Showing papers on "Rhizoctonia solani published in 2022"

Design, Synthesis, and Antifungal Activity of Novel Chalcone Derivatives Containing a Piperazine Fragment.

Abstract: In an attempt to find the biorational pesticides, 20 novel chalcone derivatives containing a piperazine fragment were designed and synthesized. Their fungicidal activities and preliminarily action mechanism against Rhizoctonia solani were evaluated. Strikingly, the biological activity of compound D2 was obtained by optimizing the structure of the system. Subsequently, the practical value of compound D2 was ascertained by the relative surveys on in vivo anti-R. solani and anti-Colletotrichum gloeosporioides. The results revealed by scanning electron microscopy demonstrated that compound D2 could induce irregular and shrivelled growth of mycelium and rupture of the mycelium surface. This study indicates that chalcone derivatives containing a piperazine skeleton had better inhibitory effect on plant fungi, providing further complementary research on new pesticides.

Functional interplay between antagonistic bacteria and Rhizoctonia solani in the tomato plant rhizosphere

Abstract: Microbial interactions with plant roots play an imperial role in tomato plant growth and defense against the Rhizoctonia solani. This study performed a field experiment with two antagonistic bacteria (Pseudomonas and Bacillus) inoculated in healthy and Rhizoctonia solani treated soil in tomato rhizosphere to understand the metabolic pattern and microbial function during plant disease suppression. In the present study, we assessed soil and microbial enzymes, bacterial and fungal cell forming unit (CFU), and carbon utilization profiling through Bio-Eco plates of rhizoplane samples. Antagonist bacteria and pathogen interaction significantly (p < 0.05) influenced the bacterial count, soil enzymes (chitinase and glucanase), and bacterial function (siderophore and chitinase production). These results indicated that these variables had an imperial role in disease suppression during plant development. Furthermore, the metabolic profiling showed that carbon source utilization enhanced under fruit development and ripening stages. These results suggested that carbon sources were essential in plant/pathogen/antagonist interaction. Substrates like β-methyl-D-glucoside, D-mannitol, D-galacturonic acid, N-acetyl-D-glucosamine, and phenylethylamine strongly connect with the suppuration of root rot disease. These carbon sources may help to propagate a healthy microbial community to reduce the pathogen invasion in the plant root system, and these carbon sources can be stimulators of antagonists against pathogens in the future.

Trichoderma spp. Genes Involved in the Biocontrol Activity Against Rhizoctonia solani

Abstract: Rhizoctonia solani is a pathogen that causes considerable harm to plants worldwide. In the absence of hosts, R. solani survives in the soil by forming sclerotia, and management methods, such as cultivar breeding, crop rotations, and fungicide sprays, are insufficient and/or inefficient in controlling R. solani. One of the most challenging problems facing agriculture in the twenty-first century besides with the impact of global warming. Environmentally friendly techniques of crop production and improved agricultural practices are essential for long-term food security. Trichoderma spp. could serve as an excellent example of a model fungus to enhance crop productivity in a sustainable way. Among biocontrol mechanisms, mycoparasitism, competition, and antibiosis are the fundamental mechanisms by which Trichoderma spp. defend against R. solani, thereby preventing or obstructing its proliferation. Additionally, Trichoderma spp. induce a mixed induced systemic resistance (ISR) or systemic acquired resistance (SAR) in plants against R. solani, known as Trichoderma-ISR. Stimulation of every biocontrol mechanism involves Trichoderma spp. genes responsible for encoding secondary metabolites, siderophores, signaling molecules, enzymes for cell wall degradation, and plant growth regulators. Rhizoctonia solani biological control through genes of Trichoderma spp. is summarized in this paper. It also gives information on the Trichoderma-ISR in plants against R. solani. Nonetheless, fast-paced current research on Trichoderma spp. is required to properly utilize their true potential against diseases caused by R. solani.

Evaluation of Phoma sp. Biomass as an Endophytic Fungus for Synthesis of Extracellular Gold Nanoparticles with Antibacterial and Antifungal Properties

