Rhizoctonia Solani Research Articles

A small antimicrobial peptide derived from a Burkholderia bacterium exhibits a broad-spectrum and high inhibiting activities against crop diseases.

Crop diseases cause significant quality and yield losses to global crop products each year and are heavily controlled by chemicals along with very limited antibiotics composed of small molecules. However, these methods often result in environmental pollution and pest resistance, necessitating the development of new bio-controlling products to mitigate these hazards. To identify effective antimicrobial peptides (AMPs) considered as potential sources of future antibiotics, AMPs were screened from five bacterial strains showing antagonism against a representative phytopathogenic fungus (Rhizoctonia Solani) through the Bacillus subtilis expression system, which has been developed for identifying bacterial AMPs by displaying autolysis morphologies. A total of 5000 colonies were screened, and five displaying autolysis morphologies showed antagonism against R. solani. A novel AMP with the strongest antagonism efficiency was determined and tentatively named HR2-7, which is composed of 24 amino acids with an alpha-helical structure. HR2-7 has strong and broad-spectrum antimicrobial activity, tested against 10 g-positive and -negative bacteria and four phytopathogenic fungi by contact culture in plates with minimal lethal concentrations of 4.0 μM. When applied as purified peptide or in fermented B. subtilis culture solution, HR2-7 showed strong controlling efficiency on plants against diverse fungal and bacterial pathogens. Based on current understanding, HR2-7 is recognized as the first AMP derived from an agricultural antagonistic bacterium. It exhibits wide-ranging and notable antimicrobial efficacy, offering a supplementary approach for managing plant diseases, in addition to conventional chemical pesticides and antibiotics.

In vitro inhibition mechanisms of Trichoderma yunnanense TM10 against Pyricularia oryzae and Rhizoctonia solani causing blast and sheath blight diseases in rice (Oryza sativa L.)

Blast and sheath blight diseases, caused by Pyricularia oryzae and Rhizoctonia solani, respectively, are major threats to rice production worldwide. Efforts should be made to limit the spread of these phytopathogens, preferably through sustainable methods. In this study, we investigated the antagonistic potential of the local isolate Trichoderma yunnanense TM10 against the pathogenic fungi P. oryzae and R. solani. The results demonstrated that T. yunnanense TM10 inhibited the growth of P. oryzae and R. solani through mechanisms such as competition, mycoparasitism, and antibiosis. Dual culture, filtrate culture, and double plate assays showed that T. yunnanense TM10 could inhibit the growth of both P. oryzae and R. solani. Slide culture and scanning electron microscope (SEM) tests confirmed that T. yunnanense TM10 exhibited mycoparasitic activity, including attachment, coiling, penetration, lysis, and destruction of pathogen hyphae. Additionally, T. yunnanense TM10 was capable of producing cell wall-degrading enzymes (CWDEs) such as chitinase and cellulase, as well as volatile organic compounds (VOCs) such as hydrogen cyanide (HCN). The multifaceted abilities of T. yunnanense TM10 for limiting the growth of P. oryzae and R. solani underscore its potential as an effective biocontrol agent for enhancing productivity and sustainability in rice cultivation.

Fungi Preference of Fungivorous Nematode Aphelenchus avenae (Aphelenchida: Aphelenchidae) and Its Impact on Strawberry (Fragaria ananassa Duch.) Root

In continuously cropped strawberry soil, a large population of the fungivorous nematode, Aphelenchus avenae, was observed to increase significantly over time. This nematode, which feeds on pathogenic fungi affecting strawberries, has significant potential as a biocontrol agent. The purpose of this article is to discuss the nematode’s preference for fungi associated with strawberries and its impact on the growth of strawberry roots. With the exception of Trichoderma harzianum, most of the pathogenic fungi commonly found in strawberry soil, such as Fusarium oxysporum, Rhizoctonia solani, Verticillium, Phytophthora infestans, and Botrytis cinerea Pers. attracted A. avenae and supported their propagation. All treatments with A. avenae and the non-nematode control showed a consistent trend throughout strawberry development, indicating that a moderate amount of A. avenae does not adversely affect strawberry roots. Moderate and low levels of A. avenae significantly increased the activity of antioxidant enzymes, superoxide dismutase (SOD), and peroxidase (POD) in strawberry roots in all treatments during the entire growth stages. Also, the malondialdehyde (MDA) content of strawberry roots in all nematode treatments was lower than that in the no-nematode control. Despite an overabundance of A. avenae, which negatively affected the redox system balance of strawberry roots, A. avenae can protect the roots from pathogenic fungi by preventing infection and damage. These results lay the foundation for the potential use of A. avenae as a biological agent to control these pathogenic fungi in strawberry soil, in combination with the biological fungi (T. harzianum).

