Viewed by 155
Abstract
Incorporating foliar zinc (Zn) spray into existing pesticide application is considered highly cost-effective to biofortify wheat (Triticum aestivum) with Zn. However, the effectiveness of this combined approach in terms of Zn enrichment and bioavailability in grain and its milling fractions is [...] Read more.
Incorporating foliar zinc (Zn) spray into existing pesticide application is considered highly cost-effective to biofortify wheat (Triticum aestivum) with Zn. However, the effectiveness of this combined approach in terms of Zn enrichment and bioavailability in grain and its milling fractions is not well examined. Two-year field experiments were conducted in 2017 and 2018 with three sets of foliar applications (nil Zn as control, foliar Zn alone, and foliar Zn plus pesticides) at the anthesis, milk stage, or both. Compared to the control, grain yield was not affected by foliar Zn application alone or combined with pesticides, while the Zn concentrations and bioavailability substantially increased in the whole-grain, bran, and flour irrespective of spray timing. Yield losses by 28%–39% (2018 vs. 2017) led to 7%–18% and 18%–38% increase of Zn density in grain and flour, respectively. Further, such negative responses were uncoupled by foliar spray of Zn or Zn plus pesticides, and absent from the control plants. Nonetheless, grain Zn biofortification was achieved in both low- and high-yield plants with either Zn spray alone or combined with pesticides. Together with the enhanced Zn bioavailability in grain, bran, and flour, the effectiveness of this combined strategy is validated to biofortify wheat with Zn. Full article
(This article belongs to the Special Issue Biofortification of Crops)
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Open AccessReview
Deciphering the Symbiotic Plant Microbiome: Translating the Most Recent Discoveries on Rhizobia for the Improvement of Agricultural Practices in Metal-Contaminated and High Saline Lands
Agronomy 2019, 9(9), 529; https://doi.org/10.3390/agronomy9090529 - 10 Sep 2019
Viewed by 214
Abstract
Rhizosphere and plant-associated microorganisms have been intensely studied for their beneficial effects on plant growth and health. These mainly include nitrogen-fixing bacteria (NFB) and plant-growth promoting rhizobacteria (PGPR). This beneficial fraction is involved in major functions such as plant nutrition and plant resistance [...] Read more.
Rhizosphere and plant-associated microorganisms have been intensely studied for their beneficial effects on plant growth and health. These mainly include nitrogen-fixing bacteria (NFB) and plant-growth promoting rhizobacteria (PGPR). This beneficial fraction is involved in major functions such as plant nutrition and plant resistance to biotic and abiotic stresses, which include water deficiency and heavy-metal contamination. Consequently, crop yield emerges as the net result of the interactions between the plant genome and its associated microbiome. Here, we provide a review covering recent studies on PGP rhizobia as effective inoculants for agricultural practices in harsh soil, and we propose models for inoculant combinations and genomic manipulation strategies to improve crop yield. Full article
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Open AccessReview
Jerusalem Artichoke (Helianthus tuberosus L.): A Versatile and Sustainable Crop for Renewable Energy Production in Europe
Agronomy 2019, 9(9), 528; https://doi.org/10.3390/agronomy9090528 - 10 Sep 2019
Viewed by 180
Abstract
Recently, biofuels have become a strategic focus to reduce vehicle emissions and increase sustainability of the transport sector. However, the sustainability of biofuels production has been questioned owing to its implications for future land footprint. In this respect, the EU Commission has very [...] Read more.
Recently, biofuels have become a strategic focus to reduce vehicle emissions and increase sustainability of the transport sector. However, the sustainability of biofuels production has been questioned owing to its implications for future land footprint. In this respect, the EU Commission has very recently classified as low indirect land-use change (ILUC)–risk biofuels those obtained by crops grown on marginal lands and with low external inputs. Only few crops can reach high yields under both of these conditions across Europe. From this point of view, Jerusalem artichoke (Helianthus tuberosus L.) is certainly a species worthy of remark since it has all the attributes to accomplish the aims of the updated EU Renewable Energy Directive (RED II). Starting from physiological aspects, the present review examines and summarizes literature on the ecology, genetic resources, agronomic practices and sustainability of this species. The goal is to point out the recent advances of research in Jerusalem artichoke (JA) potential as alternative biofuel feedstock and to identify what is still needed to better characterize its environmental benefits and agronomic performance. Full article
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Open AccessArticle
Genome-Wide Characterization and Expression Profiling of Squamosa Promoter Binding Protein-like (SBP) Transcription Factors in Wheat (Triticum aestivum L.)
