Rice Sheath Research Articles

Molecular Detection Assays for Rapid Field-Detection of Rice Sheath Blight.

Rhizoctonia solani (Rs), a soil-borne fungal pathogen, can result in rice sheath blight (ShB), which causes yield loss. To prevent outbreaks of ShB and enhance the sustainability of rice production, it is critical to develop a rapid ShB detection method for specific, fast, and on-site disease management. In this study, a reagent for the rapid extraction of this pathogen was developed for on-site detection. The specificity and sensitivity of a novel SMS RS1-F/SMS RS1-R primer set and a ITS1/GMRS-3 reference primer set were tested, while four different extraction protocols for ShB were developed. Moreover, intraday and interday assays were performed to evaluate the reproducibility of the detection methods developed. The results indicated that all of the developed protocols are suitable for use in detecting ShB. In addition, all the samples of infected rice yielded positive Rs detection results when subjected to TaqMan probe-based real-time PCR and SYBR green-based real-time PCR (SMS RS1-F/SMS RS1-R) tests in which automatic magnetic bead-based DNA extraction was performed. These results indicated that the two molecular detection protocols were suitable for the field diagnosis of ShB for all asymptomatic and symptomatic rice samples.

History of Sheath Rot Disease in Indonesia and Disease Severity in Two Rice Production Centres of West Java

The observation conducted from 2000 to 2018 found that rice sheath rot has become an emerging disease in several regions. The disease was able to reduce quality and quantity of rice yield. This research objective was to study the history and status of rice sheath rot caused by Sarocladium oryzae. Data was obtained from literature study, farmer interview, and field survey. Data were used to calculate disease incidence followed by visual observation of the symptoms caused by this disease. Identification of sheath rot pathogen was done using microscopic and molecular techniques using specific primers. Rice sheath rot was first reported in Indonesia as a minor disease in 1987 and has only currently become an important disease. This fungus generally causes rice sheath rot in Karawang and Cianjur Regency. Disease incidence of rice sheath rot was 12.56% without considering the varieties at all generative growth stages. Average disease incidence on all rice varieties observed was 12.64%, except for IR 42 (0%). The level of rice plants damage due to rice sheath rot in Cianjur was higher than Karawang with average disease incidence of 11.58% and 9.27%, respectively. Rice sheath rot symptoms have often been found in the last 10 years with average level of damage of 3%‒18% and yield loss of 10%-15%. This disease has proven to be important and has become a challenge in rice cultivation. The fungus that infect rice plants in Karawang and Cianjur had different morphotypes, namely KP, KP2, KP3, PW3, and PW03. The amplification results showed that all fungal isolates were S. oryzae.

LAMP-based foldable microdevice platform for the rapid detection of Magnaporthe oryzae and Sarocladium oryzae in rice seed

Rice blast (caused by Magnaporthe oryzae) and sheath rot diseases (caused by Sarocladium oryzae) are the most predominant seed-borne pathogens of rice. The detection of both pathogens in rice seed is essential to avoid production losses. In the present study, a microdevice platform was designed, which works on the principles of loop-mediated isothermal amplification (LAMP) to detect M. oryzae and S. oryzae in rice seeds. Initially, a LAMP, polymerase chain reaction (PCR), quantitative PCR (qPCR), and helicase dependent amplification (HDA) assays were developed with primers, specifically targeting M. oryzae and S. oryzae genome. The LAMP assay was highly efficient and could detect the presence of M. oryzae and S. oryzae genome at a concentration down to 100 fg within 20 min at 60 °C. Further, the sensitivity of the LAMP, HDA, PCR, and qPCR assays were compared wherein; the LAMP assay was highly sensitive up to 100 fg of template DNA. Using the optimized LAMP assay conditions, a portable foldable microdevice platform was developed to detect M. oryzae and S. oryzae in rice seeds. The foldable microdevice assay was similar to that of conventional LAMP assay with respect to its sensitivity (up to 100 fg), rapidity (30 min), and specificity. This platform could serve as a prototype for developing on-field diagnostic kits to be used at the point of care centers for the rapid diagnosis of M. oryzae and S. oryzae in rice seeds. This is the first study to report a LAMP-based foldable microdevice platform to detect any plant pathogens.