Detection of Seed Mycoflora Associated with Indian Mustard (Brassica juncea L.) by Various Seed Health Testing Methods

India is one of the major oilseed crops grower. Mustard (Brassica juncea L.) is an important oilseed crop second after groundnut. Mustard is majorly grown in India which carry many seedborne diseases which causes not only seed rot, seedling blight but also reduction in quality of seed parameters which results qualitative and quantitative yield losses. In standard agar plate seed germination per centage ranged from 78.50 to 85.00% and in Modified PDA method ranged from 70.00 to 78.00%. In standard agar plate and Modified PDA method highest per cent of infected seed was observed in Pusa bold 74.25% and 64.50%, respectively. In two seed health testing methods (SHT) were evaluated standard agar plate show higher seed mycoflora than modified PDA method. All two methods were found effective and reliable for the detection of seedborne fungi such as Alternaria brassicae, Fusarium oxysporum, Aspergillus niger, Aspergillus flavus, Rhizoctonia solani, Penicillium sp. and Rhizopus stolonifer isolated from mustard seeds of varieties Krishna, Kranti, Local and Pusa bold.

Comparison of rDNA-ITS Sequences, Vegetative Compatibility, Biological Characteristics, and Thifluzamide Sensitivity of Rhizoctonia solani AG-3 PT, TM, and TB Subgroup Isolates Collected from Potato and Tobacco in China.

Potato black scurf and tobacco target spot are significant agricultural diseases primarily caused by Rhizoctonia solani AG-3, which is further classified into PT (potato type), TM (tomato type), and TB (tobacco type) subgroups, with the naming of these subgroups originally indicating their respective infection hosts potato, tomato, and tobacco. This study determined the subgroup classification of 129 R. solani AG-3 isolates recovered from tobacco leaves exhibiting target spot disease in major tobacco-cultivating regions of China, as well as 80 R. solani AG-3 isolates obtained from potato stem cankers and tuber sclerotia in Liaoning, Jilin, and Heilongjiang provinces, and Inner Mongolia autonomous region of China. Sequence analysis of the internal transcribed spacer (ITS) regions revealed that all potato isolates belonged to the R. solani AG-3 PT subgroup, whereas the tobacco isolates were classified into TM and TB subgroups. Specifically, 51 strains from the northeast (Liaoning, Jilin, and Heilongjiang provinces) belonged to the TM subgroup, while the others belonged to the TB subgroup. Phylogenetic analysis indicated a closer relationship between AG-3 TM and AG-3 PT compared to AG-3 TB. Population genetic analysis highlighted distinct genetic variations among the subgroups, with the AG-3 TB subgroup isolates exhibiting fewer ITS1 variable sites and the AG-3 PT subgroup displaying a higher number of ITS2 variable sites. Furthermore, comparisons were made regarding macroscopic vegetative interactions, biological characteristics, pathogenicity to potato and tobacco, and susceptibility to thifluzamide among the three subgroups. The results indicated no macroscopic somatic interactions among the subgroups, with the highest frequency of somatic incompatibility observed within AG-3 PT, followed by AG-3 TM, and AG-3 TB. Additionally, the three subgroups differed in colony color, sclerotium morphology, production time, and distribution location on potato-dextrose-agar (PDA) medium, with AG-3 TM being the least likely to produce sclerotia. Regarding temperature, optimal growth conditions varied among the subgroups. Regarding pathogenicity, the AG-3 PT subgroup strains were more pathogenic on tobacco and potato stem bases compared to the AG-3 TB subgroup, whereas the AG-3 TB and TM subgroup strains were more pathogenic on leaves. Notably, AG-3 TM exhibited remarkable virulence towards both the stem base and leaves. The AG-3 PT subgroup strains exhibited the highest susceptibility to thifluzamide, with a susceptibility baseline of 0.037±0.013 mg·L-1, followed by the AG-3 TM subgroup strains with a baseline of 0.111±0.034 mg·L-1, and the AG-3 TB subgroup strains with a baseline of 0.137±0.035 mg·L-1. This study contributes to a deeper understanding of the biology and etiology of the three subgroups of R. solani AG-3, providing a valuable theoretical basis for the scientific control and management of tobacco target spot and potato black scurf diseases in China.

