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6 pages, 516 KiB

Open AccessEditorial

Plant-Growth-Promoting Bacteria

by Carmen Bianco

Plants 2024, 13(10), 1323; https://doi.org/10.3390/plants13101323 - 11 May 2024

Cited by 1 | Viewed by 1143

Abstract

Global food-production levels may soon be insufficient for feeding the population, and changing climatic conditions could further limit agri-food production [...] Full article

(This article belongs to the Special Issue Plant Growth Promoting Bacteria)

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Research

Jump to: Editorial, Review

16 pages, 6205 KiB

Open AccessArticle

Effect of Co-Application of Azospirillum brasilense and Rhizobium pisi on Wheat Performance and Soil Nutrient Status under Deficit and Partial Root Drying Stress

by Bushra Ahmed Alhammad, Muhammad Saqlain Zaheer, Hafiz Haider Ali, Akhtar Hameed, Kholoud Z. Ghanem and Mahmoud F. Seleiman

Plants 2023, 12(17), 3141; https://doi.org/10.3390/plants12173141 - 31 Aug 2023

Cited by 4 | Viewed by 1353

Abstract

Water management techniques are improving at the farm level, but they are not enough to deal with the limited availability of water and increased crop yields. Soil microbes play a vital role in nitrogen fixation, improving soil fertility and enhancing plant growth hormones [...] Read more.

Water management techniques are improving at the farm level, but they are not enough to deal with the limited availability of water and increased crop yields. Soil microbes play a vital role in nitrogen fixation, improving soil fertility and enhancing plant growth hormones under drought conditions. Therefore, this study was conducted to investigate the impact of water management combined with Azospirillum brasilense and Rhizobium pisi on wheat crop productivity and soil properties in dry regions. Three water management techniques were compared, normal irrigation as a control (C), deficit irrigation (DI), and partial root drying irrigation (PRD), together with the interaction of plant-growth-promoting rhizobacteria (PGPR). Experiments were conducted with six treatments in total: T₁ = C + No PGPR, T₂ = C + PGPR, T₃ = DI + No PGPR, T₄ = DI + PGPR, T₅ = PRD + No PGPR, and T₆ = PRD + PGPR. The highest grain yield was achieved in the control irrigation treatment using seeds inoculated with rhizobacteria, followed by control treatment without any inoculation, and the lowest was recorded with deficit irrigation without rhizobacteria inoculated in the seeds. However, PRD irrigation resulted in significantly higher plant growth and grain yield than the DI treatment. PGPR inoculation combined with PRD resulted in a 22% and 20% higher number of grains per spike, a 19% and 21% higher grain yield, and a 25% and 22% higher crop growth rate compared to rhizobacteria inoculation combined with the DI system in 2021-22 and 2022-23, respectively. This increase was due to the higher production of growth hormones and higher leaf area index under water-limited conditions. A greater leaf area index leads to a higher chlorophyll content and higher food production for plant growth. Full article

(This article belongs to the Special Issue Plant Growth Promoting Bacteria)

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10 pages, 2587 KiB

Open AccessArticle

Plant Growth-Promoting Rhizobacteria Improve Rice Response to Climate Change Conditions

by Susana Redondo-Gómez, Jennifer Mesa-Marín, Jesús A. Pérez-Romero, Vicente Mariscal, Fernando P. Molina-Heredia, Consolación Álvarez, Eloísa Pajuelo, Ignacio D. Rodríguez-Llorente and Enrique Mateos-Naranjo

Plants 2023, 12(13), 2532; https://doi.org/10.3390/plants12132532 - 3 Jul 2023

Cited by 3 | Viewed by 2161

Abstract

Rice is one of the most important crops in the world and is considered a strategic crop for food security. Furthermore, the excessive use of chemical fertilizers to obtain high yields causes environmental problems. A sustainable alternative includes taking advantage of beneficial bacteria [...] Read more.

