Growth-promoting Characteristics Research Articles

Evaluating Plant Growth-Promoting Rhizobacteria to Improve the Productivity of Forage Pearl Millet.

India's livestock industry is grappling with a shortage of green fodder, necessitating concerted efforts to boost organized production and ensure a sufficient supply of high-quality forages, crucial for formulating nutritionally balanced, cost-effective, and rumen-healthy animal diets. Hence, this study was conducted to assess the plant growth-promoting characteristics of liquid microbial inoculants and their impact on the yield of forage pearl millet. The bacterial cultures utilized included Sphingobacterium sp., Stenotrophomonas maltophilia, and an isolate from vegetable cowpea, subsequently identified as Burkholderia seminalis. These cultures were initially characterized for their plant growth-promoting traits at different temperature and physiological conditions. All the bacterial cultures were found promising for PGPR traits over varied temperature conditions and the optimum activity was recorded at 40°C, with tolerance to saline and drought stresses as well as wide pH and temperature ranges. A field experiment was conducted during kharif 2020 at Punjab Agricultural University, Ludhiana and Punjab Agricultural University, Regional Research Station, Bathinda, involving combinations of liquid microbial inoculants along with 100% Recommended Dose of Fertilizer (RDF). It was observed that the treatment including B. seminalis + S. maltophilia along with RDF yielded the highest green fodder and dry matter yield, In conclusion, it is evident that the utilization of these liquid microbial inoculants holds significant potential for playing a pivotal role in the integrated nutrient management of forage pearl millet, thereby contributing to heightened productivity and sustained soil health.

Diversity and growth-promoting characteristics of rhizosphere bacteria of three naturally growing plants at the sand iron ore restoration area in Qinghe County

It is a great challenge to restore northern mines after mining and achieve optimal results due to the extremely harsh environment and climate, as in Qinghe County of Xinjiang Province, China. Qinghe County has a climate of drought, cold, strong winds, and high altitude. After sand and iron mining, the soil in this area contains a large amount of sand and gravel with extremely low organic matter, nitrogen deficiency, and a high pH of 9.26. Our preliminary studies disclosed that only three plants, including Caligonum junceum, Atraphaxis virgata, and Melilotus albus Medic, can grow naturally in this environment without any artificial management. For effective ecology restoration, this study explored the mechanism of plant-microbial interaction and stress resistance in this environment. It was found that although the soil condition in the sand iron ore landfill area is extreme, the bacterial diversity remained high, with Shannon and Simpson indices reaching 9.135 and 0.994, respectively. The planting of three types of remediation plants did not significantly improve, or even decreased, the soil bacterial diversity index, but greatly changed the composition of dominant bacterial genera. Significant differences in the composition of rhizosphere soil bacterial communities among these three remediation plants were observed. Potential new bacterial species accounted for 9.8 %, and the proportion of unique genera reached 30 % or 50 %, respectively. Among all the isolated strains, 74 % had nitrogen fixation and other growth-promoting properties. In summary, the soil microbial community structure in this extreme environment is unique and diverse. The types of remediation plants play a major role in the composition of the rhizosphere bacterial community structure, and the recruited growth-promoting bacteria are diverse and functional. This study may offer valuable information for further studies in vegetation restoration and aid in ecology restoration, especially under extreme conditions.

The novel Pseudomonas thivervalensis strain JI6 promotes growth and controls rusty root rot disease in Panax ginseng

The bacterial strain JI6, which has plant growth-promoting characteristics, was isolated from ginseng rhizosphere soil. It can produce indoleacetic acid (IAA), dissolve phosphorus, dissolve potassium and fix nitrogen and significantly promoted the growth of ginseng. The strain was identified as Pseudomonas thivervalensis by morphological, physiological and biochemical characteristics and 16S rDNA sequence analysis. The bud length of ginseng seeds treated with 109 CFU/mL JI6 suspension increased significantly by 42.76 % after 15 days. The fresh weight and the ginsenoside content of 3-year-old ginseng roots significantly increased by 38.72 % and 24.20 %, respectively with the 108 CFU/mL JI6 suspension for five months in the field. The strain JI6 can inhibit the six fungal pathogens and control rusty root rot of ginseng. For the biocontrol mechanism, the strain JI6 can colonize in ginseng rhizosphere soil. After treatment with JI6, the activitie of five ginseng defence enzymes of β-1.3 glucanase, peroxidase and phenylalanine ammonia-lyase, chitinase and superoxide dismutase and four soil enzymes of urease, phosphatase, invertase, and catalase significantly increased. The effect of strain JI6 on soil microbial community showed that the microbial diversity increased and the abundance of beneficial microorganisms elevated, while the abundance of pathogenic microorganisms decreased. This study indicate the great potential of P. thivervalensis JI6 for use as a biological agent for the control of ginseng rusty root rot.

