Characterization of rhizosphere Streptomyces virginiae IRHB6 as a dual-agent for disease suppression and growth promotion in soybean

ABSTRACTCompost applications vary in their plant growth promotion and plant disease suppression, likely due to differences in physico-chemical and biological parameters. Our hypothesis was that bacteria are important for plant growth promotion and disease suppression of composts and, therefore, composts having these traits would contain similar sets of indicative bacterial taxa. Seventeen composts prepared from five different commercial providers and different starting materials were classified accordingly with bioassays using cress plants and the pathogen Pythium ultimum. Using a metabarcoding approach, bacterial communities were assessed in bulk composts and cress rhizoplanes. Six and nine composts showed significant disease suppression or growth promotion, respectively, but these traits did not correlate. Growth promotion correlated positively with nitrate content of composts, whereas disease suppression correlated negatively with factors representing compost age. Growth promotion and disease suppression explained significant portions of variation in bacterial community structures, i.e. 11.5% and 14.7%, respectively. Among the sequence variants (SVs) associated with growth promotion, Microvirga, Acinetobacter, Streptomyces, Bradyrhizobium and Bacillus were highly promising, while in suppressive composts, Ureibacillus,Thermogutta and Sphingopyxis were most promising. Associated SVs represent the basis for developing prediction tools for growth promotion and disease suppression, a highly desired goal for targeted compost production and application.

The soil microbiome provides essential services in agroecosystems that can increase plant health and productivity, such as disease suppression and growth promotion. A small number of microbial groups have been proposed as main players behind disease suppression, but the complete picture of the underlying mechanisms remains unclear for both functions in many soil systems. Here, we investigated broad and fine‐scale microbial community features for their contributions to disease suppression and growth promotion for potato plants. In a greenhouse study, we grew potato plants in pots sharing a common background soil and inoculated with living soil microbial communities with or without a separate inoculation with Streptomyces scabiei, the causal agent of potato common scab disease. The suppression of common scab and growth promotion abilities of a variety of soil microbial communities were estimated and related to quantitative patterns in microbial community structure. We found that suppression of common scab was mostly driven by fine‐scale microbial community features, especially the diversity within the Actinomycetota phylum. Even though opposing components of microbial community structure might be related to the two functions, disease suppression did not cause a negative trade‐off in growth promotion. This suggests high functional redundancy in growth promotion. It may be possible to improve the multi‐functionality of soil microbial communities by engineering the communities toward optimized disease suppression and growth promotion ability.

Thirty rhizobacterial isolutes from sorghum were evaluated for potential for seedling growth promotion and charcoal rot suppression in sorghum. Seven isolates repeatedly promoted early stage plant growth on the sorghum eultivar M35-I. Few isolates increased seed germination up to 43 percent and improved biotuass up to 66 percent on 30-day-old seedlings. Two isolates of fluorescent pseudomonads showed combined efficacy lor seedling growth promotion and disease suppression and reduced charcoal rot incidence considerably. In vitro properties of these isolates such as growth hormone, siderophore, HCN and ammonia prodnction, P-solubilization, antibiosis and production of volatile growth inhibitor have been discussed in relation to plant growth promotion and disease suppression.

