Nature’s Pharmacy under Siege: Investigating Antibiotic Resistance Pattern in Endophytic Bacteria of Medicinal Plants

Antibiotic resistance poses a significant global health threat, necessitating a thorough understanding of its prevalence in various ecological contexts. Medicinal plants, renowned for their therapeutic properties, host endophytic bacteria that produce bioactive compounds. Understanding antibiotic resistance dynamics in these bacteria is vital for human health and antibiotic efficacy preservation. In this study, we investigated antibiotic resistance profiles in endophytic bacteria from five medicinal plants: Thankuni, Neem, Aparajita, Joba, and Snake plant. We isolated and characterized 113 endophytic bacteria, with varying resistance patterns observed against multiple antibiotics. Notably, 53 strains were multidrug-resistant (MDR), with 14 exhibiting extensive drug resistance (XDR). Thankuni-associated bacteria displayed 44% MDR and 11% XDR, while Neem-associated bacteria showed higher resistance (60% MDR, 13% XDR). Aparajita-associated bacteria had lower resistance (22% MDR, 6% XDR), whereas Joba-associated bacteria exhibited substantial resistance (54% MDR, 14% XDR). Snake plant-associated bacteria showed 7% MDR and 4% XDR. Genus-specific distribution revealed Bacillus (47%), Staphylococcus (21%), and Klebsiella (11%) as major contributors to MDR. Our findings highlight diverse drug resistance patterns among plant-associated bacteria and underscore the complexity of antibiotic resistance dynamics in diverse plant environments. Identification of XDR strains emphasizes the severity of the antibiotic resistance problem, warranting further investigation into contributing factors.

Endophytic Bacteria Promote the Growth of Suaeda glauca in Saline-Alkali Stress:Regulation of Osmotic Pressure and Antioxidative Defense System

Endophytic bacteria are promising bacterial fertilizers to improve plant growth under adverse environment.For ecological remediation of coastal wetlands,it was necessary to investigate the effect and interaction of endophytes on halophytes under saline-alkali stress.In this study,an endophytic bacterium strain HK1 isolated from halophytes was selected to infect Suaeda glauca under pH(7 and 8)and salinity gradient(150,300 and 450mmolL^(-1)).Strain HK1 was identified as Pantoea ananatis and it had ability to fix nitrogen,dissolve inorganic phosphorus and produce indole-3-aceticacid(IAA).The results showed that strain HK1 could promote the growth of S.glauca seedings when the salinity was less than 300mmolL^(-1),in view of longer shoot length and heavier fresh weight.The infected plants could produce more proline to decrease the permeability of cells,which content increased by 26.2%–61.1%compared to the non-infected group.Moreover,the oxidative stress of infected plants was relieved with the malondialdehyde(MDA)content decreased by 16.8%–32.9%,and the peroxidase(POD)activity and catalase(CAT)activity increased by 100%–500%and 6.2%–71.4%,respectively.Statistical analysis revealed that increasing proline content and enhancing CAT and POD activities were the main pathways to alleviate saline-alkali stress by strain HK1 infection,and the latter might be more important.This study illustrated that endophytic bacteria could promote the growth of halophytes by regulation of osmotic substances and strengthening antioxidant activities.This finding would be helpful for the bioremediation of coastal soil.

Plant growth-promoting properties and anti-fungal activity of endophytic bacterial strains isolated from Thymus altaicus and Salvia deserta in arid lands

