Bacterial Culture Filtrates Research Articles

Preserving snake fruit (Salacca zalacca) Voss) quality: Effective control of Peniophora salaccae SKRU002 with fungicides and biological agents

Peniophora salaccae (Russulales, Basidiomycota), a newly identified pathogen of Salacca zalacca, is a major cause of snake fruit rot, resulting in significant agricultural losses. This study evaluates the efficacy of chemical fungicides and biological controls against P. salaccae SKRU002, focusing on disease suppression and fruit quality preservation. Commercial fungicides (propiconazole®, prochloraz®, metalaxyl®, azoxystrobin®, thiram®) and Streptomyces philanthi strains RM-1-138 and RL-1-178 were tested. In vitro, prochloraz® (1000 μL mL−1) fully inhibited P. salaccae growth, outperforming other fungicides. Both S. philanthi strains exhibited strong antifungal activity through volatile and non-volatile compounds. Additionally, autoclaved (at 121 °C for 15 min) and diluted (1/1000) bacterial culture filtrates (BCF) from both strains achieved over 55 % inhibition of P. salaccae. In liquid culture, RM-1-138 (86.80 %) and RL-1-178 (80.86 %) demonstrated greater inhibition than metalaxyl® (9.34 %) and azoxystrobin® (56.84 %), though prochloraz® and propiconazole® remained the most effective (100 %). In vivo, untreated fruits inoculated with P. salaccae showed 100 % disease incidence, significant weight loss (13.28 %), color changes (L∗, a∗, and b∗), and reductions in total soluble solids, total phenolic content, and antioxidant activity, while titratable acidity remained unchanged. Both biological and chemical treatments effectively controlled the pathogen and preserved fruit quality. These findings highlight the potential of S. philanthi strains and fungicides in managing P. salaccae, offering promising strategies for snake fruit cultivation.

Exploration of antimicrobial activities and mechanisms of biocontrol agent Serratia nematodiphila BC-SKRU-1 against Penicillium digitatum in tangerine fruit

The isolate BC-SKRU-1, identified as Serratia nematodiphila from fungal culture contamination, was investigated for its biocontrol potential against Penicillium digitatum in vitro and on tangerine fruit, with a focus on its mechanisms of action. In vitro tests on PDA plates revealed BC-SKRU-1's broad-spectrum antifungal activity, achieving up to 74.68% inhibition against seven plant pathogenic fungi, including P. digitatum NKP4321. Bacterial culture filtrates from BC-SKRU-1 (BCF BC-SKRU-1) at 5–10% concentrations inhibited NKP4321 mycelial growth in PDB medium (78.41–83.68%) more effectively than in PDA medium (46.20–72.61%), with complete suppression at 15% (v/v) in both media. BCF BC-SKRU-1's efficacy was comparable to chemical fungicides such as propiconazole®, prochloraz®, and mancozeb®. Notably, BCF BC-SKRU-1 retained its antifungal activity after dilution (1/1000), autoclaving (at 121 °C), and storage (at −20 °C). In vivo evaluations on tangerine fruit showed significant reduction in the severity of postharvest green mold disease with BC-SKRU-1 treatments, especially at a concentration of 108 CFU mL−1. Both preventive and curative applications were effective, with curative treatments being more successful. Mechanistic studies indicated that BCF BC-SKRU-1 reduces intracellular ergosterol content, compromises plasma membrane integrity, and attenuates antioxidant defense activities (SOD, CAT, GSH, GSSG, and GSH/GSSG ratio). These findings highlight BC-SKRU-1 and its metabolites as promising biocontrol agents against green mold in tangerine fruits and provide insights into their antifungal mechanisms.

