Special Issue "Biostimulants as Growth Promoting and Stress Protecting Compounds"

A special issue of Plants (ISSN 2223-7747). This special issue belongs to the section "Plant Response to Abiotic Stress and Climate Change".

Deadline for manuscript submissions: 30 November 2021.

Special Issue Editors

Dr. Chrystalla Antoniou
E-Mail Website
Guest Editor
Department of Agricultural Sciences, Biotechnology & Food Science, Cyprus University of Technology, P.O. Box 50329, 3603 Lemesos, Cyprus
Interests: Plant growth promotion; abiotic stresses; priming technologies; biostimulants; plant biotechnology; plant physiology; plant molecular biology.
Prof. Dr. Raffaella Maria Balestrini
E-Mail Website
Guest Editor
Dr. Vasileios Fotopoulos
E-Mail Website
Guest Editor
Department of Agricultural Sciences, Biotechnology & Food Science Cyprus University of Technology P.O. Box 50329, 3603 Lemesos, Cyprus
Interests: abiotic stress; antioxidants; priming; reactive oxygen species; reactive nitrogen species; reactive sulfur species; growth promotion; cellular signaling; plant biotechnology
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Special Issue Information

Dear Colleagues,

Plant biostimulants, or sometimes referred to as agricultural biostimulants, are a diverse category of substrates derived from natural and biological sources with functions in plant growth and development from seed germination to plant maturity. The use of biostimulants in agriculture has become a common practice, providing a number of benefits to plants and the environment, since they are an attractive alternative to synthetic compounds. Biostimulants are usually a mixture of microorganisms and natural products, such as protein hydrolysates, humic and fulvic basic nutrients, and extracts from plants and algae. The application of biostimulants improves the efficiency of plant metabolism that further induces plant growth and yield, enhancing plant tolerance against abiotic and biotic stresses and improving the quality of crops. Exploring the benefits of existing and novel biostimulants in plants and the mechanisms underlying the beneficial effects opens up new directions of research.

The general concept of this Special Issue is to provide an up-to-date overview in the use of biostimulants in agriculture to enhance plant growth and plant adaptation to stress factors. In particular, submissions of review and original research articles reporting novel scientific findings on the following, but not limited to, topics are welcome:

  • Biostimulants to promote plant growth;
  • Biostimulants to enhance plant stress tolerance against abiotic stresses;
  • Biostimulants to enhance plant stress tolerance against biotic stresses;
  • Biostimulants to improve crop quality;
  • Novel biostimulants in agriculture.

Dr. Chrystalla Antoniou
Dr. Raffaella Maria Balestrini
Dr. Vasileios Fotopoulos
Guest Editors

Manuscript Submission Information

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Keywords

  • biostimulants
  • algal extracts
  • amino acids
  • plant growth
  • plant metabolism
  • plant nutrients
  • stress tolerance
  • biotic stress
  • abiotic stress
  • yield
  • crop physiology
  • crop quality

Published Papers (15 papers)