Abstract: The aim of our study was to examine the different concentrations of AuNPs as a new antimicrobial substance to control the pathogenic activity. The extracellular synthesis of AuNPs performed by using Phoma sp. as an endophytic fungus. Endophytic fungus was isolated from vascular tissue of peach trees (Prunus persica) from Baft, located in Kerman province, Iran. The UltraViolet-Visible Spectroscopy (UV–Vis spectroscopy) and Fourier transform infrared spectroscopy provided the absorbance peak at 526 nm, while the X-ray diffraction and transmission electron microscopy images released the formation of spherical AuNPs with sizes in the range of 10–100 nm. The findings of inhibition zone test of Au nanoparticles (AuNPs) showed a desirable antifungal and antibacterial activity against phytopathogens including Rhizoctonia solani AG1-IA (AG1-IA has been identified as the dominant anastomosis group) and Xanthomonas oryzae pv. oryzae. The highest inhibition level against sclerotia formation was 93% for AuNPs at a concentration of 80 μg/mL. Application of endophytic fungus biomass for synthesis of AuNPs is relatively inexpensive, single step and environmentally friendly. In vitro study of the antifungal activity of AuNPs at concentrations of 10, 20, 40 and 80 μg/mL was conducted against rice fungal pathogen R. solani to reduce sclerotia formation. The experimental data revealed that the Inhibition rate (RH) for sclerotia formation was (15, 33, 74 and 93%), respectively, for their corresponding AuNPs concentrations (10, 20, 40 and 80 μg/mL). Our findings obviously indicated that the RH strongly depend on AuNPs rates, and enhance upon an increase in AuNPs rates. The application of endophytic fungi biomass for green synthesis is our future goal.

Novel Dioxolane Ring Compounds for the Management of Phytopathogen Diseases as Ergosterol Biosynthesis Inhibitors: Synthesis, Biological Activities, and Molecular Docking.

Abstract: Thirty novel dioxolane ring compounds were designed and synthesized. Their chemical structures were confirmed by 1H NMR, HRMS, and single crystal X-ray diffraction analysis. Bioassays indicated that these dioxolane ring derivatives exhibited excellent fungicidal activity against Rhizoctonia solani, Pyricularia oryae, Botrytis cinerea, Colletotrichum gloeosporioides, Fusarium oxysporum, Physalospora piricola, Cercospora arachidicola and herbicidal activity against lettuce (Lactuca sativa), bentgrass (Agrostis stolonifera), and duckweed (Lemna pausicostata). Among these compounds, 1-((2-(4-chlorophenyl)-5-methyl-1,3-dioxan-2-yl)methyl)-1H-1,2,4-triazole (D17), 1-(((4R)-2-(4-chlorophenyl)-4-methyl-1,3-dioxolan-2-yl)methyl)-1H-1,2,4-triazole (D20), 1-((5-methyl-2-(4-(trifluoromethyl)phenyl)-1,3-dioxan-2-yl)methyl)-1H-1,2,4-triazole (D22), and 1-((2-(4-fluorophenyl)-1,3-dioxolan-2-yl)methyl)-1H-1,2,4-triazole (D26) had broad spectrum fungicidal and herbicidal activity. The IC50 values against duckweed were 20.5 ± 9.0, 14.2 ± 6.7, 24.0 ± 11.0, 8.7 ± 3.5, and 8.0 ± 3.1 μM for D17, D20, D22, and D26 and the positive control difenoconazole, respectively. The EC50 values were 7.31 ± 0.67, 9.74 ± 0.83, 17.32 ± 1.23, 11.96 ± 0.98, and 8.93 ± 0.91 mg/L for D17, D20, D22, and D26 and the positive control difenoconazole against the plant pathogen R. solani, respectively. Germination experiments with Arabidopsis seeds indicated that the target of these dioxolane ring compounds in plants is brassinosteroid biosynthesis. Molecular simulation docking results of compound D26 and difenoconazole with fungal CYP51 P450 confirmed that they both inhibit this enzyme involved in ergosterol biosynthesis. The structure-activity relationships (SAR) are discussed by substituent effect, molecular docking, and density functional theory analysis, which provided useful information for designing more active compounds.

Rhizoctonia solani Kühn Pathophysiology: Status and Prospects of Sheath Blight Disease Management in Rice

Abstract: Sheath blight caused by necrotrophic fungus Rhizoctonia solani Kühn is one of the most serious diseases of rice. Use of high yielding semi dwarf cultivars with dense planting and high dose of nitrogenous fertilizers accentuates the incidence of sheath blight in rice. Its diverse host range and ability to remain dormant under unfavorable conditions make the pathogen more difficult to manage. As there are no sources of complete resistance, management through chemical control has been the most adopted method for sheath blight management. In this review, we provide an up-to-date comprehensive description of host-pathogen interactions, various control measures such as cultural, chemical, and biological as well as utilizing host plant resistance. The section on utilizing host plant resistance includes identification of resistant sources, mapping QTLs and their validation, identification of candidate gene(s) and their introgression through marker-assisted selection. Advances and prospects of sheath blight management through biotechnological approaches such as overexpression of genes and gene silencing for transgenic development against R. solani are also discussed.

