Potassium Solubilizing Research Articles

Screening and promoting effect of grow-promoting fungi in rhizosphere of Angelica dahurica var. formosana

Excessive application of chemical fertilizer has caused many problems in Angelica dahurica var. formosana planting, such as yield decline and quality degradation. In order to promote the green cultivation mode of A. dahurica var. formosana and explore rhizosphere fungus resources, the rhizosphere fungi with nitrogen fixation, phosphorus solubilization, potassium solubilization, iron-producing carrier, and IAA-producing properties were isolated and screened in the rhizosphere of A. dahurica var. formosana from the genuine and non-genuine areas, respectively. The strains were identified comprehensively in light of the morphological characteristics and ITS rDNA sequences, and the growth-promoting effect of the screened strains was verified by pot experiment. The results showed that 37 strains of growth-promoting fungi were isolated and screened from the rhizosphere of A. dahurica var. formosana, mostly belonging to Fusarium. The cultured rhizosphere growth-promoting fungi of A. dahurica var. formosana were more abundant and diverse in the genuine producing areas than in the non-genuine producing areas. Among all strains, Aspergillus niger ZJ-17 had the strongest growth promotion potential. Under the condition of no fertilization outdoors, ZJ-17 inoculation significantly promoted the growth, yield, and accumulation of effective components of A. dahurica var. formosana planted in the soil of genuine and non-genuine producing areas, with yield increases of 73.59% and 37.84%, respectively. To a certain extent, it alleviated the restriction without additional fertilization on the growth of A. dahurica var. formosana. Therefore, A. niger ZJ-17 has great application prospects in increasing yield and quality of A. dahurica var. formosana and reducing fertilizer application and can be actually applied in promoting the growth of A. dahurica var. formosana and producing biofertilizer.

Exploring the Phosphate Solubilizing Potential and Acid-Alkaline Phosphatase Activity of Two Multitrait Heavy Metal Tolerant Bacterial Strains Isolated from North Gujarat, India

A study was conducted to isolate and characterize phosphate solubilizing bacteria (PSB) from soils of various locations in North Gujarat. A total of 40 PSB isolates were obtained, exhibiting a phosphate solubilizing index (PSI) ranging from 2.11 to 4.33. Interestingly, among 40 PSB isolates, a subset of 16 displayed an additional trait of potassium solubilization, as evidenced by their potassium solubilizing index (KSI) values falling within the range of 2.10 to 3.10. These 16 PSB isolates were screened for tolerance to heavy metal stressors, namely CdCl2, HgCl2, Pb(NO3)2, and ZnSO4, spanning a concentration gradient from 0.1 mM to 10 mM. Remarkably, among the tested isolates, two, namely, D4 and G2, exhibited exceptional resilience against the heavy metal stressors, as indicated by their minimum inhibitory concentration (MIC). Specifically, isolate D4 showed MIC values of 5 mM, 0.2 mM, 18 mM, and 12 mM, respectively, against CdCl2, HgCl2, Pb(NO3)2, and ZnSO4. For isolate G2, the corresponding MIC values were 6 mM, 0.2 mM, 21 mM, and 11 mM. The bacterial isolates were molecularly identified as strains Klebsiella pneumoniae PHmD4 (abbreviated as D4) and Enterobacter chuandaensis PHmG2 (abbreviated as G2), based on sequence homology obtained from 16S rDNA gene sequencing and subsequent BLAST analysis. In Pikovskaya’s broth, K. pneumoniae PHmD4 and E. chuandaensis PHmG2 had phosphate solubilization values of 4.30 μ moles mL⁻¹ and 3.51 μmoles mL⁻¹, respectively, with terminal pH values of 3.06 and 4.07. Enzymatic activity assays conducted after 96 hours of incubation in Pikovskaya’s broth revealed that the highest acid phosphatase activity was 21.62 U mL⁻¹ for K. pneumoniae PHmD4 and 21.09 U mL⁻¹ for E. chuandaensis PHmG2. The highest alkaline phosphatase activity was 5.85 U mL⁻¹ and 6.38 U mL⁻¹, respectively. In the tomato seed germination study, both non-bacterized and bacterized tomato seeds achieved a 100% germination rate. However, increasing metal concentrations diminished the germination percentage of heavy metal-treated seeds. Interestingly, bacterization with K. pneumoniae PHmD4 and E. chuandaensis PHmG2 ameliorated germination under cadmium stress but had no mitigative effect under mercury and zinc stress conditions.

