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

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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: 31 August 2023 | Viewed by 65915

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Special Issue Editors

Dr. Chrystalla Antoniou

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Guest Editor

Department of Agricultural Sciences, Biotechnology & Food Science, Cyprus University of Technology, P.O. Box 50329, Lemesos 3603, Cyprus
Interests: plant growth promotion; abiotic stresses; priming technologies; biostimulants; plant biotechnology; plant physiology; plant molecular biology.

Prof. Dr. Raffaella Maria Balestrini

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Guest Editor

Institute for Sustainable Plant Protection, CNR, Strada delle Cacce 73, 10135 Torino, Italy
Interests: plant-microbe interactions, mycorrhizal fungi, response to environmental stresses
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Dr. Vasileios Fotopoulos

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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
Special Issues, Collections and Topics in MDPI journals

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

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Plants is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2400 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

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 (29 papers)

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Research

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Open AccessArticle

Effects of Plant Biostimulation Time Span and Soil Electrical Conductivity on Greenhouse Tomato ‘Miniplum’ Yield and Quality in Diverse Crop Seasons

Alessio V. Tallarita

Lorenzo Vecchietti

Nadezhda A. Golubkina

and

Plants 2023, 12(7), 1423; https://doi.org/10.3390/plants12071423 - 23 Mar 2023

Viewed by 222

Abstract

Biostimulants help plants cope with environmental stresses and improve vegetable yield and quality. This study was conducted to determine the protein hydrolysate (PH) effect of three different durations (weekly applications: three, six, or nine times plus an untreated control) in factorial combination with four soil electrical conductivities (EC: 1.5, 3.0, 4.5, or 6.0 mS·cm⁻¹) on yield, fruit quality, and elemental composition of tomato ‘miniplum’ grown in a greenhouse. Fruit yield was best affected, during the summer, by six and nine biostimulant applications at EC 3.0 mS·cm⁻¹, and in the same season, the six treatments led to the highest fruit number with no difference compared to nine applications; during the winter, the three and six treatments improved the mentioned variables at each EC level. Fruits’ dry residue and Brix^o were positively affected by biostimulation both in summer and winter. In summer, the 6.0 mS·cm⁻¹ EC led to the highest dry residue and Brix^o values, though the latter did not show any significant difference compared to 4.5 mS·cm⁻¹; in winter, the best results corresponded to 4.5 and 6.0 mS·cm⁻¹. A higher beneficial effect of PH on fruit antioxidant status, i.e., lycopene, polyphenols, ascorbic acid levels, and lipophilic (LAA) and hydrophilic (HAA) activity, was recorded in winter compared with summer. Positive correlations between polyphenols and LAA, as well as ascorbic acid content and HAA were found for all EC and PH treatments. Most of the mineral elements tested demonstrated concentration stability, whereas the highest EC decreased P, Mg, Cu, and Se accumulation. The opposite effect was shown by PH application on Se and Mn levels, with P tending to increase. The concentrations of Fe, Zn, and Cu were the lowest under the longest duration of PH supply. These results further confirm the essential role of plant biostimulation in enhancing tomato yield and quality, with a particular focus on the treatment duration. Full article

(This article belongs to the Special Issue Biostimulants as Growth Promoting and Stress Protecting Compounds)

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Open AccessArticle

Characterizing Root Morphological Responses to Exogenous Tryptophan in Soybean (Glycine max) Seedlings Using a Scanner-Based Rhizotron System

Atsushi Sanada

and

Shinsuke Agehara

Plants 2023, 12(1), 186; https://doi.org/10.3390/plants12010186 - 01 Jan 2023

Viewed by 796

Abstract

Tryptophan is a precursor of indole-3-acetic acid (IAA), which is the major auxin involved in the regulation of lateral root formation. In this study, we used a scanner-based rhizotron system to examine root growth and morphological responses of soybean (Glycine max, ‘Golden Harvest’) seedlings to exogenous tryptophan. Seeds were sown directly in the rhizotron filled with field soil. Tryptophan was applied at 1.9 and 3.8 mg plant⁻¹ by soil drenching or foliar spray. Canopy and root projected area were monitored by analyzing canopy and rhizotron images using ImageJ software. Seedlings were sampled at the first trifoliate stage, 18 days after sowing (DAS), and root morphology was determined by analyzing washed root images using WinRHIZO software. According to contrast analysis, when all tryptophan treatments were pooled, tryptophan application increased canopy and root projected area by 13% to 14% compared with the control at 18 DAS. Tryptophan application also increased root dry matter accumulation by 26%, root:shoot ratio by 24%, and secondary root number by 13%. Tryptophan applied by soil drenching also increased root length and surface area of fine roots (<0.2 mm diameter) by 25% and 21%, respectively, whereas it slightly inhibited primary root elongation. The efficacy of tryptophan soil drenching in stimulating root formation became greater with increasing the application rate. These results suggest that exogenous tryptophan induces auxin-like activities in root development. Soil drenching of tryptophan appears to be an effective strategy in improving the establishment of soybean. Importantly, this strategy is easily implementable by commercial growers with no negative side effect. Full article