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Research

Jump to: Review

Article
Deep-Sea Actinobacteria Mitigate Salinity Stress in Tomato Seedlings and Their Biosafety Testing
Plants 2021, 10(8), 1687; https://0-doi-org.brum.beds.ac.uk/10.3390/plants10081687 - 17 Aug 2021
Viewed by 728
Abstract
Soil salinity is an enormous problem affecting global agricultural productivity. Deep-sea actinobacteria are interesting due to their salt tolerance mechanisms. In the present study, we aim to determine the ability of deep-sea Dermacoccus (D. barathri MT2.1T and D. profundi MT2.2T [...] Read more.
Soil salinity is an enormous problem affecting global agricultural productivity. Deep-sea actinobacteria are interesting due to their salt tolerance mechanisms. In the present study, we aim to determine the ability of deep-sea Dermacoccus (D. barathri MT2.1T and D. profundi MT2.2T) to promote tomato seedlings under 150 mM NaCl compared with the terrestrial strain D. nishinomiyaensis DSM20448T. All strains exhibit in vitro plant growth-promoting traits of indole-3-acetic acid production, phosphate solubilization, and siderophore production. Tomato seedlings inoculated with D. barathri MT2.1T showed higher growth parameters (shoot and root length, dry weight, and chlorophyll content) than non-inoculated tomato and the terrestrial strain under 150 mM NaCl. In addition, hydrogen peroxide (H2O2) in leaves of tomatoes inoculated with deep-sea Dermacoccus was lower than the control seedlings. This observation suggested that deep-sea Dermacoccus mitigated salt stress by reducing oxidative stress caused by hydrogen peroxide. D. barathri MT2.1T showed no harmful effects on Caenorhabditis elegans, Daphnia magna, Eisenia foetida, and Escherichia coli MC4100 in biosafety tests. This evidence suggests that D. barathri MT2.1T would be safe for use in the environment. Our results highlight the potential of deep-sea Dermacoccus as a plant growth promoter for tomatoes under salinity stress. Full article
(This article belongs to the Special Issue Biostimulants as Growth Promoting and Stress Protecting Compounds)
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Article
Identification of Plant Growth Promoting Rhizobacteria That Improve the Performance of Greenhouse-Grown Petunias under Low Fertility Conditions
Plants 2021, 10(7), 1410; https://0-doi-org.brum.beds.ac.uk/10.3390/plants10071410 - 09 Jul 2021
Viewed by 516
Abstract
The production of greenhouse ornamentals relies on high fertilizer inputs to meet scheduling deadlines and quality standards, but overfertilization has negative environmental impacts. The goals of this study were to identify plant-growth-promoting rhizobacteria (PGPR) that can improve greenhouse ornamental crop performance with reduced [...] Read more.
The production of greenhouse ornamentals relies on high fertilizer inputs to meet scheduling deadlines and quality standards, but overfertilization has negative environmental impacts. The goals of this study were to identify plant-growth-promoting rhizobacteria (PGPR) that can improve greenhouse ornamental crop performance with reduced fertilizer inputs, and to identify the best measurements of plant performance for assessing the beneficial impact of PGPR on ornamentals. A high-throughput greenhouse trial was used to identify 14 PGPR isolates that improved the flower/bud number and shoot dry weight of Petunia × hybrida ‘Picobella Blue’ grown under low fertility conditions in peat-based media. These 14 PGPR were then applied to petunias grown under low fertility conditions (25 mg L−1 N). PGPR-treated plants were compared to negative (untreated at 25 mg L−1 N) and positive (untreated at 50, 75, 100, and 150 mg L−1 N) controls. Multiple parameters were measured in the categories of flowering, vegetative growth, and vegetative quality to determine the best measurements to assess improvements in ornamental plant performance. Caballeronia zhejiangensis C7B12-treated plants performed better in almost all parameters and were comparable to untreated plants fertilized with 50 mg L−1 N. Genomic analysis identified genes that were potentially involved in plant growth promotion. Our study identified potential PGPR that can be used as biostimulants to produce high-quality greenhouse ornamentals with lower fertilizer inputs. Full article
(This article belongs to the Special Issue Biostimulants as Growth Promoting and Stress Protecting Compounds)
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Article
Interactive Impacts of Beneficial Microbes and Si-Zn Nanocomposite on Growth and Productivity of Soybean Subjected to Water Deficit under Salt-Affected Soil Conditions
Plants 2021, 10(7), 1396; https://0-doi-org.brum.beds.ac.uk/10.3390/plants10071396 - 08 Jul 2021
Viewed by 471
Abstract
Water stress or soil salinity is considered the major environmental factor affecting plant growth. When both challenges are present, the soil becomes infertile, limiting plant productivity. In this work a field experiment was conducted during the summer 2019 and 2020 seasons to evaluate [...] Read more.