Analysis of the Potassium-Solubilizing Priestia megaterium Strain NK851 and Its Potassium Feldspar-Binding Proteins.

Potassium-solubilizing bacteria are an important microbial group that play a critical role in releasing mineral potassium from potassium-containing minerals, e.g., potassium feldspar. Their application may reduce eutrophication caused by overused potassium fertilizers and facilitate plants to utilize environmental potassium. In this study, a high-efficiency potassium-solubilizing bacterium, named NK851, was isolated from the Astragalus sinicus rhizosphere soil. This bacterium can grow in the medium with potassium feldspar as the sole potassium source, releasing 157 mg/L and 222 mg/L potassium after 3 days and 5 days of incubation, respectively. 16S rDNA sequencing and cluster analysis showed that this strain belongs to Priestia megaterium. Genome sequencing further revealed that this strain has a genome length of 5,305,142 bp, encoding 5473 genes. Among them, abundant genes are related to potassium decomposition and utilization, e.g., the genes involved in adherence to mineral potassium, potassium release, and intracellular trafficking. Moreover, the strong potassium-releasing capacity of NK851 is not attributed to the acidic pH but is attributed to the extracellular potassium feldspar-binding proteins, such as the elongation factor TU and the enolase that contains potassium feldspar-binding cavities. This study provides new information for exploration of the bacterium-mediated potassium solubilization mechanisms.

Seed Priming for Enhancement of Seed Quality in Quality Protein Maize (QPM) (Zea mays L.)

An investigation was carried out with HQPM-5 maize hybrid and its parental lines HKI-163 and HKI-161 seeds during rabi 2022-23 to evaluate the effect of liquid biofertilizers (Azospirillum, Phosphorus solubilizing bacteria and Potassium solubilizing bacteria) on seed quality attributes in Quality Protein Maize (QPM) genotypes. The seeds were subjected to different concentration and duration of hydropriming and biopriming (Concentration: 10,15 and 20%; Duration: 6,12,18 and 24h). The non primed seeds were used as control. HQPM-5 seeds bioprimed with combination of Azospirillum @ 20 % + Phosphorous solubilizing bacteria @ 20 % + Potassium solubilizing bacteria @ 20 % at 12h (T9) recorded higher seed quality i.e., germination, field emergence, root length, shoot length, seedling length, seedling fresh weight, root dry weight, shoot dry weight, seedling dry weight, seed vigour index I & II, nitrogen and protein content and lower EC of seed leachates than the parental lines, HKI-163 and HKI-161. The overall performance of female parent was found to be better compared to the male parent.

Vermicast Analysis with the Earthworm Species Pheretima losbanosensis (Crassiclitellata: Megascolecidae): Bacterial Profiles for Potential Applications in Agriculture

In the Philippines, the use of non-native earthworm species in vermicomposting is popular. Given that the country is a vital geographical resource for earthworm diversity, the study of earthworm species to establish the potential of their vermicasts in agricultural applications is essential. In this study, the bacteria associated with the vermicasts of the recently described indigenous species, Pheretima losbanosensis, were investigated using next-generation sequencing, community-level physiological profiling, and NPK activity screening. The results showed diverse bacterial species belonging to the phyla Proteobacteria, Bacteroidetes, Acidobacteria, Actinobacteria, Chloroflexi, Firmicutes, Gemmatimonadetes, Nitrospirae, Planctomycetes, Spirochaetes, Thermodesulfobacteria, and Verrucomicrobia. Higher diversity and carbon substrate utilization (p < 0.05) of amines and amides, phenolic compounds, polymers, and carboxylic and acetic acids were exhibited by the bacterial communities of P. losbanosensis compared to those of Eudrilus eugeniae. Likewise, bacteria (n = 25) isolated from P. losbanosensis vermicasts had higher nitrogen fixation and phosphate and potassium solubilization activities (p < 0.05) than the bacteria (n = 20) isolated from E. eugeniae vermicasts. Overall, our results indicate that the diverse bacterial communities inhabiting the vermicasts of P. losbanosensis have nutrient mineralization and carbon substrate utilization activities that may have applications in sustainable agriculture as a potential organic input to promote plant growth and improve soil substrate.