(This article belongs to the Special Issue Biostimulants as Growth Promoting and Stress Protecting Compounds)

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Open AccessArticle

Can Microbial Consortium Applications Affect Yield and Quality of Conventionally Managed Processing Tomato?

Giovanna Marta Fusco

Andrea Burato

Alfonso Pentangelo

Mariateresa Cardarelli

Rosalinda Nicastro

Petronia Carillo

and

Mario Parisi

Plants 2023, 12(1), 14; https://doi.org/10.3390/plants12010014 - 20 Dec 2022

Viewed by 892

Abstract

Three commercial microbial-based biostimulants containing fungi (arbuscular mycorrhizae and Trichoderma spp.) and other microrganisms (plant growth-promoting bacteria and yeasts) were applied on a processing tomato crop in a two-year field experiment in southern Italy. The effects of the growing season and the microorganism-based treatments on the yield, technological traits and functional quality of the tomato fruits were assessed. The year of cultivation affected yield (with a lower fruit weight, higher marketable to total yield ratio and higher percentage of total defective fruits in 2020) and technological components (higher dry matter, titratable acidity, total soluble solids content in 2020). During the first year of the trial, the consortia-based treatments enhanced the soluble solids content (+10.02%) compared to the untreated tomato plants. The sucrose and lycopene content were affected both by the microbial treatments and the growing season (greater values found in 2021 with respect to 2020). The year factor also significantly affected the metabolite content, except for tyrosine, essential (EAA) and branched-chain amino acids (BCAAs). Over the two years of the field trial, FID-consortium enhanced the content of proteins (+53.71%), alanine (+16.55%), aspartic acid (+31.13%), γ-aminobutyric acid (GABA) (+76.51%), glutamine (+55.17%), glycine (+28.13%), monoethanolamine (MEA) (+19.57%), total amino acids (TAA) (+33.55), EAA (+32.56%) and BCAAs (+45.10%) compared to the control. Our findings highlighted the valuable effect of the FID microbial inoculant in boosting several primary metabolites (proteins and amino acids) in the fruits of the processing tomato crop grown under southern Italian environmental conditions, although no effect on the yield and its components was appreciated. Full article

(This article belongs to the Special Issue Biostimulants as Growth Promoting and Stress Protecting Compounds)

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Open AccessArticle

Application of Biostimulants in Tomato Plants (Solanum lycopersicum) to Enhance Plant Growth and Salt Stress Tolerance

and

Plants 2022, 11(22), 3082; https://doi.org/10.3390/plants11223082 - 14 Nov 2022

Cited by 3 | Viewed by 1374

Abstract

Under the era of climate change, plants are forced to survive under increasingly adverse conditions. Application of biostimulants in plants is shown to mitigate the deleterious effects of abiotic stresses including salinity, enhancing plant tolerance and performance. The present study focuses on the effects of five biostimulants based on biocompost and biofertilizer compounds that have been applied to tomato plants grown in the presence (salt-stressed plants) or absence of salt stress (control plants). To study the beneficial effects of the biostimulants in tomato plants, a series of analyses were performed, including phenotypic and agronomic observations, physiological, biochemical and enzymatic activity measurements, as well as gene expression analysis (RT-qPCR) including genes involved in antioxidant defense (SlCu/ZnSOD, SlFeSOD, SlCAT1, SlcAPX), nitrogen (SlNR, SlNiR, SlGTS1) and proline metabolism (p5CS), potassium transporters (HKT1.1, HKT1.2), and stress-inducible TFs (SlWRKY8, SlWRKY31). Among all the biostimulant solutions applied to the plants, the composition of 70% biofertilizer and 30% biocompost (Bf70/Bc30) as well as 70% biocompost and 30% biofertilizer (Bc70/Bf30) formulations garnered interest, since the former showed growth promoting features while the latter displayed better defense responses at the time of harvesting compared with the other treatments and controls. Taken together, current findings provide new insight into the beneficial effects of biostimulants, encouraging future field studies to further evaluate the biostimulant effects in plants under a real environment which is compromised by a combination of abiotic and biotic stresses. Full article