Endophytes,as crucial components of plant microbial communities,significantly contribute to enhancing the absorption of nutrients such as nitrogen and phosphorus by their hosts,promote plant growth,and degrade pathogenic fungal mycelia.In this study,an experiment was conducted in August 2022 to explore the growth-promoting potential of endophytic bacterial strains isolated from two medical plant species,Thymus altaicus and Salvia deserta,using a series of screening media.Plant samples of Thymus altaicus and Salvia deserta were collected from Zhaosu County and Habahe County in Xinjiang Uygur Autonomous Region,China,in July 2021.Additionally,the inhibitory effects of endophytic bacterial strains on the four pathogenic fungi(Fusarium oxysporum,Fulvia fulva,Alternaria solani,and Valsa mali)were determined through the plate confrontation method.A total of 80 endophytic bacterial strains were isolated from Thymus altaicus,while a total of 60 endophytic bacterial strains were isolated from Salvia deserta.The endophytic bacterial strains from both Thymus altaicus and Salvia deserta exhibited plant growth-promoting properties.Specifically,the strains of Bacillus sp.TR002,Bacillus sp.TR005,Microbacterium sp.TSB5,and Rhodococcus sp.TR013 demonstrated strong cellulase-producing activity,siderophore-producing activity,phosphate solubilization activity,and nitrogen-fixing activity,respectively.Out of 140 endophytic bacterial strains isolated from Thymus altaicus and Salvia deserta,104 strains displayed anti-fungal activity against Fulvia fulva,Alternaria solani,Fusarium oxysporum,and Valsa mali.Furthermore,the strains of Bacillus sp.TR005,Bacillus sp.TS003,and Bacillus sp.TSB7 exhibited robust inhibition rates against all the four pathogenic fungi.In conclusion,the endophytic bacterial strains from Thymus altaicus and Salvia deserta possess both plant growth-promoting and anti-fungal properties,making them promising candidates for future development as growth-promoting agents and biocontrol tools for plant diseases.

Isolation and Identification of Houttuynia cordata Endophytic Bacteria and Study of Antibiotic Activity

[Objectives]To further explore the resources of biocontrol strains and provide new options for the control of pathogenic bacteria.[Methods]Houttuynia cordata endophytic bacteria were isolated and identified,and the antibiotic activity was explored.[Results]There are 8 strains(H1-H8)of endophytic bacteria isolated from the healthy plants of H.cordata,which had an antagonistic effect on the pathogenic bacteria.According to the gene sequence,the 8 strains were identified as Stenotrophomonas,Pseudomonas,and Bacillus,which strongly inhibited Colletotrichum(HC1),Fusarium(HC2),and Rhizoctonia(HC5)of H.cordata.On the PDA culture dish,the inhibition diameter of the 8 strains on Colletotrichum,Fusarium,and Rhizoctonia was 6,8,and 5 mm,respectively.[Conclusions]Pathogenic bacteria and endophytic bacteria inoculated with H.cordata seedlings showed that endophytic bacteria have certain antagonistic activity,and have the potential for development and application.

Biogenesis of antibacterial silver nanoparticles using the endophytic bacterium Bacillus cereus isolated from Garcinia xanthochymus

Objective:To synthesize the ecofriendly nanoparticles,which is viewed as an alternative to the chemical method which initiated the use of microbes like bacteria and fungi in their synthesis.Methods:The current study uses the endophytic bacterium Bacillus cereus isolated from the Garcinia xanthochymus to synthesize the silver nanoparticles(AgNPs).The AgNPs were synthesized by reduction of silver nitrate solution by the endophytic bacterium after incubation for 3-5 d at room temperature.The synthesis was initially observed by colour change from pale white to brown which was confirmed by UV-Vis spectroscopy.The AgNPs were further characterized using FTIR,SEM-EDX and TEM analyses.Results:The synthesized nanoparticles were found to he spherical with the size in the range of 20-40 nm which showed a slight aggregation.The energy-dispersive spectra of the nanoparticle dispersion confirmed the presence of elemental silver.The AgNPs were found to have antibacterial activity against a few pathogenic bacteria like Escherichia coli,Pseudomonas aeruginosa,Staphylococcus aureus,Salmonella typhi and Klebsiella pneumoniae.Conclusions:The endophytic bacteria identified as Bacillus cereus was able to synthesize silver nanoparticles with potential antibacterial activity.