Water stress or soil salinity is considered the major environmental factor affecting plant growth. When both challenges are present, the soil becomes infertile, limiting plant productivity. In this work a field experiment was conducted during the summer 2019 and 2020 seasons to evaluate whether plant growth-promoting microbes (PGPMs) and nanoparticles (Si-ZnNPs) have the potential to maintain soybean growth, productivity, and seed quality under different watering intervals (every 11 (IW0), 15 (IW1) and 19 (IW2) days) in salt-affected soil. The most extended watering intervals (IW1 and IW2) caused significant increases in Na+ content, and oxidative damage indicators (malondialdehyde (MDA) and electrolyte leakage (EL%)), which led to significant reductions in soybean relative water content (RWC), stomatal conductance, leaf K+, photosynthetic pigments, soluble protein. Subsequently reduced the vegetative growth (root length, nodules dry weight, and total leaves area) and seeds yield. However, there was an enhancement in the antioxidants defense system (enzymatic and non-enzymatic antioxidant). The individual application of PGPMs or Si-ZnNPs significantly improved leaf K+ content, photosynthetic pigments, RWC, stomatal conductance, total soluble sugars (TSS), CAT, POD, SOD, number of pods plant−1, and seed yield through decreasing the leaf Na+ content, MDA, and EL%. The combined application of PGPMs and Si-ZnNPs minimized the adverse impact of water stress and soil salinity by maximizing the root length, heavier nodules dry weight, leaves area, TSS and the activity of antioxidant enzymes, which resulted in higher soybean growth and productivity, which suggests their use under harsh growing conditions. Full article
(This article belongs to the Special Issue Biostimulants as Growth Promoting and Stress Protecting Compounds)
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Communication
Biopriming with Seaweed Extract and Microbial-Based Commercial Biostimulants Influences Seed Germination of Five Abelmoschus esculentus Genotypes
Plants 2021, 10(7), 1327; https://0-doi-org.brum.beds.ac.uk/10.3390/plants10071327 - 29 Jun 2021
Viewed by 508
Abstract
Seed germination is a crucial step in plant propagation, as it controls seedling production, stand establishment and ultimately crop yield. Approaches that can promote seed germination of valuable crops remain of great interest globally. The current study evaluated the effect of biostimulant (Kelpak [...] Read more.
Seed germination is a crucial step in plant propagation, as it controls seedling production, stand establishment and ultimately crop yield. Approaches that can promote seed germination of valuable crops remain of great interest globally. The current study evaluated the effect of biostimulant (Kelpak® and plant-growth-promoting rhizobacteria—PGPR) biopriming on the seed germination of five (VI037996, VI046567, VI055421, VI050956, and VI033796) Abelmoschus esculentus genotypes. The germination responses of the bio-primed seeds were measured using six parameters, including final germination percentage (FGP), mean germination time (MGT), germination index (GI), coefficient of velocity of germination (CVG), germination rate index (GRI), and time spread of germination (TSG). Biostimulant application significantly affected MGT (1.1–2.2 days), CVG (1.4–5.9), and TSG (1.2–3.0 days). Genotype also significantly influenced the TSG (1–3 days). Significant interaction effect of biostimulant treatment and genotype was evident on the FGP, GI, and GRI of the germinated seeds. The most noteworthy effect was demonstrated by Kelpak® (1:100) applied to genotype VI037996, with significantly improved FGP (82%), GI (238), and GRI (77%/day) when compared to the control. Overall, the current findings suggest the potential stimulatory effect of biostimulants (especially Kelpak®) on the germination of Abelmoschus esculentus seeds. However, this influence was strongly dependent on the type of genotype. Full article
(This article belongs to the Special Issue Biostimulants as Growth Promoting and Stress Protecting Compounds)
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Article
Impact of Ecklonia maxima Seaweed Extract and Mo Foliar Treatments on Biofortification, Spinach Yield, Quality and NUE
Plants 2021, 10(6), 1139; https://0-doi-org.brum.beds.ac.uk/10.3390/plants10061139 - 03 Jun 2021
Cited by 3 | Viewed by 857
Abstract
Seaweed extract (SE) application is a contemporary and sustainable agricultural practice used to improve yield and quality of vegetable crops. Plant biofortification with trace element is recognized as a major tool to prevent mineral malnourishment in humans. Mo deficiency causes numerous dysfunctions, mostly [...] Read more.