Efficacy of Bacillus subtilis XZ18-3 as a Biocontrol Agent against Rhizoctonia cerealis on Wheat

Abstract: Rhizoctonia cerealis is a major fungal pathogen of wheat that causes great yield losses in all wheat-growing regions of the world. The biocontrol agent Bacillus subtilis XZ18-3 was investigated for inhibiting R. cerealis growth in wheat. The results of the mycelial growth test showed that the sterile filtrate of B. subtilis XZ18-3 could significantly inhibit the mycelial growth of R. cerealis and cause swelling and rupture of the mycelium. Observation by transmission electron microscopy indicated that the sterile filtrate could penetrate the cellular membrane of Rhizoctoniacerealis, resulting in organelle destruction. The effect of the sterile filtrates on the pathogen cells, shown through fluorescent microscopy using different stains, revealed the mechanism by which the sterile filtrate caused DNA fragmentation, accumulation of ROS and changes in cell membrane permeability. To reach a better treatment of the soil-borne fungi, the components of a wettable powder were screened and an optimised formula determined (30.0% kaolin, 4.0% polyvinyl alcohol, 8.0% Tween-80, 2.0% polyethylene glycol and 100% fermentation broth). A quality index analysis revealed that the wetting powder reached acceptable biological pesticide standards. Pot control experiments showed that the wettable powder of B. subtilis XZ18-3 effectively controlled the pathogens with an efficacy of 88.28%. This study has provided the potential biocontrol agents (BCAs) for wheat sharp eyespot disease.

Fermentation optimization of surfactin production of Bacillus amyloliquefaciens HM618

Abstract: This work isolated a strain named Bacillus amyloliquefaciens HM618 from the soil, which can inhibit the growths of Botrytis cinerea, Rhizoctonia solani, and Escherichia coli DH5α. Based on the results of response surface methodology, the surfactin levels of strain HM618 were elevated from 0.724 to 1.876 g/L and 0.995 to 1.888 g/L under the pure culture with the optimized medium (containing 62.39 g/L sucrose, 15.06 g/L yeast extracts, and 3.27 g/L aspartate) and under the coculture of strains HM618 and Bacillus subtilis 168 with the optimized medium (containing 50.52 g/L sucrose, 19.76 g/L yeast extracts, and 1.02 g/L glutamate), respectively. Additionally, influences of nonconstitutive amino acids involved in the biosynthesis of surfactin were also explored. The highest surfactin level reached 2.04 g/L after adding 3.0 g/L exogenous ornithine. However, the surfactin production of strain HM618 was significantly inhibited after adding the mixtures of nonconstitutive amino acids.

Ascophyllum nodosum Extract and Mycorrhizal Colonization Synergistically Trigger Immune Responses in Pea Plants against Rhizoctonia Root Rot, and Enhance Plant Growth and Productivity

Abstract: Rhizoctonia root rot is one of the most destructive diseases affecting pea crops, resulting in up to 75% loss. In this study, the biocontrol activity of seaweed (Ascophyllum nodosum) extract at 1, 2, and 3% and/or mycorrhization of pea roots was investigated against Rhizoctonia root rot under greenhouse conditions. In addition, their effects on the transcriptional, physiological, ultrastructural, and growth status of pea plants were also studied. The results showed that the mycorrhizal colonization of pea roots and the application of the seaweed extract at 3% synergistically overexpressed the responsive factor (JERF3) recording 18.2-fold, and the defense-related genes peroxidase (23.2-fold) and chitinase II (31.8-fold). In addition, this treatment improved the activity of the antioxidant enzymes POD and PPO, increased the phenolic content in pea roots, and triggered multiple hypersensitivity reactions at the ultrastructural level of the cell, leading to a 73.1% reduction in disease severity. Moreover, a synergistic growth-promoting effect on pea plants was also observed. The photosynthetic pigments in pea leaves were enhanced in response to this dual treatment, which significantly improved their yield (24 g/plant). The inducing effect of mycorrhizal colonization on plant resistance and growth has been extensively studied. However, developing improved and synergistically acting biological agents for plant disease control and growth promotion as alternatives to the chemical fungicides is crucial for safety and food security. Based on these results, it can be concluded that the mycorrhizal colonization of pea roots and soaking their seeds in the A. nodosum extract at 3% have a promising and improved biocontrol activity against R. solani, and a growth-promoting effect on pea plants. However, field applications should be evaluated prior to any use recommendations.

