Bacterial Biocontrol Agents Research Articles

Evaluation of Bioagents against Stemphylium vesicarium Inducing Stemphylium Blight in Onions (Allium cepa L.)

Stemphylium blight of onion incited by S. vesicarium is one of the economically important diseases, causing severe yield losses in onion crop. The present investigation was carried out to evaluate efficacy of different bioagents against S. vesicarium under in vitro conditions. The experiment was laid out in a Completely Randomized Design (CRD) with three replications per treatment. Five fungal biocontrol agents viz., Trichoderma harzianum, T. viride, T. hamatum, T. virens and a fungal consortium from MPKV, Rahuri along with two bacterial biocontrol agents namely Pseudomonas fluorescens and Bacillus subtilis were evaluated for their effectiveness against S. vesicarium. The results showed significant variation in the inhibitory effects of bioagents on the mycelial growth of the test pathogen with percent growth inhibition ranging between 53.70 to 85.19 per cent. T. harzianum was reported to be most effective, showing a minimum colony diameter of 13.33 mm with the highest growth inhibition (85.19%) thus reported as superior to all other treatments whereas, Pseudomonas fluorescens was reported with a least percent growth inhibition (53.70%).

Sustainable management of blister and grey blight diseases of tea using antagonistic and plant growth promoting microbes in Western Ghats of India

The blister and grey blights are the devastating leaf diseases in tea. The severity of blister and grey blight diseases in tea ranged from 22% to 68% and 11.41%–57.02%, respectively in a survey conducted in Southern India during 2022–2023. The morphological and molecular identifications of pathogens revealed that Exobasidium vexans and Neopestalotiopsis clavispora were responsible for causing blister and grey blights on tea in southern India. The conventional management strategy with foliar spray of synthetic fungicides result in fungicidal residue in tea causes environmental pollution and health hazards to human. To overcome this the current study aims to manage the blister and grey blight diseases of tea through the microbial biocontrol agents. The bacterial biocontrol agents viz., Bacillus subtilis (BBV57), Bacillus amyloliquefaciens (TNAU), Pseudomonas fluorescens (Pf1) and the fungal antagonist, Trichoderma asperellum (TV 1) were evaluated for their efficacy against the both blight diseases. All the bio agents have significantly reduced the basidiospore germination and the mycelial growth of E. vexans and N. clavispora, respectively. Among the bio agents, B. amyloliquefaciens registered 88.36% reduction in the germination of E. vexans basidiospore and 85.56% of mycelial growth reduction of N. clavispora in vitro (P < 0.05). Under field conditions the combined soil and foliar application of bacterial antagonists viz., B. subtilis, B. amyloliquefaciens and P. fluorescens each with 1 ˟ 1011 CFU/ml @ 5% concentration at 7 days interval significantly reduced the blister blight incidence with 53.53% & 51.53% reduction over control and 51.53% & 43.65% of reduction over initial during first and second year, respectively. The combined application also reduced the grey blight incidence with 53.53% & 52.00% reduction over control and 56.81% & 47.65% of reduction over initial during first and second year, respectively. This treatments with bioagents were almost comparable with synthetic treatments, such as copper oxy chloride (0.25%) and hexaconazole (0.25%) with 64.63% and 64.76% reduction of blister and grey blight reduction in first year; 59.74%, 51.11% reduction in second year over control (P < 0.05), respectively. Thus, the application of B. subtilis, B. amyloliquefaciens and P. fluorescens can be recommended for the sustainable management of tea blister and grey blight diseases in tea gardens.