Seaweed extract (SE) application is a contemporary and sustainable agricultural practice used to improve yield and quality of vegetable crops. Plant biofortification with trace element is recognized as a major tool to prevent mineral malnourishment in humans. Mo deficiency causes numerous dysfunctions, mostly connected to central nervous system and esophageal cancer. The current research was accomplished to appraise the combined effect of Ecklonia maxima brown seaweed extract (SE) and Mo dose (0, 0.5, 2, 4 or 8 µmol L−1) on yield, biometric traits, minerals, nutritional and functional parameters, as well as nitrogen indices of spinach plants grown in a protected environment (tunnel). Head fresh weight (FW), ascorbic acid, polyphenols, N, P, K, Mg and nitrogen use efficiency (NUE) were positively associated with SE treatment. Moreover, head FW, head height (H), stem diameter (SD), ascorbic acid, polyphenols, carotenoids as well as NUE indices were enhanced by Mo-biofortification. A noticeable improvement in number of leaves (N. leaves), head dry matter (DM) and Mo concentration in leaf tissues was observed when SE application was combined with a Mo dosage of 4 or 8 µmol L−1. Overall, our study highlighted that E. maxima SE treatment and Mo supply can improve both spinach production and quality via the key enzyme activity involved in the phytochemical homeostasis of SE and the plant nutritional status modification resulting in an enhanced spinach Mo tolerance. Full article
(This article belongs to the Special Issue Biostimulants as Growth Promoting and Stress Protecting Compounds)
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Article
Ulva lactuca Extract and Fractions as Seed Priming Agents Mitigate Salinity Stress in Tomato Seedlings
Plants 2021, 10(6), 1104; https://0-doi-org.brum.beds.ac.uk/10.3390/plants10061104 - 30 May 2021
Viewed by 1066
Abstract
The present study investigates the effect of Ulva lactuca extract as seed-priming agent for tomato plants under optimal and salinity stress conditions. The aims of this experiment were to assess the effect of seed priming using Ulva lactuca extract in alleviating the salinity [...] Read more.
The present study investigates the effect of Ulva lactuca extract as seed-priming agent for tomato plants under optimal and salinity stress conditions. The aims of this experiment were to assess the effect of seed priming using Ulva lactuca extract in alleviating the salinity stress tomato plants were subjected to, and to find out the possible mechanism of actions behind such a positive effect via means of fractionation of the crude extract and characterization. Salinity application decreased the plant biomass and altered different physiological traits of tomato. However, the application of Ulva lactuca methanol extract (ME) and its fractions (residual fraction (RF), chloroform fraction (CF), butanol fraction (BF), and hexane fraction (HF)) at 1 mg·mL−1 as seed priming substances attenuated the negative effects of salinity on tomato seedlings. Under salinity stress conditions, RF application increased the tomato fresh weight; while ME, RF, and HF treatments significantly decreased the hydrogen peroxide (H2O2) concentration and antioxidant activity in tomato plants. The biochemical analyses of Ulva lactuca extract and fractions showed that the RF recorded the highest concentration of glycine betaine, while the ME was the part with the highest concentrations of total phenols and soluble sugars. This suggests that these compounds might play a key role in the mechanism by which seaweed extracts mitigate salinity stress on plants. Full article
(This article belongs to the Special Issue Biostimulants as Growth Promoting and Stress Protecting Compounds)
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Article
Strain-Specific Biostimulant Effects of Chlorella and Chlamydomonas Green Microalgae on Medicago truncatula
Plants 2021, 10(6), 1060; https://0-doi-org.brum.beds.ac.uk/10.3390/plants10061060 - 25 May 2021
Viewed by 1064
Abstract
Microalgae have been identified to produce a plethora of bioactive compounds exerting growth stimulating effects on plants. The objective of this study was to investigate the plant-growth-promoting effects of three selected strains of eukaryotic green microalgae. The biostimulatory effects of two Chlorella species [...] Read more.
Microalgae have been identified to produce a plethora of bioactive compounds exerting growth stimulating effects on plants. The objective of this study was to investigate the plant-growth-promoting effects of three selected strains of eukaryotic green microalgae. The biostimulatory effects of two Chlorella species (MACC-360 and MACC-38) and a Chlamydomonas reinhardtii strain (cc124) were investigated in a Medicago truncatula model plant grown under controlled greenhouse conditions. The physiological responses of the M. truncatula A17 ecotype to algal biomass addition were characterized thoroughly. The plants were cultivated in pots containing a mixture of vermiculite and soil (1:3) layered with clay at the bottom. The application of live algae cells using the soil drench method significantly increased the plants’ shoot length, leaf size, fresh weight, number of flowers and pigment content. For most of the parameters analyzed, the effects of treatment proved to be specific for the applied algae strains. Overall, Chlorella application led to more robust plants with increased fresh biomass, bigger leaves and more flowers/pods compared to the control and Chlamydomonas-treated samples receiving identical total nutrients. Full article
(This article belongs to the Special Issue Biostimulants as Growth Promoting and Stress Protecting Compounds)