Vali@mPEG‐TK‐COS: A Dual‐Function Nano‐Pesticide for Fungicidal Action and Plant Immune Modulation

ABSTRACTPesticides play a crucial role in safeguarding crops against pathogens and pests, yet the limited bioavailability of conventional formulations leads to excessive usage, causing environmental and health concerns. In this study, we developed a novel intelligent response‐controlled release nano‐pesticide, Vali@mPEG‐TK‐COS, by coupling chitosan oligosaccharide (COS), a plant immunity regulator, and methoxy polyethylene glycols (mPEG) at either end of thioketal (TK), a material responsive to reactive oxygen species (ROS), and incorporating validamycin (Vali) for controlled release. Vali@mPEG‐TK‐COS exhibits ROS‐responsive behaviour, releasing Vali and COS in response to plant ROS bursts, exhibiting dual capabilities in pathogen control and plant immunity induction during pathogenic attacks. Plant disease experiments confirmed the superior efficacy of Vali@mPEG‐TK‐COS against Rhizoctonia solani, surpassing the control effects of Vali or COS alone. This study presents a sophisticated ROS‐responsive controlled‐release nano‐pesticide with dual fungicidal and plant immunomodulatory properties, offering an advanced strategy to enhance the efficiency of existing pesticides and promote sustainable crop production by reducing overall pesticide usage.

Effects of Thifluzamide Treatment on the Production of Cell Wall Degrading Enzymes in Rhizoctonia solani and Phenylpropane Metabolism in Pear Fruit

The study aimed to investigate the effects of thifluzamide (2.67 mg/L) on ‘Huangguan’ pear fruit rot caused by Rhizoctonia solani during storage, as well as the activities of polygalacturonase (PG), pectin methylesterase (PME), polygalacturonic acid trans-eliminase (PGTE), pectin methyl trans-eliminase (PMTE), xylanase, and pectate lyase (PL) secreted by R. solani. The results showed that thifluzamide treatment significantly inhibited the activities of PG, PME, PGTE, PMTE, xylanase, and PL secreted by R. solani after 3 days in vitro culture, compared to the control. Thifluzamide also increased the activities of phenylalanine ammonia-lyase (PAL), cinnamate-4-hydroxylase (C4H), and 4-coumarate CoA ligase (4CL), and the contents of flavonoids and total phenolic compounds in pear fruit. Furthermore, thifluzamide increased the expression of PcPAL, PcC4H, Pc4CL, Pcβ-1,3-GA, PcLCH, PcF3H, and PcDFR involved in phenylpropanoid metabolism in pear fruit. In conclusion, thifluzamide treatment reduced the infection ability of R. solani by inhibiting the expression of the genes encoding cell wall-degrading enzymes in R. solani. At the same time, it inhibited the activities of cell wall-degrading enzymes induced resistance against R. solani infection in ‘Huangguan’ pears by promoting phenylpropane metabolism.

Structural analysis of Pleurotus ferulae polysaccharide and its effects on plant fungal disease and plant growth

A novel polysaccharide, named as PFP1–1 (23 kDa), was isolated from the fruiting body of Pleurotus ferulae. Structural analysis revealed that PFP1–1 is primarily composed of mannose, galactose, glucose and fucose, with a molar ratio of 41.50:41.92:4.65:1.93. Infrared spectroscopy analysis showed the presence of characteristic absorption peaks associated with polysaccharides. Further analysis using gas chromatography–mass spectrometry (GC–MS) and Nuclear Magnetic Resonance (NMR) indicated that the polysaccharide mainly composed of → 6) -α-D-Galp- (1 →, → 2,6) -α-D-Galp- (1 → and a small amount of → 4) -α-D-Glcp- (1 →. The branched chain is mainly composed of β-D-Manp- (1 → and α-D-Glcp- (1 → connected at the O-2 position of the sugar residue → 2,6) -α-D-Galp- (1 →. PFP1–1 exhibited significant antifungal activity against Rhizoctonia solani and promoted cucumber plant growth. The mycelial growth inhibition rate of PFP1–1 against R. solani reached 70 %. In pot experiments, cucumber seedlings treated with PFP1–1 demonstrated resistance to R. solani infection and the incidence rate was significantly reduced to 22.92 %. PFP1–1 increased the root length and fresh weight of cucumber seedlings and enhanced the stress and disease resistance of plants by increasing the activities of superoxide dismutase, peroxidase and polyphenol oxidase. In conclusion, the present study provides a theoretical and experimental basis for the application of P. ferulae polysaccharide in promoting plant growth and controlling plant diseases.