Multifaceted Proficiencies of Thermotolerant Phosphate Solubilizing Bacteria from the Kutch Desert, Gujarat, India

Aims: This study aimed to isolate and characterize thermotolerant phosphate solubilizing bacteria (PSB) for potential agricultural applications. We aimed to identify promising PSB isolates and evaluate their traits.
 Study Design: Conducted a comprehensive screening of PSB isolates and selected three top candidates based on their phosphate-solubilizing index. These isolates underwent various tests, including thermotolerance assessment, biochemical profiling, and enzymatic assays. Soluble phosphorus and pH levels were also monitored over time.
 Methodology: Screened multiple PSB isolates, selecting PT26, PT31, and PT35. Conducted growth measurements under elevated temperatures, assessed biochemical profiles, and tested the antibiotic susceptibility. Also monitored soluble phosphorus and pH of PSB isolates over 96 hours and measured acid and alkaline phosphatase activities. Molecular identification was done through 16S rRNA gene sequencing.
 Results: Among the selected PSB isolates, PT35 showed superior thermotolerance and potassium solubilization capacity, while PT26 exhibited indole-3-acetic acid synthesis ability. Soluble phosphorus levels varied among isolates, affecting pH. Acid and alkaline phosphatase activities differed significantly. Molecular identification confirmed PT26, PT31, and PT35 as Enterobacter cloacae, Klebsiella quasipneumoniae, and Enterobacter bugandensis, respectively.
 Conclusion: This study highlights the potential significance of PT35, PT26, and PT31 in agriculture. Their diverse traits and metabolic activities offer adaptability to varying conditions, and thus can benefit soil health and nutrient cycling. These findings contribute to agricultural microbiology research, potentially enhancing sustainable farming practices and soil fertility.

Endophytic Seed-Associated Bacteria as Plant Growth Promoters of Cuban Rice (Oryza sativa L.).

Cuban rice cultivars INCA LP-5 and INCA LP-7 are widely distributed in Cuba and Caribbean countries. Although there are studies about rhizospheric bacteria associated with these cultivars, there are no reports about their seed-associated bacteria. This study aimed to isolate endophytic bacteria from rice seeds and select those with the greatest plant growth-promoting traits. A total of nineteen bacterial strains from the genera Pantoea, Bacillus, Paenibacillus, and Pseudomonas were isolated from the husk and endosperm of rice seeds. The strains Pantoea sp. S5-1, Pseudomonas sp. S5-38, and Pseudomonas sp. S7-1 were classified as the most promissory to increase rice growth as they demonstrated the presence of multiple plant growth-promoting traits such as the production of auxins, phosphate, and potassium solubilization, the production of siderophores, and the inhibition of the phytopathogen Pyricularia oryzae. The inoculation of strains of Pantoea sp. and Pseudomonas spp. in rice improves the height, root length, fresh weight, and dry weight of the shoot and root after 21 days post-inoculation in hydroponic assays. This study constitutes the first report on Cuban rice cultivars about the presence of endophytes in seeds and their potential to promote seedling growth. Pantoea sp. S5-1, Pseudomonas sp. S5-38, and Pseudomonas sp. S7-1 were selected as the more promising strains for the development of bio-stimulators or bio-inoculants for Cuban rice crops.

Effect of Potassium Solubilizing Bacteria (KSB) on the Performance of Sweet Corn (Zea mays L. saccharata) in Potassium Sufficient Soils of Semi-arid Tropic

An experiment was conducted on potassium sufficient sandy loam soil (Alfisols) to evaluate the impact of potassium solubilizing bacteria (KSB) on the performance of rabi sweet corn. The study consisted of 10 treatments with different doses of potassium with and without KSB treatment [Seed treatment (ST) + Soil drenching (SD) at Knee height (KH) stage]. Result of this experiment indicated that sweet corn yield was gradually reduced with reduction of recommended dose of potassium (RDK) irrespective of KSB treatment. Amongst all treatments, application of 100% RDK in 2 equal splits at sowing and KH stage + KSB (ST + SD) (T10) resulted in highest growth, yield (19.7 t ha-1) and yield attributes. However, T10 was on par with the result of [100% RDK + KSB (ST) + KSB (SD) at KH stage], (50% RDK at basal + 50% RDK at KH stage), [100% RDK+ KSB (ST) +KSB (SD) at KH stage] and [75% RDK at basal + KSB (ST) +KSB (SD) at KH stage] treatments. Whereas, implication of 25% or 50% reduction of RDK was significantly inferior to 100% RDK. The study revealed that KSB could substitute 25% of RDK supplied to nutrient exhaustive crop like rabi sweet corn without compromising the economic yield in potassium rich alfisols of semi-arid tropic.

