Multifarious Indigenous Diazotrophic Rhizobacteria of Rice (Oryza sativa L.) Rhizosphere and Their Effect on Plant Growth Promotion

Development, Shelf Stability, and In-Vitro Evaluation of Liquid Bacterial Inoculant Acinetobacter lwoffii Strain PAU_31LN

Acinetobacter has been recognized as a versatile plant growth promoting (PGP) rhizobacteria (PGPR) that produce multiple PGP traits. The present study was conducted to formulate an efficient and stable liquid bacterial inoculant (LBI) of Acinetobacter lwoffii strain PAU_31LN. In the current investigation, total 16 endophytic bacteria were isolated from cotton leaves and evaluated for plant growth-promoting features such as production of phytohormones, mineral solubilization, siderophore production, hydrogen cyanide (HCN) production, and 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity. The leaf endophytic bacteria designated as 31LN was found promising for all the PGP traits and it was identified as A. lwoffii strain PAU_31LN by 16S rRNA gene sequencing. For the development of LBI of A. lwoffii strain PAU_31LN, 4.5 g/L yeast extract, 5 g/L NaCl, 5 g/L peptone, and 12.5 mM food-grade trehalose was optimized as appropriate medium composition using response surface methodology (RSM) and Box-Behnken design. Further, the viability of A. lwoffii strain PAU_31LN in the optimized formulation was observed as 1.1 folds higher over the control after 180 days of storage at room temperature. Moreover, nonsignificant variation was recorded in the functional traits of 180 days old LBI of A. lwoffii strain PAU_31LN and freshly prepared LBI. The in-vitro plant growth parameters such as length and seed vigor index of 7-day-old cotton seedlings were enhanced by the seed bio-priming with LBI of A. lwoffii strain PAU_31LN over the control. The results of the present study signify the importance of endophytes and statistical methods to formulate prominent LBI.

Diversity and Plant Growth-Promoting Activities of Culturable Seed Endophytes in Abies pindrow (Royle ex D. Don) Royle: Their Role in Seed Germination and Seedling Growth

Abies pindrow, a vital conifer in the Kashmir Himalayan forests, faces threats from low regeneration rates, deforestation, grazing, and climate change, highlighting the urgency for restoration efforts. In this context, we investigated the diversity of potential culturable seed endophytes in A. pindrow, assessed their plant growth-promoting (PGP) activities, and their impact on seed germination and seedling growth. We cultured 729 microbial isolates that were resolved into 30 bacterial and 18 fungal species across various phyla. All 48 isolates exhibited various PGP activities. Specifically, all the cultured isolates showed IAA activity with concentrations ranging from 2.07 to 8.453 μg/ml, while ammonia production ranged from 0.936 to 3.436 mM/ml. Only 18 isolates, predominantly fungi, tested positive for phosphate solubilisation. Additionally, 20 isolates exhibited the ability to inhibit the growth of Fusarium oxysporum f.sp. pini. We selected four bacterial and six fungal isolates, which showed positive results for all PGP activities, to evaluate their effects on seed germination and seedling growth. Notably, seed germination rates increased by 750.9% under bacterial and consortium treatments and by 550.45% under fungal treatment. The consortium treatment also led to a 96% increase in needle count, while bacterial treatment enhanced stem length by 55.4%. Furthermore, shoot biomass also showed a significant increase with both bacterial and fungal treatments, underscoring the potential of harnessing seed endophytes to boost A. pindrow seedling health and resilience. This study underscores the crucial role of seed endophytic diversity in enhancing seed germination, seedling growth, and forest restoration efforts.

Synthetic communities derived from the core endophytic microbiome of hyperaccumulators and their role in cadmium phytoremediation

BACKGROUND

Although numerous endophytic bacteria have been isolated and characterized from cadmium (Cd) hyperaccumulators, the contribution and potential application of the core endophytic microbiomes on facilitating phytoremediation were still lack of intensive recognition. Therefore, a 2-year field sampling in different location were firstly conducted to identify the unique core microbiome in Cd hyperaccumulators, among which the representative cultivable bacteria of different genera were then selected to construct synthetic communities (SynComs). Finally, the effects and mechanisms of the optimized SynCom in regulating Cd accumulation in different ecotypes of Sedum alfredii were studied to declare the potential application of the bacterial agents based on core microbiome.