Unveiling Bacillus rugosus CRI: A multi-stress tolerant endophyte revolutionizing rice resilience

The application of endophytes to mitigate stress in plants, particularly drought and salinity stress, has gained considerable attention, yet their role in rice remains underexplored. This study aimed to investigate the isolation and characterization of multi-stress-tolerant endophytic isolates with multiple plant growth-promoting attributes, including biocontrol potential against plant pathogens, from surface-sterilized leaf, stem, and root samples of various rice cultivars in Kerala. A total of 20 bacterial endophytes were isolated from rice plants and assessed for their plant growth-promoting (PGP) capabilities, biocontrol potential, and resilience to drought and salinity stress. Of these, 7 endophytic isolates exhibited notable PGP traits, and 3 demonstrated antifungal activity against Rhizoctonia solani and Fusarium oxysporum. Notably, only 3 endophytic isolates showed significant tolerance to drought conditions (−1.0 MPa) and salinity (150 mM), alongside strong growth-promoting abilities. The selected isolates significantly increased seed germination and seedling vigour (p ≤ 0.05), highlighting their effectiveness. Among these, the isolate CRI, identified as Bacillus rugosus through morphological, biochemical, and molecular (16S rRNA) analysis, stood out for its remarkable performance. Under stress conditions, rice seedlings treated with the multi-stress-tolerant CRI showed significant improved biomass, resilience, and enhanced biochemical processes, including better photosynthetic pigment levels and maintained membrane integrity. Field emission scanning electron microscopy (FE-SEM) confirmed the presence of these bacteria within the rice roots, underscoring their potential as a novel approach for enhancing stress tolerance and promoting rice growth. This study represents the first discovery of Bacillus rugosus as a potent multi-stress-tolerant endophyte, with dual benefits of promoting plant growth and exhibiting biocontrol activity. These findings pave the way for innovative strategies aimed at enhancing crop resilience and productivity, particularly in the face of increasing abiotic stressors in agricultural systems.

Characterization of Trichoderma spp. and their antagonistic activity against soilborne fungi associated with chickpea wilt in Sinaloa, Mexico

Chickpea wilt, caused by a complex of soilborne fungi (Fusarium spp. Macrophomina phaseolina, Rhizoctonia solani, Sclerotium rolfsii, and Sclerotinia sclerotiorum), is the most important disease of chickpeas (Cicer arietinum) in Mexico. The aims of this study were to characterize Trichoderma isolates using a combination of phenotypic and molecular approaches and to evaluate their antagonistic activity against soilborne fungi associated with chickpea wilt. A total of 30 Trichoderma isolates were obtained from rhizospheric soil samples collected from chickpea fields in different locations of Sinaloa, Mexico. Dual confrontation assays showed the potential antagonistic effect of Trichoderma isolates against F. languescens, M. phaseolina, R. solani, S. rolfsii, and S. sclerotiorum. Five Trichoderma isolates (FAVF335, FAVF340, FAVF345, FAVF349, and FAVF351) exhibited mycelial growth inhibition of the five pathogens that ranged from 56 to 71%. These isolates were characterized using cultural, morphological, and molecular studies and tested in vivo for their ability to control soilborne pathogens in two chickpea cultivars (Blanco Sinaloa-92 and P2245) under greenhouse conditions. Phylogenetic analysis based on a combined ITS, EF-1α, and rpb2 sequence dataset identified T. afroharzianum (FAVF345, FAVF349, and FAVF351) and T. longibrachiatum (FAVF335 and FAVF340). Coating of chickpea seeds with T. longibrachiatum (FAVF335 and FAVF340) significantly reduced the disease severity and improved the plant growth-promoting attributes.