Managing the Imminent Danger of Rice Blast (<i>Pyricularia oryzae</i> Cav.) and Sheath Blight (<i>Rhizoctonia solani</i> Kühn) Disease: A Critical Review Article

Rice is one of the most important crop planted on earth. It provide food and employment for thousands of persons daily through out the world. In Guyana the rice industry is one of the largest user of agricultural lands and contributies more than 20% to the country gross domestic product (GDP). The rice crop is known to suffer from several biotic and abiotic factors. Of which rice blast (<i>P. oryzae</i>) and sheath blight (<i>R. solani</i>) disease identified as two of the most devastating disease affecting the rice cultivation in Guyana. In this context, the present critical review article entitled ‘Managing the imminent danger of Rice Blast (<i>Pyricularia oryzae</i> Cav.) and Sheath Blight (<i>Rhizoctonia solani</i> Kühn) Disease’ was taken up to look at the most practical disease management approaches available and can be utilized to mitigate the imminent threat pose by the rice blast and sheath blight disease. The review will focus on: disease resistant screening and understand the genotype and environment interactions; study the expression pattern of proteins in resistant and susceptible genotypes against blast pathogen (<i>P. oryzae</i>); examine the efficacy of botanicals, biocontrol agents and new generation fungicides against blast and sheath blight disease under different conditions. This will form a foundation for the exploration of the various disease management stratigies for blast and sheath blight disease.

Survey and incidence of rice sheath blight in major rice growing areas of eastern Uttar Pradesh

Rice is an important food grain and is a staple food for majority of the world’s population. Sheath blight (ShB), caused by the soilborne necrotrophic fungal pathogen Rhizoctonia solani Kuhn, is an economically important disease in rice. A purposive disease survey was conducted during Kharif-2019 to assess the occurrence and spread of rice sheath blight disease in five districts of eastern Uttar Pradesh. The percent disease incidence (PDI) ranged from 20 to 80%. Maximum PDI (80) was noticed at paddy field of Sadalpura block (80%), while minimum (20) was recorded at Narayanpur, and Maudli villages. The maximum severity (9 scale) was observed at Sadalpura, Satahara, Naini, Cholapur. The disease was recorded from panicle initiation to grain hardening stage.

Biocontrol of rice sheath blight with microorganisms obtained in rice cultivated soils

Actinobacteria of the genus Streptomyces are part of the soil microbiota from rice-growing areas and along with other microorganisms, such as Trichoderma spp., combine to act as natural enemies against the destructive soil-borne pathogen Rhizoctonia solani, causal agent of rice sheath blight disease. In this study, seven actinobacteria of the genus Streptomyces and three fungi of the genera Trichoderma and Purpureocillium were isolated from soils cultivated with rice using the serial dilution method. Streptomyces spp. M2A2 was selected for its ability to significantly reduce the in vitro growth of R. solani by 52% after 96 h by antibiosis in dual culture, while in the control treatment the mycelial growth was 100%. Furthermore, biocontrol efficacy of treated plants of the susceptible cultivar Fedearroz 68 with actinobacteria was confirmed and the onset of symptoms were delayed up to 14 days, compared to the control treatment. Rice plants treated with Streptomyces spp. M2A2 showed lesions of R. solani reaching 0.7% of the plant height, the effectiveness of this treatment was similar to the difenoconazole treatment, whereas in the control treatment, the lesions covered 34% of the plant height. When compared to the antagonist fungus Trichoderma spp. M2H1, Streptomyces spp. M2A2 presented a better performance of biological control. The results clearly demonstrated that Streptomyces spp. M2A2 isolate from soils of rice growing areas has biocontrol efficiency against R. solani and therefore can be a promising biocontrol agent.