The Research of Antagonistic Endophytic Bacterium Bacillus velezensis CSUFT-BV4 for Growth Promotion and Induction of Resistance to Anthracnose in Camellia oleifera.

Camellia oleifera (C. oleifera) is one of the four main, woody, edible oil tree species in the world, while C. oleifera anthracnose is mainly caused by the fungus Colletotrichum fructicola (C. fructicola), which severely affects the yield of C. oleifera and the quality of tea oil. Bacillus velezensis (B. velezensis) CSUFT-BV4 is an antagonistic endophytic bacterium isolated from healthy C. oleifera leaves. This study aimed to investigate the biocontrol potential of strain CSUFT-BV4 against C. oleifera anthracnose and its possible functional mechanism, and to determine its growth-promoting characteristics in host plants. In vitro, CSUFT-BV4 was shown to have efficient biofilm formation ability, as well as significant functions in the synthesis of metabolic substances and the secretion of probiotic substances. In addition, the CSUFT-BV4 fermentation broth also presented efficient antagonistic activities against five major C. oleifera anthracnose pathogens, including C. fructicola, C. gloeosporioides, C. siamense, C. camelliae, and C. kahawae, and the inhibition rate was up to 73.2%. In vivo, it demonstrated that the growth of C. oleifera treated with CSUFT-BV4 fermentation broth was increased in terms of stem width, plant height, and maximum leaf area, while the activities of various defense enzymes, e.g., superoxide dismutase (SOD), phenylalanine aminotransferase (PAL), and polyphenol oxidase (PPO), were effectively increased. The remarkable antagonistic activities against C. oleifera anthracnose, the growth-promoting characteristics, and the induction of host defense responses indicate that endophytic bacterium CSUFT-BV4 can be effectively used in the biological control of C. oleifera anthracnose in the future, which will have a positive impact on the development of the C. oleifera industry.

Effects of Klebsiella michiganensis LDS17 on Codonopsis pilosula growth, rhizosphere soil enzyme activities, and microflora, and genome-wide analysis of plant growth-promoting genes.

We comprehensively evaluated the plant growth-promoting characteristics and heavy metal (HM) resistance ability of the LDS17 strain, as well as the effects of strain LDS17 inoculation on the Codonopsis pilosula seedling growth and the soil qualities in the Codonopsis pilosula rhizosphere. We conducted whole-genome analysis and identified lots of genes and gene clusters contributing to plant-beneficial functions and HM resistance, which is critical for further elucidating the plant growth-promoting mechanism of strain LDS17 and expanding its application in the development of plant growth-promoting agents used in the environment under HM stress.

Amelioration of growth of maize (Zea mays L.) seedling using plant growth promoting bacteria

This research was aimed to screen plant growth promoting bacteria (PGPB) from soil and study its effect on maize plant growth. PGPB were isolated from Saurashtra coastal region soil and cultured in Nitrogen fixing Ashby’s medium to find potent of PGPBs, we conducted a thorough screening process, assessed their abilities in phosphate and zinc solubilization, siderophore production, hydrogen cyanide (HCN) release and the antifungal activity was performed against Fusarium oxysporum, a pathogenic fungus. These tests helped us identify bacteria with plant growth-promoting characteristics for plants. Bacterial isolates which provided better results were sequenced and sequences were submitted to NCBI. Bacterial isolates selected for application on maize in primary screening showed most treated seeds increased the seedling vigor of maize. In the latter stages of screening where bacterial consortia were developed from primary and secondary screening. In 30 days, the experiment in maize plant height, number of leaves, chlorophyll content and anatomy was analysed. All the bacterium consortiums displayed an increase in height (24.75%), number of leaves (47.77%) and total chlorophyll content (23.59%) as compared to the control maize plant. Additionally, microscopic examination of the treated plants showed improved growth, especially in the increased starch grain content in the leaves, stems and roots. Out of the eleven PGPB consortia, 3 specific PGPB consortia in this study have significantly substantiated the growth of maize plants as evidenced by the comprehensive analysis of anatomical features.

