Combining Biocontrol Agent With Plant Nutrients for Integrated Control of Tomato Early Blight Through the Modulation of Physio-Chemical Attributes and Key Antioxidants

Synthesis and effects of zinc-chitosan complex on morpho-growth and biochemical responses in Alternaria alternata, a cause of leaf blights and spots on plants

The increasing resistance of fungal pathogens to synthetic fungicides necessitates eco-friendly alternatives. Zinc-chitosan (Zn-Ch) complexe offer a sustainable solution due to their biocompatibility and antifungal properties. This study synthesized and characterized Zn-Ch using UV-vis spectroscopy, Fourier transform infrared (FTIR) spectroscopy, dynamic light scattering (DLS), zeta potential, X-ray diffraction (XRD), and fluorescence spectral analysis, confirming strong Zn²⁺ interactions with chitosan. In vitro bioassays evaluated antifungal efficacy across different treatments: Mancozeb (chemical control), chitosan alone (Ch), non-complexed Zn (2.5 and 5.0 ppm) + Ch, and the Zn (5.0 ppm)-Ch complex. In all treatments, Mancozeb and Ch were tested at identical concentrations (0.5-2.5%) to ensure comparative analysis. Mancozeb and Ch exhibited dose-dependent inhibition, reaching 66.67% and 78.57% at 2.5%, respectively. Non-complexed Zn (2.5 and 5.0 ppm) + Ch demonstrated enhanced antifungal activity, with 5.0 ppm achieving 89.03% inhibition, while the Zn (5.0 ppm)-Ch complex exhibited the highest antifungal efficacy (99% inhibition) with severe hyphal distortion and delayed sporulation. Biochemical assays revealed an initial increase in catalase (CAT), peroxidase (POX), polyphenol oxidase (PPO), and phenylalanine ammonia-lyase (PAL) activities, peaking at 1.0-1.5%, followed by significant declines at higher concentrations. The Zn (5.0 ppm)-Ch complex caused the steepest enzymatic decline at 2.0-2.5%, suggesting oxidative stress-induced fungal suppression. Collectively, these findings confirmed the potential of the Zn-Ch complex in enhancing antifungal efficacy by altering fungal morphology, suppressing growth, and activating enzymatic defense responses in plants. Zn-Ch emerged as a promising, biocompatible alternative to synthetic fungicides, warranting further in vivo validation for its application in sustainable crop protection strategies.

Melatonin induced reversibility of vanadium toxicity in muskmelon by regulating antioxidant defense and glyoxalase systems

Agricultural lands with vanadium (V), pose a significant and widespread threat to crop production worldwide. The study was designed to explore the melatonin (ME) treatment in reducing the V-induced phytotoxicity in muskmelon. The muskmelon seedlings were grown hydroponically and subjected to V (40 mg L-1) stress and exogenously treated with ME (100 μmol L-1) to mitigate the V-induced toxicity. The results showed that V toxicity displayed a remarkably adverse effect on seedling growth and biomass, primarily by impeding root development, the photosynthesis system and the activities of antioxidants. Contrarily, the application of ME mitigated the V-induced growth damage and significantly improved root attributes, photosynthetic efficiency, leaf gas exchange parameters and mineral homeostasis by reducing V accumulation in leaves and roots. Additionally, a significant reduction in the accumulation of reactive oxygen species (ROS), malondialdehyde (MDA) along with a decrease in electrolyte leakage was observed in muskmelon seedlings treated with ME under V-stress. This reduction was attributed to the enhancement in the activities of antioxidants in leaves/roots such as ascorbate (AsA), superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), glutathione peroxidase (GPX), glutathione S-transferase (GST) as compared to the V stressed plants. Moreover, ME also upregulated the chlorophyll biosynthesis and antioxidants genes expression in muskmelon. Given these findings, ME treatment exhibited a significant improvement in growth attributes, photosynthesis efficiency and the activities of antioxidants (enzymatic and non-enzymatic) by regulating their expression of genes against V-stress with considerable reduction in oxidative damage.

Biological control of tomato early blight in Pakistan using local rhizobacteria

BACKGROUND

The biocontrol potential of soil microbes can reduce the extensive use of hazardous synthetic fungicides. This study was designed to find a strain of rhizobacteria indigenous to Pakistan with potential biocontrol against early blight of tomato caused by Alternaria solani and to characterize its biocontrol mechanisms.