RESULTS

Through an innovative network analysis workflow, 97 core bacterial taxa unique to hyperaccumulator Sedum was identified based on a 2-year field 16S rRNA sequencing data. A SynCom comprising 13 selected strains belonging to 6 different genera was then constructed. Under the combined selection pressure of the plant and Cd contamination, Alcaligenes sp. exhibited antagonistic relationships with other genera and plant Cd concentration. Five representative strains of the other five genera were further conducted genome resequencing and developed six SynComs, whose effects on Cd phytoremediation were compared with single strains by hydroponic experiments. The results showed that SynCom-NS comprising four strains (including Leifsonia shinshuensis, Novosphingobium lindaniclasticum, Ochrobactrum anthropi, and Pseudomonas izuensis) had the greatest potential to enhance Cd phytoremediation. After inoculation with SynCom-NS, genes related to Cd transport, antioxidative defense, and phytohormone signaling pathways were significantly upregulated in both ecotypes of S. alfredii, so as to promote plant growth, Cd uptake, and translocation.

CONCLUSION

In this study, we designed an innovative network analysis workflow to identify the core endophytic microbiome in hyperaccumulator. Based on the cultivable core bacteria, an optimized SynCom-NS was constructed and verified to have great potential in enhancing phytoremediation. This work not only provided a framework for identifying core microbiomes associated with specific features but also paved the way for the construction of functional synthetic communities derived from core microbiomes to develop high efficient agricultural agents. Video Abstract.

Enhancing Agricultural Sustainability Through Rhizomicrobiome: A Review

Sustainable agriculture represents the responsible utilization of natural resources while safeguarding the well-being of the natural environment. It encompasses the objectives of preserving the environment, fostering economic growth, and promoting socioeconomic equality. To achieve sustainable development for humanity, it is imperative to prioritize sustainable agriculture. One significant approach to achieving this transition is the extensive utilization of microbes, which play a crucial role due to the genetic reliance of plants on the beneficial functions provided by symbiotic microbes. This review focuses on the significance of rhizospheric microbial communities, also known as the rhizomicrobiome (RM). It is a complex community of microorganisms that live in the rhizosphere and influence the plant's growth and health. It provides its host plant with various benefits related to plant growth, including biocontrol, biofertilization, phytostimulation, rhizoremediation, stress resistance, and other advantageous properties. Yet, the mechanisms by which the RM contributes to sustainable agriculture remain largely unknown. Investigating this microbial population presents a significant opportunity to advance toward sustainable agriculture. Hence, this study aims to provide an overview of the diversity and applications of RM in sustainable agriculture practices. Lately, there has been growing momentum in various areas related to rhizobiome research and its application in agriculture. This includes rhizosphere engineering, synthetic microbiome application, agent-based modeling of the rhizobiome, and metagenomic studies. So, developing bioformulations of these beneficial microorganisms that support plant growth could serve as a promising solution for future strategies aimed at achieving a new green revolution.

Proclaiming Plant Growth-Promoting and Antifungal Properties of Pseudomonas lurida and Bacillus velezensis Isolated from Rhododendrons of Darjeeling Hills