Rice is one of the most important crops in the world and is considered a strategic crop for food security. Furthermore, the excessive use of chemical fertilizers to obtain high yields causes environmental problems. A sustainable alternative includes taking advantage of beneficial bacteria that promote plant growth. Here, we investigate the effect of five bacterial biofertilizers from halophytes on growth, and we investigate photosynthetic efficiency in rice plants grown under saline conditions (0 and 85 mmol L⁻¹ NaCl) and future climate change scenarios, including increased CO₂ concentrations and temperature (400/700 ppm and 25/+4 °C, respectively). Biofertilizers 1–4 increased growth by 9–64% in plants grown with and without salt in both CO₂- temperature combinations, although there was no significant positive effect on the net photosynthetic rate of rice plants. In general, biofertilizer 1 was the most effective at 400 ppm CO₂ and at 700 ppm CO₂ +4 °C in the absence of salt. Inocula 1–5 also stimulated plant length at high CO₂ levels without salt. Finally, the positive effect of biofertilization was attenuated in the plants grown under the interaction between salt and high CO₂. This highlights the significance of studying biofertilization under stress interaction to establish the real potential of biofertilizers in the context of climate change conditions. Full article

(This article belongs to the Special Issue Plant Growth Promoting Bacteria)

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21 pages, 3829 KiB

Open AccessArticle

Antifungal Activity and Effect of Plant-Associated Bacteria on Phenolic Synthesis of Quercus robur L.

by Svitlana Bilous, Artur Likhanov, Vira Boroday, Yurii Marchuk, Liubov Zelena, Oleksandr Subin and Andrii Bilous

Plants 2023, 12(6), 1352; https://doi.org/10.3390/plants12061352 - 17 Mar 2023

Cited by 5 | Viewed by 3055

Abstract

Europe’s forests, particularly in Ukraine, are highly vulnerable to climate change. The maintenance and improvement of forest health are high-priority issues, and various stakeholders have shown an interest in understanding and utilizing ecological interactions between trees and their associated microorganisms. Endophyte microbes can [...] Read more.

Europe’s forests, particularly in Ukraine, are highly vulnerable to climate change. The maintenance and improvement of forest health are high-priority issues, and various stakeholders have shown an interest in understanding and utilizing ecological interactions between trees and their associated microorganisms. Endophyte microbes can influence the health of trees either by directly interacting with the damaging agents or modulating host responses to infection. In the framework of this work, ten morphotypes of endophytic bacteria from the tissues of unripe acorns of Quercus robur L. were isolated. Based on the results of the sequenced 16S rRNA genes, four species of endophytic bacteria were identified: Bacillus amyloliquefaciens, Bacillus subtilis, Delftia acidovorans, and Lelliottia amnigena. Determining the activity of pectolytic enzymes showed that the isolates B. subtilis and B. amyloliquefaciens could not cause maceration of plant tissues. Screening for these isolates revealed their fungistatic effect against phytopathogenic micromycetes, namely Fusarium tricinctum, Botrytis cinerea, and Sclerotinia sclerotiorum. Inoculation of B. subtilis, B. amyloliquefaciens, and their complex in oak leaves, in contrast to phytopathogenic bacteria, contributed to the complete restoration of the epidermis at the sites of damage. The phytopathogenic bacteria Pectobacterium and Pseudomonas caused a 2.0 and 2.2 times increase in polyphenol concentration in the plants, respectively, while the ratio of antioxidant activity to total phenolic content decreased. Inoculation of Bacillus amyloliquefaciens and Bacillus subtilis isolates into oak leaf tissue were accompanied by a decrease in the total pool of phenolic compounds. The ratio of antioxidant activity to total phenolic content increased. This indicates a qualitative improvement in the overall balance of the oak leaf antioxidant system induced by potential PGPB. Thus, endophytic bacteria of the genus Bacillus isolated from the internal tissues of unripe oak acorns have the ability of growth biocontrol and spread of phytopathogens, indicating their promise for use as biopesticides. Full article

(This article belongs to the Special Issue Plant Growth Promoting Bacteria)

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15 pages, 1840 KiB

Open AccessEditor’s ChoiceArticle

Community Profiling of Seed Endophytes from the Pb-Zn Hyperaccumulator Noccaea caerulescens and Their Plant Growth Promotion Potential

by Tori Langill, Lambert-Paul Jorissen, Ewa Oleńska, Małgorzata Wójcik, Jaco Vangronsveld and Sofie Thijs

Plants 2023, 12(3), 643; https://doi.org/10.3390/plants12030643 - 1 Feb 2023

Cited by 9 | Viewed by 2512

Abstract

Endophytes within plants are known to be crucial for plant fitness, and while their presence and functions in many compartments have been studied in depth, the research on seed endophytes is still limited. This work aimed to characterize the seed endophytic and rhizospheric [...] Read more.