RESULTS

Among 88 strains tested for antagonism against A. solani on agar media, S27, Dt10 and 423, identified by 16S rRNA sequencing as strains of Bacillus amyloliquefaciens, B. cereus and Stenotrophomonas rhizophila, respectively, were the most inhibitory. When applied to detached tomato leaflets in Petri dish assays, the strains reduced lesion development by over 30% compared to the control. In greenhouse pot trials, the bacterial strains reduced early blight severity by over 50%. In three field trials, all three strains applied to tomato foliage slowed early blight disease progress and reduced disease severity, with B. amyloliquefaciens S27 reducing the area under the disease progress curve by up to 70%. All three strains showed protease, catalase and oxidase activities in vitro, but none produced β-1,3-glucanase and only B. cereus Dt10 showed slight chitinase activity. In a greenhouse experiment in which the bacteria were applied to tomato foliage prior to pathogen inoculation, bacteria-treated leaves had higher β-1,3-glucanase and chitinase levels than leaves inoculated only with the pathogen, indicating priming induction of response.

CONCLUSION

Three rhizobacteria strains have the potential to control early blight of tomato under Pakistan's growing conditions, with B. amyloliquefaciens S27 being the most promising candidate for commercial development. Antagonism and induction of the priming response may be mechanisms of biocontrol by the bacterial strains. © 2023 Society of Chemical Industry.

Use of ginger extract and bacterial inoculants for the suppression of Alternaria solani causing early blight disease in Tomato

Early blight (EB), caused by Alternaria solani, is a serious problem in tomato production. Plant growth-promoting rhizobacteria promote plant growth and inhibit plant disease. The present study explored the bio-efficacy of synergistic effect of rhizobacterial isolates and ginger powder extract (GPE) against tomato EB disease, singly and in combination. Six fungal isolates from symptomatic tomato plants were identified as A. solani on the basis of morphological features i.e., horizontal septation (6.96 to 7.93 µm), vertical septation (1.50 to 2.22 µm), conidia length (174.2 to 187.6 µm), conidial width (14.09 to 16.52 µm), beak length (93.06 to 102.26 µm), and sporulation. Five of the twenty-three bacterial isolates recovered from tomato rhizosphere soil were nonpathogenic to tomato seedlings and were compatible with each other and with GPE. Out of five isolates tested individually, three isolates (St-149D, Hyd-13Z, and Gb-T23) showed maximum inhibition (56.3%, 48.3%, and 42.0% respectively) against mycelial growth of A. solani. Among combinations, St-149D + GPE had the highest mycelial growth inhibition (76.9%) over the untreated control. Bacterial strains molecularly characterized as Pseudomonas putida, Bacillus subtilis, and Bacillus cereus and were further tested in pot trials through seed bacterization for disease control. Seeds treated with bacterial consortia + GPE had the highest disease suppression percentage (78.1%), followed by St-149D + GPE (72.2%) and Hyd-13Z + GPE (67.5%). Maximum seed germination was obtained in the bacterial consortia + GPE (95.0 ± 2.04) followed by St-149D + GPE (92.5 ± 1.44) and Hyd-13Z + GPE (90.0 ± 2.04) over control (73.8 ± 2.39) and chemical control as standard treatment (90.0 ± 2). Ginger powder extracts also induce the activation of defence-related enzymes (TPC, PO, PPO, PAL, and CAT) activity in tomato plants. These were highly significant in the testing bacterial inoculants against A. solani infection in tomato crops.

Seed biopriming with Ochrobactrum ciceri mediated defense responses in Zea mays (L.) against Fusarium rot