Endophytes have drawn attentions due to their effectiveness in providing benefits to host and non-host plants. In this study endophytic bacteria were isolated from stem and leaf samples of medicinally important plants Rhododendron griffithianum Wight and Rhododendron arboreum Smith subsp. cinnamomeum (Wall. ex G. Don) grown at higher altitudes of Darjeeling, India. Two endophytic bacteria, Pseudomonas lurida RGDS03 and Bacillus velezensis RCDL12 were identified based on 16S rRNA gene sequencing analysis. The endophytes exhibited indole acetic acid (IAA), gibberellic acid (GA), siderophore production, phosphate solubilization, nitrogen-fixing abilities, though B. velezensis RCDL12 showed superior production of IAA (126.04 ± 0.40 µg/mL), GA (241.00 ± 0.44 µg/mL), and phosphate (74.4 ± 0.41 µg/mL) solubilization as compared to P. lurida RGDS03. Purity of extracted IAA from these two endophytes was confirmed by HPLC and LC-MS analysis. In this study, P. lurida RGDS03 inhibited mycelial growth of two tested phytopathogens Phytophthora sp. and Pestalotiopsis sp. of broad host range. However, only against Pestalotiopsis sp. did B. velezensis RCDL12 exhibit antifungal activity. Study was conducted on growth promotion capabilities of isolates on rice and mung bean seedlings. P. lurida RGDS03, B. velezensis RCDL12 and consortium of both the strains reported with promising growth promotion on both rice (85-97%) and mung bean (86-99%) in terms of their seed germination, vegetative growth (root and shoot length, fresh and dry weight), and chlorophyll content as compared to the control plants (untreated). This study has emphasized growth-promoting and biocontrol activities of endophytic bacteria from rhododendrons, and application to enhance crop development for sustainable agriculture.

Effectiveness of local isolates of Trichoderma spp. in imparting drought tolerance in rice, Oryza sativa

Rice is a crop that requires high amount of water, and the drought is a major constraint in paddy cultivation. Water stress condition frequently prevails due to shortage of rain which results in significantly reduced plant growth and yield of rice. In the present study capability of Trichoderma spp. in imparting drought tolerance to rice, Oryza sativa was explored. Eleven local strains of Trichoderma spp. were applied to rice cv. Swarna Sub-1 through soil application (2 g/kg soil) and seed treatment (20 g/kg seed) under 0, 25, 50 and 75% less watering of the recommended amount. The soil application of T. harzianum AMUTHZ84 significantly promoted the shoot and root length (23.6 and 21.3%) followed by seed treatment (19.7 and 18.2%) under recommended level of irrigation condition (100% irrigation). Next in effectiveness was T. viride AMUTVR73 (21.5 and 18.1%) over untreated control. However, under 75% water availability, soil application with T. harzianum AMUTHZ82 was found superior over other isolates in enhancing shoot and root length (17.7 and 16.4%). The same isolate was also recorded to be superior under 50% (12.4 and 10.1%) and 25% water availability (9.3 and 8.1%) in enhancing the plant growth and biomass of rice cv. Swarna Sub-1. The isolate also significantly enhanced the leaf pigments, and photosynthesis in the rice plants grown under 25-75% water stress condition. In general, soil application of Trichoderma isolates was found more effective than seed treatment, and the T. harzianum AMUTHZ82 provided 8-17% enhancement in the plant growth, biomass, leaf pigments and photosynthesis of rice cv. Swarna Sub-1 grown under 25-75% water stress condition.

Plant-Growth-Promoting Rhizobacteria Improve Seeds Germination and Growth of Argania spinosa