Endophytic bacteria residing within plant seeds are increasingly recognized for their potential to enhance plant growth and provide biocontrol against pathogens. Despite this, seed-borne endophytes remain underexplored in many crops, including tomato. In this study, we isolated and characterized bacterial endophytes from tomato seeds and evaluated their plant growth-promoting traits and antifungal activities. The taxonomic analysis of the Hawaii 7996 tomato seed endophyte collection revealed a diverse community, predominantly from the phylum Bacillota, with Paenibacillaceae and Bacillaceae as the most abundant families. Among the 35 unique strains identified, 19 produced indole-3-acetic acid, four exhibited siderophore production, and 12 could solubilize phosphate. These traits contribute to growth promotion and disease suppression in plants. In the plant growth promotion assay, several bacterial strains, notably Streptomyces olivaceus (BHM1), Streptomyces variegatus (BHM3), Bacillus stercoris (BHR2), and Moraxella osloensis (YHT4-1), demonstrated significant potential for tomato cultivation by positively affecting fresh weight, stem length, and root length. These strains consistently promoted growth across all three parameters evaluated in this study. Furthermore, several strains exhibited strong antifungal activity against major tomato pathogens, including Fusarium oxysporum race 1 and 2, and Botrytis cinerea. Notably, Bacillus subtilis (BHN1), Bacillus stercoris (BHR2), and Paenibacillus peoriae (YHR2-1) showed broad-spectrum antifungal efficacy. Our findings highlight the potential of seed-associated endophytic bacteria as growth promoters and biological control agents, offering promising avenues for sustainable agricultural practices.

Cucumber wilt, caused by Fusarium oxysporum f. sp. cucumerinum (FOC), is a soilborne disease that poses a significant threat to cucumber production, resulting in substantial yield losses. This study aimed to evaluate the biocontrol and growth-promoting effects of Bacillus velezensis, a highly active bacterial strain. In vitro assays revealed that B. velezensis F9 exhibited broad-spectrum antifungal activity against eight plant pathogenic fungi, with inhibition ratio ranging from 62.66% to 88.18%. Additionally, the strain displayed the ability to produce IAA (5.97 ± 1.75 µg/mL), fix nitrogen, produce siderophores, and form biofilms. In vitro growth promotion assays demonstrated that different concentrations of B. velezensis F9 significantly promoted cucumber seedling growth. Furthermore, two pot experiments revealed that the strain exhibited biocontrol efficacy against cucumber wilt, with disease control rates ranging from 42.86% to 67.78%. Notably, the strain significantly increased the plant height, fresh weight, and dry weight, with increases ranging from 20.67% to 60.04%, 40.27% to 75.51%, and 22.07% to 52.54%, respectively. Two field trials confirmed the efficacy of B. velezensis F9 in controlling cucumber wilt, with disease control rates of 44.95% and 33.99%, respectively. The strain effectively alleviated the dwarfing and wilting symptoms caused by the pathogen. Compared with the FOC treatment, the F9 + FOC treatment significantly increased the plant height, fresh weight, and dry weight, with increases of 43.85% and 56.28%, 49.49% and 23.70%, and 36.25% and 73.63%, respectively. Enzyme activity assays indicated that inoculation significantly increased SOD activity in cucumber leaves and neutral phosphatase, sucrase, and urease activity in rhizosphere soil. Correlation analysis revealed a negative correlation between the disease index and plant height, fresh weight, dry weight, and peroxidase activity, with correlation coefficients of -0.53, -0.60, -0.38, and -0.45, respectively. These findings suggest that plant height, fresh weight, and dry weight are significantly negatively correlated with the cucumber disease index, highlighting their importance as indicators for evaluating the biocontrol efficacy of B. velezensis F9. In conclusion, B. velezensis F9 is a highly effective plant growth-promoting rhizobacterium with excellent biocontrol potential, showcasing promising applications in agricultural production.

Bacteria consortium optimization improves nutrient uptake, nodulation, disease suppression and growth of the common bean (Phaseolus vulgaris) in both pot and field studies