Bacillus thuringiensis israelensis VCRC B650 culture filtrate useful for mosquito oviposition attractant and larvicidal action

Oviposition attractants hold the potential attention for monitoring and controlling mosquitoes by enticing them to deposit eggs at specific locations. In this study, the bacterial culture filtrate of Bacillus thuringiensis var. israelensis VCRC B650, previously isolated from clay soil at an agricultural site in U.T of Puducherry, was investigated for the first time. This larvicidal bacterium was assessed for oviposition attractancy against dengue and filarial vectors, namely, gravid females of Aedes aegypti and Culex quinquefasciatus, respectively. The investigation revealed that, at 1:1 dilution of bacterial culture filtrate and water, Cx. quinquefasciatus exhibited significant attraction, with an oviposition activity index (OAI) value of +0.92, surpassing the standard threshold value of +0.30. The OAI of Bti culture filtrate at a 1:1 dilution was also compared with a standard oviposition attractant, p-cresol, at a concentration of 10ppm. It was observed that the Bti culture filtrate demonstrated a significant oviposition attractant effect, with 80 per cent more egg rafts laid, compared to p-cresol at 20 per cent. GC-MS analysis showed that there were 25 compounds present in the Bti culture supernatant, and out of those, only one compound, namely, benzaldehyde, was effective in showing oviposition attraction.

Biocontrol of Grey Mold on Strawberry Fruit by Bacillus spp. and Study of the Mechanisms Involved

<p>Grey mold, caused by the fungus <em>Botrytis cinerea</em>, is one of the most prevalent diseases affecting strawberry plants (<em>Fragaria ananassa</em>). The objective of this study was to assess the antagonistic effect of 5 bacterial strains belonging to the genus <em>Bacillus </em>spp<em>.</em> (BA1, BF2, BB3, BI3, and BO4) against <em>B. cinerea</em>, tested both <em>in vitro</em> and <em>in vivo</em> on strawberry fruits. The strains exhibited antifungal activity against <em>B. cinerea</em> under <em>in vitro</em> conditions, both through direct confrontations and antibiosis tests, as well as through the effect of organic compounds. Strain BO4 could inhibit mycelial growth by 62.92% through direct confrontation and 64.58% through the secretion of volatile organic compounds. Additionally, the strain BF2 demonstrated a high antibiosis effect (74.64%) compared to the control at a concentration of 25%. Treating fruits with the bacterial suspension and culture filtrate of the 5 studied strains controlled grey mold growth <em>in vivo</em>, as indicated by low severity indices in strawberries treated with strains BI3, BF2, and BA1, marked by percentages of 24.44%, 24.44%, and 37.78%, respectively, for preventive treatment. The difference in the effectiveness of various strains depended on the treatment mode; preventive treatment proved to be more effective compared to curative treatment.</p>

Endophytic bacterium Sphingomonas panaciterrae NB5 influences soil properties and improves growth, nutrient contents, and yield of red amaranth (Amaranthus tricolor L.)

Plant growth promoting rhizobacteria (PGPR) are crucial for enhancing plant growth and restoring soil health. Despite the excellent plant growth promoting traits, information is limited on the efficacy of Sphingomonas as a PGPR, especially in vegetable crops. In this study, we used Sphingomonas panaciterrae NB5 as a biofertilizer in leafy vegetable red amaranth in three methods: seed priming (SP), root drenching + foliar (RD + FA), and bacterial culture filtrate (BCF) foliar application. Bio-inoculation of NB5 significantly increased the plant height, number of leaves, leaf area, stem girth, total chlorophyll, vitamin C, and antioxidant contents of red amaranth in all methods of application. Bacterial treatment resulted in notable alterations to the root structure, consisting of the formation of secondary, tertiary, and fibrous roots, particularly in the BCF foliar application and RD + FA treatment.The fresh and dry biomass significantly increased both in root and shoot, resulting in improved yield. The nutritional profile revealed that bacterial application significantly increased the nitrogen, potassium, magnesium, iron, and zinc content, with a slight increase in phosphorus content, in shoots and roots in all the methods of bacterial application compared to control. In post-harvest soil, NB5 boosted total nitrogen, available phosphorus, calcium, and sulfur, as well as soil organic carbon (SOC) and total bacterial populations, regardless of the application methods. The RD+FA treatment outperformed the other methods of application in most of the plant and soil parameters, and the next was the BCF foliar application. Multivariate analysis also confirmed the better performance of RD+ FA and BCF foliar applications. Therefore, simultaneous application of NB5 through root drenching and foliar application could be recommended to the farmers for increasing the yield of red amaranth with improved nutrients and restoring soil health and productivity.