Metabolite profiling and molecular characterization of NBAIR BSWG1: A potential strain of Bacillus subtilis against Fusarium oxysporium f. sp. udum

To address the fungal wilt of pigeon pea caused by Fusarium oxysporium f. sp. udum, farmers currently rely on chemical fungicides, despite their harmful effects. However, there is a growing need for safer alternatives like green pesticides. Bacterial biocontrol agents and their derivatives serve as potential green pesticides in the management of plant pathogens. In the present study, we aimed to identify indigenous Bacillus subtilis strains effective against F. oxysporium f. sp. udum. We used PCR and MALDI-TOF analysis to identify the active components responsible for the efficiency of efficient strain. Biochemical studies of cell-free extracts extracted from B. subtilis strains demonstrated the highest biosurfactant activity in NBAIR BSWG1, with an oil displacement of 2 cm and an emulsification index of 60 %. Molecular characterization confirmed the presence of surfactin, fengycin, and iturin coding genes in the B. subtilis strains, among them, NBAIR BSWG1 showed the highest number of lipopeptide-producing genes. Meanwhile, NBAIR BSWG1 showed inhibition of 79.84 % against F. oxysporium f. sp. udum using cell-free extract. Further metabolite profiling of NBAIR BSWG1 using MALDI-TOF analysis further confirmed surfactin, fengycin, and iturin in the purified cell-free extract of NBAIR BSWG1. Two peaks with m/z of 923.77 and 1149.92 were identified as novel lipopeptide compounds which need further characterization. The present study identified NBAIR BSWG1 as an efficient bacterial strain for the inhibition of F. oxysporium f. sp. udum and its antifungal properties are mainly due to the production of cyclic lipopeptides.

Persistence and Microbiome Modification in Rhizoctonia solani-Inoculated Rhizosphere Following Amendment with a Bacillus Biocontrol Agent

Bacterial biocontrol agents that antagonize soilborne pathogens are increasingly considered alternatives to chemical pesticides, but their in vivo efficacy is often inconsistent, restricting commercial use. The efficacy of a biocontrol agent can depend on rhizosphere competence and its interaction with native microbiomes, which can affect ecosystem functioning. This study investigated the capacity of a Bacillus cereus sensu lato biocontrol strain (S-25) to persist on roots and in the rhizosphere of cucumber and evaluated its impact on bacterial and fungal community composition in the rhizosphere in the absence and presence of Rhizoctonia solani, the causative agent of damping-off disease in young seedlings. Following amendment, S-25 abundance in the cucumber rhizosphere decreased by two orders of magnitude but remained relatively high for the duration of the experiment, in contrast to the root surface, where it was not detected. Amendment with S-25 significantly reduced the incidence of disease caused by R. solani without reducing the relative abundance of the fungal pathogen. Interestingly, R. solani did not substantially alter the rhizosphere microbial community, whereas S-25 reduced bacterial diversity and facilitated a shift in community composition, with increased relative abundance of Acidobacteriota and Actinomycetota, and reduced abundance of Pseudomonadota, Bacteroidota, and Verrucomicrobiota. Collectively, this study provides important insights into the mode of persistence of biocontrol agents and their effect on native microbiomes in the rhizosphere of pathogen-inoculated plants. It demonstrates that amendment can significantly alter local microbiomes and suggests that optimizing amendment regimes or selecting strains with higher rhizosphere competence can enhance future biocontrol agents.

2-heptanone and 2,3-butanediol from endophytic Bacillus subtilis GEB-1 against root-knot nematode, Meloidogyne enterolobii: a computational and experimental approach

