Plant Growth-promoting Potential Research Articles

Pomegranate Rhizosphere Microbial Diversity Revealed by Metagenomics: Toward Organic Farming, Plant Growth Promotion and Biocontrol?

Food production must undergo systems change to meet the sustainable development goals (SDGs). For example, organic farming can be empowered by soil microorganisms with plant growth promotion (PGP) and biocontrol features. In this context, there have been limited studies on pomegranate. We investigated microbial diversity in rhizosphere of the pomegranate "Bhagwa" variety and its potential role in PGP and biocontrol. Both bulk and rhizosphere soil samples were analyzed for their physicochemical properties. Whole metagenome sequencing was conducted using the Illumina NovaSeq6000 platform. Surprisingly, we found that bulk and rhizosphere soil samples had comparable microbial diversity. Metagenome sequencing revealed the abundance of Streptomyces indicus, Bradyrhizobium kalamazoonesis, and Pseudomonas cellulosum in the rhizosphere that are reported here for the first time in agricultural literature. Pathway prediction analysis using KEGG (Kyoto Encyclopedia for Genes and Genomes) and COG (clusters of orthologous genes) databases identified metabolic pathways associated with biocontrol properties against pathogens. We confirmed the metagenome data in vitro, which demonstrated their PGP potential and antimicrobial properties. For instance, S. indicus produced high concentration of indole-3-acetic acid, a PGP phytohormone, that can stimulate plant growth. In addition, an antimicrobial susceptibility assay suggested that bacterial extracts displayed activity against Xanthomonas, a primary pathogen causing the pomegranate wilt disease. In conclusion, this study suggests that S. indicus, B. kalamazoonesis, and P. cellulosum can potentially be PGP and biocontrol agents that may contribute to increased crop productivity in pomegranate cultivation. These agents and their combinations warrant future research with an eye on SDGs and so as to enable and innovate organic farming and pomegranate agricultural practices.

Beneficial effects of plant growth-promoting yeasts (PGPYs) on the early stage of growth of zucchini plants

The use of microbes capable of beneficially interacting with plants is essential for advancing climate-smart agriculture. This approach aims to reduce chemical use while simultaneously enhancing crop productivity. This implies efforts to optimize the criteria for selecting potential plant growth promoters (PGPs), focusing also on yeasts, only recently investigated for their PGP potential. The present study employed a set of Ascomycetes and Basidiomycetes yeasts to test their PGP properties on zucchini (Cucurbita pepo L.), chosen as a fast-growing plant with a vast economical interest. Yeasts were tested alone and as consortium. Seed inoculation with yeasts boosted the early phase of growth of the zucchini plants, primarily affecting the root development. Three strains belonging to the species Schwanniomyces etchellsii, Zygotorulaspora florentina and Holtermanniella festucosa induced a strong and significant enhancement of weight and length of both epi- and hypogeal parts of the plant. Furthermore, the presence of yeasts induced strain-specific modulations in the biochemical profiles of soil, primarily detected in the rhizosphere. This suggests an active interaction between the roots and the inoculated yeast cultures.

Onion Peel Waste Has the Potential to Be Converted into a Useful Agricultural Product to Improve Vegetable Crop Growth

The onion processing industry produces hundreds of thousands of tons of onion waste annually. Normally, onion peel waste is dumped in landfills, which creates additional sources of greenhouse gases. Research has validated that onion peel is a concentrated source of bioactive compounds; therefore, it can be turned into useful agricultural products such as soil amendments and possibly biostimulants. This study conducted three experiments to investigate the plant growth-promoting potential of an onion juice concentrate (OJC). The first experiment explored whether the application of OJC could increase plant growth of Bermuda grass, lettuce, and bok choy. The second experiment evaluated the effects of foliar and subsurface drench applications of OJC on bok choy and lettuce growth. The third experiment investigated the interaction between OJC application methods and fertilizer type on bok choy and radish growth. The results indicated that foliar applications of OJC of 1% to 2% concentrations increased the yield of bok choy and its overall growth. Subirrigation with OJC, however, enhanced the root growth of bok choy, lettuce, and radish. Notably, the combined approach of foliar and subirrigation applications further promoted the growth of both bok choy and radish. Comparing across experiments, longer OJC application periods emerged as a promising strategy for amplifying its growth-promoting benefits. Overall, our findings suggest that OJC holds promise for promoting sustainable agriculture. This potential comes from its ability to enhance both the growth and yield of vegetable crops like bok choy, lettuce, and radish while simultaneously reducing waste.