Selection of the Dominant Endophytes Based on Illumina Sequencing Analysis for Controlling Bacterial Wilt of Patchouli Caused by Ralstonia solanacearum.

Bacterial wilt caused by Ralstonia solanacearum (RS) is one of the most devastating diseases in patchouli (Pogostemon cablin [Blanco] Benth.), which results in low yield and quality of patchouli. However, no stable and effective control methods have been developed yet. To evaluate the potential of dominant bacterial endophytes in biocontrol, the endophytic bacterial diversity of patchouli was investigated based on Illumina sequencing analysis, and the ability of isolates belonging to the dominant bacterial genera to control RS wilt of patchouli was explored in pot experiments. A total of 245 bacterial genera were detected in patchouli plants, with the highest relative abundance of operational taxonomic units belonging to the genus Pseudomonas detected in roots, leaves, and stems. The Pseudomonas isolates S02, S09, and S26 showed antagonistic activity against RS in vitro and displayed many plant growth-promoting characteristics, including production of indole-3-acetic acid, siderophores, and 1-aminocyclopropane-1-carboxylic acid deaminase and phosphate- and potassium-solubilizing capability. Inoculation of patchouli plants with the isolates S02, S09, and S26 significantly improved shoot growth and decreased the incidence of bacterial wilt caused by RS. The results suggest that screening of dominant bacterial endophytes for effective biocontrol agents based on Illumina sequencing analysis is more efficient than random isolation and screening procedures.

Cadmium-resistant bacterium Ralstonia sp. YDR alleviated Cd toxicity in rice seedlings by enhancing antioxidant defense and inhibiting Cd2+ influx and H+ efflux

Cadmium (Cd) accumulation in rice (Oryza sativa L.) and its potential risks for human health have attracted great attention. Several Cd-resistant bacteria can promote plant growth and alleviate Cd toxicity to rice, but how they regulate Cd2+ flux in rice roots is still poorly understood. Here, a new Cd-resistant endophytic bacterium Ralstonia sp. YDR was isolated and used to evaluate its role in reducing rice Cd accumulation. Ralstonia sp. YDR tolerated 80 mg L−1 Cd and removed amounts of Cd via bio-adsorption and bio-absorption. Ralstonia sp. YDR also harbored good alkalizing ability and exhibited typical plant growth-promoting characteristics. Hydroponic experiment showed that inoculation with Ralstonia sp. YDR not only significantly promoted rice growth but also decreased rice Cd by 14.4–41.3%. Further analyses verified the involvement of Ralstonia sp. YDR in increasing the activities of catalase, glutathione, peroxidase, and superoxide dismutase by 27.7–77.3%, 1.7–57.6%, 57.4–100.8%, and 5.31–60.2%, and decreasing the activity of malonaldehyde by up to 56% in rice seedlings as compared with control. Moreover, a significant reduction in Cd2+ influx and H+ efflux occurred in rice roots after inoculating with Ralstonia sp. YDR. Collectively, bacterial adsorption and absorption of Cd, bacteria-aided antioxidation, and bacterial regulation of Cd2+ and H+ fluxes all contributed to a low Cd accumulation in rice. Our study provides new clues to better understand microbial mechanisms underlying the low Cd accumulation in rice plants, which helps to enhance the production of low Cd rice in agricultural practice.

Comparative Analysis of Plant Growth-Promoting Rhizobacteria's Effects on Alfalfa Growth at the Seedling and Flowering Stages under Salt Stress.