Agronomy 2019, 9(9), 527; https://doi.org/10.3390/agronomy9090527 - 09 Sep 2019
Viewed by 242
Abstract
Transcription factors (TFs) play fundamental roles in the developmental processes of all living organisms. Squamosa Promoter Binding Protein-like (SBP/SBP-Box) is a major family of plant-specific TFs, which plays important roles in multiple processes involving plant growth and development. While some work has been [...] Read more.
Transcription factors (TFs) play fundamental roles in the developmental processes of all living organisms. Squamosa Promoter Binding Protein-like (SBP/SBP-Box) is a major family of plant-specific TFs, which plays important roles in multiple processes involving plant growth and development. While some work has been done, there is a lot more that is yet to be discovered in the hexaploid wheat SBP (TaSBP) family. With the completion of whole genome sequencing, genome-wide analysis of SBPs in common hexaploid wheat is now possible. In this study, we used protein–protein Basic Local Alignment Search Tool (BLASTp) to hunt the newly released reference genome sequence of hexaploid wheat (Chinese spring). Seventy-four TaSBP proteins (belonging to 56 genes) were identified and clustered into five groups. Gene structure and motif analysis indicated that most TaSBPs have relatively conserved exon–intron arrangements and motif composition. Analysis of transcriptional data showed that many TaSBP genes responded to some biological and abiotic stresses with different expression patterns. Moreover, three TaSBP genes were generally expressed in the majority of tissues throughout the wheat growth and also responded to many environmental biotic and abiotic stresses. Collectively, the detailed analyses presented here will help in understanding the roles of the TaSBP and also provide a reference for the further study of its biological function in wheat. Full article
(This article belongs to the Section Crop Breeding and Genetics)
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Open AccessArticle
Chlorophyll α Fluorescence Parameters as an Indicator to Identify Drought Susceptibility in Common Bush Bean
Agronomy 2019, 9(9), 526; https://doi.org/10.3390/agronomy9090526 - 09 Sep 2019
Viewed by 118
Abstract
The common bean is susceptible to drought conditions and the evaluation of plant responses to low water availability can be difficult. The quantification of chlorophyll fluorescence as a sensitive trait to environmental stresses is an important alternative in the characterization of drought-susceptible genotypes. [...] Read more.
The common bean is susceptible to drought conditions and the evaluation of plant responses to low water availability can be difficult. The quantification of chlorophyll fluorescence as a sensitive trait to environmental stresses is an important alternative in the characterization of drought-susceptible genotypes. The objective of this study was to evaluate mainly the use of chlorophyll α fluorescence (maximum efficiency of PSII (Fv/Fm), photochemical quenching (qP), non-photochemical quenching (NPQ)) and rapid light-response curves (RLCs) (initial slope of the curve (α), minimum saturation irradiance (Ik) and maximum relative electron transport rate (ETRmax)) parameters as tools for the identification of susceptible or tolerant bush bean cultivars to water deficit stress conditions in two different phenological stages. Using a randomized block design in a factorial arrangement, five bush bean cultivars (Cerinza, Bachue, NUA35, Bacata and Bianca) were evaluated under water deficit conditions by the suspension of irrigation for 15 days from 40 to 55 Days after Emergence (DAE) (vegetative stage) or 50 to 65 DAE (reproductive stage). The results showed that Fv/Fm and NPQ recorded the highest variation due to water deficit conditions, especially in the vegetative stage. The greatest reductions in Fv/Fm (0.67) and NPQ (0.71) were evidenced in cultivar NUA35 compared to its control plants (0.78 and 1.07, respectively). The parameters obtained from RLCs showed that cultivar Bacata registered the lowest α (0.17) and Ik (838.19 μmol∙m−2∙s−1) values compared to its control plants (α 0.23; Ik 769.99 μmol∙m−2∙s−1). Differences were only obtained in ETRmax in the reproductive stage (50–65 DAE) in which cultivar NUA35 reached values of 158.5 in stressed plants compared to control plants (251.22). In conclusion, the parameters derived from RLCs such as α and Ik can be used as tools to identify drought susceptibility in the vegetative stage, whereas ETRmax can be used in the reproductive stage. In addition, PSII photochemistry (Fv/Fm and NPQ) can also help to understand the agronomic responses of common bush bean cultivars to drought conditions. Full article
(This article belongs to the Special Issue Fluorescence Techniques: Understanding Crop Performance)
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Open AccessArticle
Long-Term Impact of Potassium Fertilization on Soil and Productivity in Intensive Olive Cultivation
Agronomy 2019, 9(9), 525; https://doi.org/10.3390/agronomy9090525 - 09 Sep 2019
Viewed by 152
Abstract
The olive growing sector is transitioning from traditional to intensive irrigated cultivation, dictating a need to reconsider orchard management practices including fertilization. Potassium (K) is an essential nutrient, typically found in high concentrations in plants. Orchard K fertilization requirements are commonly derived from [...] Read more.