Improving Lead Phytoremediation Using Endophytic Bacteria Isolated from the Pioneer Plant Ageratina adenophora (Spreng.) from a Mining Area.

This study aimed to isolate and characterise endophytic bacteria from the pioneer plant Ageratina adenophora in a mining area. Seven strains of metal-resistant endophytic bacteria that belong to five genera were isolated from the roots of A. adenophora. These strains exhibited various plant growth-promoting (PGP) capabilities. Sphingomonas sp. ZYG-4, which exhibited the ability to secrete indoleacetic acid (IAA; 53.2 ± 8.3 mg·L-1), solubilize insoluble inorganic phosphates (Phosphate solubilization; 11.2 ± 2.9 mg·L-1), and regulate root ethylene levels (1-aminocyclopropane-1-carboxylic acid deaminase activity; 2.87 ± 0.19 µM α-KB·mg-1·h-1), had the highest PGP potential. Therefore, Sphingomonas sp. ZYG-4 was used in a pot experiment to study its effect on the biomass and Pb uptake of both host (Ageratina adenophora) and non-host (Dysphania ambrosioides) plants. Compared to the uninoculated control, Sphingomonas sp. ZYG-4 inoculation increased the biomass of shoots and roots by 59.4% and 144.4% for A. adenophora and by 56.2% and 57.1% for D. ambrosioides, respectively. In addition, Sphingomonas sp. ZYG-4 inoculation enhanced Pb accumulation in the shoot and root by 268.9% and 1187.3% for A. adenophora, and by 163.1% and 343.8% for D. ambrosioides, respectively, compared to plants without bacterial inoculation. Our research indicates that endophytic bacteria are promising candidates for enhancing plant growth and facilitating microbe-assisted phytoremediation in heavy metal-contaminated soil.

Characterisation of the Endophytic and Rhizospheric Bacillus licheniformis Strains Isolated from Sweet Potato with Plant Growth-Promoting and Yield Enhancing Potential

The primary aim of the present study was to identify bacterial isolates with yield-enhancing potential for application as biofertilisers in the cultivation of sweet potato. Therefore, endophytic and rhizospheric strains were isolated from sweet potato plantations in Hungary to identify bacterial strains with plant growth-promoting and antifungal potential. In total, seven Bacillus licheniformis strains were identified and subjected to detailed ecophysiological investigations. Experiments have been conducted to investigate the tolerance of selected strains to different limiting factors such as pH, temperature, and water activity, which affect survivability in various agricultural environments. The majority of tested B. licheniformis strains exhibited plant growth-promoting potential (e.g., production of indole-3-acetic acid up to 40.42 μg mL−1, production of ammonia up to 0.87 mg mL−1, phosphorus solubilising activity, siderophore production), with two strains (SZMC 27713 and SZMC 27715) demonstrating inhibitory activity (ranging between 7% and 38%) against plant pathogenic fungi prevalent in sweet potato cultivation. Furthermore, strain SZMC 27715 induced accelerated germination and a significantly higher germination rate in tomato seeds compared to the control. In a field study, it was observed that strain SZMC 27715 had a potent yield enhancing effect in sweet potato, where a significant yield per plant increase was observed in all treatments (1.13, 1.09 and 1.40 kg) compared to the control plants (0.92 kg). The highest yield per plant was observed when the cuttings were soaked combined with two additional foliar treatments. To the best of our knowledge, this is the first report of the successful utilisation of the B. licheniformis strain as a biofertiliser for yield enhancement in sweet potato cultivation. Based on our results, strain SZMC 27715 has potential for application as a biofertiliser in sweet potato cultivation either as a standalone option or in a microbial consortium.

Will the beneficial properties of plant-growth promoting bacteria be affected by waterlogging predicted in the wake of climate change: A model study