(This article belongs to the Special Issue Biostimulants as Growth Promoting and Stress Protecting Compounds)

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Open AccessArticle

Screening of Durum Wheat Cultivars for Selenium Response under Contrasting Environments, Based on Grain Yield and Quality Attributes

Sourour Ayed

Imen Bouhaouel

and

Afef Othmani

Plants 2022, 11(11), 1437; https://doi.org/10.3390/plants11111437 - 28 May 2022

Cited by 1 | Viewed by 1122

Abstract

In the literature, little information is available on the effect of Selenium (Se) on durum wheat yield and grain quality performances. A field investigation was conducted to explore the effect of exogenous Se foliar supply on two types of durum wheat germplasm; i.e., 16 advanced lines and nine modern varieties. The Se effect was assessed on grain yield as well as on technological quality traits (moisture, protein and gluten contents, Zeleny sedimentation index, and deformation energy) in two contrasting environments in Tunisia, namely Kef–Boulifa (semi-arid region) and Beja (sub-humid region). The results displayed significant effects of environments, Se foliar application, and cultivars on grain yield and quality attributes. For grain yield performance, the beneficial effect of Se was more pronounced under the Kef–Boulifa environment, and conversely for the grain quality. A genetic variation was observed within and among the two environments under both Se treatments (with and without Se). Notably, the Se-treated advanced lines displayed the highest grain yield under Kef–Boulifa and Beja conditions. Although these cultivars showed better grain quality in both sites, the modern varieties valorized the Se foliar application better. Cultivars that recorded the highest values for the studies attributes were not necessarily those that valorized the Se supply better. Interestingly, some advanced lines have noted superiority compared to the modern varieties. In this study, cultivars that combine both good yield and good grain quality were determined for semi-arid (L11, L1, Dhahbi, and Maali) and sub-humid (L2, L14, L6, L3, Salim, and INRAT 100) zones. The screening results provide genetic material that could be exploited in breeding programs to improve Se use efficiency. Full article

(This article belongs to the Special Issue Biostimulants as Growth Promoting and Stress Protecting Compounds)

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Open AccessArticle

Growth Regulators Improve Outcrossing Rate of Diverse Rice Cytoplasmic Male Sterile Lines through Affecting Floral Traits

Mahmoud A. A. ElSayed

and

Plants 2022, 11(10), 1291; https://doi.org/10.3390/plants11101291 - 12 May 2022

Cited by 6 | Viewed by 1202

Abstract

Cytoplasmic male sterility (CMS) provides an irreplaceable strategy for commercial exploitation of heterosis and producing high-yielding hybrid rice. The exogenous application of plant growth regulators could improve outcrossing rates of the CMS lines by affecting floral traits and accordingly increase hybrid rice seed production. The present study aimed at exploring the impact of growth regulators such as gibberellic acid (GA₃), indole-3-acetic acid (IAA), and naphthalene acetic acid (NAA) on promoting floral traits and outcrossing rates in diverse rice CMS lines and improving hybrid rice seed production. The impact of foliar applications of growth regulators comprising GA₃ at 300 g/ha or GA₃ at 150 g/ha + IAA at 50 g/ha + NAA at 200 g/ha versus untreated control was investigated on floral, growth, and yield traits of five diverse CMS lines. The exogenously sprayed growth regulators, in particular, the combination of GA₃, IAA, and NAA (T3) boosted all studied floral, growth, and yield traits in all tested CMS lines. Moreover, the evaluated CMS lines exhibited significant differences in all measured floral traits. L2, L3, and L1 displayed the uppermost spikelet opening angle, duration of spikelet opening, total stigma length, style length, stigma brush, and stigma width. In addition, these CMS lines exhibited the highest plant growth and yield traits, particularly under T3. Consequently, exogenous application of GA₃, IAA, and NAA could be exploited to improve the floral, growth, and yield traits of promising CMS lines such as L2, L3, and L1, hence increasing outcrossing rates and hybrid rice seed production. Full article

(This article belongs to the Special Issue Biostimulants as Growth Promoting and Stress Protecting Compounds)