Rapid Contamination Detection in Validamycin A Production by HS-SPME/GC-MS

Background: Validamycin A (Val-A) is one of the most widely used agricultural antibiotics in East Asia especially for controlling rice sheath blight disease. Fermentation contamination of the industrial Val-A producing strain is a common occurrence. Methods: Fermentation culture of S. hygroscopicus 5008 has a special smell that could be distinguished from other tainted samples. The change of the volatiles in untainted and tainted samples was characterized using headspace solid phase microextraction (HS-SPME) combined with gas chromatography- mass spectrometry (GC-MS). Results: Seventy-one volatile compounds (including alkanes, amines, alcohols, esters, aldehydes and others) were identified and there were significant differences in the composition of volatiles among different samples. Principal component analysis (PCA) based on the GC-MS data was used to identify the important volatile compounds that contributed to the differentiation of the fermentation samples under different fermentation stages, as well as among different pollution species and fermentation media. Contamination could be discovered in time irrespective of the stage of fermentation and the contaminating bacteria in broth. Conclusion: It is the first report to detect contamination by volatile compounds in the antibiotic fermentation and it was proved that HS-SPME/GC-MS is an effective contamination detection method in Val-A production.

Bamboo Tar as a Novel Fungicide: Its Chemical Components, Laboratory Evaluation, and Field Efficacy Against False Smut and Sheath Blight of Rice and Powdery Mildew and Fusarium Wilt of Cucumber.

The application of agricultural and forest residues can benefit the environment and the economy; however, they also generate a large amount of byproducts. In this study, bamboo tar (BT), a waste product of bamboo charcoal production, was dissolved in natural ethanol and the surfactant alkyl glucoside to manufacture a 50% (wt/wt) BT emulsifiable concentrate (BTEC) biopesticide. BTEC was screened for fungicidal activity against pathogens. The greatest activity was seen against Ustilaginoidea virens with a half-maximal effective concentration (EC50) value of 6 mg/liter. Four phytopathogenic fungi, Podosphaera xanthii, Rhizoctonia solani, Fusarium oxysporum, and Botrytis cinerea, showed EC50 values of <60 mg/liter. Greenhouse tests in vivo showed 2,000 mg/liter BTEC had a 78.4% protective effect against U. virens, and replicated treatments had an 80.6% protective effect. In addition, replicated 2-year field trials were conducted in two geographic locations with four plant diseases: false smut (U. virens), rice sheath blight (Thanatephorus cucumeris [Frank] Donk), cucumber powdery mildew (P. xanthii), and cucumber Fusarium wilt (F. oxysporum). Results showed that 1,000 to 2,000 mg/liter BTEC significantly inhibited these diseases. Gas chromatography-mass spectrometry analysis showed that the total phenolic mass fractions of two BT samples were 45.39 and 48.26%. Eleven components were detected, and their percentage content was as follows (from high to low): 2,6-dimethoxyphenol > 2- or 4-ethylphenol > 2- or 4-methylphenol > phenol > 4-ethylguaiacol > dimethoxyphenol > 4-methylguaiacol > 4-propenyl-2,6-dimethoxyphenol > 2,4-dimethylphenol. Some of the phenolic compounds identified from the tar might be fungicidally active components. BT is a biochar waste, which has potential as a biofungicide and has promise in organic agriculture. The value of this tar may not be because of any fundamental physical differences from other synthetic fungicides but rather caused by reduced production expenses and more efficient use of waste products.

Synthesis and in vitro Antifungal Efficacy of Copper-silica Nanocomposites against Pathogenic Fungi of Rice

In this study, copper-silica nanocomposites were synthesized by using silica nanoparticles extracted from rice husks as carriers for copper nanoparticles. Copper-silica nanocomposites (Cu-silicaNPs) were synthesized by a simple and effectively chemical reduction process with hydrazine as a reducing agent. Cu-silica NPs were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, high-resolution transmission microscopy, infrared spectroscopy and energy-dispersive X-ray spectroscopy. The average size of nanocomposite materials is about 20 nm. Cu-silica NPs products had a high inhibitory effect on Pyricularia oryzae and Rhizoctonia solani, causing rice blast and sheath blight.