Intrinsic Natural Resistance of Various Plant Pathogens to Ipflufenoquin, a New DHODH (Dihydroorotate Dehydrogenase)-inhibiting Fungicide, in Relation to Unaltered Amino Acid Sequence of the Target Site.

In recent years, increasingly stringent pesticide regulations have made the development of new chemistries challenging. Under these regulations, the new fungicide ipflufenoquin (FRAC Code 52) was first released in Japan. Its mode of action is new; it inhibits dihydroorotate dehydrogenase (DHODH), a key enzyme in the biosynthesis of pyrimidine-based nucleotides. However, because it is a single-site inhibitor, the risk of resistance developing in pathogens must be carefully considered. The risk for dual use of DHODH inhibitors in agriculture and medicine has also become a great concern because a new antifungal olorofim is under development against human pathogens now and cross-resistance has recently been reported between ipflufenoquin and olorofim in Aspergillus fumigatus. In this study, the sensitivity to ipflufenoquin was examined in culture and in plants using "baseline" isolates, which had never been exposed to DHODH inhibitors. Isolates of Alternaria alternata, Botrytis cinerea, B. elliptica, Colletotrichum fioriniae, C. fructicola, C. nymphaeae, C. orbiculare, C. siamense, C. tropicale, C. truncatum, and Sclerotinia sclerotiorum were highly sensitive to ipflufenoquin in culture, but isolates of Coniella vitis, Corynespora cassiicola, Pseudocercospora fuligena, and Rhizoctonia solani were inherently resistant. Ipflufenoquin had low efficacy against C. cassiicola and C. vitis after inoculation of cucumber and grapevine leaves, respectively. To understand the mechanism of natural resistance, we analyzed the partial sequence of pyrE genes, which encode the DHODH enzyme, but did not find any differences in the deduced amino acids that were thought to be associated with resistance. Thus, mechanisms other than target-site mutations might be involved in the intrinsic resistance.

Labor-saving application of thifluzamide and tricyclazole to seedling trays for integrated control of rice blast and sheath blight

Rice blast (Magnaporthe grisea) and sheath blight (Rhizoctonia solani) are limiting factors for rice production. Co-infection of these pathogens results in a disease complex which is difficult to control. In China, growers are accustomed to applying individual fungicides to manage blast and sheath blight, which require large amounts of labor. Application to seedling trays is a new promising solution for saving labor. In this study, application of combined fungicides with different modes of action to seedling trays to integrate control rice blast and sheath blight was evaluated in vitro assays and field trials. The results showed that the combination of thifluzamide and tricyclazole in the 1:2 ratio had significant synergistic inhibitory effects on the mycelial growth of M. grisea and R. solani, with a synergistic ratio (SR) of 2.17 and 1.49. Results from field trials revealed that thifluzamide + tricyclazole at 1107 and 958.5 g/ha applied to seedling trays was the most effective treatment to reduce the disease index of rice blast with control effects of 83.74–84.96% and 81.34–83.26% in 2022 and 2023, respectively, and no significant differences were observed from tricyclazole at 300 g/ha as foliar sprays twice. Compared to the untreated control, disease index of rice sheath blight was notably reduced by all treatments containing thifluzamide. The highest control was recorded in the treatment of thifluzamide + tricyclazole applied at 1107 g/ha to seedling trays. Moreover, compared to the untreated control, all treatments significantly enhanced rice grain yield by 7.67–17.86% and 3.38–18.91% in 2022 and 2023, respectively. The greatest yield (7429.73 and 7404.73 kg/ha in 2022 and 2023, respectively) was observed from the treatment of thifluzamide + tricyclazole at 1107 g/ha applied to seedling trays, with no significant differences among all the treatments containing tricyclazole. Taken together, these results indicated that seedling tray application of thifluzamide + tricyclazole could be a labor-saving approach to the integrated control of rice blast and sheath blight disease complex, while increasing rice grain yield.

Design, synthesis and antifungal activity of arylhydrazine analogs containing diphenyl ether fragments.

