Mangrove endophyte promotes reforestation tree (Acacia polyphylla) growth

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.

The soil microbiome affects patterns of local adaptation in an alpine plant under moisture stress

PREMISE

The soil microbiome plays a role in plant trait expression and fitness, and plants may be locally adapted or maladapted to their soil microbiota. However, few studies of local adaptation in plants have incorporated a microbial treatment separate from manipulations of the abiotic environment, so our understanding of microbes in plant adaptation is limited.

METHODS

Here we tested microbial effects on local adaptation in four paired populations of an abundant alpine plant from two community types, dry and moist meadow. In a 5-month greenhouse experiment, we manipulated source population, soil moisture, and soil microbiome and measured plant survival and biomass to assess treatment effects.

RESULTS

Dry meadow populations had higher biomass than moist meadow populations at low moisture, demonstrating evidence of local adaptation to soil moisture in the absence of microbes. In the presence of microbes, dry meadow populations had greater survival than moist meadow populations when grown with dry meadow microbes regardless of moisture. Moist meadow populations showed no signs of adaptation or maladaptation.

CONCLUSIONS

Our research highlights the importance of microbial mutualists in local adaptation, particularly in dry environments with higher abiotic stress. Plant populations from environments with greater abiotic stress exhibit different patterns of adaptation when grown with soil microbes versus without, while plant populations from less abiotically stressful environments do not. Improving our understanding of the role microbes play in plant adaptation will require further studies incorporating microbial manipulations.

Screening of endophytic fungi from Cremastra appendiculata and their potential for plant growth promotion and biological control

Biocontrol fungi are widely used to promote plant growth and pest control. Four fungi were isolated from Cremastra appendiculata tubers and screened for plant growth-promoting and antagonistic effects. Based on the morphological characterization and ITS, 18S rRNA and 28S rRNA gene sequencing analysis, the fungi were identified to be related to Colletotrichum gloeosporioides (DJL-6), Trichoderma tomentosum (DJL-9), Colletotrichum godetiae (DJL-10) and Talaromyces amestolkiae (DJL-15). The growth inhibition tests showed that the four isolates had different inhibitory effects on Colletotrichum fructicola, Alternaria alternata and Alternaria longipes, among which DJL-9 showed the highest inhibitory activity. Their culture filtrates (especially that of DJL-15) can also inhibit pathogens. Four isolates were positive for the production of indole-3-acid (IAA) and β-1,3-glucanase and possessed proteolytic activity but were negative for the production of iron siderophore complexes. The four fungi showed strong nitrogen fixation and potassium dissolution abilities. In addition to DJL-9 being able to solubilize phosphate, DJL-10 was able to produce chitinase and cellulase. Pot experiments indicated that the four fungi increased the germination rate of C. appendiculata and soybean seeds and increased soybean radicle growth and plant biomass. Among them, DJL-6 had a better growth-promoting effect. Therefore, we successfully screened the biocontrol potential of endophytes from C. appendiculata, with a focus on preventing fungal diseases and promoting plant growth, and selected strains that could provide nutrients and hormones for plant growth.

A Comprehensive Overview of Nanotechnology in Sustainable Agriculture

Plant nutrition is crucial in crop productivity and providing food security to the ever-expanding population. Application of chemical/biological fertilizers and pesticides are the mainstays for any agricultural economy. However, there are unintended consequences of using chemical fertilizers and pesticides. The environment and ecological balance are adversely affected by their usage. Biofertilizers and biopesticides counter some undesired environmental effects of chemical fertilizers/pesticides; inspite of some drawbacks associated with their use. The recent developments in nanotechnology offer promise towards sustainable agriculture. Sustainable agriculture involves addressing the concerns about agriculture as well as of the environment. This review briefs about important nanomaterials used in agriculture as nanofertilizers, nanopesticides, and a combination called nanobiofertilizers. Both nanofertilizers and nanopesticides enable slow and sustained release besides their eco-friendly environmental consequences. They can be tailored to specific needs to crop. Nanofertilizers also offer greater stress tolerance and, therefore, of considerable value in the era of climate change. Furthermore, nanofertilizers/nanopesticides are applied in minute amounts, reducing transportation costs associated and thus positively affecting the economy. Their uses extend beyond such as if nanoparticles (NPs) are used at high concentrations; they affect plant pathogens adversely. Polymer-based biodegradable nanofertilizers and nanopesticides offer various benefits. There is also a dark side to the use of nanomaterials in agriculture. Nanotechnology often involves the use of metal/metal oxide nanoparticles, which might get access to human bodies leading to their accumulation through bio-magnification. Although their effects on human health are not known, NPs may reach toxic concentrations in soil and runoff into rivers, and other water bodies with their removal to become a huge economic burden. Nevertheless, a risk-benefit analysis of nanoformulations must be ensured before their application in sustainable agriculture.