Alfalfa (Medicago sativa L.), a forage legume known for its moderate salt-alkali tolerance, offers notable economic and ecological benefits and aids in soil amelioration when cultivated in saline-alkaline soils. Nonetheless, the limited stress resistance of alfalfa could curtail its productivity. This study investigated the salt tolerance and growth-promoting characteristics (in vitro) of four strains of plant growth-promoting rhizobacteria (PGPR) that were pre-selected, as well as their effects on alfalfa at different growth stages (a pot experiment). The results showed that the selected strains belonged to the genera Priestia (HL3), Bacillus (HL6 and HG12), and Paenibacillus (HG24). All four strains exhibited the ability to solubilize phosphate and produce indole-3-acetic acid (IAA) and 1-aminocyclopropane-1-carboxylate (ACC) deaminase. Among them, except for strain HG24, the other strains could tolerate 9% NaCl stress. Treatment with 100 mM NaCl consistently decreased the IAA production levels of the selected strains, but inconsistent changes (either enhanced or reduced) in terms of phosphate solubilization, ACC deaminase, and exopolysaccharides (EPS) production were observed among the strains. During the various growth stages of alfalfa, PGPR exhibited different growth-promoting effects: at the seedling stage, they enhanced salt tolerance through the induction of physiological changes; at the flowering stage, they promoted growth through nutrient acquisition. The current findings suggest that strains HL3, HL6, and HG12 are effective microbial inoculants for alleviating salt stress in alfalfa plants in arid and semi-arid regions. This study not only reveals the potential of indigenous salt-tolerant PGPR in enhancing the salt tolerance of alfalfa but also provides new insights into the mechanisms of action of PGPR.

Mitigation of Salt Stress in Rice by the Halotolerant Plant Growth-Promoting Bacterium Enterobacter asburiae D2.

Salinity is a major abiotic stress that seriously affects crop growth worldwide. In this work, we aimed to isolate potential halotolerant plant growth-promoting rhizobacteria (PGPR) to mitigate the adverse impacts of salt stress in rice. An isolate, D2, with multiple plant growth-promoting (PGP) characteristics was identified as Enterobacter asburiae D2. Strain D2 could produce indole-3-acetic acid and siderophore. It also exhibited phosphate solubilization and 1-aminocyclopropane-1-carboxylic deaminase activity. Genome analysis further provided insights into the molecular mechanism of its PGP abilities. Strain D2 inoculation efficiently stimulated rice growth under both normal and saline conditions. Compared with the non-inoculated plants, a significant increase in plant height (18.1-34.7%), root length (25.9-57.1%), root dry weight (57.1-150%), and shoot dry weight (17.3-50.4%) was recorded in inoculated rice seedlings. Meanwhile, rice seedlings inoculated with strain D2 showed improvement in chlorophyll and proline content, while the oxidant damage was reduced in these plants in comparison with the control group. Moreover, the K+/Na+ ratio of the inoculated rice seedlings exposed to NaCl and Na2CO3 was higher than that of the uninoculated groups. These results imply that Enterobacter asburiae D2 is a potential PGPR that can be used for alleviation of salt stress in rice.

Development of a composite microbial agent beneficial to improve drought and salt tolerance of Glycyrrhiza uralensis Fisch.

Plant growth is enhanced by microbiological agents. In order to develop environment friendly composite microbial agent that can also improve the salt and drought tolerance of plants, the orthogonal experiment and response surface methodology were used to screen nutrients and fermentation conditions of composite microbial agent, and pot experiment was conducted to validate the application effect of optimized and complex microbial agent. Compatibility test showed that G2 (Bacillus cereus) and G5 (Bacillus pumilus) did not show any inhibitory effect on each other’s growth in nutrient agar, moreover, in both the growth promotion characteristics and the seed germination tests, G2+G5 showed a synergistic effect. The process optimization results showed that the optimal carbon and nitrogen sources for the medium nutrients was maltose and yeast extract, and the optimal carbon-nitrogen ratio was 5:1; the optimal fermentation conditions included initial pH at 5.17, inoculation amount of 2.28%, liquid volume of 105.96 mL(250 mL)−1, and incubation temperature at 30.06℃. Pot experiment showed that application with composite microbial agent was able to increase antioxidant enzyme activities, ascorbat, proline content, and reduce reactive oxygen species accumulation and membrane peroxidation of G. uralensis seedlings under salt-drought stress. In conclusion, the composite G2+G5 agent possessed remarkable synergistic effect for improve plant tolerance to drought combined with salt stress, suggesting a noticeble practical potential in agricultural practice, and it can be used to develop newtype environment friendly microbial fertilizer.