Argania spinosa is among the most important species of the Moroccan forest in terms of ecological, environmental, and socio-economic aspects. However, it faces a delicate balance between regeneration and degradation in its natural habitat. Hence, the efforts to preserve and regenerate argan forests are crucial for biodiversity, soil quality, and local livelihoods, yet they face challenges like overgrazing and climate change. Sustainable management practices, including reforestation and community engagement, are vital for mitigating degradation. Similarly, exploiting the argan tree's rhizosphere can enhance soil quality by leveraging its rich microbial diversity. This approach not only improves crop growth but also maintains ecosystem balance, ultimately benefiting both agriculture and the environment. This enrichment can be achieved by different factors: mycorrhizae, plant extracts, algae extracts, and plant growth-promoting rhizobacteria (PGPR). The benefits provided by PGPR may include increased nutrient availability, phytohormone production, shoot, root development, protection against several plant pathogens, and disease reduction. In this study, the effect of rhizobacteria isolated from the Agran rhizosphere was evaluated on germination percentage and radicle length for Argania spinosa in vitro tests, growth, collar diameter, and branching number under greenhouse conditions. One hundred and twenty (120) bacteria were isolated from the argan rhizosphere and evaluated for their capacity for phosphate solubilization and indole acetic acid production. The results showed that 52 isolates could solubilize phosphorus, with the diameters of the solubilization halos varying from 0.56 ± 0.14 to 2.9 ± 0.08 cm. Among 52 isolates, 25 were found to be positive for indole acetic acid production. These 25 isolates were first tested on maize growth to select the most performant ones. The results showed that 14 isolates from 25 tested stimulated maize growth significantly, and 3 of them by 28% (CN005, CN006, and CN009) compared to the control. Eight isolates (CN005, CN006, CN004, CN007, CN008, CN009, CN010, and CN011) that showed plant growth of more than 19% were selected to evaluate their effect on argan germination rate and radicle length and were subjected to DNA extraction and conventional Sanger sequencing. The 8 selected isolates were identified as: Brevundimonas naejangsanensis sp2, Alcaligenes faecalis, Brevundimonas naejangsanensis sp3, Brevundimonas naejangsanensis sp4, Leucobacter aridicollis sp1, Leucobacter aridicollis sp2, Brevundimonas naejangsanensis sp1, and Staphylococcus saprophyticus. The results showed that Leucobacter aridicollis sp2 significantly increased the germination rate by 95.83%, and the radicle length with a value of 2.71 cm compared to the control (1.60 cm), followed by Brevundimonas naejangsanensis sp3 and Leucobacter aridicollis sp1 (2.42 cm and 2.11 cm, respectively). Under greenhouse conditions, the results showed that the height growth increased significantly for Leucobacter aridicollis sp1 (42.07%) and Leucobacter aridicollis sp2 (39.99%). The isolates Brevundimonas naejangsanensis sp3 and Leucobacter aridicollis sp1 increased the gain of collar diameter by 41.56 and 41.21%, respectively, followed by Leucobacter aridicollis sp2 and Staphyloccocus saprophyticus (38.68 and 22.79%). Leucobacter aridicollis sp1 increased the ramification number per plant to 12 compared to the control, which had 6 ramifications per plant. The use of these isolates represents a viable alternative in sustainable agriculture by improving the germination rate and root development of the argan tree, as well as its development, while increasing the availability of nutrients in the soil and consequently improving fertilization.

Mangrove endophytic fungi: Biocontrol potential against Rhizoctonia solani and biofertilizers for fragrant rice cultivation

The mangrove ecosystem has emerged as a fascinating source for exploring novel bioresources which have multiple applications in modern agriculture. This study evaluates the potential applications of mangrove endophytic fungi (MEF), such as biocontrol agents against Rhizoctonia solani and as biofertilizers for improving the yield of fragrant rice variety Malaysian Rice Quality 76 (MRQ76). Through the antagonism assays, it is observed that among the 14 MEF studied, 4 fungal isolates (Colletotrichum sp. MEFN02, Aspergillus sp. MEFN06, Annulohypoxylon sp. MEFX02 and Aspergillus sp. MEFX10) exhibited promising antagonistic effect against the pathogen R. solani compared to the chemical fungicide (Benomyl). These isolates also revealed significant production of enzymes, phytochemicals, indoleacetic acid (40.96 mg/mL) and ammonia (32.54 mg/mL) and displayed tolerance to salt and temperature stress up to 2000 mM and >40 °C respectively. Furthermore, employing the germination and pathogenicity test, inoculation of these endophytes showed lower percentage of disease severity index (DSI%) against R. solani, ranging from (24 %-46 %) in MRQ76 rice seedlings. The in-vivo experiments of soil and seed inoculation methods conducted under greenhouse conditions revealed that these endophytes enhanced plant growth (8-15 % increase) and increased crop yield (≥50 %) in comparison to control treatments. The current findings provide valuable insights into eco-friendly, cost-effective and sustainable alternatives for addressing R. solani infection and improving the agronomic performance of the fragrant rice cultivar MRQ76, contributing to food security.