Novel herbicide from an optimized Bacillus altitudinis D30202 solvent extract

AbstractThe herbicidal activity of the fermentation broth, filtrate, and extracts of Bacillus altitudinis D30202 was evaluated against seed germination and seedling growth of wild oat (Avena fatua L.). The bacterial culture filtrate exhibited greater inhibition of the wild oat weed than the fermentation broth. The filtrate was also extracted with organic solvents. The herbicidal potency of the extracts on the growth of wild oat plants was as follows: chloroform (100% inhibition of germination) > n‐butanol (93.8%) > ethyl acetate (66.7%) > petroleum ether (6.3%) > aqueous phase (2.1%); so the chloroform extract was evaluated further. It inhibited wild oat radicle growth by 100%, and plumule growth by 97.9%, while spraying young plants with a 5 mg/mL extract caused severe desiccation of the leaves, stalk wilting, and plant death. IC50 values for inhibition of plumule and radicle growth and germination were 0.64–0.72 mg/mL. Scanning electron microscopy and transmission electron microscopy revealed changes in the microstructure of the leaves and root tips, and degradation of organelles following chloroform extract treatment. The 5 mg/mL extract had no adverse impact on the growth or health of highland barley (Hordeum vulgare L.), corn (Zea mays), and broad bean (Vicia faba L.), indicating that this novel bioherbicide is suitable for control of wild oat weeds in the production of these food crops (while having a minor impact on the health of pea plants and being phytotoxic to wheat plants).

Novel report of Acinetobacter johnsonii as an indole-producing seed endophyte in Tamarindus indica L.

Plant-microbe associations have been regarded as an exciting topic of research due to their potential as environment friendly alternatives for stimulating crop growth and development. Seeds of Tamarindus indica L. have been chosen for the present study as seed endophytes prefer larger or nutritive cotyledon and hard seed coats for their colonization. The main objectives of our study were to isolate and identify the seed endophytes, their bioefficacy, and responsible chemical compounds. In a dose-dependent experiment, tamarind seed exudates (TSE) showed plant growth-promoting properties on Oryza sativa (53-81%), Daucus carota (10-31%), and Raphanus sativa (21-42%). Identification of the bacterial load in TSE through 16S rRNA sequencing revealed the existence of two bacterial species, Acinetobacter johnsonii and Niallia nealsonii. This is the first report of these two bacteria as seed endophytes of Tamarindus indica L. HRLC-MS analysis of TSE confirmed the presence of indole derivatives, primarily indole-3-lactic acid (ILA). The quantitative phytochemical estimation of bacterial culture filtrates revealed that indole-like substances were present in the extracts only in A. johnsonii at a concentration of 0.005mg/ml of indole acetic acid equivalent. Experimental results suggested that the stimulatory activity of TSE was caused by the presence of A. johnsonii, a potential plant growth-promoting bacteria that produced indole-like compounds. This study suggests tamarind seed exudates with its endophytic microbiota as a potent plant growth-promoting agent that may find use as a cheap and sustainable source of metabolites useful in the agro-industries.

Evaluation of the Most Effective Plant Extracts, Bioagents and Chemical Fungicides In vitro against Powdery Mildew of Pea

The present investigation was carried during 2022-23 at Plant Pathology Section, College of Agriculture, Pune-05 with the objectives of evaluation of the most effective plant extracts, bioagents and chemical fungicides in vitro. Effect of six plant extracts, bioagents and chemical fungicides were studied in vitro by hanging drop method where the study revealed that garlic (Allium sativum), followed by neem (Azadiracta indica) showed highest inhibition of spore germination for powdery mildew. After 48 hours of incubation, the spore germination rate ranged from 3.15 % to 34.45 %, where garlic showed the highest inhibition at 95.30 %, followed by neem at 91.03 %. The efficacy of bioagents was evaluated by preparing the bacterial and fungal culture filtrates where Trichoderma harzianum and Pseudomonas fluorescens were found to be the most effective with tune of 56.86% and 50.72% of efficacy respectively against Erysiphe pisi. Among all chemical fungicides, hexaconazole (0.05 %) resulted as the most effective chemical fungicide against powdery mildew of pea. These findings can be useful in developing safer and more eco-friendly methods to control powdery mildew and protect crops.