Endophytic bacteria associated with endangered plant Ferula sinkiangensis K. M. Shen in an arid land： diversity and plant growth-promoting traits

Ferula spp. are traditional medicinal plants found in arid land. Large-scale excavation for extracting bioactive compounds from the plants in arid regions of Xinjiang over the last few years has, however, significandy decreased their distributions. Due to the urgent need for preservation of these plant resources, along with the need of searching for alternative source of the useful metabolites, it is important to screen the endophytic microbial resources associated with the plant Ferula sinkiangensis K. M. Shen. In the study, a total of 125 endophytic bacteria belonging to 3 phyla, 13 orders, 23 families, and 29 genera were isolated based on 16S rRNA gene sequencing data. Among the different isolates, three strains isolated from roots were potential novel species of the genera Porphyrobacter, Paracoccus and draycofatopsis. In this study, 79.4% and 57.1% of the total isolates were capable of producing indole-3-acetic acid （IAA） and siderophore, respectively. And, 40.6% of the strains inhibit the growth of fungal pathogen Afternaria alternata, 17.2% and 20.2% strains were positive for antagonism against Vertidllium dahlia 991 and V. dahlia 7, respectively. These results demonstrated that E sinkiangensis is a rich reservoir of endophytic bacterial resources with potential for production of biologically important functions such as plant growth-promoting factors.

The diversity and potential function of endophytic bacteria isolated from Kobreasia capillifolia at alpine grasslands on the Tibetan Plateau, China

A total of 50 endophytic bacterial isolates were obtained from Kobreasia capillifolia at alpine grasslands in the Eastern Qilian Mountains on the Tibetan Plateau in China. Based on the sequencing and phylogenetic analysis of 16 S r DNA genes, all isolates phylogenetically related closely to Bacillus, Acinetobacter, Stenotrophomonas, Brevundimonas, Arthrobacter, Curtobacterium, Paenibacillus, Plantibacter, Promicromonospora, Serratia, and Microbacterium, among which Bacillus was the predominant genus（47.8% of the total number of endophytic isolates）. These isolates possessed different biological functions. In 50 endophytic bacteria, 42 isolates produced indole acetic acid（IAA） on King medium. There were seven isolates showing potency of mineral phosphate solubilization in Pikovaskaia＇s（PKO） liquid medium. Seven isolates exhibited antagonistic effect against Fusarium avenaceum, Colletotrichum coccodes and Phoma foveata. This was the first report on diversity and plant growth promotion of endophytic bacteria from K. capillifolia on alpine grassland in the Eastern Qilian Mountains, Chain. It is essential for revealing the relationship among plant, microorganism, and the special environment because the potential function of endophytic bacteria made a contribution to the interactions of plants and endophytic bacteria.

In vitro establishment of shoot meristems of Ilex paraguariensis and identification of endophytic bacteria

Yerba mate(Ilex paraguariensis A.St.-Hil.)is a species of great economic,social and environmental importance for the southern regions of Brazil,Uruguay and Argentina.Currently the most diverse products are obtained from mate leaves,including mate tea.The objective of this study was to establish shoot meristem cultures(meristematic dome and a few primordia)of elite clones and identify the endophytic bacteria present in the explants.We tested the effect of clones(F1,F2,A03 and A07),culture media(MS,1/2MS,1/4MS and WPM),cytokinins(kinetin,BA and 2iP),activated charcoal(1,2 and 3 g L^-1),and disinfecting agent(sodium hypochlorite and mercuric chloride)on in vitro establishment.F1 and F2 clones were the most responsive for shoot meristem in vitro culture.WPM medium supplemented with 8.8 lM 2iP,0.2 lM NAA and 3 g L^-1 activated charcoal was the most suitable for the in vitro establishment of the F1 clone.No phytotoxic effect of the disinfectant was observed and some meristems sprouted.The isolated endophytic bacterium was identified for the first time in yerba mate as Agrobacterium larrymoorei.To conclude,we were able to establish in vitro culture of yerba mate using meristems as explants but the tissues were not free of endophytic microorganisms which could interfere with explant response.

Diversity and Plant Growth Promoting Ability of Culturable Endophytic Bacteria in Nepalese Sweet Potato

There is no information on Nepalese sweet potato endophytes. We isolated 243 endophytic bacteria belonging to 34 genera in six classes from 12 locations of Nepal. Among them, the predominant classes were Bacilli and Gammaproteobacteria. The principal component analysis revealed that the composition of bacterial classes was unrelated to the environmental parameters of the sampling sites. Regarding their plant growth promoting potentials, 57% of the strains demonstrated indole-3-acetic acid (IAA) producing ability while 5% strains had nitrogen fixing gene (nifH) and acetylene reduction assay (ARA) activity. The representative strains in all six classes showed antagonistic effect against bacterial pathogens while only Bacillus strain showed the effect against fungal pathogen. For endophytic traits, cellulase activity was observed in 5 classes, while pectinase activity was only in Proteobacteria. Fresh weight and vine length of sweet potato increased by inoculating mixed cultures of the isolates from each location.