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Open AccessArticle

Grain-Priming with L-Arginine Improves the Growth Performance of Wheat (Triticum aestivum L.) Plants under Drought Stress

Hebat-Allah A. Hussein

and

Plants 2022, 11(9), 1219; https://doi.org/10.3390/plants11091219 - 30 Apr 2022

Cited by 13 | Viewed by 1717

Abstract

Drought is the main limiting abiotic environmental stress worldwide. Water scarcity restricts the growth, development, and productivity of crops. Wheat (Triticum aestivum L.) is a fundamentally cultivated cereal crop. This study aimed to evaluate the effect of grain-priming with arginine (0.25, 0.5, and 1 mM) on growth performance and some physiological aspects of wheat plants under normal or drought-stressed conditions. Morphological growth parameters, photosynthetic pigments, soluble sugars, free amino acids, proline, total phenols, flavonoids, and proteins profiles were determined. Drought stress lowered plant growth parameters and chlorophyll a and b contents while increasing carotenoids, soluble sugars, free amino acids, proline, total phenols, and flavonoids. Soaking wheat grains with arginine (0.25, 0.5, and 1 mM) improves plant growth and mitigates the harmful effects of drought stress. The most effective treatment to alleviate the effects of drought stress on wheat plants was (1 mM) arginine, that increased root length (48.3%), leaves number (136%), shoot fresh weight (110.5%), root fresh weight (110.8%), root dry weight (107.7%), chlorophyll a (11.4%), chlorophyll b (38.7%), and carotenoids content (41.9%) compared to the corresponding control values. Arginine enhanced the synthesis of soluble sugars, proline, free amino acids, phenols, and flavonoids in wheat plants under normal or stressed conditions. Furthermore, the protein profile varies in response to drought stress and arginine pretreatments. Ultimately, pretreatment with arginine had a powerful potential to face the impacts of drought stress on wheat plants by promoting physiological and metabolic aspects. Full article

(This article belongs to the Special Issue Biostimulants as Growth Promoting and Stress Protecting Compounds)

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Open AccessArticle

Soaking Maize Seeds in Zeatin-Type Cytokinin Biostimulators Improves Salt Tolerance by Enhancing the Antioxidant System and Photosynthetic Efficiency

and

Plants 2022, 11(8), 1004; https://doi.org/10.3390/plants11081004 - 07 Apr 2022

Cited by 8 | Viewed by 1372

Abstract

There is an urgent need for innovative strategies to raise the performance of environmentally stressed plants. The seeds of single-cross yellow Zea mays (L.) hybrid Giza-168 were soaked in Cis-(c-Z-Ck) or trans-zeatin-type cytokinin (t-Z-Ck) solutions at a concentration of 50 or 40 µM, respectively. Salinity stress was imposed at 0, 75 or 150 mM NaCl in the Hoagland nutrient solution (full strength) used for irrigation. The total carotenoids content was negatively affected by only 150 mM NaCl, while both 75 and 150 mM NaCl negatively affected the growth and yield components, relative water content, membrane stability index, photochemical activity, gas exchange, K⁺ and chlorophyll contents, K⁺/Na⁺ ratio, and photosynthetic efficiency. However, all of these traits were significantly improved by c-Z-Ck pretreatment and further enhanced by t-Z-Ck pretreatment compared with the corresponding controls. Furthermore, the contents of proline, soluble sugars, ascorbate, and glutathione, as well as enzymatic antioxidant activities, were significantly elevated by both salt stress concentrations and increased more by both biostimulators compared to the control. Compared to c-Z-Ck, t-Z-Ck was superior in mitigating the harmful effects of the high H₂O₂ levels caused by salt stress on the levels of malondialdehyde and ion leakage compared to the control. Under normal or stress conditions, t-Z-Ck pretreatment was better than c-Z-Ck pretreatment, while both positively affected maize hormonal contents. As a result, t-Z-Ck is recommended to enhance the growth and productivity of maize plants by suppressing the effects of oxidative stress caused by saline water irrigation. Full article

(This article belongs to the Special Issue Biostimulants as Growth Promoting and Stress Protecting Compounds)

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Open AccessCommunication

Effects Induced by the Agricultural Application of Probiotics on Antioxidant Potential of Strawberries