Screening Plant Growth-Promoting Bacteria with Antimicrobial Properties for Upland Rice

This study explores beneficial bacteria isolated from the roots and rhizosphere soil of Khao Rai Leum Pua Phetchabun rice plants. A total of 315 bacterial isolates (KK001 to KK315) were obtained. Plant growth-promoting traits (phosphate solubilization and indole-3-acetic acid (IAA) production), and antimicrobial activity against three rice pathogens (Curvularia lunata NUF001, Bipolaris oryzae 2464, and Xanthomonas oryzae pv. oryzae) were assessed. KK074 was the most prolific in IAA production, generating 362.6 ± 28.0 μg/ml, and KK007 excelled in tricalcium phosphate solubilization, achieving 714.2 ± 12.1 μg/ml. In antimicrobial assays using the dual culture method, KK024 and KK281 exhibited strong inhibitory activity against C. lunata, and KK269 was particularly effective against B. oryzae. In the evaluation of antimicrobial metabolite production, KK281 and KK288 exhibited strong antifungal activities in cell-free supernatants. Given the superior performance of KK281, taxonomically identified as Bacillus sp. KK281, it was investigated further. Lipopeptide extracts from KK281 had significant antimicrobial activity against C. lunata and a minimum inhibitory concentration (MIC) of 3.1 mg/ml against X. oryzae pv. oryzae. LC-ESI-MS/MS analysis revealed the presence of surfactin in the lipopeptide extract. The crude extract was non-cytotoxic to the L-929 cell line at tested concentrations. In conclusion, the in vitro plant growth-promoting and disease-controlling attributes of Bacillus sp. KK281 make it a strong candidate for field evaluation to boost plant growth and manage disease in upland rice.

Impact of Rhizospheric Microbiome on Rice Cultivation

The rhizosphere niche is extremely important for the overall growth and development of plants. Evidently, it is necessary to understand the complete mechanism of plant microbe interactions of the rhizosphere for sustainable and low input productivity. To meet the increasing global food demand, rice (Oryza sativa L.) agriculture seeks optimal conditions. The unique oxic-anoxic interface of rice-growing soil has invited divergent microbes with dynamic biogeochemical cycles. This review provides the systematic analysis of microbes associated with the major biogeochemical cycles with the aim to generate better management strategies of rhizospheric microbiome in the field of rice agriculture. For instance, several methanogenic and methanotrophic bacteria in the rice rhizosphere make an equilibrium for methane concentration in the environment. The carbon sequestration in paddy soil is again done through many rhizospheric microorganisms that can directly assimilate CO2 with their photoautotrophic mode of nutrition. Also the phosphate solubilizing microbes remain to be the most important keys for the PGPR activity of the paddy ecosystem. In addition, rhizospheric microbiome remain crucial in degradation and solubilization of organo-sulfur and insoluble inorganic sulfides which can be taken by the plants. Further, this review elucidates on the advantages of using metagenomic and metaproteomic approaches as an alternative of traditional approaches to understand the overall metabolic pathways operational in paddy-field. These knowledges are expected to open new possibilities for designing the balanced microbiome used as inoculum for intensive farming and will eventually lead to exert positive impacts on rice cultivation.

Diazotrophic abundance and community structure associated with three meadow plants on the Qinghai-Tibet Plateau