Antibacterial and Antifungal Activity of Organic and Peptidic Extracts of Ecuadorian Endophytic Fungi

Antibacterial and antifungal activities of 32 organic and 14 peptidic extracts obtained from twelve endophytic fungi of the Collection of Endophytes Quito-Catolica were tested against the pathogenic bacteria Staphylococcus aureus, Pseudomonas aeruginosa, Serratia marcescens, Escherichia coli and Salmonella enteritidis, and against the fungal oomycete Pythium ultimum. It was observed that the extracts of Marasmiellus candidus (CEQCA-O1113), Xylaria laevis (CEQCA-O1399), Fusarium solani (CEQCA-O1393), Diaporthe helianthi (CEQCA-O1394) and Xylaria sp. (CEQCA-O1400) partially or totally inhibited the microorganisms tested. The extracts CEQCA-O1399.P1 and CEQCA-O1113.D1 showed fungistatic and fungicidal effects against P. ultimum, respectively. Six extracts strongly inhibited S. aureus, and E. coli was strongly inhibited by the extract CEQCA-O1113.E2. Based on a bioassay-guided approach, the extracts with strong bioactivity in the antibacterial assays by an agar diffusion method were also tested by a disk diffusion method, and the minimal inhibitory concentrations were determined by a microdilution assay. The most bioactive extract, CEQCA-O1113.D1, was also purified by high performance liquid chromatography. The extract recovered its initial bioactivity against S. aureus in two fractions after the purification. Overall, the results of this study highlight the potential of the fungal endophytes as producers of bioactive compounds.

Study on Endophytic Bacteria Diversity in the Root of Peperomia dindygulensis Miq. by Applying Clone Library Construction Method

[Objectives] To study the endophytic bacteria diversity in the root of Peperomia dindygulensis Miq. [Methods] The root of P.dindygulensis Miq. was taken as materials,culture-independent method was applied to build 16 S rDNA clone library for endophytic bacteria of P. dindygulensis Miq. [Results] In the 16 S rDNA clone library for endophytic bacteria of P. dindygulensis Miq.,95 clones separately belonged to 46 OTUs,Phylogenetic analysis indicated that these cloning sequences separately belonged to phylum Proteobacteria,phylum Bacteroidetes,phylum Actinobacteria,phylum Nitrospirae,and phylum Gemmatimonadetes. In these,phylum Proteobacteria accounted for 70. 53% of total number of clones,so it was the most dominant group in this library. [Conclusions]The endophytic bacteria diversity in the root of P.dindygulensis Miq. is rich and this study is expected to provide scientific basis for protection,development and use of resources of P. dindygulensis Miq.

Community Structure of Endophytic Bacteria in Chestnut, Castanea mollissima

[ Objective] The paper was to detect the species of endophytic bacteria in Chestnut （Castanea mollissima）. [ Method ] The 16S rDNA-V4 region of endophytic bacteria in chestnut （sample name BL） was sequenced by Illumina MiSeq high-throughput sequencing technology. The number of sequences and op- erational taxonomic units （OTUs） for each sample was sorted and calculated using Qiime and Mothur software. The abundance and α-diversity of species were analyzed. [ Result] The number of effective sequences and OTUs were 21 167/191. The rarefaction curves showed that adequate sampling was achieved, and the number of OTUs was close to saturation. The endophytic bacteria of chestnut belonged to 10 genera, including Koribacter （3.48%） , Solibacter （2.59%） , Bra- d^hizobium （ 3. 57% ）, Rhodoplanes （ 7. 41% ）, Methylobacterium （ 4. 20% ）, Agrobacterium （ 19. 73% ）, Kaistobacter （ 2. 05% ）, Sphingomonas （18.66%）, Acidovorax （35.98%）, and Methylibium （2.32%）. The dominant species were Acidovorax, Agrobacterium and Sphingomonas. [ Conclusion] Illumina high-throughput sequencing technology provided more accurate and scientific data resources for the study of endophytic bacteria in chestnut.