Biocontrol and Action Mechanism of Bacillus subtilis Lipopeptides’ Fengycins Against Alternaria solani in Potato as Assessed by a Transcriptome Analysis

Abstract: Alternaria solani is an airborne fungus and the primary causal agent of potato early blight worldwide. No available fungicides that are both effective and environmentally friendly are usable to control this fungus. Therefore, biological control is a potential approach for its suppression. In this study, Bacillus subtilis strain ZD01’s fermentation broth strongly reduced A. solani pathogenicity under greenhouse conditions. The effects of strain ZD01’s secondary metabolites on A. solani were investigated. The exposure of A. solani hyphae to the supernatant resulted in swelling and swollen sacs, and the ZD01 supernatant reduced A. solani conidial germination significantly. Matrix-assisted laser desorption/ionization time of flight mass spectrometry and pure product tests revealed that fengycins were the main antifungal lipopeptide substances. To elucidate the molecular mechanism of the fengycins’ biological control, RNA sequencing analyses were performed. A transcriptome analysis revealed that 304 and 522 genes in A. solani were differentially expressed after 2-h and 6-h fengycin treatments, respectively. These genes were respectively mapped to 53 and 57 Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways. In addition, the most enriched KEGG pathway analysis indicated that the inhibitory mechanisms of fengycins against A. solani regulated the expression of genes related to cell wall, cell membrane, transport, energy process, protein synthesis and genetic information. In particular, cell wall and cell membrane metabolism were the main processes affected by fengycin stress. Scanning and transmission electron microscope results revealed hyphal enlargement and a wide range of abnormalities in A. solani cells after exposure to fengycins. Furthermore, fengycins induced chitin synthesis in treated cells, and also caused the capture of cellular fluorescent green labeling and the release of adenosine triphosphate (ATP) from outer membranes of A. solani cells, which may enhance the fengycins ability to alter cell membrane permeability. Thus, this study increases the transcriptome data resources available and supplies a molecular framework for B. subtilis ZD01 inhibition of A. solani HWC-168 through various mechanisms, especially damaging A. solani cell walls and membranes. The transcriptomic insights may lead to an effective control strategy for potato early blight.

Trichogenic Silver-Based Nanoparticles for Suppression of Fungi Involved in Damping-Off of Cotton Seedlings

Abstract: Mycogenic silver nanoparticles (AgNPs) produced by some biocontrol agents have shown the ability to inhibit the growth of numerous plant pathogenic fungi, which may be a unique method of disease management. This study describes the extracellular production of AgNPs by Trichoderma harzianum. The size, shape, charge, and composition of the AgNPs were subsequently studied by UV-visible spectroscopy, DLS, zeta potential, TEM, SEM, and EDX, among other methods. The AgNPs had sizes ranging from 6 to 15 nm. The antifungal activities of bio-synthesized AgNPs and two commercial fungicides (Moncut and Maxim XL) were tested against three soil-borne diseases (Fusarium fujikuroi, Rhizoctonia solani, and Macrophomina phaseolina). Cotton seedling illnesses were significantly reduced under greenhouse settings after significant in vitro antifungal activity was documented for the control of plant pathogenic fungi. The use of biocontrol agents such as T. harzianum, for example, may be a safe strategy for synthesizing AgNPs and using them to combat fungus in Egyptian cotton.

Synthesis of novel antibacterial and antifungal quinoxaline derivatives

Abstract: A series of quinoxaline derivatives were designed, synthesized and evaluated as antimicrobial agents against plant pathogenic bacteria and fungi. Some of these compounds exhibited significant antibacterial and antifungal activities in vitro. Compound 5k displayed good antibacterial activity against Acidovorax citrulli (Ac). Compounds 5j and 5t exhibited the most potent anti-RS (Rhizoctonia solani) activity, with the corresponding EC50 values of 8.54 and 12.01 μg mL−1, respectively, which are superior to that of the commercial azoxystrobin (26.17 μg mL−1). Further, the scanning electron microscopy results proved that compound 5j had certain effects on the cell morphology of RS. Moreover, an in vivo bioassay also demonstrated that the anti-RS activity of compound 5j could effectively control rice sheath blight. These results indicate that quinoxaline derivatives could be promising agricultural bactericides and fungicides.

