Control Of Rice Sheath Blight Research Articles

Synthesis, antifungal activity and action mechanism of novel citral amide derivatives against Rhizoctonia solani.

Rice sheath blight caused by Rhizoctonia solani is a severe threat to the yield and quality of rice. Due to the unscientific abuse of common fungicides causing resistance and environmental issues, the development of new fungicides is necessary. In this study, we used citral as the lead compound, designed and synthesized a series of novel citral amide derivatives, and evaluated their antifungal activity and mode of action against R. solani. Bioassay results indicated that the antifungal activities of most citral amide derivatives against R. solani were significantly improved compared to citral, with EC50 values ranging from 9.50-27.12 mg L-1. Among them, compound d21 containing the N-(pyridin-4-yl)carboxamide group exhibited in vitro and in vivo fungicidal activities, with curative effects at 500 mg L-1 as effectively as the commercial fungicide validamycin·bacillus. Furthermore, d21 prolonged the lag phase of the growth curve of R. solani, reduced the amount of growth, and inhibited sclerotium germination and formation. Mechanistically, d21 deformed the mycelia, increased cell membrane permeability, and inhibited the activities of antioxidant and tricarboxylic acid cycle (TCA)-related enzymes. Metabolome analysis showed the abundance of some energy-related metabolites within R. solani increased, and simultaneously the antifungal substances secreted by itself reduced. Transcriptome analysis showed that most genes encoding ATP-binding cassette (ABC) transporters and peroxisomes upregulated after the treatment of d21 and cell membrane destruction. This study indicates that novel citral amide derivatives possess antifungal activity against R. solani and are expected to develop an alternative option for chemical control of rice sheath blight. © 2024 Society of Chemical Industry.

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

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

Mycoviruses: Antagonistic Potential, Fungal Pathogenesis, and Their Interaction with Rhizoctonia solani.

Mycoviruses, or fungal viruses, are prevalent in all significant fungal kingdoms and genera. These low-virulence viruses can be used as biocontrol agents to manage fungal diseases. These viruses are divided into 19 officially recognized families and 1 unclassified genus. Mycoviruses alter sexual reproduction, pigmentation, and development. Spores and fungal hypha spread mycoviruses. Isometric particles mostly encapsulate dsRNA mycoviruses. The widespread plant-pathogenic fungus Rhizoctonia solani, which has caused a rice sheath blight, has hosted many viruses with different morphologies. It causes significant crop diseases that adversely affect agriculture and the economy. Rice sheath blight threatens the 40% of the global population that relies on rice for food and nutrition. This article reviews mycovirology research on Rhizoctonia solani to demonstrate scientific advances. Mycoviruses control rice sheath blight. Hypovirulence-associated mycoviruses are needed to control R. solani since no cultivars are resistant. Mycoviruses are usually cryptic, but they can benefit the host fungus. Phytopathologists may use hypovirulent viruses as biological control agents. New tools are being developed based on host genome studies to overcome the intellectual challenge of comprehending the interactions between viruses and fungi and the practical challenge of influencing these interactions to develop biocontrol agents against significant plant pathogens.

Aspergillus sclerotiorum Whole-Cell Biocatalysis: A Sustainable Approach to Produce 3-Hydroxy-phenazine 1-Carboxylic Acid from Phenazine 1-Carboxylic Acid

In green chemistry, filamentous fungi are regarded as a kind of robust microorganism for the biotransformation of natural products. Nonetheless, the screening of microorganisms is crucial for the effective biotransformation of natural products, such as phenazine compounds. The precursor metabolite of most phenazine derivatives in Pseudomonas spp. is phenazine-1-carboxylic acid (PCA), the key constituent of shenqinmycin, widely used to control rice sheath blight in southern China. In this study, a new fungus strain Aspergillus sclerotiorum was isolated, which can efficiently convert PCA into 3-hydroxy-phenazine 1-carboxylic acid (3-OH-PCA). Moreover, an effective whole cells biotransformation system was designed by screening optimal reaction conditions and carbon sources. Hence, Aspergillus sclerotiorum exhibited desirable adaptation by the consumption of different carbon sources and maximum whole-cell biomass (10.6 g/L DCW) was obtained as a biocatalyst from glucose. Optimal conditions for whole-cell biocatalysis of PCA were evaluated, including a PCA concentration of 1120 mg/L, a pH of 7.0, a temperature of 25 °C, a rotation rate of 200 rpm, and dry cell weight of 15 g/L for 60 h; thus, 1060 mg/L of 3-OH-PCA was obtained and the conversion efficiency of PCA was 94%. Hence, the results of the repeated batch mood revealed that the biotransformation efficiency of fungus pellets reduced with each subsequent cycle, but remained stable in all five cycles with the provision of a glucose supplement. These findings present the prospect of using filamentous fungi for the whole-cell biocatalysis of phenazine in enormous amounts and the efficient production of 3-OH-PCA. Moreover, these results laid the foundation for further research to disclose the genetic-based mechanism of the strain responsible for PCA biotransformation.