Visual screening of potassium solubilizing bacteria for increasing the solubilization of potassium minerals

Research on potassium solubilizing bacteria (KSB) has recently gained attention, most of it has been focused on the size of the halo zone; however, information regarding KSB growth duration and their potential to reduce the use of chemical fertilizers for sustainable agriculture and to be used as a biofertilizer are still lacking. The aim of this study was to offer a complete, long-term observation of KSB growth. We monitored the growth of two KSB strains that were isolated from the rhizosphere for 7 days on Modified Aleksandrov Medium (MAM) plates. We specifically designed the observation times. These methods were used to distinguish KSB’s capability to solubilize potassium minerals. The results indicated that KSB-12 isolate was capable of producing organic acid and thus solubilizing potassium faster than KSB-19 isolate at 1-4 days of incubation. Interestingly, the solubilizing zone of the KSB-12 isolate decrease after 5 days of incubation, while KSB-19 isolate continued to grow, maintain cell numbers, produce organic acids, and continuously release potassium. Different types of volatile and non-volatile organic acids have an effect on this phenomenon. In conclusion, we provided a well-designed time series study regarding the potassium solubilization efficiency of KSB, determining the fastest and longest strains of potential KSBs.

Contribution of potassium solubilizing bacteria in improved potassium assimilation and cytosolic K+/Na+ ratio in rice (Oryza sativa L.) under saline-sodic conditions.

Sodium-induced potassium (K+) deficiency is more prevalent in salt-affected soils. Plants experience K+ starvation thus cytosolic K+/Na+ ratio is lowered, which is a prerequisite for their survival. K+ enrichment in crops can be acquired via K-solubilizing bacteria as a sustainable green agriculture approach. This study was conducted to explore potent K-solubilizing bacteria from the rhizosphere of wheat, rice, and native flora grown in salt-affected soils in two distinct regions of Pakistan. The aim of this work was to evaluate the contribution of microbial consortiums to the improvement of K+ assimilation and cytosolic K+/Na+ ratios in rice crops under saline-sodic conditions. Among 250 bacterial isolates, 9 were selected based on their salt (11% NaCl) and alkali (9) tolerance and K-solubilization indices (1.57-5.67). These bacterial strains were characterized for their plant growth-promoting traits and identified based on 16S rRNA gene sequencing. A consortium of five strains, namely, Enterobacter hormaechei, Citrobacter braakii, Pseudomonas putida, Erwinia iniecta, and Pantoea agglomerans, was used as a bio-inoculant to evaluate its role in K+ assimilation, cytosolic K+/Na+ ratio, and subsequent yield enhancement in rice grown under saline-sodic conditions. The impact of applied consortium on rice was assessed under variable salt levels (Control, 40, 80, and 120 mM) in a pot experiment and under natural saline-sodic conditions in the field. Plant agronomical parameters were significantly higher in the bacterial consortium-treated plants, with a concomitant increase in K+-uptake in root and shoot (0.56 and 0.35 mg g-1 dry wt.) of the salt-tolerant rice variety Shaheen. The root K+/Na+ ratio was significantly improved (200% in 40 mM and 126% in 80 mM NaCl) and in the shoot (99% in 40 mM and 131% in 80 mM) too. A similar significant increase was also observed in the salt-susceptible variety Kainat. Moreover, grain yield (30.39 g/1,000 grains wt.) and biomass (8.75 g) of the rice variety Shaheen, grown in field conditions, were also improved. It can be concluded that K-solubilizing bacteria can be used as bio-inoculants, contributing to growth and yield increment via enhanced K-assimilation and cytosolic K+/Na+ ratio in rice crops under salt stress.