Seed bio-priming is a simple and friendly technique to improve stress resilience against fungal diseases in plants. An integrated approach of maize seeds biopriming with Ochrobactrum ciceri was applied in Zn-amended soil to observe the response against Fusarium rot disease of Zea mays (L.) caused by Fusarium verticillioides. Initially, the pathogen isolated from the infected corn was identified as F. verticillioides based on morphology and sequences of the internally transcribed spacer region of the ribosomal RNA gene. Re-inoculation of maize seed with the isolated pathogen confirmed the pathogenicity of the fungus on the maize seeds. In vitro, the inhibitory potential of O. ciceri assessed on Zn-amended/un-amended growth medium revealed that antifungal potential of O. ciceri significantly improved in the Zn-amended medium, leading to 88% inhibition in fungal growth. Further assays with different concentrations (25, 50, and 75%) of cell pellet and the cultural filtrate of O. ciceri (with/without the Zn-amendment) showed a dose-dependent inhibitory effect on mycelial growth of the pathogen that also led to discoloration, fragmentation, and complete disintegration of the fungus hyphae and spores at 75% dose. In planta, biopriming of maize seeds with O. ciceri significantly managed disease, improved the growth and biochemical attributes (up to two-fold), and accelerated accumulation of lignin, polyphenols, and starch, especially in the presence of basal Zn. The results indicated that bioprimed seeds along with Zn as the most promising treatment for managing disease and improving plant growth traits through the enhanced accumulation of lignin, polyphenols, and starch, respectively.

Antifungal potential of volatiles produced by Bacillus subtilis BS-01 against Alternaria solani in Solanum lycopersicum

Bacterial biocontrol agent/s (BCAs) against plant diseases are eco-friendly and sustainable options for profitable agricultural crop production. Specific beneficial strains of Bacillus subtilis are effective in controlling many fungal diseases including Alternaria blight caused by a notorious pathogen "Alternaria solani". In the present study, the biocontrol attributes of a newfangled strain of B. subtilis (BS-01) have been investigated and its bioactive compounds were also identified against A. solani. The volatile organic compounds (VOCs) produced by BS-01 in organic solvents viz., n-hexane, dichloromethane, and ethyl acetate were extracted and their antifungal efficacy has evaluated against A. solani. Also, the preventive and curative biocontrol method to reduce the fungal load of A. solani was estimated by both foliar and seed applications on infected tomato (Solanum lycopersicum) plants as determined by quantitative PCR assays. Growth chamber bioassay revealed that both foliar and seed application of BS-01 on tomato plants previously or subsequently infected by A. solani significantly reduced the pathogen load on inoculated tomato foliage. Results showed that antifungal bioassays with various concentrations (10-100 mg mL^-1) of extracted metabolites produced by BS-01 in ethyl acetate fraction showed the highest inhibition in fungal biomass (extracellular metabolites: 69-98% and intracellular metabolites: 48-85%) followed by n-hexane (extracellular metabolites: 63-88% and intracellular metabolites: 35-62%) and dichloromethane (extracellular metabolites: 41-74% and intracellular metabolites: 42-70%), respectively. The extracted volatile compounds of BS-01 were identified via GC-MS analysis and were found in great proportions in the organic fractions as major potent antifungal constituents including triphenylphosphine oxide; pyrrolo[1,2-a] pyrazine-1,4-dione, hexahydro-3-(2-methylpropyl); pyrrolo[1,2-a] pyrazine-1,4-dione, hexahydro-3-(phenylmethyl); n-hexadecanoic acid; n-tridecan-1-ol; octadecane; octadecanoic acid; eicosane and dodecyl acrylate. Separate or mixture of these bioactive VOCs had the potential to mitigate the tomato early blight disease severity in the field that would act as a sustainable plant protection strategy to generate profitable tomato production.

Biocontrol potential and action mechanism of Bacillus amyloliquefaciens DB2 on Bipolaris sorokiniana

Introduction

Bipolaris sorokiniana is the popular pathogenic fungi fungus which lead to common root rot and leaf spot on wheat. Generally, chemical fungicides are used to control diseases. However, the environmental pollution resulting from fungicides should not be ignored. It is important to study the mode of antagonistic action between biocontrol microbes and plant pathogens to design efficient biocontrol strategies.

Results

An antagonistic bacterium DB2 was isolated and identified as Bacillus amyloliquefaciens. The inhibition rate of cell-free culture filtrate (CF, 20%, v/v) of DB2 against B. sorokiniana reached 92.67%. Light microscopy and scanning electron microscopy (SEM) showed that the CF significantly altered the mycelial morphology of B. sorokiniana and disrupted cellular integrity. Fluorescence microscopy showed that culture filtrate destroyed mycelial cell membrane integrity, decreased the mitochondrial transmembrane potential, induced reactive oxygen species (ROS) accumulation, and nuclear damage which caused cell death in B. sorokiniana. Moreover, the strain exhibited considerable production of protease and amylase, and showed a significant siderophore and indole-3-acetic acid (IAA) production. In the detached leaves and potted plants control assay, B. amyloliquefacien DB2 had remarkable inhibition activity against B. sorokiniana and the pot control efficacy was 75.22%. Furthermore, DB2 suspension had a significant promotion for wheat seedlings growth.