Endophytes within plants are known to be crucial for plant fitness, and while their presence and functions in many compartments have been studied in depth, the research on seed endophytes is still limited. This work aimed to characterize the seed endophytic and rhizospheric bacterial community of two Noccaea caerulescens Pb-Zn hyperaccumulator populations, growing on two heavy-metal-polluted sites in Belgium. Cultured representatives were evaluated for their potential to enhance seed germination and root length of the model species Arabidopsis thaliana. The results indicated that the community structure within the seed is conserved between the two locations, comprising mainly of Proteobacteria (seeds), and Actinobacteria in the bulk soil. Root length of A. thaliana was significantly increased when inoculated with Sphingomonas vulcanisoli. The results of this paper offer insights into the importance of the selection of the core seed endophytic microbiome and highlight the precarious symbiotic relationship they have with the plant and seed. Full article

(This article belongs to the Special Issue Plant Growth Promoting Bacteria)

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13 pages, 3059 KiB

Open AccessArticle

Effects of Organophosphate-Degrading Bacteria on the Plant Biomass, Active Medicinal Components, and Soil Phosphorus Levels of Paris polyphylla var. yunnanensis

by Zhuo-Wei Li, Yue-Heng Wang, Chang Liu, Ying-Mei Wu, Guo-Xin Lan, Yan-Bin Xue, Qiang-Sheng Wu and Nong Zhou

Plants 2023, 12(3), 631; https://doi.org/10.3390/plants12030631 - 31 Jan 2023

Cited by 2 | Viewed by 1758

Abstract

Paris polyphylla var. yunnanensis, a medicinal plant that originated in Yunnan (China), has been over-harvested in the wild population, resulting in its artificial cultivation. Given the negative environmental impacts of the excessive use of phosphorus (P) fertilization, the application of organophosphate-degrading bacteria [...] Read more.

Paris polyphylla var. yunnanensis, a medicinal plant that originated in Yunnan (China), has been over-harvested in the wild population, resulting in its artificial cultivation. Given the negative environmental impacts of the excessive use of phosphorus (P) fertilization, the application of organophosphate-degrading bacteria (OPDB) is a sustainable approach for improving the P use efficiency in Paris polyphylla var. yunnanensis production. The present work aimed to analyze the effects of three organic phosphate-solubilizing bacteria of Bacillus on the yield and quality of P. polyphylla var. yunnanensis and the P concentrations in the soil. All the inoculation treatments distinctly increased the rhizome biomass, steroidal, and total saponin concentrations of the rhizomes and the Olsen-P and organic P in the soil. The highest growth rate of rhizomes biomass, steroidal saponins, available phosphorus, and total phosphorus content was seen in the S7 group, which was inoculated with all three OPDB strains, showing increases of 134.58%, 132.56%, 51.64%, and 17.19%, respectively. The highest total saponin content was found in the group inoculated with B. mycoides and B. wiedmannii, which increased by 33.68%. Moreover, the highest organic P content was seen in the group inoculated with B. wiedmannii and B. proteolyticus, which increased by 96.20%. In addition, the rhizome biomass was significantly positively correlated with the saponin concentration, together with the positive correlation between the Olsen-P and organic P and total P. It is concluded that inoculation with organophosphate-degrading bacteria improved the biomass and medicinal ingredients of the rhizome in P. polyphylla var. yunnanensis, coupled with increased soil P fertility, with a mixture of the three bacteria performing best. Full article

(This article belongs to the Special Issue Plant Growth Promoting Bacteria)

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19 pages, 2806 KiB

Open AccessArticle

Exploring the Plant Growth-Promotion of Four Streptomyces Strains from Rhizosphere Soil to Enhance Cucumber Growth and Yield

by Ayman F. Omar, Adil H. A. Abdelmageed, Ahmad Al-Turki, Noha M. Abdelhameid, R. Z. Sayyed and Medhat Rehan

Plants 2022, 11(23), 3316; https://doi.org/10.3390/plants11233316 - 1 Dec 2022

Cited by 24 | Viewed by 3329

Abstract

The genus Streptomyces is the most abundant and essential microbes in the soil microbial community. Streptomyces are familiar and have great potential to produce a large variety of bioactive compounds. This genus considers an efficient biofertilizer based on its plant growth-promoting activities. Based [...] Read more.