Survival of the fittest: how the rice microbial community forces Sarocladium oryzae into pathogenicity.

The fungus Sarocladium oryzae (Sawada) causes rice sheath rot and produces the phytotoxins cerulenin and helvolic acid. Both toxins show antimicrobial activity but only helvolic acid production in the rice sheath correlates with virulence. Sarocladium oryzae isolates that differ in their toxin production were used to study their interaction with the rice culturable bacterial endophyte community. The diversity and community structure was defined in the edge of sheath rot lesions, followed by a null model-based co-occurrence analysis to discover pairwise interactions. Non-random pairs were co-cultured to study the nature of the interactions and the role of the toxins herein. Compared to healthy sheaths, endophyte diversity strongly increased when infected with the least virulent S. oryzae isolates producing low amounts of toxins. Virulent S. oryzae isolates did not affect diversity but caused strong shifts in species composition. The endophyte community of healthy rice plants was dominated by B. cereus. This bacterium was enriched in lesions produced by low-virulent S. oryzae isolates and caused hyphal lysis. Contrarily, helvolic acid producers eliminated this bacterium from the sheath endosphere. We conclude that S. oryzae needs to produce antibiotics to defend itself against antagonistic rice endophytes to successfully colonize and infect the rice sheath.

Estimates of occurrence of rice sheath blight disease and damage of yield reduction on a high temperature by the global warming.

Estimates of occurrence of rice sheath blight disease and damage of yield reduction on a high temperature by the global warming.

Auxin, Abscisic Acid and Jasmonate Are the Central Players in Rice Sheath Rot Caused by Sarocladium oryzae and Pseudomonas fuscovaginae

Sheath rot is an emerging rice disease that causes severe yield losses worldwide. The main causal agents are the toxin producers Sarocladium oryzae and Pseudomonas fuscovaginae. The fungus S. oryzae produces helvolic acid and cerulenin and the bacterium P. fuscovaginae produces cyclic lipopeptides. Helvolic acid and the lipopeptide, fuscopeptin, inhibit membrane-bound H+-ATPase pumps in the rice plant. To manage rice sheath rot, a better understanding of the host response and virulence strategies of the pathogens is required. This study investigated the interaction of the sheath rot pathogens with their host and the role of their toxins herein. Japonica rice was inoculated with high- and low-helvolic acid-producing S. oryzae isolates or with P. fuscovaginae wild type and fuscopeptin mutant strains. During infection, cerulenin, helvolic acid and the phytohormones abscisic acid, jasmonate, auxin and salicylic acid were quantified in the sheath. In addition, disease severity and grain yield parameters were assessed. Rice plants responded to high-toxin-producing S. oryzae and P. fuscovaginae strains with an increase in abscisic acid, jasmonate and auxin levels. We conclude that, for both pathogens, toxins play a core role during sheath rot infection. S. oryzae and P. fuscovaginae interact with their host in a similar way. This may explain why both sheath rot pathogens cause very similar symptoms despite their different nature.

Investigation on Data Fusion of Multisource Spectral Data for Rice Leaf Diseases Identification Using Machine Learning Methods.