Conclusion

B. amyloliquefaciens DB2 can be taken as a potential biocontrol agent to inhibit B. sorokiniana on wheat and promote wheat growth.

Integrated management of charcoal rot disease in susceptible genotypes of mungbean with soil application of micronutrient zinc and green manure (prickly sesban)

Charcoal rot disease is incited by the soil-borne fungus Macrophomina phaseolina (Tassi). Goid is a challenging disease due to long-term persistence of fungus sclerotia in the soil. This study assessed the potential of zinc (Zn: 1.25, 2.44, and 5 mg/kg) and green manure (GM: 1 and 2%) in solitary and bilateral combinations to alleviate infection stress incited by M. phaseolina on disease, growth, physiology, and yield attributes in mungbean. A completely randomized design experiment was conducted in potted soil, artificially inoculated with the pathogen, and sown with surface-sterilized seeds of mungbean genotypes (susceptible: MNUYT-107 and highly susceptible: MNUYT-105). Concealment of plant resistance by M. phaseolina in both genotypes resulted in 53-55% disease incidence and 40-50% plant mortality, which contributed in causing a significant reduction of 30-90% in attributes of growth, biomass, yield, photosynthetic pigment, and total protein content with an imbalance of production of antioxidant enzymes (polyphenol oxidase, superoxide dismutase, catalase, and peroxidase). Soil application with Zn-based fertilizer (ZnSO4: 33%) in combination with GM significantly managed up to 80% of the charcoal rot disease, hence improving growth (50-100%) and physiochemical (30-100%) attributes and sustainably enhancing grain average yield (300-600%), biological yield (100-200%), and harvest index (100-200%) in mungbean plants. The heat map and principal component analyses based on 19 measured attributes with 16 treatments separated Zn (2.44 or 5 mg/kg) combined with 2% GM as the best treatments for alleviating charcoal rot disease stress by improving growth, yield, and biological attributes to an extent to profitable farming in terms of harvest index (HI) and benefit-cost ratio (BCR).

Optimal NPK Fertilizer Combination Increases Panax ginseng Yield and Quality and Affects Diversity and Structure of Rhizosphere Fungal Communities

Soil microorganisms affect crop rhizospheres via the transformation and transport of nutrients, which has important influences on soil fertility, carbon sequestration, and plant yield and health in agroecosystems. There are few reports on the effects of fertilizer application on the growth of Panax ginseng (C. A. Mey.) or the structure of its rhizosphere microbial communities. In this study, an orthogonal experimental design was used to explore the effects of nine different combinations of nitrogen (N), phosphorus (P), and potassium (K) fertilizers with different amounts and proportions on ginseng growth and accumulation of ginsenosides and the structure of rhizosphere soil fungal communities. Soil without fertilization was the control. With the combined application of NPK, ginseng growth and development increased. The fertilization scheme N₃P₁K₃, with N fertilizer at 50 g·m⁻², P fertilizer at 15 g·m⁻², and K fertilizer at 60 g·m⁻², had the most comprehensive benefit and significantly increased ginseng rhizome biomass and ginsenoside contents (Rg1, Re, Rf, Rg2, Rb1, Ro, Rc, Rb2, Rb3, and Rd). Amplicon sequencing showed that NPK application increased the diversity of fungal communities in ginseng rhizospheres, whereas richness was bidirectionally regulated by proportions and amounts of NPK. Ascomycota was the dominant fungal phylum in ginseng rhizosphere soil, and relative abundances decreased with combined NPK application. Combined NPK application increased the relative abundance of potential beneficial fungi, such as Mortierella, but decreased that of potentially pathogenic fungi, such as Fusarium. Correlation analysis showed that potential beneficial fungi were significantly positively correlated with ginseng rhizome yield and ginsenoside contents, whereas the opposite relation was observed with potential pathogenic fungi. Thus, in addition to directly increasing crop growth, precise NPK application can also increase crop adaptability to the environment by shaping specific microbial communities. The results of this study suggest that the combined effects of biotic and abiotic processes on agricultural production determine crop yield and quality.