The genus Streptomyces is the most abundant and essential microbes in the soil microbial community. Streptomyces are familiar and have great potential to produce a large variety of bioactive compounds. This genus considers an efficient biofertilizer based on its plant growth-promoting activities. Based on their ability to produce a wide varieties of bioactive molecules, the present study aimed to explore the potential plant growth promotion of four Streptomyces strains and their role in enhancing cucumber growth and yield under greenhouse conditions. Streptomyces sp. strain HM2, Streptomyces thinghirensis strain HM3, Streptomyces sp. strain HM8, and Streptomyces tricolor strain HM10 were chosen for the current study. Plant growth-promoting (PGP) features, i.e., indole acetic acid (IAA) production, siderophore excretion, and solubilizing phosphate, were evaluated in vitro. All four strains produced IAA, siderophore, and immobilized inorganic phosphate. Following 4 days of incubation at 30 °C, strains HM2, HM3, HM8, and HM10 produced copious amounts of IAA (18, 22, 62, and 146 µg/mL, respectively) and siderophores (42.59, 40.01, 16.84, 64.14% SU, respectively). At the same time, P solubilization efficacy scored 64.3%, 84.4%, 57.2%, and 81.6% with the same frequency. During in planta evaluation, selected Streptomyces strains combined with rock phosphate were assessed as biofertilizers on the growth and yield of cucumber plants. Under all treatments, positive and significant differences in studied traits were manifested except dry stem matter (SDM), net assimilation rate (NAR), relative growth rate (RGR), and fruit firmness (FF). Treatment T4 (rock phosphate + strain HM3) followed by T5 (rock phosphate + strain HM8) revealed the best results for plant height (PH), number of leaves per plant (NLPP), root length (RL), number of fruits per plant (NFPP), fruit length (FL), fruit diameter (FD), fruit fresh weight per plant (FFWPP), soil P (SP) after 21 DAT, and soil P at the end of the experiment. Notably, T6 (rock phosphate + strain HM10) caused a considerable increase in leaf area (LA). Plant growth-promoting bacteria enhance plant growth and yield through phosphorus solubilizing, improve nutrient availability, produce phytohormones, and support plant growth under abiotic stress. These features are important for sustainable agriculture and reducing environmental pollution with chemical fertilizers and pesticides. Full article

(This article belongs to the Special Issue Plant Growth Promoting Bacteria)

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16 pages, 1819 KiB

Open AccessArticle

Discerning Transcriptomic and Biochemical Responses of Arabidopsis thaliana Treated with the Biofertilizer Strain Priestia megaterium YC4-R4: Boosting Plant Central and Secondary Metabolism

by Ana Sofia Rodrigues-dos Santos, Inês Rebelo-Romão, Huiming Zhang and Juan Ignacio Vílchez

Plants 2022, 11(22), 3039; https://doi.org/10.3390/plants11223039 - 10 Nov 2022

Cited by 4 | Viewed by 2158

Abstract

As a response to the current challenges in agriculture, the application of alternatives to a more sustainable management is required. Thus, biofertilizers begin to emerge as a reliable alternative to improve crop development and resistance to stresses. Among other effects on the plant, [...] Read more.

As a response to the current challenges in agriculture, the application of alternatives to a more sustainable management is required. Thus, biofertilizers begin to emerge as a reliable alternative to improve crop development and resistance to stresses. Among other effects on the plant, the use of beneficial strains may cause changes in their metabolic regulation, as in cell wall biogenesis and in nutrient/ion transportation, improving their growth process. Previous works showed that inoculation with the strain Priestia megaterium YC4-R4 effectively promoted vegetative growth of Arabidopsis thaliana Col-0 plants. Hence, the present work recorded a strain-mediated induction of several pathways of the central and secondary metabolism of the plant, as the induction of lipid, cellulose, phenol, and flavonoid biosynthesis, by using transcriptomic and biochemical analyses. Full article

(This article belongs to the Special Issue Plant Growth Promoting Bacteria)

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19 pages, 1633 KiB

Open AccessEditor’s ChoiceArticle

Bioprospecting Soil Bacteria from Arid Zones to Increase Plant Tolerance to Drought: Growth and Biochemical Status of Maize Inoculated with Plant Growth-Promoting Bacteria Isolated from Sal Island, Cape Verde

by Catarina Cruz, Paulo Cardoso, Jacinta Santos, Diana Matos and Etelvina Figueira

Plants 2022, 11(21), 2912; https://doi.org/10.3390/plants11212912 - 29 Oct 2022

Cited by 9 | Viewed by 2702

Abstract

Climate change and anthropogenic activities are responsible for extensive crop yield losses, with negative impact on global agricultural production. The occurrence of extreme weather events such as drought is a big challenge for agriculture, negatively impacting crops. Thus, methodologies reducing crop dependence on [...] Read more.