Succinate dehydrogenase (SDH) represents a critical target in the development of novel fungicides. To address the growing issue of resistance and safeguard the economic viability of agricultural production, the pursuit of new succinate dehydrogenase inhibitors (SDHIs) has emerged as a significant focus of contemporary research. In this project, 32 arylhydrazine derivatives containing diphenyl ether structural units were synthesized and evaluated for their fungicidal activities against Rhizoctonia solani, Sclerotinia sclerotiorum, Alternaria alternata, Gibberella zeae, Alternaria solani and Colletotrichum gloeosporioides. In an in vitro fungicidal activity assay, compound D6 showed significant inhibitory activity against R. solani with a half-maximum effective concentration (EC50) of 0.09 mg L-1. The in vivo fungicidal activity demonstrated that compound D6 inhibited R. solani by 95.39% in rice leaves, which was significantly better than that of boscalid (85.76%). The results of SDH enzyme assay, molecular docking simulation, mitochondrial membrane potential assay, cytoplasmic release studies and morphological observations demonstrated that the target compound D6 not only had significant SDH inhibitory activity, but also affected the membrane integrity of mycelium. Bioactivity screening and validation of the mechanism of action indicated that compound D6 was a potentially unique SDHI, acting on SDH while also affecting cell membrane permeability, which deserved further study. © 2024 Society of Chemical Industry.

Investigate the efficacy of compounds found in the crude extract of the fungus Aspergillus niger on seeds germination of zucchini

For a long time, fungi have been considered the richest source of bioactive metabolites with numerous applications. Hence, this study was performed to identify various bioactive compounds contained in the ethyl acetate extract of the fungus Aspergillus niger that isolates from infected garlic by using Gas Chromatography-Mass Spectrometry and their effect on seed germination of Zucchini. The current results showed a variety of bioactive compounds such as n-hexadecanoic acid, Hexadecanoic acid, Methyl stearate, Benzoic acid, Hexamethyl-1,3,5-trithiane, and cis-aconitic anhydride with an area percentage of 15.37, 13.93, 6.87, 5.67, 4.75 and 3.59% respectively. The results were performed using the fungus extract that protected the zucchini seed from pathogenic fungi (Botrytis cinerea, Fusarium oxysporum, and Rhizoctonia solani) when soaking for less than 72 h and promoted increased seed germination by high percentage ratio of seeding (66.67%, 80.00%, and 80.00%) respectively, radical length (66.67, 80.00 and 7.67), plumule length (4.67, 7.67 and 6.00) and Number of secondary roots (7.00,8.00 and 7.00) respectively compared with control treatment.

Sensitivity of Rhizoctonia solani to fertilizers and fungicides and their synergistic effects

AbstractRhizoctonia solani reduces yield and quality of potato worldwide and some studies report the appearance of resistant strains due to the extensive use of fungicides. To overcome this problem, we studied the effect of commercial fertilizers alone and in combination with fungicides on the in‐vitro growth of R. solani in order to manage the use of fungicides and reduce the risk of resistance development in this pathogen. First, the study of the effect of three fungicides, azoxystrobin, pencycuron and fludioxonil, on the in‐vitro growth of R. solani showed that fludioxonil (EC50 = 0.06 × 10−3 μg a.i./mL) and pencycuron (EC50 = 0.1 × 10−3 μg a.i./mL) were very effective in inhibiting the growth of this pathogen at very low concentrations; however, azoxystrobin showed less antifungal activity (EC50 = 74.85 × 10−3 μg a.i./mL). The effect of five commercial fertilizers, namely di‐ammonium phosphate, superphosphate, phosphoric acid, potassium sulphate and ammonium nitrate, at different concentrations (0, 0.01, 0.1, 1 and 10 mg of fertilizer element [P2O5, K2O or N]/mL) showed that all fertilizers reduced the in‐vitro growth of R. solani. Furthermore, the studied fertilizers, particularly phosphorus‐based ones, improved the antifungal activity of the three fungicides. For instance, superphosphate at 0.1 mg of P2O5/mL in combination with pencycuron reduced the diameter of the fungal colony by 76.7% in comparison to the fungicide alone. In addition, the antifungal activity of azoxystrobin was improved by the NPK fertilizers, indicating their effect in reducing the risk of resistance development in R. solani to this fungicide. This study demonstrates the usefulness of fertilizers in an integrated management programme to enhance fungicide efficacy against R. solani, reducing the risk of resistance development in this pathogen.