Harnessing the Power of Zinc-Solubilizing Bacteria: A Catalyst for a Sustainable Agrosystem

A variety of agrochemicals, especially fertilizers, are applied indiscriminately by farmers across trapezoidal landscapes to increase productivity and satisfy the rising food demand. Around one-third of the populace in developing nations is susceptible to zinc (Zn) deficiency as a result of their direct reliance on cereals as a source of calories. Zinc, an essential micronutrient for plants, performs several critical functions throughout the life cycle of a plant. Zinc is frequently disregarded, due to its indirect contribution to the enhancement of yield. Soil Zn deficiency is one of the most prevalent micronutrient deficiencies that reduces crop yield. A deficiency of Zn in both plants and soils results from the presence of Zn in fixed forms that are inaccessible to plants, which characterizes the majority of agricultural soils. As a result, alternative and environmentally sustainable methods are required to satisfy the demand for food. It appears that the application of zinc-solubilizing bacteria (ZSB) for sustainable agriculture is feasible. Inoculating plants with ZSB is likely a more efficacious strategy for augmenting Zn translocation in diverse edible plant components. ZSB possessing plant growth-promoting characteristics can serve as bio-elicitors to promote sustainable plant growth, through various methods that are vital to the health and productivity of plants. This review provides an analysis of the efficacy of ZSB, the functional characteristics of ZSB-mediated Zn localization, the mechanism underlying Zn solubilization, and the implementation of ZSB to increase crop yield.

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.

Occurrence of diverse plant growth promoting bacteria in soybean [Glycine max (L.) Merrill] root nodules and their prospective role in enhancing crop yield

Root nodules are the small nitrogen fixing factories housing endophytic bacteria. In this study, seventeen endophytic bacteria were isolated from the root nodules of soybean, which were subjected to the in vitro testing of plant growth-promoting characteristics. Bacterial isolates were able to produce indole acetate ranging from 0.7 to 18.3 μg ml−1. Five isolates were able to solubilize inorganic phosphate, in which NSB15 exhibited maximum solubilization potential. All bacterial isolates showed growth on nitrogen-free mineral media, except NSB7 and NSB11. Bacterial isolates were able to form biofilm, therein NSB10 displayed a maximum efficiency of 2.6 at OD570 nm. Seven isolates were positive for cellulase activity and five for pectinase activity. Based on the in vitro characterization, five efficient endophytic bacteria were phylogenetically identified by 16 S rRNA sequence analysis. NSB5 showed 99.52% identity with different species of Pseudomonas, and NSB9 showed 99.68% sequence identity with Bradyrhizobium. NSB15 and NSB16 showed maximum sequence identity with Comamonas terrigena, and NSB17 showed 100% sequence identity with Pseudomonas indica. This study represents the first international report of C. terrigena and P. indica in soybean host. In a pot experiment, inoculation of NSB9 and NSB17 significantly increased plant dry weight by 29% and 35%, respectively, compared to control. In a field trial, inoculation of NSB9, NSB15 and NSB17 significantly improved grain yield by 30%, 31% and 45%, respectively, compared to control. Conclusively, Bradyrhizobium sp. NSB9, C.terrigena NSB15 and P.indica NSB17 could be used as biofertilizers to improve the yield of soybean in a sustainable manner.

Effects of Combined Stress of High Density Polyethylene Microplastics and Chlorimuron-ethyl on Soybean Growth and Rhizosphere Bacterial Community

With the vigorous development of agriculture in China， plastic mulch film and pesticides are widely used in agricultural production. However， the accumulation of microplastics （formed by the degradation of plastic mulch film） and pesticides in soil has also caused many environmental problems. At present， the environmental biological effects of microplastics or pesticides have been reported， but there are few studies on the combined effects on crop growth and the rhizosphere soil bacterial community. Therefore， in this study， the high density polyethylene microplastics （HDPE， 500 mesh） were designed to be co-treated with sulfonylurea herbicide chlorimuron-ethyl to study their effects on soybean growth. In addition， the effects of the combined stress of HDPE and chlorimuron-ethyl on soybean rhizosphere soil bacterial community diversity， structure composition， microbial community network， and soil function were investigated using high-throughput sequencing technology， interaction network， and PICRUSt2 function analysis to clarify the combined toxicity of HDPE and chlorimuron-ethyl to soybean. The results showed that the half-life of chlorimuron-ethyl in soil was prolonged by the 1% HDPE treatment （from 11.5 d to 14.3 d）， and the combined stress of HDPE and chlorimuron-ethyl had more obvious inhibition effects on soybean growth than that of the single pollutant or control. The HiSeq 2 500 sequencing showed that the rhizosphere bacterial community of soybean was composed of 20 phyla and 312 genera under combined stress， the number of phyla and genera was significantly less than that of the control and single pollutant treatment， and the relative abundances of bacteria with potential biological control and plant growth-promoting characteristics （such as Nocardioides and Sphingomonas） were reduced. Alpha diversity analysis showed that the combined stress significantly reduced the richness and diversity of the soybean rhizosphere bacterial community， and Beta diversity analysis showed that the combined stress significantly changed the structure of the bacterial community. The dominant flora of the rhizosphere bacterial community were regulated， and the abundances of secondary functional layers such as amino acid metabolism， energy metabolism， and lipid metabolism were reduced under combined stress by the analysis of LEfSe and PICRUSt2. It was inferred from the network analysis that the combined stress of HDPE and chlorimuron-ethyl reduced the total number of connections and network density of soil bacteria， simplified the network structure， and changed the important flora species to maintain the stability of the network. The results above indicated that the combined stress of HDPE and chlorimuron-ethyl significantly affected the growth of soybean and changed the rhizosphere bacterial community structure， soil function， and network structure. Compared with that of the single pollutant treatment， the potential risk of combined stress was greater. The results of this study can provide guidance for evaluating the ecological risks of polyethylene microplastics and chlorimuron-ethyl and for the remediation of contaminated soil.