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Article
Foliar-Applied Potassium Silicate Coupled with Plant Growth-Promoting Rhizobacteria Improves Growth, Physiology, Nutrient Uptake and Productivity of Faba Bean (Vicia faba L.) Irrigated with Saline Water in Salt-Affected Soil
Plants 2021, 10(5), 894; https://0-doi-org.brum.beds.ac.uk/10.3390/plants10050894 - 28 Apr 2021
Cited by 1 | Viewed by 716
Abstract
The continuity of traditional planting systems in the last few decades has encountered its most significant challenge in the harsh changes in the global climate, leading to frustration in the plant growth and productivity, especially in the arid and semi-arid regions cultivated with [...] Read more.
The continuity of traditional planting systems in the last few decades has encountered its most significant challenge in the harsh changes in the global climate, leading to frustration in the plant growth and productivity, especially in the arid and semi-arid regions cultivated with moderate or sensitive crops to abiotic stresses. Faba bean, like most legume crops, is considered a moderately sensitive crop to saline soil and/or saline water. In this connection, a field experiment was conducted during the successive winter seasons 2018/2019 and 2019/2020 in a salt-affected soil to explore the combined effects of plant growth-promoting rhizobacteria (PGPR) and potassium (K) silicate on maintaining the soil quality, performance, and productivity of faba bean plants irrigated with either fresh water or saline water. Our findings indicated that the coupled use of PGPR and K silicate under the saline water irrigation treatment had the capability to reduce the levels of exchangeable sodium percentage (ESP) in the soil and to promote the activity of some soil enzymes (urease and dehydrogenase), which recorded nearly non-significant differences compared with fresh water (control) treatment, leading to reinstating the soil quality. Consequently, under salinity stress, the combined application motivated the faba bean vegetative growth, e.g., root length and nodulation, which reinstated the K+/Na+ ions homeostasis, leading to the lessening or equalizing of the activity level of enzymatic antioxidants (CAT, POD, and SOD) compared with the controls of both saline water and fresh water treatments, respectively. Although the irrigation with saline water significantly increased the osmolytes concentration (free amino acids and proline) in faba bean plants compared with fresh water treatment, application of PGPR or K-silicate notably reduced the osmolyte levels below the control treatment, either under stress or non-stress conditions. On the contrary, the concentrations of soluble assimilates (total soluble proteins and total soluble sugars) recorded pronounced increases under tested treatments, which enriched the plant growth, the nutrients (N, P, and K) uptake and translocation to the sink organs, which lastly improved the yield attributes (number of pods plant−1, number of seeds pod−1, 100-seed weight). It was concluded that the combined application of PGPR and K-silicate is considered a profitable strategy that is able to alleviate the harmful impact of salt stress alongside increasing plant growth and productivity. Full article
(This article belongs to the Special Issue Biostimulants as Growth Promoting and Stress Protecting Compounds)
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Article
Plant-Based Biostimulant as Sustainable Alternative to Synthetic Growth Regulators in Two Sweet Cherry Cultivars
Plants 2021, 10(4), 619; https://0-doi-org.brum.beds.ac.uk/10.3390/plants10040619 - 24 Mar 2021
Cited by 1 | Viewed by 649
Abstract
Sweet cherry is a high value crop and the economic success of its cultivation depends not only on yield but also on fruit visual and nutritional quality attributes that influence consumer acceptability, as well as on fruit post-harvest performance and resistance to cracking. [...] Read more.
Sweet cherry is a high value crop and the economic success of its cultivation depends not only on yield but also on fruit visual and nutritional quality attributes that influence consumer acceptability, as well as on fruit post-harvest performance and resistance to cracking. During the last few decades, cherry growers have tried to achieve these goals through exogenous applications of synthetic plant hormones and/or nutrients, but there is growing concern about the sustainability of the extensive use of these compounds in agriculture. For this reason, there is increasing interest in the possible adoption of different classes of biostimulants as sustainable alternatives to plant growth regulators. This research aimed to study the impact of foliar application of a novel tropical-plant extract, performed between full bloom and fruit set, on the yield and fruit quality of two important commercial sweet cherry cultivars, Kordia and Regina. The experimental design included a commercial control involving the application of a cytokinin promoter. In both cultivars, the tropical-plant extract induced significant increases in fruit yield. In addition, in the cultivar Kordia, the tropical-plant extract enhanced fruit calcium concentration, soluble solids content, flesh firmness, and skin color by 26.2%, 11.8%, 6.7%, and 12.0% (of fruits with mahogany skin color), respectively. Our results suggest that the tropical-plant extract tested as a biostimulant may be a sustainable and effective alternative to the exogenous application of synthetic hormones for sweet cherry cultivation. Full article