The PGPR Bacillus aryabhattai promotes soybean growth via nutrient and chlorophyll maintenance and the production of butanoic acid.

Plant growth-promoting rhizobacteria (PGPR) colonize plant roots, establish a mutualistic relationship with the plants and help them grow better. This study reports novel findings on the plant growth-promoting effects of the PGPR Bacillus aryabhattai. Soil was collected from a soybean field, PGPR were isolated, identified, and characterized for their ability to promote plant growth and development. The bacterium was isolated from the soybean rhizosphere and identified as B. aryabhattai strain SRB02 via 16s rRNA sequencing. As shown by SEM, the bacterium successfully colonized rice and soybean roots within 2 days and significantly promoted the growth of the GA-deficient rice cultivar Waito-C within 10 days, as well as the growth of soybean plants with at least six times longer shoots, roots, higher chlorophyll content, fresh, and dry weight after 10 days of inoculation. ICP analysis showed up to a 100% increase in the quantity of 18 different amino acids in the SRB02-treated soybean plants. Furthermore, the 2-DE gel assay indicated the presence of several differentially expressed proteins in soybean leaves after 24 hrs of SRB02 application. MALDI-TOF-MS identified β-conglycinin and glycinin along with several other proteins that were traced back to their respective genes. Analysis of bacterial culture filtrates via GCMS recorded significantly higher quantities of butanoic acid which was approximately 42% of all the metabolites found in the filtrates. The application of 100 ppm butanoic acid had significantly positive effects on plant growth via chlorophyll maintenance. These results establish the suitability of B. aryabhattai as a promising PGPR for field application in various crops.

In vitro characterization of a Bacillus velezensis isolate as an antagonist of grapevine trunk disease pathogens

AbstractOne of the major and yet unsolved threats for viticulture is the group of vascular fungal infections, the so-called grapevine trunk diseases. Besides their latent nature and the enormous number of associated pathogens, their control is also hampered by the lack of effective fungicides, directing growing attention toward the use of biocontrol agents. In the present study the isolation, identification, and characterization of a bacterial strain are presented, showing biocontrol potential against some main causal agents of grapevine trunk diseases. The strain was isolated from the wood of an asymptomatic grapevine and selected for the fungicidal activity against the pathogen Phaeomoniella chlamydospora. According to 16S rDNA, gyrA, and gyrB sequences, the isolate belongs to Bacillus velezensis species. Confrontation tests with the bacterium or with its fermentation broth further revealed growth inhibition and fungicide activity against Botryosphaeria dothidea, Eutypa lata and Diaporthe ampelina pathogens. Fractionation of the bacterial culture filtrate suggests that the antifungal agents secreted by the B. velezenzis isolate are mainly lipoproteins. Phytotoxicity tests were also carried out with the isolate, showing no harmful effects on grapevine foliar disks.

Biocontrol efficacy of Burkholderia pyrrocinia S17-377 in controlling rice sheath blight