Isolation and molecular characterization of potassium-solubilizing bacteria from limestone mountain of Bahorok, Langkat District, Indonesia

Abstract. Bangun IH, Hanum H, Sabrina T. 2023. Isolation and molecular characterization of potassium-solubilizing bacteria from limestone mountain of Bahorok, Langkat District, Indonesia. Biodiversitas 24: 4175-4184. In agricultural practices, ensuring an adequate supply of potassium to plants is crucial for optimal growth and productivity. However, the exchangeable K is tightly bound to soil minerals such as mica, feldspar, and clay minerals, making it unavailable for plant uptake. K-solubilizing bacteria K can dissolve potassium from the mineral layer and be available to plants. The Previous study has found 11 bacterial isolates capable of solubilizing K in Aleksandrov solid media. This study aimed to select the best K-solubilizing bacteria for solubilizing K in soil and to perform molecular identification of these bacteria. A novel finding from this study is that specific KSBs enhance the levels of exchangeable K in the soil through various mechanisms, as evidenced by increased exchangeable Ca, Mg, and soil pH. Additionally, the research identified two newly discovered bacterial species capable of potassium solubilization: Paraburkholderia phymatum and Burkholderia paludis. Furthermore, the study suggests the existence of an unknown mechanism for K solubilization, indicated by the observed increase in soil pH during the process.

Combined Use of a Bacterial Consortium and Early-Colonizing Plants as a Treatment for Soil Recovery after Fire: A Model Based on Los Guájares (Granada, Spain) Wildfire.

During 2022, intense heat waves, together with particularly extreme dry conditions, created a propitious scenario for wildfires, resulting in the area of vegetation consumed in Europe doubling. Mediterranean countries have been particularly affected, reaching 293,155 hectares in Spain, the worst data in the last 15 years. The effects on the vegetation and the soil are devastating, so knowing the recovery factors is essential for after-fire management. Resilient microorganisms play a fundamental role in rapid nutrient recycling, soil structure, and plant colonization in fire-affected soils. In this present work, we have studied emergent microbial communities in the case of the Los Guájares (Granada, Spain) fire, one of the most extensive of the year, to evaluate their role in the recovery of soil and vegetation cover. We aim to discern which are the main actors in order to formulate a new treatment that helps in the ecosystem recovery. Thus, we have found the relevant loss in phosphorous and potassium solubilizers, as well as siderophores or biofilm producers. Here, we decided to use the strains Pseudomonas koreensis AC, Peribacillus frigoritolerans CB, Pseudomonas fluorescens DC, Paenibacillus lautus C, Bacillus toyonensis CD, and Paenarthrobacter nitroguajacolicus AI as a consortium, as they showed most of the capacities required in a regenerative treatment. On the other hand, the microcosm test showed an enhanced pattern of germination of the emerging model plant, Bituminaria bituminosa, as well as a more aggregated structure for soil. This new approach can create a relevant approach in order to recover fire-affected soils in the future.

Isolation and characterization of novel potassium-solubilizing purple nonsulfur bacteria from acidic paddy soils using culture-dependent and culture-independent techniques.

The current research as aimed (i) to isolate and select the purple nonsulfur bacteria (PNSB) possessing the potassium-solubilizing ability from acid paddy fields and (ii) to evaluate the ability to release the plant growth-promoting substances (PGPS) of selected PNSB. A total of 35 acid sulfate (AS) soil samples were collected in An Giang province, Vietnam. Then, 70 PNSB strains were isolated from the AS soil samples. In the current study, the isolated strains were screened and selected according to their tolerability to acidic conditions, ability to solubilize potassium, and characteristics of a plant growth promoter on basic isolation media with various incubation conditions. Therein, three strains, TT07.4, AN05.1, and AC04.1, presented the highest potassium solubilization under the microaerobic light (11.8-17.7 mg L-1) and aerobic dark (16.4-24.7 mg L-1) conditions and stresses from Al3+, Fe2+, and Mn2+ toxicity. The selected strains were identified as Rhodopseudomonas pentothenatexigens by the 16S rDNA sequence, with 99% similarity. The selected acidic-resistant strains possessed the traits of biofertilizers under both microaerobic light and aerobic dark conditions, with abilities to fix nitrogen (0.17-6.24; 7.93-11.2 mg L-1); solubilize phosphorus from insoluble compounds with 3.22-49.9 and 9.49-11.2 mg L-1 for Al-P, 21.9-25.8 and 20.2-25.1 mg L-1 for Ca-P, and 10.1-29.8 and 18.9-23.2 mg L-1 for Fe-P; produce 5-aminolevulinic acid (0.63-3.01; 1.19-6.39 mg L-1), exopolymeric substances (0.14-0.76; 0.21-0.86 mg L-1), indole-3-acetic acid (12.9-32.6; 13.6-17.8 mg L-1), and siderophores (28.4-30.3; 6.15-10.3%). The selected potassium-solubilizing strains have a great potential to apply in liquid form into rice seed and solid form in AS soils to supply nutrients and PGPS for enhancing rice growth and grain yield.

