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Recent Trends in Plant-Growth-Promoting Rhizobacteria Research for 21st-Century Sustainable Agriculture

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A special issue of Sustainability (ISSN 2071-1050). This special issue belongs to the section "Sustainable Agriculture".

Deadline for manuscript submissions: closed (31 December 2020) | Viewed by 74233

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Prof. Dr. Munagala S. Reddy

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Guest Editor

Department of Entomology and Plant Pathology, Auburn University, Auburn, AL 36849, USA
Interests: biological control of soil-borne diseases; IPM; biofertilizers & biofungicides (PGPR); induced systemic resistance; organic agriculture; development of safer environmentally-friendly agricultural products for sustainable agriculture with reduction of pesticide use and poverty alleviation around the world
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Prof. Dr. R. Z. Sayyed

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Department of Microbiology, PSGVPM’s Arts, Science and Commerce College SHAHADA 425409 (KBC North Maharashtra University, Jalgaon) Maharashtra, 425409, India
Interests: plant-growth-promoting rhizobacteria; microbial siderophores; microbial biopolymers
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

The future of agriculture relies solely on achieving sustainability and maintaining long-term productivity. Sustainable food production is one of the greatest global challenges, particularly in the context of an ever-increasing human population and climate change due to various anthropogenic activities. Improving crop yield through the conventional way of using agrochemicals is a continuous challenge in agricultural production. Moreover, the extensive and non-targeted use of various agrochemicals creates a negative impact with respect to pesticide resistance, decrease in soil fertility, contamination of groundwater and crop-food, etc.

Among the various strategies used to enhance agriculture productivity, use of plant-beneficial microorganisms referred to as plant-growth-promoting rhizobacteria (PGPR) has been advocated as one of the most suitable strategies for sustaining the health of soil, crop, and the agro-ecosystem. PGPR play a strategic role in improvement of crop production under a changing climate, better antioxidant defense, and nutrient uptake in plants, sustainable management of plant disease (biocontrol), and seed priming. PGPR are vital for ensuring the production of chemical-free food and for food security. Genomic approaches for understanding PGPR-mediated stress tolerance in plants, emerging trends in the role of PGPR in nano-biofertilizers and nano-biopesticides, crop microbiome, and endophytic microbiome in plant growth and health offers newer opportunities for further research and development

Recently, research has highlighted the importance of these PGPR in improvement of plant health and in combating challenges to agricultural sustainability, for feeding an overgrowing population and reducing hunger globally. Currently, the scientific world is experiencing a reinvigoration of microbial biotechnologies to improve agro-ecosystem functioning that utilize the potential of PGPR for enhanced soil health, crop vigor, pest protection, development of resistance in plants, removal of toxic substances from soil, and seed priming. Thus, the increased awareness of the importance of microorganisms for plant and soil health has fueled a boom in research on PGPR. However, there is a need to start translating the knowledge of various aspects of PGPR into management solutions for diverse agro-ecosystems.

This Special Issue on “Recent Trends in Plant-Growth-Promoting Rhizobacteria Research for 21st-Century Sustainable Agriculture” aims to gather contributions from scientists working in diverse disciplines related to PGPR–crop interactions, with focus on translation of basic knowledge to innovative applied research. In this Special Issue, we will focus on i) understanding the structure and function of crop microbiome, ii) the plausible role of soil microorganisms as biofertilizers, biopesticides, biofungicides, or biostimulants, microbial consortia for improving of crop health, crop nutrition, and resistance and protection from pests and pathogens, iii) crop microbiome evolution, iv) resilience of agricultural microbiome to climatic changes, and v) new technologies to study plant–microbe molecular interactions in agricultural systems.