Symbiotic diazotrophs form associations with legumes and substantially fix nitrogen into soils. However, grasslands on the Qinghai-Tibet Plateau are dominated by non-legume plants, such as Kobresia tibetica. Herein, we investigated the diazotrophic abundance, composition, and community structure in the soils and roots of three plants, non-legume K. tibetica and Kobresia humilis and the legume Oxytropis ochrocephala, using molecular methods targeting nifH gene. Diazotrophs were abundantly observed in both bulk and rhizosphere soils, as well as in roots of all three plants, but their abundance varied with plant type and soil. In both bulk and rhizosphere soils, K. tibetica showed the highest diazotroph abundance, whereas K. humilis had the lowest. In roots, O. ochrocephala and K. humilis showed the highest and the lowest diazotroph abundance, respectively. The bulk and rhizosphere soils exhibited similar diazotrophic community structure in both O. ochrocephala and K. tibetica, but were substantially distinct from the roots in both plants. Interestingly, the root diazotrophic community structures in legume O. ochrocephala and non-legume K. tibetica were similar. Diazotrophs in bulk and rhizosphere soils were more diverse than those in the roots of three plants. Rhizosphere soils of K. humilis were dominated by Actinobacteria, while rhizosphere soils and roots of K. tibetica were dominated by Verrumicrobia and Proteobacteria. The O. ochrocephala root diazotrophs were dominated by Alphaproteobacteria. These findings indicate that free-living diazotrophs abundantly and diversely occur in grassland soils dominated by non-legume plants, suggesting that these diazotrophs may play important roles in fixing nitrogen into soils on the plateau.

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.

Versatility of Stenotrophomonas maltophilia: Ecological roles of RND efflux pumps

S. maltophilia is a widely distributed bacterium found in natural, anthropized and clinical environments. The genome of this opportunistic pathogen of environmental origin includes a large number of genes encoding RND efflux pumps independently of the clinical or environmental origin of the strains. These pumps have been historically associated with the uptake of antibiotics and clinically relevant molecules because they confer resistance to many antibiotics. However, considering the environmental origin of S. maltophilia, the ecological role of these pumps needs to be clarified. RND efflux systems are highly conserved within bacteria and encountered both in pathogenic and non-pathogenic species. Moreover, their evolutionary origin, conservation and multiple copies in bacterial genomes suggest a primordial role in cellular functions and environmental adaptation. This review is aimed at elucidating the ecological role of S. maltophilia RND efflux pumps in the environmental context and providing an exhaustive description of the environmental niches of S. maltophilia. By looking at the substrates and functions of the pumps, we propose different involvements and roles according to the adaptation of the bacterium to various niches. We highlight that i°) regulatory mechanisms and inducer molecules help to understand the conditions leading to their expression, and ii°) association and functional redundancy of RND pumps and other efflux systems demonstrate their complex role within S. maltophilia cells. These observations emphasize that RND efflux pumps play a role in the versatility of S. maltophilia.

Characterization of Biomineralizing and Plant Growth-Promoting Attributes of Lithobiontic Bacteria

The application of mineral-solubilizing, plant growth-promoting bacteria as inoculants offers a promising alternative to chemical fertilizers. In the present study, lithic bacterial isolates were evaluated for mineral solubilization and plant growth-promoting potential. Among the 57 lithic bacterial isolates associated with different rock samples collected from various locations in Meghalaya, India, nine K-solubilizing isolates, six S-solubilizing isolates, five P- and Si-solubilizing isolates, and three Zn-solubilizing isolates with notable indole-3-acetic acid and siderophore production, and ACC deaminase activity were selected for further study. Based on 16S rRNA gene sequence analysis, isolates were affiliated to nine different genera (Arthrobacter, Acinetobacter, Pseudomonas, Halopseudomonas, Bacillus, Neobacillus, Peribacillus, Pantoea, and Priestia). On performing rice seed germination potentials, Pantoea agglomerans BL26, Priestia megaterium BL9, Bacillus subtilis GP2, Halopseudomonas xinjiangensis BL29, and Pseudomonas sp. BM1 were selected for in vitro pot experiments, being the most potent isolates. Following inoculation, all five isolates were found to significantly enhance growth of rice plants (P < 0.05). The maximum shoot length increased due to P. megaterium BL9, the maximum root length increased due to H. xinjiangensis BL29, and the maximum plant fresh weight increased due to P. megaterium BL9. The findings concluded that these five lithic bacterial isolates have potent plant growth-promoting potential with possible prospection through field trials. To the best of available literature, this is a first report on the characterization of lithic bacterial isolates as mineral solubilizers and plant growth promoters.