ABSTRACT Meloidogyne enterolobii is regarded as one of the most severe and threatening pathogens worldwide. Guava production in India is quenched by the invasion of root-knot nematode, Meloidogyne enterolobii. Bacterial bio-control agents confer resistance against nematodes by producing various bioactive molecules. Exploiting these biomolecules will lead to the development of novel nematicidal formulations for managing plant parasitic nematodes. Considering this, our present investigation was focused on the isolation and identification of endophytic bacterial communities from wild guava Psidium eugeniaefolia. Amongst various endophytes, Bacillus subtilis GEB-1 exhibited a 90% reduction in the population of M. enterolobii. Cell-free supernatant extracts of B. subtilis GEB-1 revealed the presence of seventeen unique biomolecules. Attempts were made to dock these biomolecules against major protein targets of M. enterolobii such as E3 ubiquitin ligase, Neurotransmitter-gated ion-channel, G protein-coupled receptor kinase, Peptidase M12B domain-containing protein, Hyaluronidase through molecular docking techniques. The results of in-silico studies revealed that all seventeen biomolecules had a significant impact on protein targets of M. enterolobii. Among other bacterial metabolites, 2-heptanone and 2,3-butanediol were found to have a greater binding affinity with protein targets of M. enterolobii. Furthermore, the in-vitro evaluation of 2-heptanone and 2,3-butanediol at different concentrations confirmed their nematicidal activity against eggs and second-stage juveniles of M. enterolobii. Hence our present study revealed that bacterial metabolites, 2 heptanone, and 2,3-butanediol can be explored as novel nematicidal molecules against guava root-knot nematodes, M. enterolobii.

Comparative Evaluation of Different Biocontrol Agents against Anthracnose of Nendran Banana Caused by Colletotrichum musae

India is the largest producer of banana in the world. Nendran, a French plantain, is the most important banana cultivar in Kerala. It is mainly affected by many diseases both in the field and after harvest. Being a freshly consumed fruit crop there are a lot of limitations in using chemicals for its disease control. Keeping this view, a study was conducted at the Department of Plant Pathology, College of Agriculture, Vellayani, to control anthracnose, a serious post harvest disease under tropical conditions. In this study comparative evaluation of three fungal biocontrol agents namely [Trichoderma sp. (KAU), Trichoderma sp. (TRPN-3), Trichoderma sp. (TRKR-2)] and bacterial biocontrol agents [Pseudomonas fluorescens (PN026), Bacillus sp. (B15), Bacillus sp. (B17)] were tested against Colletotrichum musae. Among the fungal biocontrol agents maximum mycelial growth inhibition was recorded with Trichoderma sp. (KAU) (77.44%) followed by Trichoderma sp. (TRKR-2) (77.11%). Minimum mycelial growth inhibition was recorded in P.fluorescens (PN026) (55.33%). Based on the results reveals that Trichoderma sp. (KAU) is a highly promising biocontrol agent for managing anthracnose of banana.

Bacillus velezensis LY7 promotes pepper growth and induces resistance to Colletotrichum scovillei

Anthracnose of pepper (Capsicum annuum L), caused by Colletotrichum scovillei, is one of the three major diseases of pepper that seriously impact yield and quality. As an alternative to the use of synthetic chemical pesticides, a variety of endophytic bacteria have been reported to be potential biocontrol agents with the ability to improve disease resistance and abiotic stress tolerance in host plants. However, the mechanisms of action by which these different bacterial biocontrol agents inhibit the onset and development of disease, in some cases, remains unclear. In the present study, the potential use of the endophytic bacterial strain Bacillus velezensis LY7, originally isolated from pepper leaves, as a biocontrol agent was evaluated. More specifically, the ability of LY7 to control anthracnose in pepper and promote growth was assessed in pot experiments in a greenhouse and in vitro assays. Results indicated that the use of B. velezensis LY7 enhanced the synthesis of jasmonic acid and other hormones in pepper plants, as well as increased disease resistance and plant growth. A 200 × dilution of LY7 fermentation broth reduced disease incidence up to 90.70 %, while also enhancing plant growth. The mechanism of action of LY7 was also evaluated. Results indicated that LY7 secreted an antibiotic protein possessing a cupin domain OS. RNA-sequence analysis of the transcriptome of C. scovillei at several timepoints after exposure to LY7 (24, 48, and 72 h) revealed the up- and down-regulation of several genes. More specifically, LY7 induced the expression of genes associated with biosynthesis pathways and transcription factors involved in anthracnose pathogenicity. Our results indicate that the LY7 strain of induces hormone synthesis in pepper plants that results in enhanced disease resistance and promotes growth, as well as enhances stress tolerance by enhancing antioxidant and defense-related enzyme activity. These results demonstrate the potential of using LY7 for the biocontrol of anthracnose in pepper plants.