Rima Mockevičiūtė

Sigita Jurkonienė

Virgilija Gavelienė

Elžbieta Jankovska-Bortkevič

Božena Šocik

Gabija Armalytė

and

Rimas Budrys

Plants 2022, 11(6), 831; https://doi.org/10.3390/plants11060831 - 21 Mar 2022

Cited by 3 | Viewed by 1517

Abstract

With the recent rapid development of the functional food sector, agriculture is looking for alternatives to improve the quality of food grown by limiting chemical fertilizers. This study evaluated the effects of two commercial plant probiotics, ProbioHumus and NaturGel, on the growth and quality of strawberry fruits. Strawberry plants were sprayed with microbial probiotics twice a year: after harvesting at the beginning of dormancy and at the stage of leaf development. Spray applications of ProbioHumus, NaturGel, and NaturGel + ProbioHumus in the organic farm fields significantly increased the fresh fruit weight up to 42%, 35%, and 37%, respectively, compared to the non-treated control. An increase in the weight of fresh strawberry fruits may be associated with an increase in dry matter accumulation. The probiotics had a positive effect on the total content of phenols, anthocyanins, and especially ascorbic acid in strawberry fruits. The increase in ascorbic acid in strawberry fruits was up to 97% compared to the non-treated control. The fruits from plants inoculated with probiotics showed significantly higher antioxidant activity. In summary, ProbioHumus and NaturGel are effective tools for improving the quality of strawberries and can be exploited in sustainable agriculture as a tool for adding value to functional food. Full article

(This article belongs to the Special Issue Biostimulants as Growth Promoting and Stress Protecting Compounds)

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Open AccessArticle

Use of Biostimulants: Towards Sustainable Approach to Enhance Durum Wheat Performances

and

Plants 2022, 11(1), 133; https://doi.org/10.3390/plants11010133 - 04 Jan 2022

Cited by 4 | Viewed by 1377

Abstract

The use of biostimulant (BS) holds a promising and environmental-friendly innovation to address current needs of sustainable agriculture. The aim of the present study is twofold: (i) assess the potential of durum wheat seed coating with microbial BS (‘Panoramix’, Koppert), a mix of Bacillus spp., Trichoderma spp., and endomycorrhiza, compared to two chemical products (‘Spectro’ and ‘Mycoseeds’) through germination bioassay, pot and field trials under semi-arid conditions, and (ii) identify the most effective method of BS supply (‘seed coating’, ‘foliar spray’, and ‘seed coating + foliar spray’) under field conditions. For this purpose, three modern durum wheat cultivars were tested. ‘Panoramix’ was the most efficient treatment and enhanced all germination (germination rate, and coleoptile and radicle length), physiological (relative water content, chlorophyll content, and leaf area), and agro-morphological (plant height, biomass, seed number per spike, thousand kernel weight, and grain yield) attributes. Unexpectedly, the individual application of ‘Panoramix’ showed better performance than the combined treatment ‘Panoramix + Spectro’. Considering the physiological and agro-morphological traits, the combined method ‘seed coating + foliar spray’ displayed the best results. Principal component analysis confirmed the superiority of ‘Panoramix’ treatment or ‘seed coating + foliar spray’ method. Among tested durum wheat cultivars, ‘Salim’ performed better especially under ‘Panoramix’ treatment, but in some case ‘Karim’ valorized better this BS showing the highest increase rates. Based on these study outcomes, ‘Panoramix’ might be used as promising sustainable approach to stimulate durum wheat performance. Full article

(This article belongs to the Special Issue Biostimulants as Growth Promoting and Stress Protecting Compounds)

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Open AccessArticle

Application of Cyanobacteria (Roholtiella sp.) Liquid Extract for the Alleviation of Salt Stress in Bell Pepper (Capsicum annuum L.) Plants Grown in a Soilless System