Rice sheath blight, caused by Rhizoctonia solani, is a major disease of rice that significantly affects rice production. To find sustainable and effective methods to control this disease, biocontrol strains have emerged as a promising solution. In this study, a total of 28 strains were screened from the rhizosphere of rice plants in order to identify strains that are effective against rice sheath blight. Among these strains, strain S17-377 showed remarkable antifungal activity, resulting in a 10 mm diameter inhibitory band against R. solani. Furthermore, it exhibited a wide range of antimicrobial properties in vitro. Through genetic analysis using the 16S rDNA and recA genes, strain S17-377 was identified as Burkholderia pyrrocinia. Importantly, it was found to be non-pathogenic to onions and did not possess the virulence genes BCESM and cblA. Therefore, this strain is safe for both people and plants. The strain S17-377 showed an efficacy of 64.81% and 55.78% in controlling rice sheath blight in pot experiments and field trials, respectively. Strain S17-377 displayed persistent colonization ability in rice plants for up to 30 days after inoculation. It also induced the expression of several rice plant genes, including NH1, PR1a, PR10, PAL/ZB8, LOX, and AOS2, as well as enzymes such as POD, PPO, and PAL. Additionally, S17-377 produced proteases, chitinases, non-volatile metabolites, and biofilms. In terms of disease control, the aseptic fermentation solution of S17-377, when diluted with PDA medium at ratios of 1:20, 1:10, and 1:5, exhibited inhibition rates of 77.14%, 86.92%, and 98.26%, respectively, against R. solani. S17-377 also had noticeable effects on the expansion and collapse of fungal mycelium. Moreover, the bacterial culture filtrates(BCF) of S17-377 demonstrated high thermal stability with an inhibition rate of 96.16%, even after being subjected to a temperature of 121 °C for 30 min. The BCF of strain S17-377 exhibited significant inhibition of R. solani, with inhibition rates of 95.23%, 94.43%, and 75.11% for the n-butanol, crude protein, and crude lipopeptide extracts, respectively. Further analysis of the n-butanol extract using liquid chromatography-mass spectrometry (LC-MS) identified eight compounds with potent antibacterial activity. These findings highlight the potential of strain S17-377 as a biocontrol agent for the management of rice sheath blight.

Microbial Filtrates Improved Growth Parameters of In vitro PVX Infected Potato Plantlets

This study focuses on utilizing the phenomenon of systemic acquired resistance (SAR) to control plant viruses and increased growth in vitro. The study demonstrated the induction of SAR in potato plantlets against Potato Virus X by using bacterial culture filtrates invitro. These biotic inducers included Pseudomonas spp. and Bacillus spp. The study observed the occurrence of induced resistance and enhanced growth in potato plantlets treated with culture filtrates containing these microorganisms. This was evident through a reduction in PVX infection, disease severity and associated biochemical changes (such as elevated levels of endogenous salicylic acid, protein content, chlorophyll content, peroxidase and polyphenol oxidase activities), as well as improvements in growth parameters.

Exploring the mechanisms of endophytic bacteria for suppressing early blight disease in tomato (Solanum lycopersicum L.).

Controlling early blight of tomatoes using endophytic bacteria is an eco-friendly and sustainable approach to manage this common fungal disease caused by Alternaria solani, Alternaria alternata, and Curvularia lunata. Endophytic bacteria are microorganisms that live inside plant tissues without causing harm and can help protect the host plant from pathogens. In this work, twenty endophytic bacterial isolates from tomato healthy plants were tested against pathogenic fungal isolates that caused early blight disease in vitro. Out of the 20 tested isolates, three (B4, B7, and B17) were considered effective isolates against the growth of fungal pathogens. The three isolates were recognized as Enterobacter cloacae HS-6 (B4), Pseudomonas gessardii HS-5 (B 7), and Pseudomonas mediterranea HS-4 (B17) using 16s-rDNA sequencing. Different concentrations of bacterial cultural diltrates at 20, 40, and 60% were tested for their antagonistic effects on the development of pathogenic fungi in vitro. The lowest dry weights of pathogenic isolates in all bacterial culture filtrates were discovered at 60%. In all culture filtrates, phenolic compounds showed the largest peak area. Under greenhouse conditions, the least disease severity of tomato early blight was found for E. cloacae and its culture filtrate compared to other treatments. Real-time PCR was used to examine the expression pattern of the defense response gene β-1.3 glucanase gene in infected tomato plants with pathogenic fungi (control) as well as its relations with efficient biocontrol agent (E. cloacae). The expression of the gene increased substantially and significantly after three days from the inoculation-infected plants with C. lunata and E. cloacae while it reached the maximum after five days from the inoculation with A. alternata, A. solani and E. cloacae. Our study concluded that the endophytic bacterial isolate E. cloacae can be considered a promising biocontrol agent for preventing tomato early blight.