Evaluating the efficacy of endophytic bacteria in controlling rice sheath blight: In vitro and In vivo studies

Rice production is highly susceptible to various pathogens, including Rhizoctonia solani, Curvularia lunata, and Epicoccum rostratum, which are major threats in Asia. Exploring biological control methods using endophytic bacteria offers promising opportunities to enhance rice resilience against these lethal diseases. Using 16S RNA sequencing, we identified four endophytic isolates of Bacillus spp. from rice roots, stems, and leaves. We evaluated the antagonistic activity of these endophytic bacterial isolates against rice pathogens both in vitro and in vivo. These isolates inhibited the growth of C. lunata by 82 %, R. solani by 79 %, and E. rostratum by 88 % in vitro. The detached leaf assay for sheath blight (ShB) disease severity in strains ranged from 10.4 % to 73.3 %. In vivo results showed that B. amyloliquefaciens (R-19) exhibited the lowest disease intensity at 7.2 % and the highest disease suppression at 78.8 %. The fungicide propiconazole at 0.1 % treatment showed the lowest disease intensity of 7.7 % and the highest disease suppression of 73.4 %, compared to the infected control. Besides biocontrol efficacy, endophytic isolates enhance plant growth parameters, including shoot height, root length, fresh and dry weights, number of tillers, and grains per tiller. Plant hormones abscisic acid (ABA) and gibberellic acids (GA3) increased by 35 % and 53 %, respectively, due to B. subtilis (R-20) and B. amyloliquefaciens (R-19), while flavonoid and indole acetic acid (IAA) concentrations surged by 30%–80 %. Similarly, chlorophyll (a, b), carotenoids, antioxidant enzymatic activity, phenolic content, carbohydrates, and proline contents were higher compared to the control. This study provides a foundation for future studies on novel and eco-friendly biocontrol agents. In addition, our study recommends the integration of endophytic bacteria into sustainable agriculture for enhancing rice production and reducing disease impacts.

Survey of Rice Sheath Blight Disease in Kuttanad and Effect of Biocontrol Agents and Fungicides against Rhizoctonia solani

Aims: Rice is an important crop cultivated worldwide, whose production is influenced by numerous factors like pest, disease, weather parameters. In India, diseases accounts for 35 per cent in yield reduction, with sheath blight being significant. This disease is notably prevalent in Kuttanad region of Kerala. This study involves a survey conducted in Kuttanad to assess the extent of the disease and in vitro management using biocontrol agents and fungicides. Study Design: Study was outlined in Completely Randomised Design (CRD) to evaluate the in vitro efficacy of bioagents. Place and Duration of Study: Department of Plant Pathology, College of Agriculture, Vellayani and M.S. Swaminathan Rice Research Station, Moncompu, between 2022 and 2023 Methodology: Survey was conducted in forty locations of Kuttanad in which the disease incidence was recorded and samples were collected. The isolates obtained were tested for pathogenicity by artificial inoculation on rice variety, Uma. Cultural characteristics of isolates were studied. The virulent culture obtained was further advanced for the in vitro studies with biocontrol agents and fungicides. The inhibition of fungal growth was also recorded. Results: Forty isolates of sheath blight pathogen (Rhizoctonia solani) were obtained. The virulent isolate among these was identified on the basis of number of days taken for symptom development by artificial inoculation and this was further advanced for the in vitro studies. Bacillus amyloliquefaciens was found to be more effective with an inhibition percentage of 68.64. Among the tested fungicides, Kresoxim methyl 40% + Hexaconazole 8% WG showed cent per cent growth inhibition of pathogen at 500 and 1000 ppm concentrations which was on par with Azoxystrobin 18.2% + Difenoconazole 11.4% SC at 1000 ppm. Conclusion: From this study, it can be concluded that, that these biocontrol agents and fungicides are very effective in the management of the pathogen and hence can be used for further field-level studies in management of the disease.

Novel SDH Inhibitors as Antifungal Leads: From Azobenzene Derivatives to the 1,2,4-Oxadiazole Compounds.