Management of fire blight is complicated by limitations on use of antibiotics in agriculture, antibiotic resistance development, and limited efficacy of alternative control agents. Even though successful in control, preventive antibiotic sprays also affect non-target bacteria, aiding the selection for resistance which could ultimately be transferred to the pathogen Erwinia amylovora. Trunk injection is a target-precise pesticide delivery method that utilizes tree xylem to distribute injected compounds. Trunk injection could decrease antibiotic usage in the open environment and increase the effectiveness of compounds in fire blight control. In field experiments, after 1–2 apple tree injections of either streptomycin, potassium phosphites (PH), or acibenzolar-S-methyl (ASM), significant reduction of blossom and shoot blight symptoms was observed compared to water injected control trees. Overall disease suppression with streptomycin was lower than typically observed following spray applications to flowers. Trunk injection of oxytetracycline resulted in excellent control of shoot blight severity, suggesting that injection is a superior delivery method for this antibiotic. Injection of both ASM and PH resulted in the significant induction of PR-1, PR-2, and PR-8 protein genes in apple leaves indicating induction of systemic acquired resistance (SAR) under field conditions. The time separating SAR induction and fire blight symptom suppression indicated that various defensive compounds within the SAR response were synthesized and accumulated in the canopy. ASM and PH suppressed fire blight even after cessation of induced gene expression. With the development of injectable formulations and optimization of doses and injection schedules, the injection of protective compounds could serve as an effective option for fire blight control.

Characterization of a free-living maize-rhizosphere population of Burkholderia cepacia: effect of seed treatment on disease suppression and growth promotion of maize

Trichoderma spp. has emerged as a potent biological control agent (BCA) for managing plant diseases, offering sustainable and eco-friendly alternatives to chemical fungicides. This review explores the multifaceted roles of Trichoderma spp. in plant disease suppression, growth promotion, and induced systemic resistance. The success of Trichoderma spp. as a BCA lies in its diverse mechanisms of action, including mycoparasitism, competition, antibiosis, and induction of systemic resistance. Notably, Trichoderma spp. produce a range of volatile compounds that inhibit plant pathogens while promoting plant growth. Furthermore, their ability to solubilize nutrients, such as iron and phosphate, and produce phytohormones like auxins, contributes to enhanced plant vitality. Molecular characterization has facilitated the identification of various Trichoderma species with distinct biocontrol properties. Application methods, including seed treatment, soil application, and foliar spray, have been developed to optimize the efficacy of Trichoderma-based biocontrol strategies. Overall, Trichoderma spp. exhibited the multiple mode of actions against the pathogens and which used as a versatile and effective biocontrol agent for integrated disease management and sustainable agriculture Keywords: Trichoderma spp., Biological control agent, Plant diseases, Disease suppression, Growth promotion, Sustainable agriculture

Numerous studies have demonstrated that soil applications of biochar contribute to plant disease suppression and growth promotion. Here, we quantitatively evaluated the performance of biochars on plant disease suppression and production using meta-analysis of literature data. The results indicated that biochar amendment dramatically reduced disease severity (DS) by 47.46% while increasing plant biomass by 44.05%. The highest disease suppression was achieved with soil application of straw-derived biochar compared to biochar from other feedstocks, while no significant increase in yield was found with straw-derived biochar. Biochars pyrolyzed at medium temperatures (350–600 °C) facilitate both disease controlling and growth promotion. Soil application of biochars between 3 and 5% significantly decreased plant DS by 59.11%, and inverted U-shaped biochar dose/DS suppression curve and biochar dose/growth curve were observed. In cash crop fields, the DS of plants amended with biochar was reduced over 50%, which was significantly higher than that of grain crops and perennial trees. Furthermore, biochar performance on plant disease suppression was higher for airborne pathogens than for soilborne pathogens, possibly due to the systemic activation of plant defences by biochar amendment. Additionally, a reduction of DS by biochar was observed on plants grown in agricultural soils. Our work contributes to the standardization of biochar production and provides a reference for improving the function of biochar in disease control.Graphical

Lysinibacillus sphaericus, an endophytic diazotroph from rice (Oryza sativa), was investigated for colonization and growth-promoting effects. Seed bacterization introduced the endophyte, confirmed through re-isolation of antibiotic media, microscopy, and molecular identification. L. sphaericus showed efficient colonization in rice tissues, maintaining stable populations across plant parts. Light and scanning electron microscopy revealed intracellular colonization in roots of inoculated plants. The endophyte enhanced plant growth, nutrient uptake, and nitrogen fixation compared with uninoculated controls and Pseudomonas fluorescens-treated plants. Increased production of phytohormones, including indole-3-acetic acid, gibberellic acid, and cytokinins, was observed in L. sphaericus-inoculated plants, correlating with improved root and shoot development. The endophyte demonstrated biocontrol activity against rice sheath blight pathogen Rhizoctonia solani, with plants showing reduced disease severity. L. sphaericus populations remained stable in host tissues following pathogen challenge. These findings highlight L. sphaericus's potential as an endophytic diazotroph for sustainable rice cultivation, growth promotion, nutrient acquisition, and disease suppression.