The olive growing sector is transitioning from traditional to intensive irrigated cultivation, dictating a need to reconsider orchard management practices including fertilization. Potassium (K) is an essential nutrient, typically found in high concentrations in plants. Orchard K fertilization requirements are commonly derived from the disparity between assumed tree requirements and extractable soil K. The long-term impact of insufficient fertilization on K available in the soil, growth, and yield of irrigated field-grown olive trees was evaluated over six consecutive seasons. Withholding of K fertilization led to lower exchangeable and soluble K concentrations in the soil and significantly impaired yield. The reduction in yield was attributed to reduced flowering and fruit set, resulting in a lower fruit number. Tree vegetative growth and flowering quality traits were not affected. In addition, trees not receiving K appeared to be more susceptible to alternate bearing. Following two seasons of omitting K fertilization, leaf K concentration did not decrease below the conventionally accepted sufficiency threshold for olive (0.8%). In spite of this, the trees produced significantly lower yields. Our results suggest that long-term insufficient K fertilization results in reduced soil available K and consequently impairs tree productivity. The results imply that the sufficiency threshold for K in diagnostic leaves should be reconsidered for intensive orchards. Moreover, the current method for K deficiency detection using leaf K concentration may be inadequate for intensive orchards. Integration of other parameters, such as fruit K content, leaf Na, and changes in soil exchangeable K content or sorption energy, may promote a more reliable analysis of orchard K nutritional status. Full article
(This article belongs to the Section Soil and Plant Nutrition)
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Open AccessArticle
The Coupling Effects of Plant Growth Promoting Rhizobacteria and Salicylic Acid on Physiological Modifications, Yield Traits, and Productivity of Wheat under Water Deficient Conditions
Agronomy 2019, 9(9), 524; https://doi.org/10.3390/agronomy9090524 - 09 Sep 2019
Viewed by 157
Abstract
Water deficit and soil infertility negatively influence the growth, nutrient uptake, and productivity of wheat. Plant growth promoting rhizobacteria (PGPR) and salicylic acid (SA) were evaluated as possible solutions to mitigate the impacts of water deficit on growth, physiology, productivity, and nutrient uptake [...] Read more.
Water deficit and soil infertility negatively influence the growth, nutrient uptake, and productivity of wheat. Plant growth promoting rhizobacteria (PGPR) and salicylic acid (SA) were evaluated as possible solutions to mitigate the impacts of water deficit on growth, physiology, productivity, and nutrient uptake of wheat (Triticum aestivum L. cv. Sakha 95). Over two growing seasons (2016/2017 and 2017/2018) field experiments were conducted to examine eight combinations of two water treatments (water deficit and well-watered) with four soil and foliar treatments (control, PGPR, SA, and combination of PGPR + SA). The application of PGPR increased soil microbial activity resulting in increased field capacity and available soil water. Likewise, the application of the combined treatment of PGPR and SA significantly increased chlorophyll content, relative water content, stomatal conductance, soil microbial population, and showed inhibitory impacts on proline content, thus improving yield-related traits, productivity, and nutrient uptake (N, P, K) under water deficit compared to the control treatment. The results show that the integrative use of PGPR in association with SA may achieve an efficacious strategy to attenuate the harmful effects of water deficit as well as the amelioration of productivity and nutrient uptake of wheat under water-deficient conditions. Full article
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