Rice diseases are major threats to rice yield and quality. Rapid and accurate detection of rice diseases is of great importance for precise disease prevention and treatment. Various spectroscopic techniques have been used to detect plant diseases. To rapidly and accurately detect three different rice diseases [leaf blight (Xanthomonas oryzae pv. Oryzae), rice blast (Pyricularia oryzae), and rice sheath blight (Rhizoctonia solani)], three spectroscopic techniques were applied, including visible/near-infrared hyperspectral imaging (HSI) spectra, mid-infrared spectroscopy (MIR), and laser-induced breakdown spectroscopy (LIBS). Three different levels of data fusion (raw data fusion, feature fusion, and decision fusion) fusing three different types of spectral features were adopted to categorize the diseases of rice. Principal component analysis (PCA) and autoencoder (AE) were used to extract features. Identification models based on each technique and different fusion levels were built using support vector machine (SVM), logistic regression (LR), and convolution neural network (CNN) models. Models based on HSI performed better than those based on MIR and LIBS, with the accuracy over 93% for the test set based on PCA features of HSI spectra. The performance of rice disease identification varied with different levels of fusion. The results showed that feature fusion and decision fusion could enhance identification performance. The overall results illustrated that the three techniques could be used to identify rice diseases, and data fusion strategies have great potential to be used for rice disease detection.

A Meta-Analysis of Quantitative Trait Loci Associated with Multiple Disease Resistance in Rice (Oryza sativa L.)

Rice blast, sheath blight and bacterial leaf blight are major rice diseases found worldwide. The development of resistant cultivars is generally perceived as the most effective way to combat these diseases. Plant disease resistance is a polygenic trait where a combinatorial effect of major and minor genes affects this trait. To locate the source of this trait, various quantitative trait loci (QTL) mapping studies have been performed in the past two decades. However, investigating the congruency between the reported QTL is a daunting task due to the heterogeneity amongst the QTLs studied. Hence, the aim of our study is to integrate the reported QTLs for resistance against rice blast, sheath blight and bacterial leaf blight and objectively analyze and consolidate the location of QTL clusters in the chromosomes, reducing the QTL intervals and thus identifying candidate genes within the selected meta-QTL. A total of twenty-seven studies for resistance QTLs to rice blast (8), sheath blight (15) and bacterial leaf blight (4) was compiled for QTL projection and analyses. Cumulatively, 333 QTLs associated with rice blast (114), sheath blight (151) and bacterial leaf blight (68) resistance were compiled, where 303 QTLs could be projected onto a consensus map saturated with 7633 loci. Meta-QTL analysis on 294 QTLs yielded 48 meta-QTLs, where QTLs with membership probability lower than 60% were excluded, reducing the number of QTLs within the meta-QTL to 274. Further, three meta-QTL regions (MQTL2.5, MQTL8.1 and MQTL9.1) were selected for functional analysis on the basis that MQTL2.5 harbors the highest number of QTLs; meanwhile, MQTL8.1 and MQTL9.1 have QTLs associated with all three diseases mentioned above. The functional analysis allows for determination of enriched gene ontology and resistance gene analogs (RGAs) and other defense-related genes. To summarize, MQTL2.5, MQTL8.1 and MQTL9.1 have a considerable number of R-genes that account for 10.21%, 4.08% and 6.42% of the total genes found in these meta-QTLs, respectively. Defense genes constitute around 3.70%, 8.16% and 6.42% of the total number of genes in MQTL2.5, MQTL8.1 and MQTL9.1, respectively. This frequency is higher than the total frequency of defense genes in the rice genome, which is 0.0096% (167 defense genes/17,272 total genes). The integration of the QTLs facilitates the identification of QTL hotspots for rice blast, sheath blight and bacterial blight resistance with reduced intervals, which helps to reduce linkage drag in breeding. The candidate genes within the promising regions could be utilized for improvement through genetical engineering.

Identification of Rice Sheath Blight through Spectral Responses Using Hyperspectral Images.