Endophytic bacterial taxonomic and functional diversity in the seeds of wheat genotypes from different agroecologies

ABSTRACT Plant genotype and agroecology influence the composition and functionality of seed endophytic bacterial communities. Taxonomic analysis of 123 wheat seeds endophytic bacteria classified these into 23 genera predominantly under Firmicutes followed by Actinobacteria and Proteobacteria. Genus Bacillus was most abundant (30.7%) followed by Streptomyces (18.4%) with other representative genera such as Stenotrophomonas, Paenibacillus, Mixta, Enterobacter, Micrococcus, Pantoea, Alkalihalobacillus, Cortiobacterium, and more. Across agroecologies, the core microbiota of seeds consists of Bacillus, Streptomyces, Paenibacillus, and Stenotrophomonas, with maximum diversity and abundance observed in seeds of the North Western Plain Zone of India. Seed endophytic bacteria had PGP traits; nitrogen fixation (n = 101), production of IAA (n = 65), siderophores (n = 43), ammonia (n = 82) and solubilization of phosphate (n = 47), potassium (n = 37), and zinc (n = 8). The isolates produced HCN and hydrolytic enzymes and displayed antagonism against fungal pathogens. Overall, the information generated on wheat seeds’ endophytic bacterial taxonomy and beneficial traits may pave the path for the development of novel bioinoculants. Key message Wheat seeds from various agro-ecologies of India harbor diverse endophytic bacteria. Firmicutes were dominant followed by Actinobacteria and Proteobacteria. Genus Bacillus, Stenotrophomonas, Streptomyces, and Paenibacillus were core endophytic bacteria in different agro-ecologies. The endophytic bacterial strains were displaying diverse functional traits.

Ignatzschineria cameli Strain KAUPDF7-A First Report on Plant Growth Promoting Rhizobacteria (PGPR) from the Post-flood Affected Soils of Kerala

Background: Kerala flood in 2018 and 2019 had reduced the yield in many agricultural plots of Attapadi, Kerala, India. The scope of the study was to identify the potential native plant growth promoting rhizobacteria from the post flood-affected sites to rejuvenate the nutrient depleted soils. Methods: The present study was carried out in the department of agricultural microbiology, College of Agriculture, Kerala Agricultural University, Vellanikara, Kerala during 2020-2022. Bacteria were isolated from post flood-affected agricultural soils of Attapadi in Palakkad district of Kerala, India. Three morphologically distinct isolates were screened for cellulase, laccase and dehydrogenase to select the best bacterial isolate that could produce the multifunctional enzymes for rejuvenation of flood-affected soils. The isolate were also screened for plant growth promotion traits such as; indole acetic acid (IAA), phosphate solubilizing ability, nitrogen fixing ability and potassium solubilizing ability. Result: The most promising isolate was identified as Ignatzschineria cameli, which was found to be a high indole acetic acid producer along with phosphate and potassium solubilizing ability and revealed as the first report of PGPR from post flood-affected soils of Kerala.

Potential Novel Plant Growth Promoting Rhizobacteria for Bio-Organic Fertilizer Production in the Oil Palm (Elaeis guineensis Jacq.) in Malaysia