(This article belongs to the Special Issue Biostimulants as Growth Promoting and Stress Protecting Compounds)
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Article
Foliar Application of Different Vegetal-Derived Protein Hydrolysates Distinctively Modulates Tomato Root Development and Metabolism
Plants 2021, 10(2), 326; https://0-doi-org.brum.beds.ac.uk/10.3390/plants10020326 - 08 Feb 2021
Cited by 9 | Viewed by 1014
Abstract
Despite the scientific evidence supporting their biostimulant activity, the molecular mechanism(s) underlying the activity of protein hydrolysates (PHs) and the specificity among different products are still poorly explored. This work tested five different protein hydrolysates, produced from different plant sources using the same [...] Read more.
Despite the scientific evidence supporting their biostimulant activity, the molecular mechanism(s) underlying the activity of protein hydrolysates (PHs) and the specificity among different products are still poorly explored. This work tested five different protein hydrolysates, produced from different plant sources using the same enzymatic approach, for their ability to promote rooting in tomato cuttings following quick dipping. Provided that all the different PHs increased root length (45–93%) and some of them increased root number (37–56%), untargeted metabolomics followed by multivariate statistics and pathway analysis were used to unravel the molecular processes at the basis of the biostimulant activity. Distinct metabolomic signatures could be found in roots following the PHs treatments. In general, PHs shaped the phytohormone profile, modulating the complex interaction between cytokinins and auxins, an interplay playing a pivotal role in root development, and triggered a down accumulation of brassinosteroids. Concerning secondary metabolism, PHs induced the accumulation of aliphatic glucosinolates, alkaloids, and phenylpropanoids, potentially eliciting crop resilience to stress conditions. Here, we confirm that PHs may have a hormone-like activity, and that their application can modulate plant growth, likely interfering with signaling processes. Noteworthy, the heterogenicity of the botanical origin supported the distinctive and peculiar metabolomic responses we observed across the products tested. While supporting their biostimulant activity, these findings suggest that a generalized crop response to PHs cannot be defined and that specific effects are rather to be investigated. Full article
(This article belongs to the Special Issue Biostimulants as Growth Promoting and Stress Protecting Compounds)
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Article
Strategy of Salt Tolerance and Interactive Impact of Azotobacter chroococcum and/or Alcaligenes faecalis Inoculation on Canola (Brassica napus L.) Plants Grown in Saline Soil
Plants 2021, 10(1), 110; https://0-doi-org.brum.beds.ac.uk/10.3390/plants10010110 - 07 Jan 2021
Cited by 9 | Viewed by 988
Abstract
A pot experiment was designed and performed in a completely randomized block design (CRBD) to determine the main effect of two plant growth-promoting rhizobacteria (PGPR) and their co-inoculation on growth criteria and physio-biochemical attributes of canola plants (Brassica napus L.) plant grown [...] Read more.
A pot experiment was designed and performed in a completely randomized block design (CRBD) to determine the main effect of two plant growth-promoting rhizobacteria (PGPR) and their co-inoculation on growth criteria and physio-biochemical attributes of canola plants (Brassica napus L.) plant grown in saline soil. The results showed that inoculation with two PGPR (Azotobacter chroococcum and/or Alcaligenes faecalis) energized the growth parameters and photosynthetic pigments of stressed plants. Moreover, soluble sugars’ and proteins’ contents were boosted due to the treatments mentioned above. Proline, malondialdehyde (MDA), and hydrogen peroxide (H2O2) contents were markedly declined. At the same time, antioxidant enzymes, viz. superoxide dismutase (SOD), ascorbate peroxidase (APX), and peroxidase (POD), were augmented due to the inoculation with Azotobacter chroococcum and/or Alcaligenes faecalis. Regarding minerals’ uptake, there was a decline in sodium (Na) and an increase in nitrogen (N), potassium (K), calcium (Ca), and magnesium (Mg) uptake due to the application of either individual or co-inoculation with the mentioned bacterial isolates. This study showed that co-inoculation with Azotobacter chroococcum and Alcaligenes faecalis was the most effective treatment and could be considered a premium tool used in facing environmental problems, especially saline soils. Full article
(This article belongs to the Special Issue Biostimulants as Growth Promoting and Stress Protecting Compounds)
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Article