Effects of Transgenic DREB Toybean Dongnong50 on Diversity of Soil Nitrogen-fixing Bacteria

Drought is a bottleneck for worldwide soybean production which is getting more serious as the climate continues to worsen. Dehydration responsive element binding（DREB） is a kind of transcription factor that regulates the expression of stress tolerance-related genes in response to drought, high salinity and cold stress in plant. Soybean with DREB gene possesses the drought resisting capability which is helpful to increase the yield. However, the potential risk of genetically modified plants（GMPs） on soil microbial community is still in debate. In order to understand the effects of transgenic DREB soybean on the nitrogen-fixing bacteria, the diversity of nif H gene in pot experiments planted transgenic soybean and near-isogenic nontransgenic soybean under normal water condition and drought stress condition was analyzed by PCR-DGGE and sequence analysis. The results showed that transgenic soybean under normal water condition decrease the diversity of the nitrogen-fixing bacteria in the seeding stage and flowering stage, but had no notable effect in other stages. Under drought stress, transgenic soybean reduced the diversity of the nitrogen-fixing bacteria in the flowering stage, but had no notable effects on other stages. Phylogenic analysis revealed that g7, g13, g15 and g19 had a close relationship with Alphaproteobacteria, g12 had a close relationship with Azonexus, others were related to Betaproteobacteria and Burkholderia.

Endophytic bacteria associated with halophyte Seidlitzia rosmarinus Ehrenb.ex Boiss.from saline soil of Uzbekistan and their plant beneficial traits

Endophytic bacteria of halophytic plants play essential roles in salt stress tolerance.Therefore,an understanding of the true nature of plant-microbe interactions under extreme conditions is essential.The current study aimed to identify cultivable endophytic bacteria associated with the roots and shoots of Seidlitzia rosmarinus Ehrenb.ex Boiss.grown in the salt-affected soil in Uzbekistan and to evaluate their plant beneficial traits related to plant growth stimulation and stress tolerance.Bacteria were isolated from the roots and the shoots of S.rosmarinus using culture-dependent techniques and identified by the 16S rRNA gene.RFLP(Restriction Fragment Length Polymorphism)analysis was conducted to eliminate similar isolates.Results showed that the isolates from the roots of S.rosmarinus belonged to the genera Rothia,Kocuria,Pseudomonas,Staphylococcus,Paenibacillus and Brevibacterium.The bacterial isolates from the shoots of S.rosmarinus belonged to the genera Staphylococcus,Rothia,Stenotrophomonas,Brevibacterium,Halomonas,Planococcus,Planomicrobium and Pseudomonas,which differed from those of the roots.Notably,Staphylococcus,Rothia and Brevibacterium were detected in both roots and shoots,indicating possible migration of some species from roots to shoots.The root-associated bacteria showed higher levels of IAA(indole-3-acetic acid)synthesis compared with those isolated from the shoots,as well as the higher production of ACC(1-aminocyclopropane-1-carboxylate)deaminase.Our findings suggest that halophytic plants are valuable sources for the selection of microbes with a potential to improve plant fitness under saline soils.

Analyses on Community Composition and Diversity of Endophytic Bacteria in Different Tissues of Anoectochilus roxburghii

[Objective] This study aimed to investigate the diversity of community composition and diversity of endophytic bacteria in Anoectochilus roxburghii.[Method] By using Illumina MiSeq high-throughput sequencing technology, the 16S rDNA-V4 region of endophytic bacteria in ^4. roxburghii was sequenced. Qiime and Mothur software packages were used to sort and count the number of sequences and operational taxonomic units （OTUs） and analyze the species abundance and distribution, Alpha diversity and differences of species abundance among samples. [Result] The number of effective sequences/OTUs for each sample was 110485/247 （stem） and 98524/259 （leaf） , respectively. The rarefaction curve showed that adequate sampling was performed. The number of OTUs had almost reached a saturation point. Endophytic bacteria in A. roxburghii mainly belonged to the genera Acidovorax, Pseudomonas, Sphingomonas and Halomonas. [Conclusions] Illumi-na MiSeq high-throughput sequencing technology provides more accurate and scientific data resources for the study of endophytic bacteria in A. roxburghii.