Antifungal activity of chitinase produced by Streptomyces species isolated from grassland soils in Futa Area, Akure

Abstract: Abstract Background This study was carried out to investigate the antifungal activity of chitinase produced by Streptomyces species isolated from grassland soils against selected pathogenic fungi, namely: Magnaporthe oryzae , Fusarium graminearum , Rhizoctonia solani , Puccinia species and Botyrtis cinerea . Chitinase produced by Streptomyces albus was purified consecutively with dialysis, gel filtration and ion- exchange chromatography, the test isolate can be exploited for large scale production of chitinase. Results Seven Streptomyces species ( Streptomyces rimosus, S. albus, S. riseoflavus, S. fumosus, S. spiralis, S. aureofaciens and S. flavogriseus) isolated from three different grassland soils were screened based on the morphology and their ability to produce chitinase. S . rimosus , S . fumosus , S . albus and S . flavogriseus were able to produce chitinase, although the enzyme chitinase was found to be higher in Streptomyces albus . The effect of environmental factors were determined on Streptomyces albus being the best chitinolytic producing isolate. Temperature of 30 ο C was favourable for Streptomyces albus and pH 6.0 was a growth factor for maximum chitinase production. The activity of the enzyme was stimulated by the addition of metal ions like Mn 2+ , K + , Na + , Mg + , Fe 2+ , Ca 2+ but Zn 2+ inhibited chitinase activity. Chitinase activity was favoured by maltose as carbon source and NH 4 (SO 4 ) 2 as nitrogen source. Culture filtrate of Streptomyces albus was able to inhibit the growth of all the selected pathogenic fungi namely Magnaporthe oryzae , Fusarium graminearum , Rhizoctonia solani , Puccinia species and Botyrtis cinerea whereas Streptomyces rimosus has the least inhibitory activity. Conclusions Streptomyces albus has the highest ability to produce chitinase which can act as antifungal for degradation of the cell wall of many phytopathogenic fungi.

Pangenome Analysis of the Soilborne Fungal Phytopathogen Rhizoctonia solani and Development of a Comprehensive Web Resource: RsolaniDB

Abstract: Rhizoctonia solani is a collective group of genetically and pathologically diverse basidiomycetous fungi that damage economically important crops. Its isolates are classified into 13 Anastomosis Groups (AGs) and subgroups having distinctive morphology and host ranges. The genetic factors driving the unique features of R. solani pathology are not well characterized due to the limited availability of its annotated genomes. Therefore, we performed genome sequencing, assembly, annotation and functional analysis of 12 R. solani isolates covering 7 AGs and select subgroups (AG1-IA; AG1-IB; AG1-IC; AG2-2IIIB; AG3-PT, isolates Rhs 1AP and the hypovirulent Rhs1A1; AG3-TB; AG4-HG-I, isolates Rs23 and R118-11; AG5; AG6; and AG8), in which six genomes are reported for the first time. Using a pangenome comparative analysis of 12 R. solani isolates and 15 other Basidiomycetes, we defined the unique and shared secretomes, CAZymes, and effectors across the AGs. We have also elucidated the R. solani-derived factors potentially involved in determining AG-specific host preference, and the attributes distinguishing them from other Basidiomycetes. Finally, we present the largest repertoire of R. solani genomes and their annotated components as a comprehensive database, viz. RsolaniDB, with tools for large-scale data mining, functional enrichment and sequence analysis not available with other state-of-the-art platforms.

Characterization of Actinobacterial Strains as Potential Biocontrol Agents against Macrophomina phaseolina and Rhizoctonia solani, the Main Soil-Borne Pathogens of Phaseolus vulgaris in Cuba

Abstract: Macrophomina phaseolina and Rhizoctonia solani are considered two major soil-borne pathogens of Phaseolus vulgaris in Cuba. Their management is difficult, not only due to their intrinsic biology as soil-borne pathogens, but also because the lack of active ingredients available against these pathogens. Actinobacteria, a heterogeneous bacterial group traditionally known as actinomycetes have been reported as promising biological control agents (BCAs) in crop protection. Thus, the main objective of this study was to evaluate the effectiveness of 60 actinobacterial strains as BCAs against M. phaseolina and R. solani in vitro by dual culture assays. The most effective strains were characterized according to their cellulolytic, chitinolytic and proteolytic extracellular enzymatic activity, as well as by their morphological and biochemical characters in vitro. Forty and 25 out of the 60 actinobacteria strains inhibited the mycelial growth of M. phaseolina and R. solani, respectively, and 18 of them showed a common effect against both pathogens. Significant differences were observed on their enzymatic and biochemical activity. The morphological and biochemical characters allow us to identify all our strains as species belonging to the genus Streptomyces. Streptomyces strains CBQ-EA-2 and CBQ-B-8 showed the highest effectiveness in vitro. Finally, the effect of seed treatments by both strains was also evaluated against M. phaseolina and R. solani infections in P. vulgaris cv. Quivicán seedlings. Treatments combining the two Streptomyces strains (CBQ-EA-2 + CBQ-B-8) were able to reduce significantly the disease severity for both pathogen infections in comparison with the non-treated and inoculated control. Moreover, they showed similar effect than that observed for Trichoderma harzianum A-34 and with Celest® Top 312 FS (Syngenta®; Basilea, Switzerland) treatments, which were included for comparative purposes.