The present study aimed to characterize the potential plant growth-promoting rhizobacteria (PGPR) based on biochemical tests based on eight bacterial isolates, and to identify potential PGPR based on the 16S rRNA sequencing molecular method. Eight potential PGPR strains (UPMC1166, UPMC1168, UPMC1254, UPMC1376, UPMC1389, UPMC1393, UPMC703 and UPMC704) isolated from the soils in the oil palm (Elaeis guineensis) estates across Malaysia were selected because of their most PGPR activities. They were screened for nitrogen fixation, phosphate and potassium solubilization, and production of indole-3-acetic acid (IAA). All isolates showed the ability to grow between pH 2 to 9 and survive from 2 to 15% (w/v) of the salt medium. Among the isolated PGPRs, four PGPRs (UPMC1166, UPMC1168, UPMC1254 and UPMC1389) showed the ability to fix nitrogen and had the potential to produce IAA. Furthermore, two PGPRs (UPMC1393 and UPMC1376) demonstrated the ability to solubilize phosphate, while three PGPRs (UPMC703, UPMC704, and UPMC1393) showed the ability to solubilize potassium. Therefore, all the above eight PGPR isolates can benefit the oil palm cultivation industry. The molecular identification based on 16S rRNA gene sequence revealed that UPMC1166 was identified as Bacillus methylotrophicus; UPMC1168 as B. siamensis; UPMC1254 as B. subtilis; UPMC1389 as B. albus; UPMC1376 as Lactobacillus plantarum; UPMC1393 as B. marisflavi; UPMC703 as Burkhoderiaanthina and UPMC704 as B. metallica. These novel strains can be further investigated for their viability and effectiveness for bio-organic fertilizer production and application in the immature stage of oil palm growth.

Rhizosphere microbiome assembly mediated by consecutive monoculture triggers the replant disease of Rehmannia glutinosa

Consecutive monoculture of Rehmannia glutinosa results in severe replant disease and remarkably reduces the yield and quality. Rhizosphere microbiome plays a crucial role in soil health and plant performance. In this study, high-throughput pyrosequencing combined with a culture-dependent approach were applied to analyze the changes in rhizosphere microbiome structure and bacteria-fungi inter-kingdom associations under R. glutinosa consecutive monoculture. The results revealed a distinct separation between the newly planted (NP) and the two-year monocultured (SM). R. glutinosa consecutive monoculture resulted in a significant decline in the Shannon and Simpson diversity indices for the fungal community, and a significant decrease in relative abundances of the phyla Actinobacteria, Chloroflexi and Basidiomycota. The relative abundances of the genera Streptomyces, Arthrobacter, Bacillus, Nocardioides and Lysobacter were significantly higher in NP than in SM, while the opposite was true for Fusarium. Quantitative PCR confirmed a significant reduction in the phylum Actinobacteria and the genus Bacillus, and a significant increase in Fusarium oxysporum. Furthermore, the abundances of Actinobacteria and Bacillus strains with antagonistic activities against Fusarium oxysporum were lower in extended monoculture soils. Most of the isolated antagonistic bacteria were found to be positive for different plant growth promotion activities such as solubilization of phosphate and potassium, production of siderophore and indolic compounds. In addition, it was found that phenolic acid mixture and catalpol, identified in the root exudates of R. glutinosa, could selectively inhibit or stimulate different microbes. Moreover, the culture filtrate and volatile organic compounds produced by F. oxysporum could in turn suppress the growth of certain antagonistic bacteria. In conclusion, these findings highlight the close association between R. glutinosa replant disease and rhizosphere microbiome assembly, which was mediated by root exudates and microbe-microbe interactions.

Culturable bacterial endophytes of Aconitum carmichaelii Debx. were diverse in phylogeny, plant growth promotion, and antifungal potential.

Medicinal plants harbor tremendously diverse bacterial endophytes that maintain plant growth and health. In the present study, a total of 124 culturable bacterial endophytes were isolated from healthy Aconitum carmichaelii Debx. plants. These strains were clustered into 10 genera based on full-length 16S rDNA sequences, among which Bacillus and Pseudomonas were the dominant genera. In addition, A. carmichaelii may capture 10 potential new bacterial species based on multi-locus sequence analysis of three housekeeping genes (gyrA, rpoB, and atpD). The majority of these bacterial endophytes exhibited plant growth-promoting ability through diverse actions including the production of either indole acetic acid and siderophore or hydrolytic enzymes (glucanase, cellulose, and protease) and solubilization of phosphate or potassium. A total of 20 strains inhibited hyphal growth of fungal pathogens Sclerotium rolfsii and Fusarium oxysporum in vitro on root slices of A. carmichaelii by the dual-culture method, among which Pseudomonas sp. SWUSTb-19 showed the best antagonistic activity. Field experiment confirmed that Pseudomonas sp. SWUSTb-19 significantly reduced the occurrence of southern blight and promoted plant biomass compared with non-inoculation treatment. The possible mode of actions for Pseudomonas sp. SWUSTb-19 to antagonize against S. rolfsii involved the production of glucanase, siderophore, lipopeptides, and antimicrobial volatile compounds. Altogether, this study revealed that A. carmichaelii harbored diverse plant growth-promoting bacterial endophytes, and Pseudomonas sp. SWUSTb-19 could be served as a potential biocontrol agent against southern blight.