Celery (Apium graveolens L.) Performances as Subjected to Different Sources of Protein Hydrolysates
Plants 2020, 9(12), 1633; https://0-doi-org.brum.beds.ac.uk/10.3390/plants9121633 - 24 Nov 2020
Cited by 6 | Viewed by 801
Abstract
The vegetable production sector is currently fronting several issues mainly connected to the increasing demand of high quality food produced in accordance with sustainable horticultural technologies. The application of biostimulants, particularly protein hydrolysates (PHs), might be favorable to optimize water and mineral uptake [...] Read more.
The vegetable production sector is currently fronting several issues mainly connected to the increasing demand of high quality food produced in accordance with sustainable horticultural technologies. The application of biostimulants, particularly protein hydrolysates (PHs), might be favorable to optimize water and mineral uptake and plant utilization and to increase both production performance and quality feature of vegetable crops. The present study was carried out on celery plants grown in a tunnel to appraise the influence of two PHs, a plant-derived PH (P-PH), obtained from soy extract and an animal PH (A-PH), derived from hydrolyzed animal epithelium (waste from bovine tanneries) on yield, yield components (head height, root collar diameter, and number of stalks), mineral composition, nutritional and functional features, as well as the economic profitability of PHs applications. Fresh weight in A-PH and P-PH treated plants was 8.3% and 38.2% higher, respectively than in untreated control plants. However, no significant difference was found between A-PH treated plants and control plants in terms of fresh weight. Head height significantly increased by 5.5% and 16.3% in A-PH and P-PH treated plants, respectively compared with untreated control (p ≤ 0.05). N content was inferior in PHs treated plants than in untreated control. Conversely, K and Mg content was higher in A-PH and P-PH treated plants as compared to the untreated ones. Furthermore, A-PH and P-PH improved ascorbic acid content by 8.2% and 8.7%, respectively compared with the non-treated control (p ≤ 0.001). Our results confirmed, also, that PHs application is an eco-friendly technique to improve total phenolic content in celery plants. In support of this, our findings revealed that animal or plants PH applications increased total phenolics by 36.9% and 20.8%, respectively compared with untreated plants (p ≤ 0.001). Full article
(This article belongs to the Special Issue Biostimulants as Growth Promoting and Stress Protecting Compounds)
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Article
Comparison of Soaking Corms with Moringa Leaf Extract Alone or in Combination with Synthetic Plant Growth Regulators on the Growth, Physiology and Vase Life of Sword Lily
Plants 2020, 9(11), 1590; https://0-doi-org.brum.beds.ac.uk/10.3390/plants9111590 - 17 Nov 2020
Cited by 1 | Viewed by 680
Abstract
Gladiolus is in demand worldwide as a cut-flower or landscaping plant, because of its superior commercial and ornamental value. Application of plant-based biostimulants has gained interest in the horticulture industry as an innovative and promising approach to ensure enhanced and sustainable yields along [...] Read more.
Gladiolus is in demand worldwide as a cut-flower or landscaping plant, because of its superior commercial and ornamental value. Application of plant-based biostimulants has gained interest in the horticulture industry as an innovative and promising approach to ensure enhanced and sustainable yields along with better product quality. The influence of pre-plant corm soaks supplemented to 5% (v/v) with an aqueous extract from Moringa oleifera leaves (MLE) either alone or in combination with 50 mg/L salicylic acid (SA) or 50 mg/L gibberellic acid (GA) on the vegetative, physiological, and ornamental characteristics of potted gladiolus (Gladiolus grandiflorus) was investigated. In general, the treatment order for greatest horticultural value for all the parameters examined was: MLE + SA + GA > MLE + GA or SA individually > MLE alone > water-only control. Compared to other treatments, corms soaked in MLE + SA + GA had the earliest sprout time (3.7 days earlier than control), shortest production time (11 days earlier than control), tallest plant (159.5 cm), greatest number of leaves per plant (8.85 leaves), greatest maximum leaf area (66 cm2), highest SPAD reading (112) and photosynthetic activity (6.7 mmol m−2 s−1), longest spike length (91 cm), greatest number of florets per spike (20 florets), longest vase life (14.8 days), greatest N (1.53%), P (0.28%), and K (0.64%) concentrations, and largest corm diameter (4.68 cm) and mass (22.25 g). The highest total protein and proline concentrations were observed with the combined application of MLE + GA + SA. Our findings suggested that MLE either alone or in combination with other plant growth regulators not only increased the yield and quality of cut spikes, but also prolonged the vase life of cut gladiolus. Full article
(This article belongs to the Special Issue Biostimulants as Growth Promoting and Stress Protecting Compounds)