The agricultural sector today is faced with climate change that amplifies extreme climatic events. The use of plant growth promoting bacteria (PGPB) could provide a new approach to increase crop production under these new conditions. In this study, PGPB were isolated from a 5-week pot experiment conducted under greenhouse conditions using cabbage (Brassica oleracea L. var. capitata f. alba) as a model plant. Plants were exposed to either one or two long-term waterlogging events at two different stages of plant development. The results clearly showed that waterlogging leads to changes in the soil microbial community affecting both its overall structure (culturable bacterial fraction) as well as the plant growth promotion (PGP) function provided by the beneficial bacteria to the plant. In general, “the core” of the bacterial community (Bacillus, Pseudomonas, Stenotrophomonas and Peribacillus populations) remained preserved under waterlogged conditions, but shifts in their abundance were observed, with Bacillus, and Pseudomonas proliferating under these conditions. The key to adaptation to waterlogging may lie in “rare” bacterial populations isolated only under certain waterlogging conditions. In our study we identified 11 different genera that can be termed as waterlogging-tolerant. Waterlogging was also shown to induce shifts in the PGP potential, as well as on the structure of a population exhibiting a particular trait, which could eventually lead to either promotion or reduction of plant growth. While the abundances of populations promoting nutrient availability to plants were found to increase after waterlogging, biocontrol protease activity proved to be the trait most sensitive to waterlogging. Enterobacter and Pantoea species were identified as main players in biofilm formation under waterlogging conditions. Waterlogging also appears to trigger the emergence of extremophilic and acidophilic bacteria, aspect important for potential adaptation of soil bacteria to future climate projections, with Bacillus and Pseudomonas showing best potential. Based on all PGP characteristics studied, we selected 11 bacterial isolates belonging to genera Enterobacter, Bacillus, Pseudomonas, Stenotrophomonas, and Pantoea designating them as the most promising bacterial bioinoculants i.e. strains with good potential for future applications in potential waterstress recover of the soil and plants.

Isolation of endophytes from Dioscorea nipponica Makino for stimulating diosgenin production and plant growth.

Both bacterial and fungal endophytes exhibited one or more plant growth-promoting (PGP) traits. Among these strains, the Paenibacillus peoriae SYbr421 strain demonstrated the greatest activity in the direct biotransformation of tuber powderfrom D. nipponica into diosgenin. Endophytes play crucial roles in shaping active metabolites within plants, significantly influencing both the quality and yield of host plants. Dioscorea nipponica Makino accumulates abundant steroidal saponins, which can be hydrolyzed to produce diosgenin.However, our understanding of the associated endophytes and their contributions to plant growth and diosgenin production is limited. The present study aimed to assess the PGP ability and potential of diosgenin biotransformation by endophytesisolatesassociated withD. nipponica for the efficient improvement of plant growth and development of a clean and effective approach for producing the valuable drug diosgenin. Eighteen bacterial endophytes were classified into six genera through sequencing and phylogenetic analysis of the 16S rDNA gene. Similarly, 12 fungal endophytes were categorized into 5 genera based on sequencing and phylogenetic analysis of the ITS rDNA gene. Pure culture experiments revealed that 30 isolated endophytic strains exhibited one or more PGP traits, such as nitrogen fixation, phosphate solubilization, siderophore synthesis, and IAA production. One strain of endophytic bacteria, P. peoriae SYbr421, effectively directly biotransformed the saponin components in D. nipponica. Moreover, a high yield of diosgenin (3.50%) was obtained at an inoculum size of 4% after 6days of fermentation. Thus, SYbr421 could be used for a cleaner and more eco-friendly diosgenin production process. In addition, based on the assessment of growth-promoting isolates and seed germination results, the strains SYbr421, SYfr1321, and SYfl221 were selected for greenhouse experiments. The results revealed that the inoculation of these promising isolates significantly increased the plant height and fresh weight of the leaves and roots compared to the control plants. These findings underscore the importance of preparing PGP bioinoculants from selected isolates as an additional option for sustainable diosgenin production.

Integrated genome-transcriptome analysis unveiled the mechanism of Debaryomyces hansenii-mediated arsenic stress amelioration in rice

Globally, rice is becoming more vulnerable to arsenic (As) pollution, posing a serious threat to public food safety. Previously Debaryomyces hansenii was found to reduce grain As content of rice. To better understand the underlying mechanism, we performed a genome analysis to identify the key genes in D. hansenii responsible for As tolerance and plant growth promotion. Notably, genes related to As resistance (ARR, Ycf1, and Yap) were observed in the genome of D. hansenii. The presence of auxin pathway and glutathione metabolism-related genes may explain the plant growth-promoting potential and As tolerance mechanism of this novel yeast strain. The genome annotation of D. hansenii indicated that it contains a repertoire of genes encoding antioxidants, well corroborated with the in vitro studies of GST, GR, and glutathione content. In addition, the effect of D. hansenii on gene expression profiling of rice plants under As stress was also examined. The Kyoto Encyclopedia of Genes and Genomes (KEGG) database revealed 307 genes, annotated in D. hansenii-treated rice, related to metabolic pathways (184), photosynthesis (12), glutathione (10), tryptophan (4), and biosynthesis of secondary metabolite (117). Higher expression of regulatory elements like AUX/IAA and WRKY transcription factors (TFs), and defense-responsive genes dismutases, catalases, peroxiredoxin, and glutaredoxins during D. hansenii+As exposure was also observed. Combined analysis revealed that D. hansenii genes are contributing to stress mitigation in rice by supporting plant growth and As-tolerance. The study lays the foundation to develop yeast as a beneficial biofertilizer for As-prone areas.