Azo-incorporating was reported to be an effective strategy for increasing SDH inhibitory activity but for poor in vivo control effects. Herein, the azo-incorporated compounds were structurally optimized to retain a preferential conformation by replacing the azo bond with their bioisosteres. Interestingly, the 1,2,4-oxadiazole compound D2 displayed a broad fungicidal spectrum as well as fluxapyroxad. More excitedly, compound D2 showed excellent antifungal activities against rice sheath blight disease both in vitro (EC50 = 0.001 μg/mL) and in vivo (EC50 = 1.08 μg/mL, EC95 = 4.67 μg/mL). In addition, an extra π-π interaction was found between the 1,2,4-oxadiazole ring of compound D2 and the phenyl ring of residue D_Y586, which might interpret the enhanced potency of compound D2 against Rhizoctonia solani. Further structural optimizations of the 1,2,4-oxadiazole compounds gave several analogues that made a breakthrough in controlling rice blast disease. These 1,2,4-oxadiazole compounds, derived from azobenzene derivatives, could be antifungal leads especially against R. solani and Magnaporthe grisea, exemplifying an interesting mode of pesticide discovery and providing theoretical guidance for innovation of the SDHI fungicide.

Rational design and discovery of novel hydrazide derivatives as potent succinate dehydrogenase inhibitors inspired by natural d/l-camphor.

Succinate dehydrogenase inhibitors (SDHIs) have rapidly become one of the fastest-growing categories of fungicides used against plant pathogenic fungi. Recent research advancements have emphasized that structural modifications of SDHIs using naturally sourced scaffolds represent an innovative strategy for developing new, highly effective, broad-spectrum fungicides. A novel series of d/l-camphorhydrazide derivatives potentially targeting fungal succinate dehydrogenase (SDH) were designed, synthesized and evaluated for their antifungal effects against Rhizoctonia solani, Fusarium graminearum, Valsa mali and Botrytis cinerea. Amongst them, compounds A1-7 (d-camphor) and A2-7 (l-camphor) displayed excellent in vitro activity against R. solani with median effective concentration (EC50) values of 0.38 and 0.48 μg mL-1, which were obviously superior to that of boscalid (0.87 μg mL-1). A2-5 (l-camphor, EC50 = 3.27 μg mL-1) exhibited good activity against V. mali. A2-7 (2.13 μg mL-1), A2-21 (5.2 μg mL-1) and A1-5 (5.15 μg mL-1) showed good antifungal activity against F. graminearum with EC50 values below that of boscalid (5.85 μg mL-1). Preliminary mechanistic studies, using scanning and transmission electron microscopy, indicated that compound A1-7 induced disordered entanglement of hyphae, shrinkage of hyphal surfaces, and vacuole swelling and rupture, which disrupted normal hyphal growth. Additionally, compound A1-7 induced the production and accumulation of reactive oxygen species, disrupted mitochondrial membrane potential, and effectively inhibited the germination and formation of sclerotia in R. solani. Moreover, the molecular docking results and SDH enzyme assays yielded promising outcomes. In this study, the designed and optimized compounds A1-7 and A2-7 emerged as promising candidates for SDH-targeting fungicides, demonstrating strong antifungal activity. These compounds hold potential as new antifungal agents for further research. © 2024 Society of Chemical Industry.

A new species of Pythium hydnosporum as a pathogen associated with vine decline of melon (Cucumis melo L.) in Iraq

Several pathogenic fungi have become an important vine decline of cantaloupe melone (Cucumis melo L.). In 2021, root rot on cantaloupe was observed during the harvest phase in the fields in Penjwen and Shahrazoor in Sulaimani governorate of Northern Kurdistan region Iraq. This present study was conducted to isolate the causal agent of fungi in lesions of root rot of cantaloupe. A total of 16 fungal isolates were obtained of which isolates Monosporascus cannonballus, M. eutypoides, Acremonium vitellinium, Fusarium oxysporium, F. equiseti, Macrophomina phaseolina, Saccharomyces kudriavzevii, F. robinianum, Rhizopus arrhizus, Botrytis cinerea, Cytospora eucalypticola, F. falciforme, Pythium hydnosporum, Alternaria tenuissima, Rhizoctonia solani and Phytophthora colocasiae were obtained from root melon. Identification of all fungal isolates was based on using both morphological characteristics and molecular analysis, on internal transcribed spacer (ITS1, ITS4, LSU) are primers that are used for identification. DNA sequences of the fungal pathogen were identified as Pythium hydnosporum a new pathogenic fungi causal agent of cantaloupe vine decline. A pathogenicity test was conducted to verify Koch's postulates and P. hydnosporum was observed to cause root rot of melon, symptoms of the disease were similar to those seen in the field.