Review

Jump to: Research

Review
Silicon Effects on the Root System of Diverse Crop Species Using Root Phenotyping Technology
Plants 2021, 10(5), 885; https://0-doi-org.brum.beds.ac.uk/10.3390/plants10050885 - 28 Apr 2021
Viewed by 638
Abstract
Roots play an essential function in the plant life cycle, as they utilize water and essential nutrients to promote growth and plant productivity. In particular, root morphology characteristics (such as length, diameter, hairs, and lateral growth) and the architecture of the root system [...] Read more.
Roots play an essential function in the plant life cycle, as they utilize water and essential nutrients to promote growth and plant productivity. In particular, root morphology characteristics (such as length, diameter, hairs, and lateral growth) and the architecture of the root system (spatial configuration in soil, shape, and structure) are the key elements that ensure growth and a fine-tuned response to stressful conditions. Silicon (Si) is a ubiquitous element in soil, and it can affect a wide range of physiological processes occurring in the rhizosphere of various crop species. Studies have shown that Si significantly and positively enhances root morphological traits, including root length in rice, soybean, barley, sorghum, mustard, alfalfa, ginseng, and wheat. The analysis of these morphological traits using conventional methods is particularly challenging. Currently, image analysis methods based on advanced machine learning technologies allowed researchers to screen numerous samples at the same time considering multiple features, and to investigate root functions after the application of Si. These methods include root scanning, endoscopy, two-dimensional, and three-dimensional imaging, which can measure Si uptake, translocation and root morphological traits. Small variations in root morphology and architecture can reveal different positive impacts of Si on the root system of crops, with or without exposure to stressful environmental conditions. This review comprehensively illustrates the influences of Si on root morphology and root architecture in various crop species. Furthermore, it includes recommendations in regard to advanced methods and strategies to be employed to maintain sustainable plant growth rates and crop production in the currently predicted global climate change scenarios. Full article
(This article belongs to the Special Issue Biostimulants as Growth Promoting and Stress Protecting Compounds)
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Review
Culturable Yeasts as Biofertilizers and Biopesticides for a Sustainable Agriculture: A Comprehensive Review
Plants 2021, 10(5), 822; https://0-doi-org.brum.beds.ac.uk/10.3390/plants10050822 - 21 Apr 2021
Cited by 1 | Viewed by 843
Abstract
The extensive use of synthetic fertilizers and pesticides has negative consequences in terms of soil microbial biodiversity and environmental contamination. Faced with this growing concern, a proposed alternative agricultural method is the use of microorganisms as biofertilizers. Many works have been focused on [...] Read more.
The extensive use of synthetic fertilizers and pesticides has negative consequences in terms of soil microbial biodiversity and environmental contamination. Faced with this growing concern, a proposed alternative agricultural method is the use of microorganisms as biofertilizers. Many works have been focused on bacteria, but the limited literature on yeasts and their potential ability to safely promote plant growth is gaining particular attention in recent years. Thus, the objective of this review is to highlight the application of yeasts as biological agents in different sectors of sustainable agricultural practices through direct or indirect mechanisms of action. Direct mechanisms include the ability of yeasts to provide soluble nutrients to plants, produce organic acids and phytohormones (indole-3-acetic acid). Indirect mechanisms involve the ability for yeasts to act as biocontrol agents through their high antifungal activity and lower insecticidal and herbicidal activity, and as soil bioremediating agents. They also act as protective agents against extreme environmental factors by activating defense mechanisms. It is evident that all the aspects that yeasts offer could be useful in the creation of quality biofertilizers and biopesticides. Hence, extensive research on yeasts could be promising and potentially provide an environmentally friendly solution to the increased crop production that will be required with a growing population. Full article
(This article belongs to the Special Issue Biostimulants as Growth Promoting and Stress Protecting Compounds)
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Planned Papers

The below list represents only planned manuscripts. Some of these manuscripts have not been received by the Editorial Office yet. Papers submitted to MDPI journals are subject to peer-review.

Title: Silicon enhances root morphological traits in diverse crops
Authors: Yong Suk Chung
Affiliation: Jeju National University
Abstract: A silicon (Si) treatment to crops enhances various physiological responses such as root and shoot growth, nutrient absorption, resistance to abiotic and biotic stresses. Si uptakes from soil as a silicic acid form by efflux transporter genes (Lsi1) and then Si transports to shoot parts with transpiration stream. Through many Si researches, we understood how Si moved to shoot parts as well as how Si induced various physiological response however, we rarely knew Si effect on root morphology relatively. The whole root system has significance in crop productivity. Extensive root studies involve investigation of root morphology and root system architecture (RSA). Root morphology represents root diameter, cap, root hairs, appearance of pattern of secondary roots, whereas RSA describes the spatial configuration in the soil and defines the shape and structure of the root system. Even root morphology is very import for increase crops yield, only few researches were conducted due to difficulty of root investigation. Recently, image analysis has evolved in agricultural area thus, several evidences related to Si effect on root morphology have been identified. For this reason, in this review, we summarized Si effect on root morphology in diverse crops to help understanding. Furthermore, we briefly discussed various root analysis methods such as root scanning method, endoscope method, 2D and 3D imaging analysis to apply high throughput phenotyping in this review.

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