Adewale Suraj Bello

Radhouane Ben-Hamadou

Helmi Hamdi

Imen Saadaoui

and

Talaat Ahmed

Plants 2022, 11(1), 104; https://doi.org/10.3390/plants11010104 - 30 Dec 2021

Cited by 5 | Viewed by 1572

Abstract

Salinity is one of the abiotic stresses that affect crop growth and productivity in arid and semi-arid regions. Unfortunately, there are few known methods to mitigate the deleterious impacts of salt stress on the development and yield of vegetable crops. Blue-green algae (cyanobacteria) are endowed with the potential to curb the negative impacts of salt stress as they are characterized by biostimulant properties. The present work aimed to investigate the effects of Roholtiella sp. as a foliar extract on the growth characteristics, physiological and biochemical responses of bell pepper (Capsicum annuum L.) plants under varying levels of salinity conditions. A soilless water experiment was carried out in a greenhouse where bell pepper seedlings were grown under five salt concentrations (0, 50, 200, 150, and 200 mM of NaCl). Growth characteristics, pigments content, relative water content, and antioxidant activity (CAT) were determined. Our results showed that growth parameters, relative water content (RWC), chlorophyll a & b concentrations under salinity conditions were negatively affected at the highest concentration (200 mM). Interestingly, the application of Roholtiella sp. foliar extract enhanced the plant growth characteristics as shoot length increased by 17.014%, fresh weight by 39.15%, dry and weight by 31.02%, at various salt treatments. Moreover, chlorophyll a and b increased significantly compared with seedlings sprayed with water. Similarly, RWC exhibited a significant increase (92.05%) compared with plants sprayed with water. In addition, antioxidants activities and accumulation of proline were improved in Roholtella sp. extract foliar sprayed seedlings compared to the plants foliar sprayed with water. Conclusively, at the expiration of our study, the Rohotiella sp. extract-treated plants were found to be more efficient in mitigating the deleterious effects caused by the salinity conditions which is an indication of an enhancement potential of tolerating salt-stressed plants when compared to the control group. Full article

(This article belongs to the Special Issue Biostimulants as Growth Promoting and Stress Protecting Compounds)

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Open AccessArticle

Natural Biostimulant Attenuates Salinity Stress Effects in Chili Pepper by Remodeling Antioxidant, Ion, and Phytohormone Balances, and Augments Gene Expression

Alaa I. B. Abou-Sreea

Atef A. S. Abdel-Kader

Ali Majrashi

and

Khaled A. M. Khaled

Plants 2021, 10(11), 2316; https://doi.org/10.3390/plants10112316 - 27 Oct 2021

Cited by 10 | Viewed by 1941

Abstract

A biostimulant is any microorganism or substance used to enhance the efficiency of nutrition, tolerance to abiotic stress and/or quality traits of crops, depending on its contents from nutrients. Plant biostimulants like honey bee (HB) and silymarin (Sm) are a strategic trend for managing stressed crops by promoting nutritional and hormonal balance, regulating osmotic protectors, antioxidants, and genetic potential, reflecting plant growth and productivity. We applied diluted honey bee (HB) and silymarin-enriched honey bee (HB- Sm) as foliar nourishment to investigate their improving influences on growth, yield, nutritional and hormonal balance, various osmoprotectant levels, different components of antioxidant system, and genetic potential of chili pepper plants grown under NaCl-salinity stress (10 dS m^‒1). HB significantly promoted the examined attributes and HB-Sm conferred optimal values, including growth, productivity, K⁺/Na⁺ ratio, capsaicin, and Sm contents. The antioxidative defense components were significantly better than those obtained with HB alone. Conversely, levels of oxidative stress markers (superoxide ions and hydrogen peroxide) and parameters related to membrane damage (malondialdehyde level, stability index, ionic leakage, Na⁺, and Cl⁻ contents) were significantly reduced. HB-Sm significantly affects inactive gene expression, as a natural biostimulator silencing active gene expression. SCoT primers were used as proof in salt-treated or untreated chili pepper plants. There were 41 cDNA amplicons selected by SCoT-primers. Twenty of them were EcDNA amplicons (cDNA-amplicons that enhanced their genes by one or more treatments) representing 49% of all cDNA amplicons, whereas 7 amplicons for ScDNA (whose genes were silenced in one or more treatments) represented 17%, and 14 McDNA (monomorphic cDNA-amplicons with control) amplicons were represented by 34% from all cDNA amplicons. This indicates the high effect of BH-Sm treatments in expression enhancement of some inactive genes and their silenced effect for expression of some active genes, also confirming that cDNA-SCoT markers succeeded in detection of variable gene expression patterns between the untreated and treated plants. In conclusion, HB-Sm as a natural multi-biostimulator can attenuate salt stress effects in chili pepper plants by remodeling the antioxidant defense system and ameliorating plant productivity. Full article

(This article belongs to the Special Issue Biostimulants as Growth Promoting and Stress Protecting Compounds)

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Open AccessArticle

Deep-Sea Actinobacteria Mitigate Salinity Stress in Tomato Seedlings and Their Biosafety Testing