Co-inoculation of the endophytes Bacillus thuringiensis CAPE95 and Paenibacillus polymyxa CAPE238 promotes Tropaeolum majus L. growth and enhances its root bacterial diversity.

Tropaeolum majus L. is a versatile edible plant that is widely explored due to its medicinal properties and as a key element in intercropping systems. Its growth could be improved by the use of biofertilizers that can enhance nutrient uptake by the plant or provide tolerance to different abiotic and biotic stresses. In a previous study, 101 endophytes isolated from T. majus roots showed more than three plant growth-promoting (PGP) features in vitro, such as phosphate mineralization/solubilization, production of siderophores, antimicrobial substances and indole-related compounds, and presence of the nifH gene. To provide sustainable alternatives for biofertilization, the genomes of two promising endophytes-CAPE95 and CAPE238-were sequenced to uncover metabolic pathways related to biofertilization. Greenhouse experiments were conducted with 216 seeds and 60 seedlings, half co-inoculated with the endophytes (treatment) and half inoculated with 1X PBS (control), and the impact of the co-inoculation on the plant's bacteriome was accessed through 16S rRNA gene metabarcoding. The strains CAPE95 and CAPE238 were taxonomically assigned as Bacillus thuringiensis and Paenibacillus polymyxa, respectively. Metabolic pathways related to the enhancement of nutrient availability (nitrogen fixation, sulfate-sulfur assimilation), biosynthesis of phytohormones (indole-3-acetic acid precursors) and antimicrobial substances (bacilysin, paenibacillin) were found in their genomes. The in vivo experiments showed that treated seeds exhibited faster germination, with a 20.3% higher germination index than the control on the eleventh day of the experiment. Additionally, treated seedlings showed significantly higher plant height and leaf diameters (p < 0.05). The bacterial community of the treated plants was significantly different from that of the control plants (p < 0.001) and showed a higher richness and diversity of species (Chao and Shannon indexes, p < 0.001). A higher relative abundance of potential synergistic PGP bacteria was also shown in the bacteriome of the treated plants, such as Lysinibacillus and Geobacter. For the first time, co-inoculation of B. thuringiensis and P. polymyxa was shown to have great potential for application as a biofertilizer to T. majus plants. The bacterial consortium used here could also be explored in other plant species in the future.

Metagenomic assembled genomes indicated the potential application of hypersaline microbiome for plant growth promotion and stress alleviation in salinized soils.

The strategic implementation of metagenomic assembled genomes (MAGs) in exploring the properties and harnessing microorganisms from ecosystems like hypersaline niches has transformative potential in agriculture. This approach promises to redefine our comprehension of microbial diversity and its ecosystem roles. Recovery and decoding of MAGs unlock genetic resources, enabling the development of new solutions for agricultural challenges. Enhanced understanding of these microbial communities can lead to more efficient nutrient cycling, pest control, and soil health maintenance. Consequently, traditional agricultural practices can be improved, resulting in increased yields, reduced environmental impacts, and heightened sustainability. MAGs offer a promising avenue for sustainable agriculture, bridging the gap between cutting-edge genomics and practical field applications.

Isolation and characterization of PGPR obtained from different arsenic-contaminated soil samples and their effect on photosynthetic characters of maize grown under arsenic stress.