Evaluation of phyllosphere bacterial biocontrol agents for the suppression of rice foliar diseases

AbstractPhyllosphere colonizing antagonistic bacterial isolates were evaluated for managing major rice foliar diseases, namely brown spot caused by Bipolaris oryzae and sheath rot caused by Sarocladium oryzae. Among these various isolates, Pseudomonas aeruginosa isolate 1 effectively inhibited the mycelial growth of B. oryzae and S. oryzae. The volatile compounds of Bacillus subtilis isolates effectively inhibited the mycelial growth of S. oryzae and B. oryzae. Non‐volatile compounds of P. aeruginosa isolate 2 and B. subtilis isolate 1 recorded the maximum inhibition of mycelial growth of B. oryzae and S. oryzae, respectively. P. aeruginosa isolates produced fluorescent pigments and hydrogen cyanide (HCN), whereas isolates of Bacillus spp. did not. All the isolates of P. aeruginosa and Bacillus spp. produced protease enzymes. P. aeruginosa isolates solubilized phosphate, whereas isolates of Bacillus spp. did not. Rice seeds treated with these bacterial suspensions showed improvement in plant growth parameters. The foliar application of two bacterial strains, namely P. aeruginosa isolate 1 + B. subtilis isolate 1 recorded the minimum brown spot and sheath rot disease incidence. Thus, the present showed that phyllosphere colonizing P. aeruginosa and B. subtilis have the potential application for managing foliar fungal diseases of rice plants.

Control of Alternaria Leaf Spot of the Common Bean (Phaseolus vulgaris L.) Using Soil-Derived Biological Agents.

Phaseolus vulgaris L. is considered one of the most essential legume crops in Kenya. Alternaria alternata is an economically significant plant pathogen that causes Alternaria leaf spot which accounts for over 70% yield losses of beans in Kenya. Chemical fungicides based on copper and sulfur are used to control Alternaria leaf spot in bean plants, but their prolonged use has adversely affected the environment and the health of workers. Herein, we tested the biocontrol potential of bacterial agents from soil planted with Rosecoco bean plants infected with A. alternata. Using bacterial suspensions at different time intervals, we evaluated the putative bacterial biocontrol activity against A. alternata under greenhouse conditions. B. subtilis and B. velezensis bacterial biocontrol agents significantly suppressed disease severity by 20% and 21.2% on the 45th day, respectively. Our study demonstrates that B. subtilis and B. velezensis are promising biocontrol agents that could be integrated in the management of Alternaria leaf spot.

Effect of Some Biological Agents on Fungi Isolated from Roots and Soil around it of Cupressus spp. Trees

Al-Ameri, H.A. 2024. Effect of Some Biological Agents on Fungi Isolated from Roots and Soil around it of Cupressus spp. Trees. Arab Journal of Plant Protection, 42(2): 224-228. https://doi.org/10.22268/AJPP-001233 Relative occurrence of fungi associated with six root and six soil samples from the rhizosphere of Cupressus/cypruss trees with root rot, leaf blight or wilt symptoms were investigated. Results of the root samples (average of six samples) showed that the relative occurrence of Fusarium culmorum was the highest (36.81%), followed by F. solani (29.7%), Alternaria. alternate (14.19%), F. oxysporum (10.67%), R. solani (5.51%), Pythium spp. (1.69%), Helminthosporium spp. (0.85%), Bipolaris spp. (0.24%) and Stemphilium herbarum (0.18%). However, the average occurrence in the six soil rhizosphere samples was the highest for F. solani (41.28%), followed by R. solani (19.76%), F. culmorum (16.5%), F. oxysporum (8.77%), Bipolaris spp. (6.17%), A. alternata (3.99%), Pythium spp. (2.70%), Stemphylium herbarum (0.60%), and Helminthosporium spp. (0.27%). Results also showed that Trichoderma harzianum had a high antagonistic efficiency against the three studied fungi isolated from cypress tree roots and the surrounding soil, namely F. culmorum, F. solani and Helminthosporium spp. Based on 1-5 scale, the inhibition level was 1.0 against each of the pathogenic fungi F. culmorum, F. solani, and 2.0 against Helminthosporium spp. The results also showed that the use of B. subitlis as bacterial bio-control agent led to a significant inhibition of the growth of the three isolated fungi, F. culmorum, F. solani and Helminthosporium spp. cultured on PDA medium. Keywords: Bio-control agents, F. culmorum, F. solani, Cypress trees.