Biotechnological Potential of Endophytic Bacteria to Improve the Micropropagated Seedling of Variety RB92579 Sugarcane(Saccharum officinarum L.)

Endophytic bacteria may influence agricultural production in several ways, including promoting plant growth. Two experiments were conducted in order to evaluate the combination of endophytic bacteria from the Brazilian Northeast region aims at the commercial introduction of the inoculation of these bacteria in micropropagated sugarcane plants using a temporary immersion bioreactor. One experiment was done in tubes with sterile commercial substrate, and the other was done in pots with soil;both were installed in a greenhouse. A mixed inoculation was performed in six inoculated endophytic diazotrophic bacteria in micropropagated sugarcane plants, variety RB92579. In the experiment with soil, the mixed inoculation significantly increased the shoot dry matter of plants without the addition of nitrogen fertilizer. However, the accumulation of total-N in the tissues showed no significant differences between treatments with and without nitrogen fertilization. The evaluation of micropropagated seedlings showed no increases in the parameters tested. The results showed that the response of inoculation in temporary immersion bioreactor micropropagation is possible, and that the application of homologous strains may have contributed to a better response by the interaction of endophytic bacteria with sugarcane RB92579. Further studies should be conducted to improve the methodology, which indicates a great potential to optimize this process on a commercial scale.

Selection of Cocoa Tree (<i>Theobroma cacao</i>Linn) Endophytic Bacteria Solubilizing Tri-Calcium Phosphate, Isolated from Seedlings Grown on Soils of Six Producing Regions of C&ocirc;te d’Ivoire

Phosphorus (P) is an essential macronutrient for the growth and development of cocoa tree (Theobroma cacao Linn). Most of the soils used for cocoa farming in C?te d’Ivoire are low in phosphorus. But cocoa farmers generally have a widespread reluctance to invest in chemicals fertilizers due to high costs and environmental associated risk. Phosphate Solubilizing Bacteria (PSB) are kwon to play an important role in supply of phosphorous to plants in a sustainable manner in P deficient soils. The aim of this research was to screen the endophytic bacteria of cocoa nurseries able to solubilize tri-calcium phosphate. Seedlings of two varieties of cocoa (P7 and NA32) and seedlings of an all-comer, were grown on eighteen (18) samples soils collected in six producing regions of C?te d’Ivoire. A total of 218 endophytic bacteria were isolated and tested on the Pikovskaya’s agar medium, containing Ca3 (PO4) 2. The colonies with clear zone around the microbial growth were suspected as phosphate solubilizing bacteria. Out of 218 bacteria, 90 (41.28%) showed a clear zone around colonies after 7 days of incubation. The Phosphate Solubilization Index (PSI) ranged from 20% to 200%. Bacterial isolated from the soils of Duékoué locality showed the highest mean index of 137.67%. Five PSB (CEBSP5, CEBSP6, CEBSP7, CEBSP8, and CEBSP9) from Duékoué soils and two PSB (CEBSP12 and CEBSP13) from Soubré soils have a PSI ranged from 150% to 200%. Further study in greenhouse and in field condition will confirm the use of these PSB as biofertilizer to increase the available P content in soils, reduce environmental pollution and promote sustainable agriculture.

Isolation and Identification of Bacterial Endophytes from Grasses along the Oregon Coast

Bacterial endophytes have been shown to improve abiotic and biotic stress responses in plants. Plants growing under harsh conditions along the Oregon Coast could contain bacterial endophytes that improve persistence and growth of grasses in this environment. Thirty-four plants consisting of eight different species were collected along the Oregon coast from four different sites. Bacterial endophytes were isolated from root crown, stem and leaf tissues. A portion of the 16S rRNA ITS regions of each isolate was amplified, sequenced, and used to perform a BLAST search against the nucleotide database collection at National Center for Biotechnology Information. One-hundred and thirty-three different bacterial isolates, ninety-four of which were unique, representing thirty-six different taxonomic groups were found. Over 50% of the total bacteria isolates were in just five taxonomic groups. Pseudomonads were the most predominant bacteria isolated, making up 20.3% of the total isolates, followed by Curtobacterium and Microbacterium, each at 8.2%, Bacillus at 7.5% and Xanthomomas at 6%. Forty-seven percent (17 of 36) of the taxonomic groups contained only a single isolate. Fourteen bacterial isolates from five taxonomic groups, nine of which were from the genus Pseudomonas, were found to have 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity, an enzyme associated with improving plant growth under stress. These newly discovered bacterial endophytes will be a valuable biological resource to develop approaches to increase the yield and adaptability of grasses and other crops grown in diverse environments and to meet the challenges associated with an unpredictable climate.