In vitro Screening of Different Rhizobacterial Strains against Egg Hatching of Rice Root-Knot Nematode, Meloidogyne graminicola

Meloidogyne graminicola is an economic yield loss causing major pest of rice globally. For managing this pest, biological control practices act as an alternate strategy, as it is the most effective and economic. Plant growth promoting rhizospheric bacteria (PGPR) are most significant because they benefit plants both directly and indirectly by enhancing plant growth and provides long lasting antagonistic effects against plant parasitic nematodes. Considering this an in vitro efficacy research experiment of nematoxicity of native rhizobacterial strains was conducted, against egg hatching of M. graminicola at S/2 and S/4 concentration levels of intact bacterial culture and cell free culture filtrates (CFCs). The hatching behavior of rice root-knot nematode eggs was observed on alternate days for ten days which resulted in inhibition of egg hatching by all bacterial cultures at both concentration levels. When compared to the untreated control, Bacillus spp. showed the most egg inhibition in the S/2 concentration of both culture filtrates i.e,86.8% and 84.8%. Similarly, in the S/4 level of concentration, most egg hating such as 83.7% and 79.8% was recorded in Bacillus spp. culture filtrates. The rate of hatching was inversely proportional to the concentration of strains at exposure time, decreasing as the concentration increased. The results of the experiment revealed the potential of rhizospheric bacteria which makes it more feasible and environmentally safe approach for the management of Meloidogyne graminicola.

Isolation, identification, and biocontrol mechanisms of endophytic Burkholderia vietnamiensis C12 from Ficus tikoua Bur against Rhizoctonia solani

Rice sheath blight is a devastating fungal disease caused by Rhizoctonia solani. Biocontrol utilizing endogenous microorganisms has been considered a safe and sustainable strategy. To obtain a new type of antagonistic bacteria with a high biocontrol effect on rice sheath blight, over 50 endophytic bacteria were isolated from the root of the medicinal plant Ficus tikoua Bur and screened for their antifungal activity by dual culture assay. Among them, strain C12 showed the strongest inhibitory activity against R. solani (inhibition rate 94.78%), and exhibited a broad-spectrum antifungal activity. According to the phylogenetic tree based on 16S rDNA and recA genes, C12 was identified as Burkholderia vietnamiensis, belonging to the Burkholderia cepacia complex, and safe for plants and humans. Through the study on B. vietnamiensis C12, the strain could secrete cell wall degrading enzymes (protease and chitinase), produce IAA, and siderophores, fix nitrogen, and solubilize phosphorus. The bacterial culture filtrate (although treated at 121 °C) of strain C12 and its ethyl acetate extract significantly inhibited the growth of R solani and resulted in distorted hyphae. Moreover, when the extract was 50 μg/mL, 100 μg/mL, 200 μg/mL, and 500 μg/mL, the diameter of mycelium was decreased by 50.44%, 56.43%, 67.27%, and 74.80% respectively, the number of sclerotia was decreased by 85.45%, 90.42%, 96.83%, and 99.22% respectively. Multiple antifungal substances in extracts of C12 were detected through LC-MS. Strain C12 gave a 70.98% reduction in lesion length in a detached inoculated leaf assay. In greenhouse and field tests, strain C12 significantly reduced the disease index of rice sheath blight, and the control efficiency reached 68.75% and 66.52%, respectively. Furthermore, C12 enhanced the resistance of rice to R. solani by increasing the activities of defense enzymes SOD, PAL, POD, CAT, and PPO. The strain also exhibited plant-promoting abilities on rice. The results indicated that B. vietnamiensis C12 had great biocontrol potential and could be used as a candidate strain for green control of rice sheath blight.