Plant Growth Promotion and Biocontrol by Endophytic and Rhizospheric Microorganisms From the Tropics: A Review and Perspectives

Currently, the tropics harbor a wide variety of crops to feed the global population. Rapid population expansion and the consequent major demand for food and agriculture-based products generate initiatives for tropical forest deforestation, which contributes to land degradation and the loss of macro and micronative biodiversity of ecosystems. Likewise, the entire dependence on fertilizers and pesticides also contributes to negative impacts on environmental and human health. To guarantee current and future food safety, as well as natural resource preservation, systems for sustainable crops in the tropics have attracted substantial attention worldwide. Therefore, the use of beneficial plant-associated microorganisms is a promising sustainable way to solve issues concerning modern agriculture and the environment. Efficient strains of bacteria and fungi are a rich source of natural products that might improve crop yield in numerous biological ways, such as nitrogen fixation, hormone production, mobilization of insoluble nutrients, and mechanisms related to plant biotic and abiotic stress alleviation. Additionally, these microorganisms also exhibit great potential for the biocontrol of phytopathogens and pest insects. This review addresses research regarding endophytic and rhizospheric microorganisms associated with tropical plants as a sustainable alternative to control diseases and enhance food production to minimize ecological damage in tropical ecosystems.

Pharmacological Properties, Volatile Organic Compounds, and Genome Sequences of Bacterial Endophytes from the Mangrove Plant Rhizophora apiculata Blume

Mangrove plant endophytic bacteria are prolific sources of bioactive secondary metabolites. In the present study, twenty-three endophytic bacteria were isolated from the fresh roots of the mangrove plant Rhizophora apiculata. The identification of isolates by 16S rRNA gene sequences revealed that the isolated endophytic bacteria belonged to nine genera, including Streptomyces, Bacillus, Pseudovibrio, Microbacterium, Brevibacterium, Microbulbifer, Micrococcus, Rossellomorea, and Paracoccus. The ethyl acetate extracts of the endophytic bacteria’s pharmacological properties were evaluated in vitro, including antimicrobial, antioxidant, α-amylase and α-glucosidase inhibitory, xanthine oxidase inhibitory, and cytotoxic activities. Gas chromatography–mass spectrometry (GC-MS) analyses of three high bioactive strains Bacillus sp. RAR_GA_16, Rossellomorea vietnamensis RAR_WA_32, and Bacillus sp. RAR_M1_44 identified major volatile organic compounds (VOCs) in their ethyl acetate extracts. Genome analyses identified biosynthesis gene clusters (BGCs) of secondary metabolites of the bacterial endophytes. The obtained results reveal that the endophytic bacteria from R. apiculata may be a potential source of pharmacological secondary metabolites, and further investigations of the high bioactive strains—such as fermentation and isolation of pure bioactive compounds, and heterologous expression of novel BGCs in appropriate expression hosts—may allow exploring and exploiting the promising bioactive compounds for future drug development.

Distinct Endophytic Bacterial Communities Inhabiting Seagrass Seeds

Seagrasses are marine angiosperms that can live completely or partially submerged in water and perform a variety of significant ecosystem services. Like terrestrial angiosperms, seagrasses can reproduce sexually and, the pollinated female flower develop into fruits and seeds, which represent a critical stage in the life of plants. Seed microbiomes include endophytic microorganisms that in terrestrial plants can affect seed germination and seedling health through phytohormone production, enhanced nutrient availability and defence against pathogens. However, the characteristics and origins of the seagrass seed microbiomes is unknown. Here, we examined the endophytic bacterial community of six microenvironments (flowers, fruits, and seeds, together with leaves, roots, and rhizospheric sediment) of the seagrass Halophila ovalis collected from the Swan Estuary, in southwestern Australia. An amplicon sequencing approach (16S rRNA) was used to characterize the diversity and composition of H. ovalis bacterial microbiomes and identify core microbiome bacteria that were conserved across microenvironments. Distinct communities of bacteria were observed within specific seagrass microenvironments, including the reproductive tissues (flowers, fruits, and seeds). In particular, bacteria previously associated with plant growth promoting characteristics were mainly found within reproductive tissues. Seagrass seed-borne bacteria that exhibit growth promoting traits, the ability to fix nitrogen and anti-pathogenic potential activity, may play a pivotal role in seed survival, as is common for terrestrial plants. We present the endophytic community of the seagrass seeds as foundation for the identification of potential beneficial bacteria and their selection in order to improve seagrass restoration.

The potential of nanomaterials associated with plant growth-promoting bacteria in agriculture

The impacts of chemical fertilizers and pesticides have raised public concerns regarding the sustainability and security of food supplies, prompting the investigation of alternative methods that have combinations of both agricultural and environmental benefits, such as the use of biofertilizers involving microbes. These types of microbial inoculants are living microorganisms that colonize the soil or plant tissues when applied to the soil, seeds, or plant surfaces, facilitating plant nutrient acquisition. They can enhance plant growth by transforming nutrients into a form assimilable by plants and by acting as biological control agents, known as plant growth-promoting bacteria. The potential use of bacteria as biofertilizers in agriculture constitutes an economical and eco-friendly way to reduce the use of chemical fertilizers and pesticides. In this context, nanotechnology has emerged as a new source of quality enrichment for the agricultural sector. The use of nanoparticles can be an effective method to meet the challenges regarding the effectiveness of biofertilizers in natural environments. Given the novel sustainable strategies applied in agricultural systems, this review addresses the effects of nanoparticles on beneficial plant bacteria for promoting plant growth.