Climate change and anthropogenic activities are responsible for extensive crop yield losses, with negative impact on global agricultural production. The occurrence of extreme weather events such as drought is a big challenge for agriculture, negatively impacting crops. Thus, methodologies reducing crop dependence on water will be a great advantage. Plant roots are colonized by soil bacteria, that can establish beneficial associations with plants, increasing crop productivity and plant tolerance to abiotic stresses. The aim of this study was to promote plant growth and to increase crop tolerance to drought by inoculation with osmotolerant bacterial strains. For that, bacteria were isolated from plants growing in Sal Island (Cape Verde) and identified. The osmotolerance and plant-growth promotion (PGP) abilities of the strains were determined. A maize seed cultivar tolerant to drought was inoculated with the strains evidencing best PGP capacity and osmo-tolerance. Results evidenced the ability of some bacterial strains increasing the development and inducing osmotolerance in plants. These results evidence the potential of osmotolerant bacteria to further increase the level of tolerance of maize varieties tolerant to drought, decreasing the dependence of this crop on irrigation, and open new perspectives to growth maize in drought affected areas and to use water more efficiently. Full article

(This article belongs to the Special Issue Plant Growth Promoting Bacteria)

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20 pages, 2628 KiB

Open AccessArticle

Isolation and Characterization of Pseudomonas chlororaphis Strain ST9; Rhizomicrobiota and in Planta Studies

by Iris Bertani, Elisa Zampieri, Cristina Bez, Andrea Volante, Vittorio Venturi and Stefano Monaco

Plants 2021, 10(7), 1466; https://doi.org/10.3390/plants10071466 - 17 Jul 2021

Cited by 9 | Viewed by 3953

Abstract

The development of biotechnologies based on beneficial microorganisms for improving soil fertility and crop yields could help to address many current agriculture challenges, such as food security, climate change, pest control, soil depletion while decreasing the use of chemical fertilizers and pesticides. Plant [...] Read more.

The development of biotechnologies based on beneficial microorganisms for improving soil fertility and crop yields could help to address many current agriculture challenges, such as food security, climate change, pest control, soil depletion while decreasing the use of chemical fertilizers and pesticides. Plant growth-promoting (PGP) microbes can be used as probiotics in order to increase plant tolerance/resistance to abiotic/biotic stresses and in this context strains belonging to the Pseudomonas chlororaphis group have shown to have potential as PGP candidates. In this study a new P. chlororaphis isolate is reported and tested for (i) in vitro PGP features, (ii) whole-genome sequence analysis, and (iii) its effects on the rhizosphere microbiota composition, plant growth, and different plant genes expression levels in greenhouse experiments. Results showed that P. chlororaphis ST9 is an efficient rice root colonizer which integrates into the plant resident-microbiota and affects the expression of several plant genes. The potential use of this P. chlororaphis strain as a plant probiotic is discussed. Full article

(This article belongs to the Special Issue Plant Growth Promoting Bacteria)

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22 pages, 5853 KiB

Open AccessArticle

The Foliar Application of Rice Phyllosphere Bacteria induces Drought-Stress Tolerance in Oryza sativa (L.)

by Arun Kumar Devarajan, Gomathy Muthukrishanan, Jaak Truu, Marika Truu, Ivika Ostonen, Subramanian Kizhaeral S., Periyasamy Panneerselvam and Sabarinathan Kuttalingam Gopalasubramanian

Plants 2021, 10(2), 387; https://doi.org/10.3390/plants10020387 - 18 Feb 2021

Cited by 38 | Viewed by 6255

Abstract

This study assessed the potential of Bacillus endophyticus PB3, Bacillus altitudinis PB46, and Bacillus megaterium PB50 to induce drought tolerance in a susceptible rice cultivar. The leaves of the potted rice plants subjected to physical drought stress for 10 days during the flowering [...] Read more.

This study assessed the potential of Bacillus endophyticus PB3, Bacillus altitudinis PB46, and Bacillus megaterium PB50 to induce drought tolerance in a susceptible rice cultivar. The leaves of the potted rice plants subjected to physical drought stress for 10 days during the flowering stage were inoculated with single-strain suspensions. Control pots of irrigated and drought-stressed plants were included in the experiment for comparison. In all treatments, the plant stress-related physiochemical and biochemical changes were examined and the expression of six stress-responsive genes in rice leaves was evaluated. The colonization potential on the surface of the rice leaves and stomata of the most successful strain in terms of induced tolerance was confirmed in the gnotobiotic experiment. The plants sprayed with B. megaterium PB50 showed an elevated stress tolerance based on their higher relative water content and increased contents of total sugars, proteins, proline, phenolics, potassium, calcium, abscisic acid, and indole acetic acid, as well as a high expression of stress-related genes (LEA, RAB16B, HSP70, SNAC1, and bZIP23). Moreover, this strain improved yield parameters compared to other treatments and also confirmed its leaf surface colonization. Overall, this study indicates that the foliar application of B. megaterium PB50 can induce tolerance to drought stress in rice. Full article