Prof. Dr. M. S. Reddy
Prof. Dr. R. Z. Sayyed
Guest Editors

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Keywords

PGPR in plant growth promotion and disease control
PGPR in agriculture sustainability
Abiotic and biotic stress alleviation
Crop microbiome
Antioxidant and hydrolytic enzymes ISR, SAR and plant defense
Bio-nanofertilizers and Bio-nanopesticides
Next-generation sequencing for PGPR-Plant interaction
PGPR in bioprospecting
PGPR and food security
PGPR and seed priming
Bioactive metabolites of PGPR

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Published Papers (6 papers)

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Research

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19 pages, 2852 KiB

Open AccessArticle

Exopolysaccharides Producing Bacteria for the Amelioration of Drought Stress in Wheat

by Noshin Ilyas, Komal Mumtaz, Nosheen Akhtar, Humaira Yasmin, R. Z. Sayyed, Wajiha Khan, Hesham A. El Enshasy, Daniel J. Dailin, Elsayed A. Elsayed and Zeshan Ali

Sustainability 2020, 12(21), 8876; https://doi.org/10.3390/su12218876 - 26 Oct 2020

Cited by 128 | Viewed by 7059

Abstract

This research was designed to elucidate the role of exopolysaccharides (EPS) producing bacterial strains for the amelioration of drought stress in wheat. Bacterial strains were isolated from a farmer’s field in the arid region of Pakistan. Out of 24 isolated stains, two bacterial strains, Bacillus subtilis (Accession No. MT742976) and Azospirillum brasilense (Accession No. MT742977) were selected, based on their ability to produce EPS and withstand drought stress. Both bacterial strains produced a good amount of EPS and osmolytes and exhibited drought tolerance individually, however, a combination of these strains produced higher amounts of EPS (sugar 6976 µg/g, 731.5 µg/g protein, and 1.1 mg/g uronic acid) and osmolytes (proline 4.4 µg/mg and sugar 79 µg/mg) and significantly changed the level of stress-induced phytohormones (61%, 49% and 30% decrease in Indole Acetic Acid (IAA), Gibberellic Acid (GA), and Cytokinin (CK)) respectively under stress, but an increase of 27.3% in Abscisic acid (ABA) concentration was observed. When inoculated, the combination of these strains improved seed germination, seedling vigor index, and promptness index by 18.2%, 23.7%, and 61.5% respectively under osmotic stress (20% polyethylene glycol, PEG6000). They also promoted plant growth in a pot experiment with an increase of 42.9%, 29.8%, and 33.7% in shoot length, root length, and leaf area, respectively. Physiological attributes of plants were also improved by bacterial inoculation showing an increase of 39.8%, 61.5%, and 45% in chlorophyll a, chlorophyll b, and carotenoid content respectively, as compared to control. Inoculations of bacterial strains also increased the production of osmolytes such asproline, amino acid, sugar, and protein by 30%, 23%, 68%, and 21.7% respectively. Co-inoculation of these strains enhanced the production of antioxidant enzymes such as superoxide dismutase (SOD) by 35.1%, catalase (CAT) by 77.4%, and peroxidase (POD) by 40.7%. Findings of the present research demonstrated that EPS, osmolyte, stress hormones, and antioxidant enzyme-producing bacterial strains impart drought tolerance in wheat and improve its growth, morphological attributes, physiological parameters, osmolytes production, and increase antioxidant enzymes. Full article

(This article belongs to the Special Issue Recent Trends in Plant-Growth-Promoting Rhizobacteria Research for 21st-Century Sustainable Agriculture)

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18 pages, 1349 KiB

Open AccessArticle

A Mixture of Piper Leaves Extracts and Rhizobacteria for Sustainable Plant Growth Promotion and Bio-Control of Blast Pathogen of Organic Bali Rice

by Ni Luh Suriani, Dewa Ngurah Suprapta, Novizar Nazir, Ni Made Susun Parwanayoni, Anak Agung Ketut Darmadi, Desy Andya Dewi, Ni Wayan Sudatri, Ahmad Fudholi, R. Z. Sayyed, Asad Syed, Abdallah M. Elgorban, Ali H. Bahkali, Hesham Ali El Enshasy and Daniel Joe Dailin