Identification of synthetic consortia from a set of plant-beneficial bacteria.

The use of microbial inoculants in agriculture as biofertilisers and/or biopesticides is an appealing alternative to replace or reduce the practice of agrochemicals. Plant microbiota studies are revealing the different bacterial groups which are populating plant microbiomes re-energising the plant probiotic bacteria (PPB) translational research sector. Some single-microbial strain bioinoculants have proven valid in agriculture (e.g., based on Trichoderma, mycorrhiza or rhizobia); however, it is now recommended to consider multistrain consortia since plant-beneficial effects are often a result of community-level interactions in plant microbiomes. A limiting step is the selection of a fitting combination of microbial strains in order to accomplish the best beneficial effect upon plant inoculation. In this study, we have used a subset of 23 previously identified and characterised rice-beneficial bacterial colonisers to design and test a series of associated experiments aimed to identify potential PPB consortia which are able to co-colonise and induce plant growth promotion. Bacterial strains were co-inoculated in vitro and in planta using several different methods and their co-colonisation and co-persistence monitored. Results include the identification of two 5-strain and one 2-strain consortia which displayed plant growth-promoting features. Future practical applications of microbiome research must include experiments aimed at identifying consortia of bacteria which can be most effective as crop amendments.

Biological control of root-knot nematodes in common beans using putative nematocidal species of Trichoderma indigenous to Pakistan

ABSTRACT The putative nematocidal strains of Trichoderma for controlling root-knot nematodes were isolated from different agricultural fields in Pakistan. The Trichoderma isolates were confirmed using morphological and molecular characterisation. The root-knot nematodes were isolated from infected common bean plants Phaseolus vulgaris and identified as Meloidogyne incognita through phenotypic characteristics. Both in vitro and in vivo assays were performed. The nematocidal activity of the selected Trichoderma spp. was assessed using culture filtrate and spore suspension assays. Parameters including J2 mortality, egg hatching inhibition, root gall index, and egg mass index were calculated. The culture filtrates of T. bevicrassum strain ISO-03 caused significantly higher J2 mortality (71%) and inhibited egg hatching (68%) as compared to the activities of culture filtrates of the other two strains used in this study. The least control activity was observed in case of the culture filtrates of T. viride strain ISO-05 with 21% J2 mortality and 19% egg hatching inhibition. Similarly, the spore suspensions of T. brevicrassum ISO-03 showed the highest mortality of M. incognita juveniles (64% with respect to control) as well as the egg-hatching inhibition rates of 59%. In the in vivo study, the same strain T. bevicrassum ISO-03 significantly reduced the root galling index and egg mass indices as compared to the control. Furthermore, T. bevicrassum ISO-03 significantly promoted plant growth compared to the control. Overall, T. bevicrassum ISO-03 was identified as a potent biocontrol strain against root-knot nematodes in addition to its plant growth-promoting characteristics.

Isolation and characterization of rhizobacteria from lentil for arsenic resistance and plant growth promotion.