Effect of application of lime with vermicompost on the activities of microorganisms of some acidic soils of West Bengal

Aim: To evaluate the efficacy of integrated application of lime at partial doses of lime requirement (LR) with vermicompost in acid soils to minimize the soil acidity, improve the population of beneficial microorganisms and their microbial activities in comparison to sole treatment of lime as per Lime Requirement dose. Methodology: Two highly acidic soils collected from the farmer’s field of South 24 Parganas district, West Bengal having no history of acidity management were used. The soils were treated with different rates of lime requirement (LR, ⅔LR & ½LR) and lime (½LR) + vermicompost (5 tha-1) treatments and incubated for 60 days. Soil pH, soil organic carbon content, different microbial populations, microbial respiration and enzymatic activities (FDHA and DHA) were assessed at different days. Results: The study indicated that the lime treatments showed rapid increase in soil pH towards the slightly alkaline condition whereas lime +vermicompost treatment (T5) successfully maintained the neutralized condition. Integrated treatment of lower doses of lime and vermicompost (T5) was found to efficiently promote the microbial population (rhizobium, phosphate and potassium solubilizing bacteria) and microbial respiration (basal and substrate induced respiration) activity, which might be attributed to the improvement soil microbial status. FDHA and DHA increased significantly with ‘lime’ as well as the ‘lime with vermicompost’ treatments in comparison to control. Interpretation: The incorporation of lower amount of lime and organic matter efficiently neutralizes the acidity and boosted up the microbial activities simultaneously that in turn might improve the soil health. The high cost to purchase the huge quantity of lime as recommended LR (9.25 tha-1) for studied soils turns the farmers uninterested to follow lime practice and interrupted the mitigation of soil acidity. Thus, the study might conclude that the integrated approach of lime application@½LR with vermicompost might successfully ameliorate the acid soils in terms of acidity as well as the soil microbial activities. Key words: Acid soil, BSR, Dehydrogenase, Fluorescein diacetate, SIR, Lime, Vermicompost

Plant-beneficial Streptomyces dioscori SF1 potential biocontrol and plant growth promotion in saline soil within the arid and semi-arid areas.

Environmental challenges like salinity, drought, fungal phytopathogens, and pesticides directly or/and indirectly influence the environment and agricultural yields. Certain beneficial endophytic Streptomyces sp. can ameliorate environmental stresses and be utilized as crop growth promoters under adverse conditions. Herein, Streptomyces dioscori SF1 (SF1) isolated from seeds of Glycyrrhiza uralensis tolerated fungal phytopathogens and abiotic stresses (drought, salt, and acid base). Strain SF1 showed multifarious plant growth promotion characteristics, including the production of indole acetic acid (IAA), ammonia, siderophores, ACC deaminase, extracellular enzymes, the ability of potassium solubilization, and nitrogen fixation. The dual plate assay showed that strain SF1 inhibited 63.21 ± 1.53%, 64.84 ± 1.35%, and 74.19 ± 2.88% of Rhizoctonia solani, Fusarium acuminatum, and Sclerotinia sclerotiorum, respectively. The detached root assays showed that strain SF1 significantly reduced the number of rotten sliced roots, and the biological control effect on sliced roots of Angelica sinensis, Astragalus membranaceus, and Codonopsis pilosula was 93.33%, 86.67%, and 73.33%, respectively. Furthermore, the strain SF1 significantly increased the growth parameters and biochemical indicators of adversity in G. uralensis seedlings under drought and/or salt conditions, including radicle length and diameter, hypocotyl length and diameter, dry weight, seedling vigor index, antioxidant enzyme activity, and non-enzymatic antioxidant content. In conclusion, the strain SF1 can be used to develop environmental protection biological control agents, improve the anti-disease activity of plants, and promote plant growth in salinity soil within arid and semi-arid regions.