Sustainability 2020, 12(20), 8490; https://doi.org/10.3390/su12208490 - 14 Oct 2020

Cited by 37 | Viewed by 4165

Abstract

Rice is a crop that is consumed as a staple food by the majority of the people in the world and therefore failure in rice crops, due to any reason, poses a severe threat of starvation. Rice blast, caused by a fungus Pyricularia oryzae, has been ranked among the most threatening plant diseases of rice and it is found wherever rice is grown. All of the rice blast disease management strategies employed so far have had limited success and rice blast has never been eliminated from rice fields. Hence, there is a need to look for the best remedy in terms of effectiveness, sustainability, and organic nature of the method. This study was aimed at determining the plant growth-promoting and fungicidal effects of a mixture of Piper caninum and Piper betle var. Nigra leaves extracts and rhizobacteria. Gas chromatography–mass spectrophotometry (GC-MS) analysis of a mixture of leaves extracts of these plants revealed the presence of new bioactive compounds such as alpha.-gurjunene, gamma.-terpinene, and ethyl 5-formyl 3-(2-ethoxycarbonyl) in a mixture of leaves extracts of P. caninum and P. betle var. Nigra. The mixture of these extracts reduced the intensity of blast disease, inhibited P. oryzae, and improved the growth, yield, and quality of Bali rice. All treatments comprising of different concentrations of a mixture of leaves extracts of P. caninum and P. betle var. Nigra plus rhizobacteria exhibited biocontrol and bioefficacy. However, a 2% concentration of a mixture of these leaves extracts with plant growth-promoting rhizobacteria (PGPR) exhibited potent inhibition of growth of P. oryzae, a significant reduction in the intensity of blast disease, and a maximum increase in growth, yield, and quality of Bali rice. In the 15th week, the intensity of blast disease decreased from 80.18% to 7.90%. The mixture of leaves extract + PGPR also improved the height of the plant, the number of tillers, number of leaves, number of grains per panicle, number of heads per panicle, and the full-grain weight per clump. Applications of various concentrations of a mixture of leaves extracts + PGPR resulted in improvement in the potential yield of rice, however, the application of 2% extracts + PGPR gave the highest potential yield of 5.61 tha⁻¹ compared to the low yields in the control and other treatments. The high grain yield observed with the treatment was caused by the low intensity of blast disease. This treatment also strengthened the stem and prevented the drooping of the plant and improved the quality of rice grain. Full article

(This article belongs to the Special Issue Recent Trends in Plant-Growth-Promoting Rhizobacteria Research for 21st-Century Sustainable Agriculture)

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9 pages, 840 KiB

Open AccessArticle

Linking Organic Metabolites as Produced by Purpureocillium Lilacinum 6029 Cultured on Karanja Deoiled Cake Medium for the Sustainable Management of Root-Knot Nematodes

by Abhishek Sharma, Aditi Gupta, Manu Dalela, Satyawati Sharma, R. Z. Sayyed, Hesham Ali El Enshasy and Elsayed Ahmed Elsayed

Sustainability 2020, 12(19), 8276; https://doi.org/10.3390/su12198276 - 8 Oct 2020

Cited by 21 | Viewed by 2675

Abstract

Root-knot nematodes pose a serious threat to agriculture and forest systems, causing significant losses of the crop worldwide. A wide range of chemical nematicides has traditionally been used to manage phyto-nematodes. However, due to their ill effects on the environment, biological control agents (BCAs) like Purpureocillium lilacinum that exhibit antagonistic effects on root-knot nematodes are preferred. The current study focused on identifying nematicidal metabolites produced by the fungus Purpureocillium lilacinum cultivated on akaranja deoiled cake-based liquid medium through bioactivity-guided fractionation against Meloidogyne incognita. Column chromatography of the ethyl acetate extract of fungal filtrate exhibited the most potent fraction (fraction 14–15), giving 94.6% egg mass hatching inhibition on the 5th day and a maximum nematicidal activity of 62% against second-stage juveniles after 48 h at 5000 mg/L. Gas chromatography coupled with mass spectrometry (GC-MS) analysis of this fraction revealed five major compounds, viz., 2-ethyl butyric acid, phenyl ethyl alcohol, benzoic acid, benzene acetic acid, and 3,5-Di-t-butylphenol. These biocompounds have potential biocontrol applications in agriculture, but further in vivo studies are warranted. Full article