Sheath blight (ShB), caused by Rhizoctonia solani AG1-I, is one of the most important diseases in rice worldwide. The symptoms of ShB primarily develop on leaf sheaths and leaf blades. Hyperspectral remote sensing technology has the potential of rapid, efficient and accurate detection and monitoring of the occurrence and development of rice ShB and other crop diseases. This study evaluated the spectral responses of leaf blade fractions with different development stages of ShB symptoms to construct the spectral feature library of rice ShB based on “three-edge” parameters and narrow-band vegetation indices to identify the disease on the leaves. The spectral curves of leaf blade lesions have significant changes in the blue edge, green peak, yellow edge, red valley, red edge and near-infrared regions. The variables of the normalized index between green peak amplitude and red valley amplitude (Rg − Ro)/(Rg + Ro), the normalized index between the yellow edge area and blue edge area (SDy − SDb)/(SDy + SDb), the ratio index of green peak amplitude and red valley amplitude (Rg/Ro) and the nitrogen reflectance index (NRI) had high relevance to the disease. At the leaf scale, the importance weights of all attributes decreased with the effect of non-infected areas in a leaf by the ReliefF algorithm, with Rg/Ro being the indicator having the highest importance weight. Estimation rate of 95.5% was achieved in the decision tree classifier with the parameter of Rg/Ro. In addition, it was found that the variety degree of absorptive valley, reflection peak and reflecting steep slope was different in the blue edge, green and red edge regions, although there were similar spectral curve shapes between leaf sheath lesions and leaf blade lesions. The significant difference characteristic was the ratio index of the red edge area and green peak area (SDr/SDg) between them. These results can provide the basis for the development of a specific sensor or sensors system for detecting the ShB disease in rice.

Validamycin A Induces Broad-Spectrum Resistance Involving Salicylic Acid and Jasmonic Acid/Ethylene Signaling Pathways

Validamycin A (VMA) is an aminoglycoside antibiotic used to control rice sheath blight. Although it has been reported that VMA can induce the plant defense responses, the mechanism remains poorly understood. Here, we found that reactive oxygen species (ROS) bursts and callose deposition in Arabidopsis thaliana, rice (Oryza sativa L.), and wheat (Triticum aestivum L.) were induced by VMA and were most intense with 10 μg of VMA per milliliter at 24 h. Moreover, we showed that VMA induced resistance against Pseudomonas syringae, Botrytis cinerea, and Fusarium graminearum in Arabidopsis leaves, indicating that VMA induces broad-spectrum disease resistance in both dicots and monocots. In addition, VMA-mediated resistance against P. syringae was not induced in NahG transgenic plants, was partially decreased in npr1 mutants, and VMA-mediated resistance to B. cinerea was not induced in npr1, jar1, and ein2 mutants. These results strongly indicated that VMA triggers plant defense responses to both biotrophic and necrotrophic pathogens involved in salicylic acid (SA) and jasmonic acid/ethylene (JA/ET) signaling pathways and is dependent on NPR1. In addition, transcriptome analysis further revealed that VMA regulated the expression of genes involved in SA, JA/ET, abscisic acid (ABA), and auxin signal pathways. Taken together, VMA induces systemic resistance involving in SA and JA/ET signaling pathways and also exerts a positive influence on ABA and auxin signaling pathways. Our study highlights the creative application of VMA in triggering plant defense responses against plant pathogens, providing a valuable insight into applying VMA to enhance plant resistance and reduce the use of chemical pesticides.[Formula: see text] Copyright © 2020 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Screening for novel rice sheath blight resistant germplasm and their biochemical characterization

Rhizoctonia solani Kuhn causes sheath blight of rice which is a common and destructive disease. The present studies focus on screening of rice genotypes against R. solani to find out promising sheath blight resistant genotypes and the role of the defense-related biochemical enzymes in six different moderately resistance, moderately susceptible and susceptible germplasm lines. A total of 196 rice germplasm lines were used to conduct a field trial to screen sheath blight resistant germplasm during 2014–2015 and 2015–2016 crop seasons. The study identified 33.1% moderately resistant, 55.6% moderately susceptible and 11.2% susceptible genotypes to sheath blight in rice. Moderately resistant cultivar IC281785 recorded higher peroxidase activity (2.990) than moderately susceptible cultivar IC282450 (1.232). Higher PPO enzyme activity was observed in Tetep (1.729) followed by IC281785 (1.423) after 24 h of inoculation. Similarly, PAL activity was highest in moderately resistant cultivars than moderately susceptible and susceptible cultivars. The highest catalase activity was observed in moderately resistant cultivar Tetep (0.963) than susceptible cultivar PB1 (0.513) after 72 h of pathogen inoculation.