Harnessing Bacterial Endophytes for Promotion of Plant Growth and Biotechnological Applications: An Overview

Endophytic bacteria colonize plants and live inside them for part of or throughout their life without causing any harm or disease to their hosts. The symbiotic relationship improves the physiology, fitness, and metabolite profile of the plants, while the plants provide food and shelter for the bacteria. The bacteria-induced alterations of the plants offer many possibilities for biotechnological, medicinal, and agricultural applications. The endophytes promote plant growth and fitness through the production of phytohormones or biofertilizers, or by alleviating abiotic and biotic stress tolerance. Strengthening of the plant immune system and suppression of disease are associated with the production of novel antibiotics, secondary metabolites, siderophores, and fertilizers such as nitrogenous or other industrially interesting chemical compounds. Endophytic bacteria can be used for phytoremediation of environmental pollutants or the control of fungal diseases by the production of lytic enzymes such as chitinases and cellulases, and their huge host range allows a broad spectrum of applications to agriculturally and pharmaceutically interesting plant species. More recently, endophytic bacteria have also been used to produce nanoparticles for medical and industrial applications. This review highlights the biotechnological possibilities for bacterial endophyte applications and proposes future goals for their application.

Robertkochia solimangrovi sp. nov., isolated from mangrove soil, and emended description of the genus Robertkochia

To date, there is sparse information for the genus Robertkochia with Robertkochia marina CC-AMO-30D^T as the only described member. We report here a new species isolated from mangrove soil collected at Malaysia Tanjung Piai National Park and perform polyphasic characterization to determine its taxonomic position. Strain CL23^T is a Gram-negative, yellow-pigmented, strictly aerobic, catalase-positive and oxidase-positive bacterium. The optimal growth conditions were determined to be at pH 7.0, 30–37 °C and in 1–2 % (w/v) NaCl. The major respiratory quinone was menaquinone-6 (MK-6) and the highly abundant polar lipids were four unidentified lipids, a phosphatidylethanolamine and two unidentified aminolipids. The 16S rRNA gene similarity between strain CL23^T and R. marina CC-AMO-30D^T is 96.67 %. Strain CL23^T and R. marina CC-AMO-30D^T clustered together and were distinguished from taxa of closely related genera in 16S rRNA gene phylogenetic analysis. Genome sequencing revealed that strain CL23^T has a genome size of 4.4 Mbp and a G+C content of 40.72 mol%. Overall genome related indexes including digital DNA–DNA hybridization value and average nucleotide identity are 17.70 % and approximately 70%, below the cutoffs of 70 and 95%, respectively, indicated that strain CL23^T is a distinct species from R. marina CC-AMO-30D^T. Collectively, based on the phenotypic, chemotaxonomic, phylogenetic and genomic evidences presented here, strain CL23^T is proposed to represent a new species with the name Robertkochia solimangrovi sp. nov. (KCTC 72252^T=LMG 31418^T). An emended description of the genus Robertkochia is also proposed.

The Effect of Microbial Endophyte Consortia on Pseudotsuga menziesii and Thuja plicata Survival, Growth, and Physiology Across Edaphic Gradients

Increased frequency of droughts and degraded edaphic conditions decreases the success of many reforestation efforts in the Pacific Northwest. Microbial endophyte consortia have been demonstrated to contribute to plant growth promotion and protection from abiotic and biotic stresses – specifically drought conditions – across a number of food crops but for limited tree species. Our research aimed to investigate the potential to improve establishment of economically and ecologically important conifers through a series of in situ field trials and ex situ simulations. Microbial endophyte consortia from Salicaceae, previously shown to confer drought tolerance, and conifer endophyte strains with potentially symbiotic traits were selected for trials with Douglas-fir (Pseudotsuga menziesii) and western redcedar (Thuja plicata). Reductive experimentation was used to subject seedlings to a spectrum of simulated drought levels or presence/absence of fertilizer, testing hypotheses that endophyte consortia impart improved drought resistance and growth promotion, respectively. Inoculation from Salicaceae consortia significantly (p ≤ 0.05) improved survival among seedlings of both species subject to increasing drought stress, with T. plicata seedlings surviving at twofold higher rates in extreme drought conditions. Both species demonstrated improved growth 540 days after inoculation of seed with conifer derived consortia. In the carefully controlled greenhouse experiments with both species, seedling Fv/Fm and SPAD values remained significantly (p ≤ 0.05) more stable in inoculated treatment groups as stress increased. Our findings confirm that multi-strain consortia may be applied as seed or field amendment to conifers, and the approach is efficient in garnering a positive growth response and can mitigate abiotic stressors.