Contamination of the environment due to speedup of anthropogenic activities has become a serious threat to modern humanity. Among the contaminants, the new emerging concern is the heavy metal (HM) contamination in the environment. Because the persistence and harmfulness of heavy metals affect the ecosystem and the health of plants, animals, and humans, they are the most toxic substances in the environment. Among them, Arsenic (As) emerged as major environmental constraint leading to enormous negative effects on the plant, animal, and human health. Even in minute quantity, As is known to cause various critical diseases in humans and toxicity in plants. Research was performed to observe the capability of plant growth-promoting strains of bacteria in enhancing Zea mays (L.) growth in arsenic polluted soil. Total 30 bacterial strains were isolated from the polluted soils, screened for plant growth promotion potential and arsenic tolerance. Eighteen isolates showed resistance to different levels of sodium arsenate (ranging from 0 to 50 mM) in agar plate using LB media. Of 18 isolates, 83.3% produced IAA, methyl red, and hydrogen cyanide; 55.5% exhibited catalase activity; 61.1% showed siderophore production; 88.8% showed phosphate solubilization; and 44.4% showed oxidase, Voges proskauer activity, and KOH solubility. The most efficient isolates SR3, SD5, and MD3 with significant arsenic tolerance and plant growth-promoting (PGP) activity were examined via sequencing of amplified 16S rRNA gene. Isolates of bacteria, i.e., SR3, SD5, and MD3, showing multiple PGP-traits were identified as Bacillus pumilus (NCBI accession number: OR459628), Paenibacillus faecalis (NCBI accession number: OR461560), and Pseudochrobactrum asaccharolyticum (NCBI accession number: OR458922), respectively. Maize seeds treated with these PGPR strains were grown in pots contaminated with 50 ppm and 100 ppm sodium arsenate. Compared to untreated arsenic stressed plants, bacterial inoculation P. asaccharolyticum (MD3) resulted 20.54%, 18.55%, 33.45%, 45.08%, and 48.55% improvement of photosynthetic pigments (carotenoid content, chlorophyll content, stomatal conductance (gs), substomatal CO2, and photosynthetic rate), respectively. Principal component analysis explained that first two components were more than 96% of the variability for each tested parameter. The results indicate that in comparison to other isolates, P. asaccharolyticum isolate can be used as efficient agent for improving maize growth under arsenic polluted soil.

Effects of steeping duration and concentration of metabolites from rhizosphere bacteria on the germinability of cowpea, soybean, sesame, and okra seeds

Seed priming enhances germination and growth, which are important determinants of crop yield. This study was carried out to assess the effect of steeping duration and metabolite concentration on the priming of five (5) different crops, using the metabolites of five (5) bacterial isolates. The crop seeds were treated in the cold-extracted metabolites of the five isolates at five (5) different steeping durations (1, 2, 3, 4, and 5 h) and then in five metabolite concentrations (200, 400, 600, 800, and 1000 mg/L) of the five extracted metabolites at the optimal steeping duration determined in the first experiment. Characterization of the cold-extracted metabolites was also carried out using gas-chromatography-mass spectrometry (GC-MS). Results revealed that steeping cowpea and soybean for longer durations (&lt; 3 h) could hinder their growth and development. Lower concentrations were observed to be optimal for cowpea and soybean, but for sesame and okra, there was no detectable pattern with metabolite concentration. The GC-MS revealed the presence of some molecules (e.g. hexadecanoic acid) that have shown plant growth promotion potential in other studies. This study showed that seeds with large endosperm, such as, cowpea and soybean, are more prone to the deleterious effects of treatment for longer durations. Further experiments should be carried out to isolate and purify the bioactive moieties for further studies and onward application.

Unlocking the plant growth-promoting potential of yeast spp.: exploring species from the Moroccan extremophilic environment for enhanced plant growth and sustainable farming.

In this study, we successfully isolated two distinct yeasts from Moroccan extreme environments. These yeasts were subjected to molecular characterization by analyzing their Internal Transcribed spacer (ITS) regions. Our research thoroughly characterizes plant growth-promoting abilities and their drought and salt stress tolerance. In a greenhouse assay, we examined the impact of selected yeasts on Medicago sativa's growth. Four treatments were employed: (i) control without inoculation (NI), (ii) inoculation with L1, (iii) inoculation with L2, and (iv) inoculation with the mixture L1+L2. L1 isolated from Toubkal Mountain shared 99.83% sequence similarity to Rhodotorula mucilaginosa. Meanwhile, L2, thriving in the arid Merzouga desert, displayed a similar identity to Naganishia albida (99.84%). Yeast strains were tolerant to NaCl (2M) and 60% PEG (polyethylene glycol P6000) in case of drought. Both strains could solubilize phsphorus, with L2 additionally demonstrating potassium solubilization. In addition, both strains produce indole acetic acid (up to 135µl ml-1), have siderophore ability, and produce aminocyclopropane-1-carboxylic acid deaminase. Isolates L1 and L2, and their consortium showed that the single or combined strain inoculation of M. sativa improved plant growth, development, and nutrient assimilation. These findings pave the way for harnessing yeast-based solutions in agricultural practices, contributing to enhanced crop productivity and environmental sustainability.