Suppression of Pepper Root Rot and Wilt Diseases Caused by Rhizoctonia solani and Fusarium oxysporum

Abstract: Pepper is vulnerable to soil-borne fungal pathogens such as Rhizoctonia solani and Fusarium oxysporum. The potential of beneficial rhizosphere microorganisms to control R. solani and F. oxysporum f.sp. capsici was evaluated in pepper plants. Paenibacillus polymyxa and Trichoderma longibrachiatum were isolated from rhizospheric soil samples of healthy pepper plants. In vitro, both isolates caused clear reductions in the radial growth of root rot and wilt pathogens. Scanning electron microscopy displayed lysis and abnormal shape of the pathogens in dual cultures with P. polymyxa and T. longibrachiatum. The incidence and severity of root rot and wilt diseases were significantly reduced in pepper plants treated with the growth-promoting fungi (PGPF isolates; Fusarium equiseti GF19-1, Fusarium equiseti GF18-3, and Phoma sp. GS8-3), P. polymyxa, or T. longibrachiatum in comparison to the control. Moreover, the induction treatments led to increased pepper growth compared with their control. The defense related gene (CaPR4) expression was shown to be significantly higher in the treated plants than in the control plants. In conclusion, the antagonistic isolates (P. polymyxa and T. longibrachiatum) and PGPF isolates have a clear impact on the prevention of root rot and wilt diseases in pepper plants incited by R. solani and F. oxysporum f.sp. capsici. The expression of the CaPR4 gene added to the evidence that PGPF isolates generate systemic resistance to pathogen infections.

Rhizospheric Actinomycetes Revealed Antifungal and Plant-Growth-Promoting Activities under Controlled Environment

Abstract: Actinomycetes has large habitats and can be isolated from terrestrial soil, rhizospheres of plant roots, and marine sediments. Actinomycetes produce several bioactive secondary metabolites with antibacterial, antifungal, and antiviral properties. In this study, some Actinomycetes strains were isolated from the rhizosphere zone of four different plant species: rosemary, acacia, strawberry, and olive. The antagonistic activity of all isolates was screened in vitro against Escherichia coli and Bacillus megaterium. Isolates with the strongest bioactivity potential were selected and molecularly identified as Streptomyces sp., Streptomyces atratus, and Arthrobacter humicola. The growth-promoting activity of the selected Actinomycetes isolates was in vivo evaluated on tomato plants and for disease control against Sclerotinia sclerotiorum. The results demonstrated that all bacterized plants with the studied Actinomycetes isolates were able to promote the tomato seedlings’ growth, showing high values of ecophysiological parameters. In particular, the bacterized seedlings with Streptomyces sp. and A. humicola showed low disease incidence of S. sclerotiorum infection (0.3% and 0.2%, respectively), whereas those bacterized with S. atratus showed a moderate disease incidence (7.6%) compared with the positive control (36.8%). In addition, the ability of the studied Actinomycetes to produce extracellular hydrolytic enzymes was verified. The results showed that A. humicola was able to produce chitinase, glucanase, and protease, whereas Streptomyces sp. and S. atratus produced amylase and pectinase at high and moderate levels, respectively. This study highlights the value of the studied isolates in providing bioactive metabolites and extracellular hydrolytic enzymes, indicating their potential application as fungal-biocontrol agents.

Metatranscriptomic Analysis Reveals Rich Mycoviral Diversity in Three Major Fungal Pathogens of Rice

Abstract: In recent years, three major fungal diseases of rice, i.e., rice blast, rice false smut, and rice-sheath blight, have caused serious worldwide rice-yield reductions and are threatening global food security. Mycoviruses are ubiquitous in almost all major groups of filamentous fungi, oomycetes, and yeasts. To reveal the mycoviral diversity in three major fungal pathogens of rice, we performed a metatranscriptomic analysis of 343 strains, representing the three major fungal pathogens of rice, Pyricularia oryzae, Ustilaginoidea virens, and Rhizoctonia solani, sampled in southern China. The analysis identified 682 contigs representing the partial or complete genomes of 68 mycoviruses, with 42 described for the first time. These mycoviruses showed affinity with eight distinct lineages: Botourmiaviridae, Partitiviridae, Totiviridae, Chrysoviridae, Hypoviridae, Mitoviridae, Narnaviridae, and Polymycoviridae. More than half (36/68, 52.9%) of the viral sequences were predicted to be members of the families Narnaviridae and Botourmiaviridae. The members of the family Polymycoviridae were also identified for the first time in the three major fungal pathogens of rice. These findings are of great significance for understanding the diversity, origin, and evolution of, as well as the relationship between, genome structures and functions of mycoviruses in three major fungal pathogens of rice.