Exploring endophytic bacteria for biocontrol and growth promotion in rice against brown spot and sheath blight diseases.

Fusarium crown and root rot (FCRR), caused by Fusarium oxysporum f. sp. radicis-lycopersici (FORL), is a soilborne tomato disease of increased importance worldwide. In this study, Withania somnifera was used as a potential source of biological control and growth-promoting agents. Seven fungal isolates naturally associated with W. somnifera were able to colonize tomato seedlings. They were applied as conidial suspensions or a cell-free culture filtrate. All isolates enhanced treated tomato growth parameters by 21.5-90.3% over FORL-free control and by 27.6-93.5% over pathogen-inoculated control. All tested isolates significantly decreased by 28.5-86.4% disease severity over FORL-inoculated control. The highest disease suppression, by 86.4-92.8% over control and by 81.3-88.8% over hymexazol-treated control, was achieved by the I6 isolate. FORL radial growth was suppressed by 58.5-82.3% versus control when dual cultured with tested isolates and by 61.8-83.2% using their cell-free culture filtrates. The most active agent was identified as Fusarium sp. I6 (MG835371), which displayed chitinolytic, proteolytic, and amylase activities. This has been the first report on the potential use of fungi naturally associated with W. somnifera for FCRR suppression and for tomato growth promotion. Further investigations are required in regard to mechanisms of action involved in disease suppression and plant growth promotion.

Pink-pigmented facultatively methylotrophic bacteria (PPFMs), persistent colonizers of plant leaf surfaces, belong to the genus Methrlobacterium and are mostly transmitted through seeds. Plant growth-promoting activity of methylotrophic bacteria and their effects on disease suppression were evaluated on rice under greenhouse conditions. Rice seeds were inoculated with Methylobacterium sp. strain PPFM-Os-07 and seed germination was evaluated in terms of morphometric measurements, seedling growth, rate of germination (R(subscript G)), and seedling vigour index (SVI). Another experiment was carried out to study the induction of pathogenesis-related proteins (PR-proteins) in rice plants that were inoculated with methylotrophic bacteria by seed imbibition or foliar spray. In the third experiment, sixty-day-old rice plants grown in pots were challenge inoculated with Rhizoctonia solani strain TNAU-01. Methylobacterium inoculation promoted seed germination and plant growth. Increased plant height, number of tillers, plant biomass, and grain yield were observed. The average yield increases for seed imbibition and phyllosphere spray were, respectively, 22.1% and 24.3% greater than control. The bacteria also significantly reduced the sheath blight incidence when applied as either bacterial culture through seed imbibition and or phyllosphere spray. The percent disease reduction recorded for seed imbibition alone and for combined applications of seed imbibition and phyllosphere spray were 17.8% and 23.5%. Rice plants sprayed with PPFM-Os-07 strain showed increased presence of PR-proteins and phenolic contents on day 1 after application. Maximum phenylalanine ammonia lyase (PAL) and peroxidase activity on day 4 and β-1,3-glucanase and chitinase activity on day 5 were recorded. The results suggest that Methylobacterium inoculation may alter rice susceptibility to R. solani. This work emphasizes the importance of evaluating induced systemic resistance while studying plant-associated growth promoting bacteria.

Disease suppression and growth promotion in cucumbers induced by integrating PGPR agent Bacillus subtilis strain B4 and chemical elicitor ASM