(This article belongs to the Special Issue Recent Trends in Plant-Growth-Promoting Rhizobacteria Research for 21st-Century Sustainable Agriculture)

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24 pages, 3155 KiB

Open AccessArticle

Identification of New Biocontrol Agent against Charcoal Rot Disease Caused by Macrophomina phaseolina in Soybean (Glycine max L.)

by Humaira Yasmin, Rabia Naz, Asia Nosheen, Muhammad Nadeem Hassan, Noshin Ilyas, Muhammad Sajjad, Seemab Anjum, Xiangkuo Gao and Zhide Geng

Sustainability 2020, 12(17), 6856; https://doi.org/10.3390/su12176856 - 24 Aug 2020

Cited by 37 | Viewed by 4727

Abstract

Controlling agricultural pests using suitable biocontrol agents has been considered the best strategy for sustainable agriculture. Charcoal rot caused by a necrotrophic fungus Macrophomina phaseolina is responsible for a 30–50% annual reduction in soybean yield worldwide. Little is known about the role of Bacillus clausii in reducing charcoal rot disease severity in the soybean crop. In this study, we investigated plant growth promoting and antagonistic potential of Pseudomonas putida (MT604992) and Bacillus clausii (MT604989) against charcoal rot disease incidence in soybean. Among twenty bacteria isolated from soil and water samples of two different hot springs of Gilgit-Baltistan, Pakistan, 80% were siderophore positive; 65% were hydrogen cyanide (HCN) positive; 55%, 30%, and 75% were phosphate, potassium, and zinc solubilizers, respectively. Based on higher antagonistic activities and plant growth promoting traits five strains were selected for in vitro screening. Out of all tested strains, Pseudomonas putida and Bacillus clausii showed a significant increase in germination, growth, and disease suppression in soybean. These strains produced a pronounced increase in relative water content, photosynthetic pigments, membrane stability, proline, antioxidant enzymes status, phytohormones content (Salicylic acid, and Jasmonic acid), and disease suppression in comparison to control plants. Bacillus clausii mitigated the disease by 97% with a marked increase in the proline content (73% and 89%), superoxide dismutase (356% and 208%), peroxidase (439% and 138.6%), catalase (255.8% and 80.8%), and ascorbate peroxidase (228% and 90%) activities in shoots and roots, respectively. Infected plants showed an increase in salicylic acid and jasmonic acid content which was further increased with the application of the selected strains to increase resistance against pathogens. To our knowledge, this is the first study showing a rise in salicylic acid and jasmonic acid in Macrophomina phaseolina infected plants. These two strains are suggested as a cost-effective, eco-friendly, and sustainable alternative to chemical fungicides. However, there is a need to explore the field testing and molecular mechanisms leading to disease suppression by these strains. Full article

(This article belongs to the Special Issue Recent Trends in Plant-Growth-Promoting Rhizobacteria Research for 21st-Century Sustainable Agriculture)

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Review

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24 pages, 2130 KiB

Open AccessReview

Bacterial Plant Biostimulants: A Sustainable Way towards Improving Growth, Productivity, and Health of Crops

by Basharat Hamid, Muzafar Zaman, Shabeena Farooq, Sabah Fatima, R. Z. Sayyed, Zahoor Ahmad Baba, Tahir Ahmad Sheikh, Munagala S. Reddy, Hesham El Enshasy, Abdul Gafur and Ni Luh Suriani