Testing of Bacterial Endophytes from Non-Host Sources as Potential Antagonistic Agents against Tomato Wilt Pathogen <i>Ralstonia solanacearum</i>

The study was taken up with the objective of testing whether the endophytic organisms isolated from crops that are normally non-hosts to the bacterial wilt pathogen Ralstonia solanacearum possessed pathogen-antagonistic activity and to evaluate the selected isolates for the alleviation of wilt disease in the target tomato crop through horizontal movement of promising organisms. Sixteen endophytic bacteria (EB) isolated from the micropropagated cultures of grape, watermelon and papaya were tested for potential antagonistic effects against R. solanacearum tomato isolate “NH-01” through agar-well diffusion assay. Enterobacter cloacae from papaya (EB-11) displayed the maximum antagonistic effect followed by Bacillus subtilis (EB-06) and B. flexus (EB-07) from watermelon and B. pumilus (EB-02) from grape. Testing the above organisms for crop protection through seed fortification of susceptible tomato cv. Arka Vikas at sowing in R. solanacearum inoculated (Ral+) organic cocopeat showed EB-02 and EB-11 promising (33% and 32% survival, respectively, four weeks after sowing against 15% in Ral+ control). A second trial showed 37%, 28%, 21% and 55% seedling survival 6 weeks after sowing for EB-02, EB-06, EB-07 and EB-11 respectively, compared to 2.5% in non-treated control. Assessing the four endophytes for crop protection in Ral+ sick-soil through seedling fortification at transplanting indicated less disease incidence in treated sets (40%, 40%, 20% and 20% survival, respectively, six weeks after transplanting) over non-fortified control (5%). Endophytic fortification of seedlings through hypocotyl inoculation showed some systemic resistance induction upon seedling transplanting to sick soil but not with petiole fortification. Seedling growth was enhanced by the isolates EB-06 and EB-07. The study thus identifies four endophytic organisms from crops unrelated to tomato possessing potential antagonistic activity against the wilt pathogen and prospects for exploitation as biocontrol agents coupled with seedling growth promotion effects.

Antimicrobial and plant growth-promoting activities of bacterial endophytes isolated from Calotropis procera(Ait.)W.T.Aiton

Bacterial endophytes are beneficial to their hosts as they can fix nitrogen in the soil and make it available to the host.Endophytic bacteria also secrete plant growth-promoting hormones to support their host plants under normal as well as stress conditions.The current study aimed to isolate endophytic bacteria from different parts of Calotropis procera,i.e.,roots,stem and leaves of Calotropis procera(Ait.)W.T.Aiton.Plants were collected from the Lundkhwar,district Mardan.A total of 12 bacterial strains,i.e.,six from roots,three from the stem and three from the leaves were isolated.The strains were screened for their growth-promoting activity in rice plants because rice shows a quick and easy response to the bioactive compounds present in the culture filtrate(CF)of the potent endophytic strains.The rice plants were cultivated in pots containing 30 mL of 0.8%w/v water-agar medium.The pots were placed in a growth chamber,operated at 28±0.3℃ for 14 h(day);and 25±0.3℃ for 10 h(night),at 70%relative-humidity.Among the isolated strains,R1,S1,S3,L1,R5 and R6 showed visible growth promotion in rice plants.The biochemical analysis revealed that the strains were able to produce indole acetic acid(IAA)and flavonoids in higher quantities.Moreover,the strains also produced bioactive compounds that inhibited the growth of Escherichia coli and Aspergillus flavus using the well diffusion method.From the results,it was concluded that these strains can secrete potent compounds that can promote the host plant growth and inhibit the growth of pathogenic microorganisms and,therefore,can be used as bio-fertilizer and bio-control agents.