Identification of Volatile Organic Compounds Emitted by Two Beneficial Endophytic Pseudomonas Strains from Olive Roots

Abstract: The production of volatile organic compounds (VOCs) represents a promising strategy of plant-beneficial bacteria to control soil-borne phytopathogens. Pseudomonas sp. PICF6 and Pseudomonas simiae PICF7 are two indigenous inhabitants of olive roots displaying effective biological control against Verticillium dahliae. Additionally, strain PICF7 is able to promote the growth of barley and Arabidopsis thaliana, VOCs being involved in the growth of the latter species. In this study, the antagonistic capacity of these endophytic bacteria against relevant phytopathogens (Verticillium spp., Rhizoctonia solani, Sclerotinia sclerotiorum and Fusarium oxysporum f.sp. lycopersici) was assessed. Under in vitro conditions, PICF6 and PICF7 were only able to antagonize representative isolates of V. dahliae and V. longisporum. Remarkably, both strains produced an impressive portfolio of up to twenty VOCs, that included compounds with reported antifungal (e.g., 1-undecene, (methyldisulfanyl) methane and 1-decene) or plant growth promoting (e.g., tridecane, 1-decene) activities. Moreover, their volatilomes differed strongly in the absence and presence of V. dahliae. For example, when co incubated with the defoliating pathotype of V. dahliae, the antifungal compound 4-methyl-2,6-bis(2-methyl-2-propanyl)phenol was produced. Results suggest that volatiles emitted by these endophytes may differ in their modes of action, and that potential benefits for the host needs further investigation in planta.

Antifungal activity of chitinase produced by Streptomyces species isolated from grassland soils in Futa Area, Akure

Abstract: Abstract Background This study was carried out to investigate the antifungal activity of chitinase produced by Streptomyces species isolated from grassland soils against selected pathogenic fungi, namely: Magnaporthe oryzae , Fusarium graminearum , Rhizoctonia solani , Puccinia species and Botyrtis cinerea . Chitinase produced by Streptomyces albus was purified consecutively with dialysis, gel filtration and ion- exchange chromatography, the test isolate can be exploited for large scale production of chitinase. Results Seven Streptomyces species ( Streptomyces rimosus, S. albus, S. riseoflavus, S. fumosus, S. spiralis, S. aureofaciens and S. flavogriseus) isolated from three different grassland soils were screened based on the morphology and their ability to produce chitinase. S . rimosus , S . fumosus , S . albus and S . flavogriseus were able to produce chitinase, although the enzyme chitinase was found to be higher in Streptomyces albus . The effect of environmental factors were determined on Streptomyces albus being the best chitinolytic producing isolate. Temperature of 30 ο C was favourable for Streptomyces albus and pH 6.0 was a growth factor for maximum chitinase production. The activity of the enzyme was stimulated by the addition of metal ions like Mn 2+ , K + , Na + , Mg + , Fe 2+ , Ca 2+ but Zn 2+ inhibited chitinase activity. Chitinase activity was favoured by maltose as carbon source and NH 4 (SO 4 ) 2 as nitrogen source. Culture filtrate of Streptomyces albus was able to inhibit the growth of all the selected pathogenic fungi namely Magnaporthe oryzae , Fusarium graminearum , Rhizoctonia solani , Puccinia species and Botyrtis cinerea whereas Streptomyces rimosus has the least inhibitory activity. Conclusions Streptomyces albus has the highest ability to produce chitinase which can act as antifungal for degradation of the cell wall of many phytopathogenic fungi.