Low-cost microbial remediation strategies serve as a viable and potent weapon for curbing the arsenic menace. In the present study, two arsenic-resistant bacteria were isolated from the contaminated lentil rhizosphere in Gangetic plain of eastern India. LAR-21 (Burkholderia cepacia, MW356875) and LAR-25 (Burkholderia cenocepacia, MW356894) could remove 87.6% and 85.9% of arsenite (10mM) from the liquid culture medium in laboratory condition. They were highly resistant to arsenate and arsenite and also had a high arsenite oxidase activity. LAR-21 showed the highest level of minimum inhibitory concentration value of 390mM for arsenate and 31mM for arsenite. The same strain was found to show highest arsenite oxidase activity, i.e., 5.2nMmin-1mg-1of protein. These two strains further possess potential plant growth-promoting characteristics like indole acetic acid production (5-15mMIAAmL-1), 1-aminocyclopropane-1-carboxylate deaminase (8-21nMα-ketobutyratemgprotein-1h-1), nitrogenase activity (3-8.99nMethylenemgcellprotein-1h-1), siderophore production (17-22.1µMdeferoxaminemesylatemL-1), phosphate solubilization (261-453µgmL-1) under arsenic stress condition. The plant growth promotion of the strains was further validated by pot study of lentil by assessing their agronomic and growth-related traits, and potential to recover from arsenic stress (17.2-21.2% arsenic reduction in root and shoot, 16-19.2% in leaf and pod, and 15-23% reduction in seeds). The LAR-21 strain, thus, emerged as the most suited candidate for bioremediation and plant (lentil) growth promotion in arsenic polluted environment.

Effects of Disease Complex of Penicellium and Root Knot Nematode on The growth and Development of Chilli (Capsicum annum L.) Crop

The behaviour of fungal pathogens in a dormant or active state under different changes by infection of the host plant parasitic nematode was related to the function of fungi. Due to RKNs on the chilli in Meloidogyneinfected pot culture, Penicillium sp. demonstrated plant growth-promoting characteristics and nematocidal activities, according to the findings of the current study. This fungus can be used as a growth promoter in Treatments 2 and 3, where a mixture of Meloidogyne sp. and Penicelliumsp. showed higher growth rates and yellowing leaves in some pots, but no knots were found in the roots however, the current research may offer a theoretical basis for a growth promoter agent for better growth in Penicillium inoculated pots and In Nematode inoculated pots, Meloidogynesp can reduce plant growth. In both Meliodogynesp and Penicillium sp inoculated pots, it was demonstrated that decreasing nematode population increased the growth habits of chilies in terms of number of leaves Therefore, it has been demonstrated that Penicellium decreases nematocidal action while promoting growth parameters in chilli plants, and that using preventative measures can somewhat lessen insect infestation in control pots.

Unraveling the new member Bacillus pumilus SH-9 of Bacillaceae family and its potential role in seed biopriming to mitigate drought stress in Oryza sativa

Rice is an important cereal crop cultivated worldwide to meet the need of hungry populations. Drought stress is a major problem that reduces crop productivity by up to 50 %. Beneficial microbes have the potential to mitigate drought stress in various crops. The use of beneficial microorganisms in seed biopriming techniques enhances germination potential through the production of antioxidants and phytohormones. In this study, the novel bacterial strain SH-9 was isolated and screened for various biological and stress tolerance assays. SH-9 exhibited plant growth-promoting characteristics such as abscisic acid production (2.18 ± 0.05 ng/ml), phosphate solubilization index (4.69 ± 0.30), and sucrose production (0.72 ± 0.05 mg/ml). The oxidative stress tolerance assay also revealed remarkable production of the antioxidant molecules catalase, superoxide dismutase, and ascorbate peroxidase. Germination metrics were also measured through seed biopriming in the experimental plant (Oryza sativa) treated with SH-9. Surprisingly, SH-9 was found to be significantly drought-tolerant as it could tolerate drought up to 35 % PEG 6000. Seed biopriming enhanced the germination potential by up to 90 % and improved the seed vigor index, germination energy, and germination rate index. It also improved the seedling characteristics of rice compared with the control group. This study demonstrated that SH-9 has excellent potential to enhance the germination metrics even under stress. Molecular identification revealed that SH-9 is a new member of the Bacillaceae family with the gene accession number ON753949. Overall, it is expected that further research on seed biopriming employing SH-9 strain in plants will lead to this technique being employed as a form of sustainable management in agriculture.