Pharada Rangseekaew

Adoración Barros-Rodríguez

Wasu Pathom-aree

and

Maximino Manzanera

Plants 2021, 10(8), 1687; https://doi.org/10.3390/plants10081687 - 17 Aug 2021

Cited by 13 | Viewed by 2415

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 MT2.1^T and D. profundi MT2.2^T) to promote tomato seedlings under 150 mM NaCl compared with the terrestrial strain D. nishinomiyaensis DSM20448^T. 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 MT2.1^T 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 MT2.1^T showed no harmful effects on Caenorhabditis elegans, Daphnia magna, Eisenia foetida, and Escherichia coli MC4100 in biosafety tests. This evidence suggests that D. barathri MT2.1^T 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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Open AccessArticle

Identification of Plant Growth Promoting Rhizobacteria That Improve the Performance of Greenhouse-Grown Petunias under Low Fertility Conditions

Kaylee A. South

Nathan P. Nordstedt

and

Michelle L. Jones

Plants 2021, 10(7), 1410; https://doi.org/10.3390/plants10071410 - 09 Jul 2021

Cited by 7 | Viewed by 2134

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 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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Open AccessArticle

Interactive Impacts of Beneficial Microbes and Si-Zn Nanocomposite on Growth and Productivity of Soybean Subjected to Water Deficit under Salt-Affected Soil Conditions

Ahmed M. Abd El-Monem

Usama A. Abd El-Razek

and

Emad M. Hafez

Plants 2021, 10(7), 1396; https://doi.org/10.3390/plants10071396 - 08 Jul 2021

Cited by 19 | Viewed by 1973

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 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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Open AccessCommunication

Biopriming with Seaweed Extract and Microbial-Based Commercial Biostimulants Influences Seed Germination of Five Abelmoschus esculentus Genotypes

Christian P. Du Plooy

and

Stephen O. Amoo

Plants 2021, 10(7), 1327; https://doi.org/10.3390/plants10071327 - 29 Jun 2021

Cited by 9 | Viewed by 2357

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^® 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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Open AccessEditor’s ChoiceArticle

Impact of Ecklonia maxima Seaweed Extract and Mo Foliar Treatments on Biofortification, Spinach Yield, Quality and NUE

Salvatore La Bella

Beppe Benedetto Consentino

and

Plants 2021, 10(6), 1139; https://doi.org/10.3390/plants10061139 - 03 Jun 2021

Cited by 17 | Viewed by 2423

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 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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Open AccessArticle

Ulva lactuca Extract and Fractions as Seed Priming Agents Mitigate Salinity Stress in Tomato Seedlings

Mohammed El Mehdi El Boukhari

and

Plants 2021, 10(6), 1104; https://doi.org/10.3390/plants10061104 - 30 May 2021

Cited by 8 | Viewed by 3050

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 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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Open AccessArticle

Strain-Specific Biostimulant Effects of Chlorella and Chlamydomonas Green Microalgae on Medicago truncatula

Margaret Mukami Gitau

and

Plants 2021, 10(6), 1060; https://doi.org/10.3390/plants10061060 - 25 May 2021

Cited by 9 | Viewed by 3117

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 (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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Open AccessArticle

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

Emad M. Hafez

Hany S. Osman

Usama A. Abd El-Razek

and

Plants 2021, 10(5), 894; https://doi.org/10.3390/plants10050894 - 28 Apr 2021

Cited by 16 | Viewed by 2884

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 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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Open AccessArticle

Plant-Based Biostimulant as Sustainable Alternative to Synthetic Growth Regulators in Two Sweet Cherry Cultivars

Boris Basile

Natalie Brown

José Miguel Valdes

Mariateresa Cardarelli

Pasquale Scognamiglio

and

Plants 2021, 10(4), 619; https://doi.org/10.3390/plants10040619 - 24 Mar 2021

Cited by 9 | Viewed by 2203

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. 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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Open AccessEditor’s ChoiceArticle

Foliar Application of Different Vegetal-Derived Protein Hydrolysates Distinctively Modulates Tomato Root Development and Metabolism

Angela Valentina Ceccarelli

Mariateresa Cardarelli

Youssef Rouphael

Giuseppe Colla

and

Luigi Lucini

Plants 2021, 10(2), 326; https://doi.org/10.3390/plants10020326 - 08 Feb 2021

Cited by 24 | Viewed by 3011

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 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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Open AccessArticle