Bacterial biocontrol agents of rice diseases: compatible with pesticide and effects on rhizospheric soil microbiota

Bacterial biocontrol agents of rice diseases: compatible with pesticide and effects on rhizospheric soil microbiota

Identification of secondary metabolites biosynthetic genes, antagonistic activity and potential mechanism of &lt;i&gt;Bacillus subtilis&lt;/i&gt; NBAIR-BSWG1 in suppression of &lt;i&gt;Alternaria alternata&lt;/i&gt;

Alternaria alternata wreaks havoc on fruit and vegetable production globally, threatening food security by causing black leaf spot disease. Bacillus subtilis, a natural inhabitant of soil, is a promising biological control agent for the management of A. alternata. In the present study, the antagonistic potential of B. subtilis NBAIR-BSWG1 was initially confirmed against A. alternata through a dual culture technique with 43.03% inhibition of mycelial growth. Subsequently, we extracted the cell-free extract from the NBAIR-BSWG1 pure culture and assessed its impact on A. alternata through the poison food technique and found mycelial growth inhibition of 85.82%. Identification of secondary metabolites biosynthetic genes using specific PCR markers showed the presence of surfactin genes (sfp, srf AA) with an amplicon size of 675 bp and 201 bp, respectively. Amplification of fengycin (fenB) and iturin (ituD) at 670 bp and 423 bp respectively, by using a specific PCR primer confirms the contribution of fengycin and iturin for the antagonistic potential of NBAIR-BSWG1. This study identifies NBAIR-BSWG1 as an effective bacterial biocontrol agent for control of A. alternata, unlocks the genetic basis of antifungal activity NBAIR-BSWG1, depicts molecular mechanisms involved in biological suppression of A. alternata by NBAIR-BSWG1 paving the way for the development of bioformulations for management of A. alternata.

Physical and bio-control methodologies for integrated management of buffalo fly-Haematobia exigua (Diptera: Muscidae)

Haematobia exigua, the buffalo fly, is a common ectoparasite of buffaloes and cattle in India causing economic losses and underlines the necessity of effective control strategies against them. The present study was planned to evaluate larvicidal activity of few methods for physical and biological control for integarated management of Haematobia exigua flies. Out of four bacterial bio-control agents evaluated by in-vitro assay and Probit analysis, two bacteria i. e. Bacillus thuringiensis var israelensis and Bacillus thuringiensis var kurstaki showed excellent larvicidal activity against H. exigua with LC50 value of 134 and 135 mg per liter of water respectively. Whereas, other two bacteria i. e. Bacillus weihenstephanensis WSBC and KBAB4 failed to show desired larvicidal activity. It can be concluded that B ti and B tk have future as effective bacterial agents (BCAs) in the control and integrated management of buffalo and horn fly. An experiment was conducted in the laboratory and on field for judging the efficacy of a physical method of tightly covering dung pats with polythene sheet for control of larvae of H. exigua. The laboratory result showed only 14.73% larvae were survived and developed per 100 gm of the faeces in the pot covered with polythene sheet as against significantly higher number 78.33% in the control group. During field trial, average larval count from dung pits before the experiment was 86.33 per 250 gm of faeces and it has been significantly reduced to 11.80 after covered with polythene sheets for two weeks. It indicated that physical method of covering the dung pits works immensely and thus can be inducted in IPM program as one of the effective physical control alternatives.