Dormancy and germination of microsclerotia of Verticillium longisporum are regulated by soil bacteria and soil moisture levels but not by nutrients

The soil-borne pathogen Verticillium longisporum infects roots of its host plant, oilseed rape, and systemically colonizes stems where it finally forms microsclerotia at crop maturity. Once returned to the soil after harvest, microsclerotia undergo a stage of dormancy, in which they may survive for several years. Since there is neither efficient chemical control nor effective resistance in oilseed rape cultivars to control the disease, alternative control strategies may consist in regulating the germination and dormancy of microsclerotia in the soil. Therefore, a series of experiments were conducted to explore the effects of nutrients, soil moisture, and the soil microbiome on germination of dormant microsclerotia. Experiments with microsclerotia exposed in vitro to different nutrients indicated that under sterile conditions the stimulating effect of nutrients on microsclerotia germination was not enhanced as compared to water. Moreover, further assays revealed a strong inhibitory effect of unsterile soil on microsclerotia germination. Accordingly, oilseed rape plants inoculated with microsclerotia of V. longisporum showed severe infection with V. longisporum when grown in autoclaved soil, in contrast to plants grown in unsterile soil. These experiments indicate a crucial role of soil fungistasis and thus the soil microbiome on microsclerotia germination. Further bioassays demonstrated that viable soil bacteria obtained from the rhizosphere of oilseed rape plants and bulk field soil effectively inhibited microsclerotia germination, whereas dead bacteria and bacterial culture filtrates hardly suppressed germination. A putative inhibitory role of volatile organic compounds (VOCs) produced by soil bacteria was confirmed in two-compartment Petri dishes, where microsclerotia germination and colony growth were significantly inhibited. Bacterial VOCs were collected and analyzed by GC–MS. In total, 45 VOCs were identified, among which two acid and two alcohol compounds were emitted by all tested bacteria. A bioassay, conducted with corresponding pure chemicals in two-compartment Petri dishes, indicated that all acidic volatile compounds, including 3-methylbutanoic acid, 2-methylbutanoic acid, hexanoic acid, and 2-methylpropionic acid, induced strong inhibitory effects on microsclerotia. We conclude that bacterial acidic volatiles play a key role in the fungistatic effect on microsclerotia of V. longisporum in the soil and could thus be targeted for development of novel strategies to control this pathogen by artificially regulating dormancy of microsclerotia in soil.

Large Scale Cultivation of Bacillus velezensis CE 100 and Effect of Its Culture on Control of Citrus Melanose Caused by Diaporthe citri

Diaporthe citri is an important fungal pathogen which causes melanose in various citrus growing regions of the world. In our study, control of D. citri was performed by using effective biocontrol agent, Bacillus velezensis CE 100. Mycelial growth of D. citri was highly restricted by strain CE 100 in dual culture plates. Our study demonstrates large-scale inoculation of strain CE 100 in non-sterilized PB medium. In addition, bacterial culture filtrate (BCF) of strain CE 100 from the large-scale culture showed better growth inhibition of D. citri than those from small-scale culture in the laboratory. Moreover, microscopic observation revealed that hyphal morphology of the pathogen was significantly affected by BCF, probably because of various cell-wall degrading enzymes and metabolites produced by strain CE 100. In addition, 50% BCF of strain CE 100 inhibited D. citri conidial germination by over 80%. Treatments, applied by foliar spray with fungicide and strain CE 100 culture, significantly lowered melanose disease incidence more than did control. The results of this study indicate that large-scale culture of strain CE 100 was effective for control of D. citri by means of adequate active metabolites and cells. Therefore, we demonstrate biocontrol applicability of B. velezensis CE 100 on control of citrus melanose by developing a low-cost PB medium using affordable large-scale fermenter. Effect of different treatments on melanose disease incidence on leaves of mandarin plants at 20 days after inoculation with D. citri. Statistical comparison between treatments was done by least significant difference (LSD) test at p < 0.05 level. Means with the same letter are not significantly different from each other. *Con- Control, CE 100- Treatment with B. velezensis CE 100 culture, F- Treatment with fungicide