Bioprospecting of endophytic fungi from medicinal plant Anisomeles indica L. for their diverse role in agricultural and industrial sectors

Endophytes are microorganisms that inhabit various plant parts and cause no damage to the host plants. During the last few years, a number of novel endophytic fungi have been isolated and identified from medicinal plants and were found to be utilized as bio-stimulants and bio fertilizers. In lieu of this, the present study aims to isolate and identify endophytic fungi associated with the leaves of Anisomeles indica L. an important medicinal plant of the Terai-Duars region of West Bengal. A total of ten endophytic fungi were isolated from the leaves of A. indica and five were identified using ITS1/ITS4 sequencing based on their ability for plant growth promotion, secondary metabolite production, and extracellular enzyme production. Endophytic fungal isolates were identified as Colletotrichum yulongense Ai1, Colletotrichum cobbittiense Ai2, Colletotrichum alienum Ai2.1, Colletotrichum cobbittiense Ai3, and Fusarium equiseti. Five isolates tested positive for their plant growth promotion potential, while isolates Ai4. Ai1, Ai2, and Ai2.1 showed significant production of secondary metabolites viz. alkaloids, phenolics, flavonoids, saponins, etc. Isolate Ai2 showed maximum total phenolic concentration (25.98 mg g−1), while isolate Ai4 showed maximum total flavonoid concentration (20.10 mg g−1). Significant results were observed for the production of extracellular enzymes such as cellulases, amylases, laccases, lipases, etc. The isolates significantly influenced the seed germination percentage of tomato seedlings and augmented their growth and development under in vitro assay. The present work comprehensively tested these isolates and ascertained their huge application for the commercial utilization of these isolates both in the agricultural and industrial sectors.

Apoplast-associated Bacillus amyloliquefaciens LAS10 for plant growth promotion and drought stress tolerance in little millet (Panicum sumatransae)

Bacterial endophytes thriving in the apoplast could be tailored to withstand environmental challenges, thereby contributing to plant stress resilience. Developing plant growth-promoting (PGP) bacteria resilient to drought is crucial for sustainable agriculture and improved crop production under stress conditions. Thus, the present study aimed to decode the drought-tolerant apoplast-associated PGP bacteria from little millet (Panicum sumatrense L.) and profile its functional traits including the metabolites for PGP and drought resilience. The drought tolerant PGP bacterial isolates from apoplastic fluids of little millet (Var. ATL1) grown under stressed conditions (-10 bars) on polyethylene glycol (PEG) (PEG 6000) infused agar plates revealed that a total of 12 isolates, were initially screened for their ability to tolerate drought up to –36.6 bars (–3.6 MPa) and of which, 6 isolates (LAS1, LAS2, LAS4, LAS6, LAS9, and LAS10) were selected. Further, screening for their plant growth-promoting (PGP) traits such as 1-aminocyclopropane-1-carboxylate deaminase (ACCd) production, exopolysaccharide production, potassium (K), phosphorous (P), and Zinc (Zn) nutrition, indole acetic acid (IAA) production, siderophore production, ammonia, and hydrogen cyanide (HCN) exhibited higher PGP potentials in LAS10 followed by LAS2 and LAS4. Of three potential isolates (LAS10, LAS2, and LAS4), LAS10 produced the highest ACCd (147 n moles α- ketobutyrate mg–1h–1), IAA (15.9 μg mL–1), siderophore (54.9 % units) and P solubilization compared to other isolates. Further, isolate LAS10 was identified as Bacillus amyloliquefaciens based on 16S rRNA sequence analysis. Metabolite profiling of B. amyloliquefaciens LAS10 in GC–MS under induced stress conditions yielded several drought-tolerant metabolites belonging to the class viz., organic acids, fatty acids, amino acid and its derivatives, organoheterocyclic compounds, and benzenoids. The compounds responsible for drought tolerance such as phenol, proline, fumaric acid, ascorbic acid, and gibberellic acid are more pronounced under induced drought stress (PEG 6000) which would aid in drought stress tolerance and facilitate plant health and fitness. These results implied that B. amyloliquefaciens LAS10, an apoplast-associated drought-tolerant endophytic bacteria, would enhance plant growth under drought stress, and can be further extrapolated as a newer bio inoculant for abiotic stress mitigation and sustainable production in little millet.

Duckweed-associated bacteria as plant growth-promotor to enhance growth of Spirodela polyrhiza in wastewater effluent from a poultry farm.