Sustainability 2021, 13(5), 2856; https://doi.org/10.3390/su13052856 - 6 Mar 2021

Cited by 186 | Viewed by 17872

Abstract

This review presents a comprehensive and systematic study of the field of bacterial plant biostimulants and considers the fundamental and innovative principles underlying this technology. Plant biostimulants are an important tool for modern agriculture as part of an integrated crop management (ICM) system, helping make agriculture more sustainable and resilient. Plant biostimulants contain substance(s) and/or microorganisms whose function when applied to plants or the rhizosphere is to stimulate natural processes to enhance plant nutrient uptake, nutrient use efficiency, tolerance to abiotic stress, biocontrol, and crop quality. The use of plant biostimulants has gained substantial and significant heed worldwide as an environmentally friendly alternative to sustainable agricultural production. At present, there is an increasing curiosity in industry and researchers about microbial biostimulants, especially bacterial plant biostimulants (BPBs), to improve crop growth and productivity. The BPBs that are based on PGPR (plant growth-promoting rhizobacteria) play plausible roles to promote/stimulate crop plant growth through several mechanisms that include (i) nutrient acquisition by nitrogen (N₂) fixation and solubilization of insoluble minerals (P, K, Zn), organic acids and siderophores; (ii) antimicrobial metabolites and various lytic enzymes; (iii) the action of growth regulators and stress-responsive/induced phytohormones; (iv) ameliorating abiotic stress such as drought, high soil salinity, extreme temperatures, oxidative stress, and heavy metals by using different modes of action; and (v) plant defense induction modes. Presented here is a brief review emphasizing the applicability of BPBs as an innovative exertion to fulfill the current food crisis. Full article

(This article belongs to the Special Issue Recent Trends in Plant-Growth-Promoting Rhizobacteria Research for 21st-Century Sustainable Agriculture)

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20 pages, 2625 KiB

Open AccessReview

Plant Growth Promoting Rhizobacteria (PGPR) as Green Bioinoculants: Recent Developments, Constraints, and Prospects

by Anirban Basu, Priyanka Prasad, Subha Narayan Das, Sadaf Kalam, R. Z. Sayyed, M. S. Reddy and Hesham El Enshasy

Sustainability 2021, 13(3), 1140; https://doi.org/10.3390/su13031140 - 22 Jan 2021

Cited by 506 | Viewed by 35266

Abstract

The quest for enhancing agricultural yields due to increased pressure on food production has inevitably led to the indiscriminate use of chemical fertilizers and other agrochemicals. Biofertilizers are emerging as a suitable alternative to counteract the adverse environmental impacts exerted by synthetic agrochemicals. Biofertilizers facilitate the overall growth and yield of crops in an eco-friendly manner. They contain living or dormant microbes, which are applied to the soil or used for treating crop seeds. One of the foremost candidates in this respect is rhizobacteria. Plant growth promoting rhizobacteria (PGPR) are an important cluster of beneficial, root-colonizing bacteria thriving in the plant rhizosphere and bulk soil. They exhibit synergistic and antagonistic interactions with the soil microbiota and engage in an array of activities of ecological significance. They promote plant growth by facilitating biotic and abiotic stress tolerance and support the nutrition of host plants. Due to their active growth endorsing activities, PGPRs are considered an eco-friendly alternative to hazardous chemical fertilizers. The use of PGPRs as biofertilizers is a biological approach toward the sustainable intensification of agriculture. However, their application for increasing agricultural yields has several pros and cons. Application of potential biofertilizers that perform well in the laboratory and greenhouse conditions often fails to deliver the expected effects on plant development in field settings. Here we review the different types of PGPR-based biofertilizers, discuss the challenges faced in the widespread adoption of biofertilizers, and deliberate the prospects of using biofertilizers to promote sustainable agriculture. Full article

(This article belongs to the Special Issue Recent Trends in Plant-Growth-Promoting Rhizobacteria Research for 21st-Century Sustainable Agriculture)

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