Bacterial biocontrol agents against diseases caused by Rhizoctonia solani in sugar beet

Bacterial biocontrol agents against diseases caused by Rhizoctonia solani in sugar beet

Biological Induction of Metabolic Defense Mechanisms Against Wheat Yellow Rust Using Bacterial and Organic Biocontrol Agents

Biological Induction of Metabolic Defense Mechanisms Against Wheat Yellow Rust Using Bacterial and Organic Biocontrol Agents

Taxonomy-guided selection of Paraburkholderia busanensis sp. nov.: a versatile biocontrol agent with mycophagy against Colletotrichum scovillei causing pepper anthracnose.

This study introduces a novel approach based on the taxonomy-guided selection of bacterial biocontrol agents from a known beneficial taxonomic group. Following 16S rRNA screening, we focused on the genus Paraburkholderia, which harbors strains with large genomes and versatile benefits to plants. A strain designated P39 was selected, identified, and characterized for its biocontrol activity against Colletotrichum scovillei. Strain P39 exhibited antagonism against C. scovillei by producing compounds, including volatiles, with antifungal activity, both in vitro and on pepper fruits. Genomic, physiological, and biochemical analyses revealed that the selected strain represents a novel species, named Paraburkholderia busanensis. Genomic analyses provided insights into the fitness and biocontrol activities of the selected strains. Moreover, P39 displays mycophagy, consuming fungal mycelia and transforming them into bacterial biomass, particularly in nutrient-poor media supplemented with fungal mycelia. The genome harbored chitin and N-acetylglucosamine utilization genes, suggesting a proposed pathway for the utilization of fungal cells as a nutrient source. Microscopic observations further supported the ability of this strain to rupture and damage fungal hyphae, depriving them of their cellular constituents. This study successfully demonstrated the implementation of a taxonomy-guided approach for the selection of bacterial strains for biocontrol. These findings contribute to our understanding of biocontrol strategies, bacteria-fungi interactions, and the identification of Paraburkholderia busanensis sp. nov. as a potential candidate for the biocontrol of pepper anthracnose. Additionally, this strain serves as a valuable resource for antifungal compounds and volatiles, and for the study of bacteria-fungal interactions and mycophagy. IMPORTANCE Traditional control methods for postharvest diseases rely on fungicides, which cause human health and environmental concerns. This study introduces a taxonomy-guided strategy for selecting biocontrol agents. By focusing on Paraburkholderia group, which harbors diverse plant-beneficial strains, the inadvertent selection of harmful strains was circumvented, thereby obviating the need for laborious in vitro screening assays. A highly promising candidate, strain P39, has been identified, exhibiting remarkable biocontrol activity against Colletotrichum scovillei. Through comprehensive genomic, physiological, and biochemical analyses, P39 was characterized as a novel species within the Paraburkholderia genus and designated Paraburkholderia busanensis. Moreover, these findings deepen our understanding of bacterial-fungal interactions, as they elucidate a potential pathway for the utilization of fungal chitin, thereby enhancing our understanding of bacterial mycophagy. P. busanensis is a promising source of antifungal volatiles and putative novel secondary metabolites.

Plant resistance to tomato yellow leaf curl virus is enhanced by Bacillus amyloliquefaciens Ba13 through modulation of RNA interference.