Duckweed has been highlighted as an invaluable resource because of its abilities to remove nitrogen and phosphorus from wastewater coupling with the production of high starch/protein-containing plant biomass. Duckweed recruits microbes and particularly forms a stable "core" bacterial microbiota, which greatly reduces the colonization efficiency of plant growth-promoting bacteria (PGPB). In this study, natural duckweeds were enriched in a sterilized-partially treated wastewater effluent from a poultry farm. After 24days of cultivation, the duckweed-associated bacteria (DAB) were isolated and evaluated for their plant growth-promoting (PGP) potentials by co-cultivation with axenic Spirodela polyrhiza. Ten species were found in more than one location and could be considered candidates for the stable "core" DAB. Among them, all isolates of Acinetobacter soli, Acidovorax kalamii, Brevundimonas vesicularis, Pseudomonas toyotomiensis, and Shinella curvata increased duckweed growth in Hoagland medium. The highest PGP ability was observed in Sh. curvata W12-8 (with EPG value of 208.72%), followed by Paracoccus marcusii W7-16 (171.31%), Novosphingobium subterraneum W5-13 (156.96%), and Ac. kalamii W7-18 (156.96%). However, the highest growth promotion in the wastewater was observed when co-cultured with W7-16, which was able to increase biomass dry weight and root length of duckweed by 3.17 and 2.26 folds, respectively.

Potential of psychrotolerant rhizobacteria for the growth promotion of wheat (Triticum aestivum L.).

Wheat is the second most important staple crop grown and consumed worldwide. Temperature fluctuations especially the cold stress during the winter season reduces wheat growth and grain yield. Psychrotolerant plant growth-promoting rhizobacteria (PGPR) may improve plant stress-tolerance in addition to serve as biofertilizer. The present study aimed to isolate and identify PGPR, with the potential to tolerate cold stress for subsequent use in supporting wheat growth under cold stress. Ten psychrotolerant bacteria were isolated from the wheat rhizosphere at 4°C and tested for their ability to grow at wide range of temperature ranging from -8°C to 36°C and multiple plant beneficial traits. All bacteria were able to grow at 4°C to 32°C temperature range and solubilized phosphorus except WR23 at 4°C, whereas all the bacteria solubilized phosphorus at 28°C. Seven bacteria produced indole-3-acetic acid at 4°C, whereas all produced indole-3-acetic acid at 28°C. Seven bacteria showed the ability to fix nitrogen at 4°C, while all the bacteria fixed nitrogen at 28°C. Only one bacterium showed the potential to produce cellulase at 4°C, whereas four bacteria showed the potential to produce cellulase at 28°C. Seven bacteria produced pectinase at 4°C, while one bacterium produced pectinase at 28°C. Only one bacterium solubilized the zinc at 4°C, whereas six bacteria solubilized the zinc at 28°C using ZnO as the primary zinc source. Five bacteria solubilized the zinc at 4°C, while seven bacteria solubilized the zinc at 28°C using ZnCO3 as the primary zinc source. All the bacteria produced biofilm at 4°C and 28°C. In general, we noticed behavior of higher production of plant growth-promoting substances at 28°C, except pectinase assay. Overall, in vitro testing confirms that microbes perform their inherent properties efficiently at optimum temperatures rather than the low temperatures due to high metabolic rate. Five potential rhizobacteria were selected based on the in vitro testing and evaluated for plant growth-promoting potential on wheat under controlled conditions. WR22 and WR24 significantly improved wheat growth, specifically increasing plant dry weight by 42% and 58%, respectively. 16S rRNA sequence analysis of WR22 showed 99.78% similarity with Cupriavidus campinensis and WR24 showed 99.9% similarity with Enterobacter ludwigii. This is the first report highlighting the association of C. campinensis and E. ludwigii with wheat rhizosphere. These bacteria can serve as potential candidates for biofertilizer to mitigate the chilling effect and improve wheat production after field-testing.

Functional Characterization of Rhizobia for Multiple Plant Growth Promoting Activities

This research focuses on the functional characterization of 19 rhizobia strains isolated from Southern Rajasthan's Udaipur and Dungarpur districts, with an emphasis on their multiple Plant Growth Promoting (PGP) activities. Through a series of tests encompassing Indole-3-Acetic Acid (IAA) production, siderophore production, phosphate solubilization, ammonia production, and hydrogen cyanide (HCN) production, this study elucidates the diverse PGP potential of these rhizobia strains. The results showcase variations in IAA production, highlighting their ability to enhance root development and overall plant growth, while also revealing strains capable of siderophore production, indicating potential iron uptake facilitation. Furthermore, some strains exhibit phosphate solubilization, ammonia production, and HCN production capabilities, signifying their potential to improve nutrient availability and protect plants from pathogens. These findings underscore the promise of harnessing the PGP activities of these rhizobia strains for sustainable agricultural practices in Southern Rajasthan and similar agroecological regions, with implications for enhanced crop yields and soil health.