Piper caninum extract and Brevibacillus agri mixture suppresses rice leaf spot pathogen; Nigrospora oryzae and improves the production of red rice (Oryza sativa L)

Under the guise of enhancing productivity, using pesticides and artificial fertilizers in agriculture affects both the environment and living things. High chemical residues in food and the environment disrupt the health of consumers. One of the solutions that can bring about a reduction in the use of pesticides and chemicals is switching to organic fertilizers. The application of biopesticides originating from biological sources such as plant extracts and the use of microbes is gaining global acceptance. Therefore, this study aimed to obtain the best biopesticides and biostimulants that could suppress the leaf spot pathogen, Nigrospora oryzae, and increase the growth and yield of Bali red rice. The study contained four treatments, namely untreated control (F0), Piper caninum leaf extract (F1), Brevibacillus agri (F2), and fermented P. caninum leaf extract plus B. agri (F3). The treatments were arranged in a randomized complete block design, and each treatment was replicated three times. The parameters measured were the number of tillers per plant, number of leafs per plant, chlorophyll content, number of grains per panicle, grain weight, and grain yield. Furthermore, antimicrobial and antioxidants were assayed using SEM. GC-MS. At the end of the experiment, the disease index of the leaf spot was measured. The results showed that F3 significantly suppressed leaf spots caused by N. oryzae compared to other treatments, including untreated control in red rice. Additionally, the F3 significantly increased the number of productive tillers, number of grains per panicle, and grain yield compared to all other treatments. The F3 enhanced the crop yield at 6.19 tons/ha, an increase of 50% compared to the untreated control. The SEM.GC-MS results showed the presence of 2.3 butanediol, tetra-decanoic acid, butanoic acid, ethyl ester, benzene propanal, 3-(1,1-dimethylethyl)-a-methyl, a-N-Normethadol in treated plants with P. canicum plus B. agri.

Bacterioplankton Associated with Toxic Cyanobacteria Promote Pisum sativum (Pea) Growth and Nutritional Value through Positive Interactions

Research on Plant Growth-Promoting Bacteria (PGPB) has focused much more on rhizospheric bacteria. However, PGPB associated with toxic cyanobacterial bloom (TCB) could enter the rhizosphere through irrigation water, helping plants such as Pisum sativum L. (pea) overcome oxidative stress induced by microcystin (MC) and improve plant growth and nutritional value. This study aimed to isolate bacteria associated with toxic cyanobacteria, test PGPB properties, and inoculate them as a consortium to pea seedlings irrigated with MC to investigate their role in plant protection as well as in improving growth and nutritional value. Two bacterioplankton isolates and one rhizosphere isolate were isolated and purified on a mineral salt medium supplemented with 1000 μg/L MC and identified via their 16S rRNA gene. The mixed strains were inoculated to pea seedlings in pots irrigated with 0, 50, and 100 μg/L MC. We measured the morphological and physiological parameters of pea plants at maturity and evaluated the efficiency of the plant’s enzymatic and non-enzymatic antioxidant responses to assess the role and contribution of PGPB. Both bacterioplankton isolates were identified as Starkeya sp., and the rhizobacterium was identified as Brevundimonas aurantiaca. MC addition significantly (p < 0.05) reduced all the growth parameters of the pea, i.e., total chlorophyll content, leaf quantum yield, stomatal conductance, carotenoids, and polyphenol contents, in an MC concentration-dependent manner, while bacterial presence positively affected all the measured parameters. In the MC treatment, the levels of the pea’s antioxidant traits, including SOD, CAT, POD, PPO, GST, and ascorbic acid, were increased in the sterile pots. In contrast, these levels were reduced with double and triple PGPB addition. Additionally, nutritional values such as sugars, proteins, and minerals (Ca and K) in pea fruits were reduced under MC exposure but increased with PGPB addition. Overall, in the presence of MC, PGPB seem to positively interact with pea plants and thus may constitute a natural alternative for soil fertilization when irrigated with cyanotoxin-contaminated water, increasing the yield and nutritional value of crops.