An Organic Electrochemical Transistor to Monitor Salmonella Growth in Real‐Time

AbstractOrganic electrochemical transistors (OECTs) are used in research and diagnostic applications due to their facile manufacture, scalability, and biocompatibility. In these devices, the source–drain current upon gate voltage application depends on ion concentration in the electrolyte. This study investigates whether an OECT can be employed to monitor bacterial growth since it is known that the concentration of charged species increases in bacterial cultures during growth. A poly(3,4‐ethylenedioxythiophene):polystyrene sulfonate‐based single‐well OECT, compatible with long‐term incubation of bacterial cultures, is fabricated. It is shown that the growth of Salmonella alters the transfer characteristics of the device and demonstrates how it can be applied to monitor growth in real‐time by recording the source–drain current at gate voltage +0.5 V. The signal can also be measured in filtrates of bacterial cultures, devoid of bacterial cells. This suggests that the signal originates from charged metabolic products. Bacterial biofilm formation does not alter the device response. This proof‐of‐principle study presents OECT recordings as an alternative to optical methods, allowing bacterial growth to be monitored in transparent and opaque media alike. By measuring metabolic products rather than bacterial cell multiplication, insight into the stationary phase and other nondividing states may be obtained in the future.

Antinematode Activity of Abomasum Bacterial Culture Filtrates against Haemonchus contortus in Small Ruminants.

Simple SummaryHaemonchus contortus is an important gastrointestinal nematode parasite of the tropical and sub-tropical regions that cause haemonchosis in small ruminants like goats and sheep. It causes low production, reduced growth and may cause death of the infected animals. Due to the resistance development and environmental issues, the use of anthelmintics can be replaced with biological control, which is an environment friendly alternative. In the present study, three bacteria viz; Comamonas testosteroni, C. jiangduensis and Pseudomonas weihenstephanesis showed significant effect on nematode mortality and egg hatch inhibition. It was also observed that the anthelmintic activity of these bacteria was dose dependent, where 100% bacterial metabolite concentration showed the highest activity. It is suggested that these bacteria may included in the integrated nematode management.Haemonchosis is a parasitic disease of small ruminants that adversely affects livestock production. Haemonchus contortus is one of the most prevalent nematode parasites that infect the abomasum of small ruminants. This parasite reduces milk production, overall growth and sometimes causes the death of the infected animals. The evaluation of the biocontrol potential of some abomasum bacterial isolates against H. contortus is investigated in this study. Out of which, three isolates—Comamonas testosteroni, Comamonas jiangduensis, Pseudomonas weihenstephanesis—show significant effect against the nematode L3, adult, and egg hatch inhibition assays. Various concentrations of metabolites from these bacteria are prepared and applied in different treatments compared with control. In the case of adult mortality assay, 50% metabolites of C. testosteroni and P. weihenstephanesis show 46% adult mortality, whereas C. jiangduensis shows 40% mortality. It is observed that decreasing the concentration of bacterial metabolite, lowers nematode mortality. The minimum nematode mortality rate is recorded at the lowest filtrates concentration of all the bacterial isolates. The same trend is observed in egg hatch inhibition assay, where the higher concentration of bacterial culture filtrates shows 100% inhibition of H. contortus egg. It is concluded that the effect of bacterial culture filtrates against H. contortus is dose-dependent for their activity against nematode L3, adult, and inhibition of egg hatchment.

Natural biostimulants as upscale substitutes to synthetic hormones for boosting tomato yield and fruits quality

Natural biostimulants are one of the most promising and eco-sustainable technologies, which can improve the qualitative and productive attributes of horticultural crops. The positive effects of their application derive from their “signaling role” as elicitors of auxin- and gibberellin-like activity, thus constituting a valid alternative to synthetic hormones. Our research aimed to assess the efficacy of a plant extract (Heptamin®) and a bacterial culture filtrate (Capxium®), both rich in natural auxins, and of a synthetic auxin (Auxyger® LG) on the quantitative and qualitative performance, as well as on the economic returns of greenhouse table tomato (Solanum lycopersicum L. cv. Pitagora). The application of plant extract increased the marketable yield (+25.8%), firmness (+25.7%), and fruit lycopene content (+42.5%) compared to the untreated control. In particular, natural biostimulants outperformed synthetic auxin by inducing higher fruit weight (13.1%) and marketable yield (16.2%). On the other hand, no significant differences were recorded as a result of the treatments regarding total soluble solids, pH, and titratable acidity of the fruit juice. Our results suggest that plant biostimulants with auxin-like activity are an excellent tool for boosting tomato production and fruit quality in an eco-sustainable approach. Finally, economic analysis revealed that the application of natural biostimulants resulted in overall higher profitability