New endophytic strains of Trichoderma promote growth and reduce clubroot severity of rapeseed (Brassica napus).

Rapeseed (Brassica napus L.) is the world's third most important edible oilseed crop after soybean and palm. The clubroot disease caused by Plasmodiophora brassicae poses a significant risk and causes substantial yield losses in rapeseed. In this study, 13 endophytic fungal strains were isolated from the healthy roots of rapeseed (B. napus) grown in a clubroot-infested field and molecularly identified. Based on germination inhibition of resting spores of P. brassicae, two endophytic fungal antagonists, Trichoderma spp. ReTk1 and ReTv2 were selected to evaluate their potential for plant growth promotion and biocontrol of P. brassicae. The Trichoderma isolates were applied as a soil drench (1×107 spore/g soil) to a planting mix and field soil, in which plants were grown under non-infested and P. brassicae-infested (2×106 spore/g soil) conditions. The endophytic fungi were able to promote plant growth, significantly increasing shoot and root length, leaf diameter, and biomass production (shoots and root weight) both in the absence or presence of P. brassicae. The single and dual treatments with the endophytes were equally effective in significantly decreasing the root-hair infection, root index, and clubroot severity index. Both ReTk1 and ReTv2 inhibited the germination of resting spores of P. brassicae in root exudates. Moreover, the endophytic fungi colonized the roots of rapeseed extensively and possibly induced host resistance by up-regulated expression of defense-related genes involved in jasmonate (BnOPR2), ethylene (BnACO and BnSAM3), phenylpropanoid (BnOPCL and BnCCR), auxin (BnAAO1) and salicylic acid (BnPR2) pathways. Based on these findings, it is evident that the rapeseed root endophytes Trichoderma spp. ReTk1 and ReTv2 could suppress the gall formation on rapeseed roots via antibiosis, induced systemic resistance (ISR), and/or systemic acquired resistance (SAR). According to our knowledge, this is the first report of the endophytic Trichoderma spp. isolated from root tissues of healthy rapeseed plants (B. napus.), promoting plant growth and reducing clubroot severity.

Mineral Solubilizing Rhizobacterial Strains Mediated Biostimulation of Rhodes Grass Seedlings.

Minerals play a dynamic role in plant growth and development. However, most of these mineral nutrients are unavailable to plants due to their presence in fixed forms, which causes significant losses in crop production. An effective strategy to overcome this challenge is using mineral solubilizing bacteria, which can convert insoluble forms of minerals into soluble ones that plants can quickly assimilate, thus enhancing their availability in nutrient-depleted soils. The main objective of the present study was to isolate and characterize mineral solubilizing rhizobacteria and to assess their plant growth-promoting potential for Rhodes grass. Twenty-five rhizobacterial strains were isolated on a nutrient agar medium. They were characterized for solubilization of insoluble minerals (phosphate, potassium, zinc, and manganese), indole acetic acid production, enzymatic activities, and various morphological traits. The selected strains were also evaluated for their potential to promote the growth of Rhodes grass seedlings. Among tested strains, eight strains demonstrated strong qualitative and quantitative solubilization of insoluble phosphate. Strain MS2 reported the highest phosphate solubilization index, phosphate solubilization efficiency, available phosphorus concentration, and reduction in medium pH. Among tested strains, 75% were positive for zinc and manganese solubilization, and 37.5% were positive for potassium solubilization. Strain MS2 demonstrated the highest quantitative manganese solubilization, while strains MS7 and SM4 reported the highest solubilization of zinc and potassium through acidifying their respective media. The strain SM4 demonstrated the most increased IAA production in the presence and absence of L-tryptophan. The majority of strains were positive for various enzymes, including urease, catalase protease, and amylase activities. However, these strains were negative for coagulase activity except strains SM7 and MS7. Based on 16S rRNA gene sequencing, six strains, namely, SM2, SM4, SM5, MS1, MS2, and MS4, were identified as Bacillus cereus, while strains SM7 and MS7 were identified as Staphylococcus saprophyticus and Staphylococcus haemolyticus. These strains significantly improved growth attributes of Rhodes grass, such as root length, shoot length, and root and shoot fresh and dry biomasses compared to the uninoculated control group. The present study highlights the significance of mineral solubilizing and enzyme-producing rhizobacterial strains as potential bioinoculants to enhance Rhodes grass growth under mineral-deficient conditions sustainably.