Tomato yellow leaf curl virus (TYLCV), which is a typical member of the genus Begomovirus, causes severe crop yield losses worldwide. RNA interference (RNAi) is an important antiviral defense mechanism in plants, but whether plant beneficial microbes used as biocontrol agents would modulate RNAi in defense against TYLCV remains unclear. Here, we employed whole-transcriptome, bisulfite, and small RNA sequencing to decipher the possible role of Bacillus amyloliquefaciens Ba13 as a bacterial biocontrol agent against TYLCV in RNAi modulation. Potted tomato plants were exposed to whiteflies for natural viral infection 14 days after bacterial inoculation. Compared with non-inoculated controls, the abundance of TYLCV gene in the leaves of inoculated plants decreased by 70.1% at 28 days post-infection, which mirrored the pattern observed for plant disease index. The expression of the ARGONAUTE family genes (e.g., AGO3, AGO4, AGO5, and AGO7) involved in antiviral defense markedly increased by 2.44-6.73-fold following bacterial inoculation. The methylation level at CpG site 228 (in the open reading frame region of the RNA interference suppressing gene AV2) and site 461 (in the open reading frame regions of AV1 and AV2) was 183.1 and 63.0% higher in inoculated plants than in non-inoculated controls, respectively. The abundances of 10 small interfering RNAs matched to the TYLCV genome were all reduced in inoculated plants, accompanied by enhancement of photosystem and auxin response pathways. The results indicate that the application of Ba. amyloliquefaciens Ba13 enhances plant resistance to TYLCV through RNAi modulation by upregulating RNAi-related gene expression and enhancing viral genome methylation.

Dimethylpolysulfides production as the major mechanism behind wheat fungal pathogen biocontrol, by Arthrobacter and Microbacterium actinomycetes.

Volatile organic compounds (VOCs) produced by plant-associated microorganisms could serve as natural biocontrol compounds. In this work, we investigate the potential of wheat rhizosphere Microbacterium and Arthrobacter actinomycetes to inhibit the growth of major wheat phytopathogenic fungi, Fusarium graminearum and Zymoseptoria tritici via production of antifungal VOCs. A correlative analysis between fungal-growth inhibition versus bacterial volatilomic profiles identified four dimethylpolysulfide (DMPS) VOCs as the main active compounds behind their biocontrol potential. Subsequent inhibition assays reveal that DMTriS (dimethyltrisulfide) exhibits the strongest inhibition effects, then dimethyldisulfide (DMDiS). Further investigation focuses on the mechanisms behind F. graminearum-growth inhibition by the most active strain Microbacterium JM188 in dual culture. Surprisingly, nine interaction-induced VOCs, including two fungal sesquiterpenes, were exclusively detected in dual cultures, suggesting a complex interplay between microbial VOC production and sensing. More importantly, all JM188 VOCs, including antifungal DMPS, were less abundant in dual cultures, suggesting an uptake of bacterial VOCs by the fungus. Quantification of pure DMPS after confrontation with F. graminearum confirmed complete and partial uptake by the fungus of DMTriS and DMDiS VOCs, respectively, suggesting a potential link between the fungal uptake level of bacterial VOCs and their toxicity. Finally, we demonstrated that F. graminearum growth inhibition leads to a complete depletion of DON (deoxynivalenol) carcinogenic mycotoxins, highlighting a significant modulation of fungal metabolism. Collectively, these results pinpoint DMPS as broad-range fungal-inhibiting VOCs produced by rhizosphere Microbacterium and Arthrobacter, and emphasize the extensive VOC-mediated interplay between bacterial biocontrol agents and fungal pathogens.IMPORTANCEAs the management of wheat fungal diseases becomes increasingly challenging, the use of bacterial agents with biocontrol potential against the two major wheat phytopathogens, Fusarium graminearum and Zymoseptoria tritici, may prove to be an interesting alternative to conventional pest management. Here, we have shown that dimethylpolysulfide volatiles are ubiquitously and predominantly produced by wheat-associated Microbacterium and Arthrobacter actinomycetes, displaying antifungal activity against both pathogens. By limiting pathogen growth and DON virulence factor production, the use of such DMPS-producing strains as soil biocontrol inoculants could limit the supply of pathogen inocula in soil and plant residues, providing an attractive alternative to dimethyldisulfide fumigant, which has many non-targeted toxicities. Notably, this study demonstrates the importance of bacterial volatile organic compound uptake by inhibited F. graminearum, providing new insights for the study of volatiles-mediated toxicity mechanisms within bacteria-fungus signaling crosstalk.