Sheath blight development and yield loss on rice in different epidemiological conditions

Rice sheath blight and its causal agent Rhizoctonia solani AG-1 IA are associated with intensive and high input production systems. To our knowledge, resistant varieties have not been introduced for this disease, thus good crop management is expected to be among viable disease control methods. The aims of the present study were to determine the effect of different rates of nitrogen fertilizer, planting spaces and inoculum densities on sheath blight incidence and severity, including grain yield loss. Additionally we aimed to identify those developmental stages that are more susceptible to the disease. Field experiments were conducted over two consecutive years, in 2017 and 2018 in the Guilan province of Iran. Results indicated that higher N rates, denser planting and higher initial inoculum density resulted in greater disease development. Among five different growth stages, inoculation of plants at booting and flowering stages, resulted in maximum disease severity and grain yield loss. Taken together, reasonable use of nitrogen fertilizer, optimum planting space and reduced inoculum density obtained by spraying fungicide at the booting and flowering stages of rice are suggested as the best options to control sheath blight epidemics in rice.

New nano-fungicides for the management of sheath blight disease (Rhizoctonia solani) in rice

Rice sheath blight, caused by Rhizoctonia solani, is one of the increasing concerns in rice causing severe economic losses worldwide. Chemical control measures are already in practice for the management of this disease but approach for discovery of new chemicals with improved disease control potential is essential. The present investigation involves the development of nanoformulations of halogen substituted azomethines as new potent fungicide for the management of sheath blight disease in rice. The halogen substituted azomethines were synthesized and screened for in-vitro bioefficacy. Then the azomethines were nanoformulated for their in-vivo pot culture evaluation against Rhizoctonia solani. Transmission electron microscopy confirmed the particle size of the developed nanoformulations in the range of 1–100 nm. In-vitro inhibition results of test compounds revealed their ED50 values in the range of 11.9 to 22.4 μg/ml with best performer 2,4,5-trichloro-N-(2,4-dichlorobenzylidene)aniline. 3-Chloro-N-(2,6-dichlorobenzylidene)-4-fluoroaniline displayed maximum in-vivo efficacy against R. Solani which was comparable with that of hexaconazole, a standard recommended fungicide.

Identification of Genes Involved in Antifungal Activity of Burkholderia seminalis Against Rhizoctonia solani Using Tn5 Transposon Mutation Method.

Rhizoctonia solani is the causative agent of rice sheath blight disease. In a previous study, we found that the growth of R. solani was inhibited by Burkholderia seminalis strain R456. Therefore, the present study was conducted to identify the genes involved in the antifungal activity of B. seminalis strain R456 by using a Tn5 transposon mutation method. Firstly, we constructed a random insertion transposon library of 997 mutants, out of which 11 mutants showed the defective antifungal activity against R. solani. Furthermore, the 10 antagonism-related genes were successfully identified based on analysis of the Tn5 transposon insertion site. Indeed, this result indicated that three mutants were inserted on an indigenous plasmid in which the same insertion site was observed in two mutants. In addition, the remaining eight mutants were inserted on different genes encoding glycosyl transferase, histone H1, nonribosomal peptide synthetase, methyltransferase, MnmG, sulfate export transporter, catalase/peroxidase HPI and CysD, respectively. Compared to the wild type, the 11 mutants showed a differential effect in bacteriological characteristics such as cell growth, biofilm formation and response to H2O2 stress, revealing the complexity of action mode of these antagonism-related genes. However, a significant reduction of cell motility was observed in the 11 mutants compared to the wild type. Therefore, it can be inferred that the antifungal mechanism of the 10 above-mentioned genes may be, at least partially, due to the weakness of cell motility. Overall, the result of this study will be helpful for us to understand the biocontrol mechanism of this bacterium.