(This article belongs to the Special Issue Plant Growth Promoting Bacteria)

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15 pages, 4965 KiB

Open AccessArticle

Specific PP2A Catalytic Subunits Are a Prerequisite for Positive Growth Effects in Arabidopsis Co-Cultivated with Azospirillum brasilense and Pseudomonas simiae

by Irina O. Averkina, Ivan A. Paponov, Jose J. Sánchez-Serrano and Cathrine Lillo

Plants 2021, 10(1), 66; https://doi.org/10.3390/plants10010066 - 30 Dec 2020

Cited by 5 | Viewed by 3028

Abstract

Plant growth-promoting rhizobacteria (PGPR) stimulate plant growth, but the underlying mechanism is poorly understood. In this study, we asked whether PROTEIN PHOSPHATASE 2A (PP2A), a regulatory molecular component of stress, growth, and developmental signaling networks in plants, contributes to the plant growth responses [...] Read more.

Plant growth-promoting rhizobacteria (PGPR) stimulate plant growth, but the underlying mechanism is poorly understood. In this study, we asked whether PROTEIN PHOSPHATASE 2A (PP2A), a regulatory molecular component of stress, growth, and developmental signaling networks in plants, contributes to the plant growth responses induced by the PGPR Azospirillum brasilense (wild type strain Sp245 and auxin deficient strain FAJ0009) and Pseudomonas simiae (WCS417r). The PGPR were co-cultivated with Arabidopsis wild type (WT) and PP2A (related) mutants. These plants had mutations in the PP2A catalytic subunits (C), and the PP2A activity-modulating genes LEUCINE CARBOXYL METHYL TRANSFERASE 1 (LCMT1) and PHOSPHOTYROSYL PHOSPHATASE ACTIVATOR (PTPA). When exposed to the three PGPR, WT and all mutant Arabidopsis revealed the typical phenotype of PGPR-treated plants with shortened primary root and increased lateral root density. Fresh weight of plants generally increased when the seedlings were exposed to the bacteria strains, with the exception of catalytic subunit double mutant c2c5. The positive effect on root and shoot fresh weight was especially pronounced in Arabidopsis mutants with low PP2A activity. Comparison of different mutants indicated a significant role of the PP2A catalytic subunits C2 and C5 for a positive response to PGPR. Full article

(This article belongs to the Special Issue Plant Growth Promoting Bacteria)

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21 pages, 4731 KiB

Open AccessArticle

Rhizobacteria and Arbuscular Mycorrhizal Fungi of Oil Crops (Physic Nut and Sacha Inchi): A Cultivable-Based Assessment for Abundance, Diversity, and Plant Growth-Promoting Potentials

by Janjira Wiriya, Chakrapong Rangjaroen, Neung Teaumroong, Rungroch Sungthong and Saisamorn Lumyong

Plants 2020, 9(12), 1773; https://doi.org/10.3390/plants9121773 - 14 Dec 2020

Cited by 9 | Viewed by 3340

Abstract

Nowadays, oil crops are very attractive both for human consumption and biodiesel production; however, little is known about their commensal rhizosphere microbes. In this study, rhizosphere samples were collected from physic nut and sacha inchi plants grown in several areas of Thailand. Rhizobacteria, [...] Read more.