Unlocking the hidden potential of Mexican teosinte seeds: revealing plant growth-promoting bacterial and fungal biocontrol agents.

The bacterial component of plant holobiont maintains valuable interactions that contribute to plants' growth, adaptation, stress tolerance, and antagonism to some phytopathogens. Teosinte is the grass plant recognized as the progenitor of modern maize, domesticated by pre-Hispanic civilizations around 9,000 years ago. Three teosinte species are recognized: Zea diploperennis, Zea perennis, and Zea mays. In this work, the bacterial diversity of three species of Mexican teosinte seeds was explored by massive sequencing of 16S rRNA amplicons. Streptomyces, Acinetobacter, Olivibacter, Erwinia, Bacillus, Pseudomonas, Cellvibrio, Achromobacter, Devosia, Lysobacter, Sphingopyxis, Stenotrophomonas, Ochrobactrum, Delftia, Lactobacillus, among others, were the bacterial genera mainly represented. The bacterial alpha diversity in the seeds of Z. diploperennis was the highest, while the alpha diversity in Z. mays subsp. mexicana race was the lowest observed among the species and races. The Mexican teosintes analyzed had a core bacteriome of 38 bacterial genera, including several recognized plant growth promoters or fungal biocontrol agents such as Agrobacterium, Burkholderia, Erwinia, Lactobacillus, Ochrobactrum, Paenibacillus, Pseudomonas, Sphingomonas, Streptomyces, among other. Metabolic inference analysis by PICRUSt2 of bacterial genera showed several pathways related to plant growth promotion (PGP), biological control, and environmental adaptation. The implications of these findings are far-reaching, as they highlight the existence of an exceptional bacterial germplasm reservoir teeming with potential plant growth promotion bacteria (PGPB). This reserve holds the key to cultivating innovative bioinoculants and formidable fungal antagonistic strains, thereby paving the way for a more sustainable and eco-friendly approach to agriculture. Embracing these novel NGS-based techniques and understanding the profound impact of the vertical transference of microorganisms from seeds could revolutionize the future of agriculture and develop a new era of symbiotic harmony between plants and microbes.

Integrated Management of Blast Disease in Finger Millet

Aims: To test the effect of bacterial biocontrol agents (Pseudomonas-TNAU-Pf1) and fungicides (Tricyclazole) individually and their integration as seed treatment and foliar spray against finger millet blast under field conditions.&#x0D; Study Design: The field experiments were conducted in a Randomized Block design.&#x0D; Place and Duration of Study: The experiments were conducted at the Regional Research Station farm, Tamil Nadu Agricultural University, Paiyur, Krishnagiri District, Tamil Nadu, India, during 2016-17 and 2017-18.&#x0D; Methodology: Two field experiments were conducted to evaluate the efficacy of talc-based formulation of Pseudomonas -TNAU-Pf1 and Tricyclazole individually and in combination as seed treatment and foliar application for the management of finger millet blast with five treatments and four replications using a variety Paiyur 2. The bioagent and the fungicide were applied as seed treatment and foliar spray.&#x0D; Results: The results revealed that seed treatment with talc-based formulation of Pseudomonas -TNAU-Pf1 (10g/kg) plus two sprays of tricyclazole (0.1%) one at the maximum tillering phase and another at the heading phase was significantly most effective in reducing leaf, neck and finger blast in both the seasons. The treatment recorded 1.65 and 1.25PDI of leaf blast, 0.33 and 0.22% of neck and 2.55 and 1.33% of finger blast in the first and second season, respectively. The treatment also recorded highest grain yield of 2663 and 2543 kg/ha with BC ratio of 1:3.94 and 1:3.85 in the first and second season, respectively.&#x0D; Conclusion: Seed treatment with Pseudomonas TNAU-Pf1 (10g/kg) plus two sprays of tricyclazole (0.1%) was found to be effective in reducing the incidence of blast disease and increasing grain yield in finger millet.