Isolation and characterization of a mycosubtilin homologue antagonizing Verticillium dahliae produced by Bacillus subtilis strain Z15

Abstract: Bacillus subtilis strain Z15 (BS-Z15) was isolated from the cotton field of Xinjiang, China, and characterized as an effective biocontrol agent antagonizing plant pathogen Verticillium dahliae 991 (VD-991). However, the chemical substance produced by BS-Z15 for resistance to VD-991 remains elusive. Here, a serial purification methods including HCl precipitation, organic solvent extraction, and separation by semi-preparative High-Performance Liquid Chromatography were performed to obtain a single compound about 3.5 mg/L from the fermentation broth of BS-Z15, which has an antifungal activity against VD-991. Moreover, Fourier Transform Infrared spectrum, Nuclear Magnetic Resonance Spectroscopy, and Tandem Mass Spectrometry analyses were carried out to finally confirm that the active compound from BS-Z15 is a mycosubtilin homologue with C17 fatty acid chain. Genomic sequence prediction and PCR verification further showed that the BS-Z15 genome contains the whole mycosubtilin operon comprising four ORFs: fenF, mycA, mycB, and mycC, and the expression levels of mycA-N, mycB-Y and mycC-N reached a peak at 32-h fermentation. Although mycosubtilin homologue at 1 μg/mL promoted the germination of cotton seed, that with high concentration at 10 μg/mL had no significant effect on seed germination, plant height and dry weight. Furthermore, mycosubtilin homologue sprayed at 10 μg/mL on two-week-old cotton leaves promotes the expression of pathogen-associated genes and gossypol accumulation, and greatly decreases VD-991 infection in cotton with disease index statistics. This study provides an efficient purification strategy for mycosubtilin homologue from BS-Z15, which can potentially be used as a biocontrol agent for controlling verticillium wilt in cotton.

GC-MS analysis & antifungal activity of Datura metel L. against Rhizoctonia solani Kuhn.

Abstract: The current study was designed to evaluate the antifungal properties of Datura metel L. against Rizoctonia solani Kuhn. To achieve this objective, six concentrations of leaves & stem methanol extract of D. metel viz. 1%, 1.5%, 2%, 2.5%, 3% & 3.5% were tested against R. solani in vitro. Leaf extract of D. metel was found more effective as its 3.5% concentration caused 75% retardation in test fungal growth as compared to the stem extract. D. metel methanolic leaf extract was fractioned between n-butanol, n-hexane, chloroform & ethyl acetate & bioactivities of isolated fractions were tested against R. solani. The chloroform fraction was found highly effective, as its concentrations 0.1% & 0.01% caused 27% & 21% growth inhibition respectively. So, this particular chloroform fraction was further analyzed to identify various chemical constituents through GC-MS (Gas chromatography mass spectroscopic) analysis. Twelve phyto-constituents viz. eugenol, 2-pentadecanone 6,10,14 trimethyl, pentadecanoic acid, pentadecanoic acid, 1 4-methyl- methyl ester, phytol, 9,12,15-octadecatrienoic acid, heptacosane, n-hexadecanoic, 6-octadecanoic acid, 9, 12 octadecanoic acid, dodecanoic & tetradecanoic acids were identified. So, the present study concluded that the presence of these bioactive constituents make D. metel as an effective antifungal agent against R. solani.

Six Novel Mycoviruses Containing Positive Single-Stranded RNA and Double-Stranded RNA Genomes Co-Infect a Single Strain of the Rhizoctonia solani AG-3 PT

Abstract: Six novel mycoviruses that collectively represent the mycovirome of Rhizoctonia solani anastomosis group (AG)-3 PT strain ZJ-2H, which causes potato black scurf, were identified through metatranscriptome sequencing and putatively designated as Rhizoctonia solani fusarivirus 4 [RsFV4, positive single-stranded RNA (+ssRNA)], Rhizoctonia solani fusarivirus 5 (RsFV5, +ssRNA), Rhizoctonia solani mitovirus 40 (RsMV40, +ssRNA), Rhizoctonia solani partitivirus 10 [RsPV10, double-stranded RNA (dsRNA)], Rhizoctonia solani partitivirus 11 (RsPV11, dsRNA), and Rhizoctonia solani RNA virus 11 (RsRV11, dsRNA). Whole genome sequences of RsFV4, RsMV40, RsPV10, RsPV11, and RsRV11, as well as a partial genome sequence of RsFV5, were obtained. The 3’- and 5’- untranslated regions of the five mycoviruses with complete genome sequences were folded into stable stem-loop or panhandle secondary structures. RsFV4 and RsFV5 are most closely related to Rhizoctonia solani fusarivirus 1 (RsFV1), however, the first open reading frame (ORF) of RsFV4 and RsFV5 encode a hypothetical protein that differs from the first ORF of RsFV1, which encodes a helicase. We confirmed that RsPV10 and RsPV11 assemble into the spherical virus particles (approximately 30 nm in diameter) that were extracted from strain ZJ-2H. This is the first report that +ssRNA and dsRNA viruses co-infect a single strain of R. solani AG-3 PT.