Nowadays, oil crops are very attractive both for human consumption and biodiesel production; however, little is known about their commensal rhizosphere microbes. In this study, rhizosphere samples were collected from physic nut and sacha inchi plants grown in several areas of Thailand. Rhizobacteria, cultivable in nitrogen-free media, and arbuscular mycorrhizal (AM) fungi were isolated and examined for abundance, diversity, and plant growth-promoting activities (indole-3-acetic acid (IAA) and siderophore production, nitrogen fixation, and phosphate solubilization). Results showed that only the AM spore amount was affected by plant species and soil features. Considering rhizobacterial diversity, two classes—Alphaproteobacteria (Ensifer sp. and Agrobacterium sp.) and Gammaproteobacteria (Raoultella sp. and Pseudomonas spp.)—were identified in physic nut rhizosphere, and three classes; Actinobacteria (Microbacterium sp.), Betaproteobacteria (Burkholderia sp.) and Gammaproteobacteria (Pantoea sp.) were identified in the sacha inchi rhizosphere. Considering AM fungal diversity, four genera were identified (Acaulospora, Claroideoglomus, Glomus, and Funneliformis) in sacha inchi rhizospheres and two genera (Acaulospora and Glomus) in physic nut rhizospheres. The rhizobacteria with the highest IAA production and AM spores with the highest root-colonizing ability were identified, and the best ones (Ensifer sp. CM1-RB003 and Acaulospora sp. CM2-AMA3 for physic nut, and Pantoea sp. CR1-RB056 and Funneliformis sp. CR2-AMF1 for sacha inchi) were evaluated in pot experiments alone and in a consortium in comparison with a non-inoculated control. The microbial treatments increased the length and the diameter of stems and the chlorophyll content in both the crops. CM1-RB003 and CR1-RB056 also increased the number of leaves in sacha inchi. Interestingly, in physic nut, the consortium increased AM fungal root colonization and the numbers of offspring AM spores in comparison with those observed in sacha inchi. Our findings proved that AM fungal abundance and diversity likely rely on plant species and soil features. In addition, pot experiments showed that rhizosphere microorganisms were the key players in the development and growth of physic nut and sacha inchi. Full article

(This article belongs to the Special Issue Plant Growth Promoting Bacteria)

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Review

Jump to: Editorial, Research

19 pages, 3969 KiB

Open AccessReview

Biocontrol Screening of Endophytes: Applications and Limitations

by Nikhil Kashyap, Sandeep Kumar Singh, Nisha Yadav, Vipin Kumar Singh, Madhuree Kumari, Dharmendra Kumar, Livleen Shukla, Kaushalendra, Nikunj Bhardwaj and Ajay Kumar

Plants 2023, 12(13), 2480; https://doi.org/10.3390/plants12132480 - 28 Jun 2023

Cited by 20 | Viewed by 4364

Abstract

The considerable loss of crop productivity each year due to plant disease or pathogen invasion during pre- or post-harvest storage conditions is one of the most severe challenges to achieving the goals of food security for the rising global population. Although chemical pesticides [...] Read more.

The considerable loss of crop productivity each year due to plant disease or pathogen invasion during pre- or post-harvest storage conditions is one of the most severe challenges to achieving the goals of food security for the rising global population. Although chemical pesticides severally affect the food quality and health of consumers, a large population relies on them for plant disease management. But currently, endophytes have been considered one of the most suitable biocontrol agents due to better colonization and acclimatization potential. However, a very limited number of endophytes have been used commercially as biocontrol agents. Isolation of endophytes and their screening to represent potential characteristics as biocontrol agents are considered challenging by different procedures. Through a web search using the keywords “endophytes as biocontrol agents” or “biocontrol mechanism of endophytes,” we have succinctly summarised the isolation strategies and different in vitro and in vivo biocontrol screening methods of endophytic biocontrol agents in the present review. In this paper, biocontrol mechanisms of endophytes and their potential application in plant disease management have also been discussed. Furthermore, the registration and regulatory mechanism of the endophytic biocontrol agents are also covered. Full article

(This article belongs to the Special Issue Plant Growth Promoting Bacteria)

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22 pages, 2928 KiB

Open AccessReview

Bacterial Siderophores: Classification, Biosynthesis, Perspectives of Use in Agriculture

by Anna M. Timofeeva, Maria R. Galyamova and Sergey E. Sedykh

Plants 2022, 11(22), 3065; https://doi.org/10.3390/plants11223065 - 12 Nov 2022

Cited by 62 | Viewed by 9359

Abstract

Siderophores are synthesized and secreted by many bacteria, yeasts, fungi, and plants for Fe (III) chelation. A variety of plant-growth-promoting bacteria (PGPB) colonize the rhizosphere and contribute to iron assimilation by plants. These microorganisms possess mechanisms to produce Fe ions under iron-deficient conditions. [...] Read more.