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

Arafat Abdel Hamed Abdel Latef

and

Plants 2021, 10(1), 110; https://doi.org/10.3390/plants10010110 - 07 Jan 2021

Cited by 31 | Viewed by 3306

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 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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Open AccessEditor’s ChoiceArticle

Celery (Apium graveolens L.) Performances as Subjected to Different Sources of Protein Hydrolysates

Beppe Benedetto Consentino

Giuseppe Virga

Gaetano Giuseppe La Placa

and

Plants 2020, 9(12), 1633; https://doi.org/10.3390/plants9121633 - 24 Nov 2020

Cited by 22 | Viewed by 2598

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 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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Open AccessArticle

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

and

Plants 2020, 9(11), 1590; https://doi.org/10.3390/plants9111590 - 17 Nov 2020

Cited by 12 | Viewed by 1880

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 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

Open AccessReview

Assessing the Usefulness of Moringa oleifera Leaf Extract as a Biostimulant to Supplement Synthetic Fertilizers: A Review

Chuene Victor Mashamaite

and

Plants 2022, 11(17), 2214; https://doi.org/10.3390/plants11172214 - 26 Aug 2022

Cited by 6 | Viewed by 2517

Abstract

The extensive use of synthetic chemical fertilizers is associated with environmental pollution and soil degradation. In addition, the high costs of these fertilizers necessitate the search for alternative, eco-friendly and safe natural sources of phytonutrients. The liquid extracted from moringa (Moringa oleifera Lam.) leaves has been used in agriculture to improve the growth and productivity of several crops. The efficacy of moringa leaf extract (MLE) is attributed to its high content of mineral nutrients, protein, vitamins, sugars, fiber, phenolics and free proline. In addition, MLE contains significant amounts of phytohormones, such as auxins, cytokinins and gibberellins. Furthermore, MLE is a valuable product promoting seed germination, plant growth and deeper root development, delaying fruit senescence and increasing the yield and quality of crops grown under normal or stressful conditions. Here, we review the research on MLE as a biostimulant to enhance crop growth and productivity. Moreover, we emphasize its possible introduction to smallholder farming systems to provide phytonutrients, and we further highlight research gaps in the existing knowledge regarding MLE application. Generally, MLE is an inexpensive, sustainable, eco-friendly and natural biostimulant that can be used to improve the growth and productivity attributes of various crops under non-stressful and stressful conditions. Full article

(This article belongs to the Special Issue Biostimulants as Growth Promoting and Stress Protecting Compounds)

Open AccessReview

The Role of Moringa Leaf Extract as a Plant Biostimulant in Improving the Quality of Agricultural Products

Nita Yuniati

Kusumiyati Kusumiyati

Syariful Mubarok

and

Bambang Nurhadi

Plants 2022, 11(17), 2186; https://doi.org/10.3390/plants11172186 - 23 Aug 2022

Cited by 2 | Viewed by 1456

Abstract

Ensuring high-quality agricultural products has become important in agriculture since society’s standard of living has risen. Meanwhile, Moringa oleifera L. leaf extract (MLE) has been used as a plant biostimulant to improve product quality. The effectiveness of MLE is associated with its beneficial components, consisting of nutrients, phytohormones, secondary metabolites, amino acids, and bioactive compounds. Previous studies have been carried out to find the effects of MLE application on the quality of different crops, including basil, kale, spinach, maize, radish, brinjal, pepper, tomato, grape, strawberry, and more. The results are generally positive concerning physical, nutritional, and chemical qualities. This review comprises recent findings regarding MLE application as a plant biostimulant to increase quality attributes, with its underlying mechanism. Full article

(This article belongs to the Special Issue Biostimulants as Growth Promoting and Stress Protecting Compounds)

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Open AccessReview

Silicon Effects on the Root System of Diverse Crop Species Using Root Phenotyping Technology

and

Plants 2021, 10(5), 885; https://doi.org/10.3390/plants10050885 - 28 Apr 2021

Cited by 7 | Viewed by 2725

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 (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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Open AccessEditor’s ChoiceReview

Culturable Yeasts as Biofertilizers and Biopesticides for a Sustainable Agriculture: A Comprehensive Review

María Hernández-Fernández

Gustavo Cordero-Bueso

Marina Ruiz-Muñoz

and

Jesús M. Cantoral

Plants 2021, 10(5), 822; https://doi.org/10.3390/plants10050822 - 21 Apr 2021

Cited by 19 | Viewed by 7966

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 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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