Siderophores are synthesized and secreted by many bacteria, yeasts, fungi, and plants for Fe (III) chelation. A variety of plant-growth-promoting bacteria (PGPB) colonize the rhizosphere and contribute to iron assimilation by plants. These microorganisms possess mechanisms to produce Fe ions under iron-deficient conditions. Under appropriate conditions, they synthesize and release siderophores, thereby increasing and regulating iron bioavailability. This review focuses on various bacterial strains that positively affect plant growth and development through synthesizing siderophores. Here we discuss the diverse chemical nature of siderophores produced by plant root bacteria; the life cycle of siderophores, from their biosynthesis to the Fe–siderophore complex degradation; three mechanisms of siderophore biosynthesis in bacteria; the methods for analyzing siderophores and the siderophore-producing activity of bacteria and the methods for screening the siderophore-producing activity of bacterial colonies. Further analysis of biochemical, molecular–biological, and physiological features of siderophore synthesis by bacteria and their use by plants will allow one to create effective microbiological preparations for improving soil fertility and increasing plant biomass, which is highly relevant for sustainable agriculture. Full article

(This article belongs to the Special Issue Plant Growth Promoting Bacteria)

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23 pages, 2586 KiB

Open AccessReview

Prospects for Using Phosphate-Solubilizing Microorganisms as Natural Fertilizers in Agriculture

by Anna Timofeeva, Maria Galyamova and Sergey Sedykh

Plants 2022, 11(16), 2119; https://doi.org/10.3390/plants11162119 - 15 Aug 2022

Cited by 107 | Viewed by 13837

Abstract

Phosphates are known to be essential for plant growth and development, with phosphorus compounds being involved in various physiological and biochemical reactions. Phosphates are known as one of the most important factors limiting crop yields. The problem of phosphorus deficiency in the soil [...] Read more.

Phosphates are known to be essential for plant growth and development, with phosphorus compounds being involved in various physiological and biochemical reactions. Phosphates are known as one of the most important factors limiting crop yields. The problem of phosphorus deficiency in the soil has traditionally been solved by applying phosphate fertilizers. However, chemical phosphate fertilizers are considered ineffective compared to the organic fertilizers manure and compost. Therefore, increasing the bioavailability of phosphates for plants is one of the primary goals of sustainable agriculture. Phosphate-solubilizing soil microorganisms can make soil-insoluble phosphate bioavailable for plants through solubilization and mineralization. These microorganisms are currently in the focus of interest due to their advantages, such as environmental friendliness, low cost, and high biological efficiency. In this regard, the solubilization of phosphates by soil microorganisms holds strong potential in research, and inoculation of soils or crops with phosphate-solubilizing bacteria is a promising strategy to improve plant phosphate uptake. In this review, we analyze all the species of phosphate-solubilizing bacteria described in the literature to date. We discuss key mechanisms of solubilization of mineral phosphates and mineralization of organic phosphate-containing compounds: organic acids secreted by bacteria for the mobilization of insoluble inorganic phosphates, and the enzymes hydrolyzing phosphorus-containing organic compounds. We demonstrate that phosphate-solubilizing microorganisms have enormous potency as biofertilizers since they increase phosphorus bioavailability for the plant, promote sustainable agriculture, improve soil fertility, and raise crop yields. The use of phosphate-solubilizing microbes is regarded as a new frontier in increasing plant productivity. Full article

(This article belongs to the Special Issue Plant Growth Promoting Bacteria)

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Open AccessReview

Bacterial Endophytes: The Hidden Actor in Plant Immune Responses against Biotic Stress

by Nadira Oukala, Kamel Aissat and Victoria Pastor

Plants 2021, 10(5), 1012; https://doi.org/10.3390/plants10051012 - 19 May 2021

Cited by 87 | Viewed by 11832

Abstract

Bacterial endophytes constitute an essential part of the plant microbiome and are described to promote plant health by different mechanisms. The close interaction with the host leads to important changes in the physiology of the plant. Although beneficial bacteria use the same entrance [...] Read more.

Bacterial endophytes constitute an essential part of the plant microbiome and are described to promote plant health by different mechanisms. The close interaction with the host leads to important changes in the physiology of the plant. Although beneficial bacteria use the same entrance strategies as bacterial pathogens to colonize and enter the inner plant tissues, the host develops strategies to select and allow the entrance to specific genera of bacteria. In addition, endophytes may modify their own genome to adapt or avoid the defense machinery of the host. The present review gives an overview about bacterial endophytes inhabiting the phytosphere, their diversity, and the interaction with the host. Direct and indirect defenses promoted by the plant–endophyte symbiont exert an important role in controlling plant defenses against different stresses, and here, more specifically, is discussed the role against biotic stress. Defenses that should be considered are the emission of volatiles or antibiotic compounds, but also the induction of basal defenses and boosting plant immunity by priming defenses. The primed defenses may encompass pathogenesis-related protein genes (PR family), antioxidant enzymes, or changes in the secondary metabolism. Full article

(This article belongs to the Special Issue Plant Growth Promoting Bacteria)

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