Effect of enzyme-response Mag@CMCS@CPSG film on rice sheath blight disease (caused by Rhizoctonia solani) control and rice quality

To find a precise, efficient, and safe method to control rice sheath blight disease (caused by Rhizoctonia solani), this study used the natural product magnolol as the fungicide. Based on the characteristics of cell wall-degrading enzymes (CWDEs) released by R. solani during the early stages of infection, a Mag@CMCS@CPSG (magnolol@carboxymethyl chitosan@carboxymethyl cellulose, pectin, sodium alginate, and glycerol) film was constructed to control the release of magnolol in response to CWDEs. The Mag@CMCS@CPSG film increased magnolol toxicity against R. solani, decreased EC50 from 7.33 μg/mL to 4.37 μg/mL, and effectively blocked the invasion of mycelia. Under the stimulation of CWDEs released during R. solani infection, the cumulative release of magnolol by the Mag@CMCS@CPSG film reached 75.62% after 96 h, and the disease index of rice treated with Mag@CMCS@CPSG film significantly decreased. The maximum field control effect of Mag@CMCS@CPSG film on rice sheath blight disease was 72.47%, which was not significantly different from that of the commercial preparation jinggangmycin; however, the holding period was better. The Mag@CMCS@CPSG film reduced the loss of rice yield and quality caused by infection with R. solani and did not cause phytotoxicity or residue. In conclusion, the Mag@CMCS@CPSG film can achieve accurate and green control of rice sheath blight.

Effects of fungicides and antagonistic marine-derived fungi on rice seedling promotion and rice sheath blight control

Fourteen fungicides and three marine-derived fungi were tested for their activities in the promotion of rice seedling development and their efficacy in controlling rice sheath blight disease in two rice varieties, RD43 and KMDL105, under greenhouse conditions. The results showed that the rice seeds treated with carbendazim 50%SC and azoxystrobin 25%SC displayed the best promotion of rice growth in root length and shoot height at seven and 14 days in rice var. RD43. Rice seeds from var. KMDL105 treated with thiophanate-methyl 70%WP exhibited significant stimulation of rice seedling growth resulting in the greatest increase in root length and shoot height at seven and 14 days. In pot experiments with rice var. RD43, spraying with triforine 19%EC, propiconazole 25%EC, trifloxystrobin 50%WG, and validamycin 3%SL showed a high level of fungicidal activity in controlling sheath blight disease, with this evidenced by significant suppression of the disease severity by 71–75% and 61–73% at seven and 14 days after inoculation, respectively. The treatment of rice var. KMDL105 with validamycin 3%SL exhibited the best activity in controlling sheath blight disease by reducing disease severity by up to 62% and 64% at seven and 14 days, respectively. The antagonistic marine fungi tested in this study displayed low activity against sheath blight disease and low effects on rice seedling promotion compared to fungicides. Specifically, Trichoderma harzianum KUFA 0689 and T. asperellum KUFA 0677 reduced sheath blight disease severity by 42–46% and 27–37% at seven and 14 days, respectively.

In vitro/vivo antifungal activity study of novel mandelic acid derivatives as potential fungicides against Thanatephorus cucumeris

To discover highly efficient and novel lead compounds against Thanatephorus cucumeris, a series of novel mandelic acid derivatives containing 1,3,4-thiadiazole thioether was designed and synthesized. The bioassay results revealed that target compound F10 exhibited excellent antifungal activity against T. cucumeris with EC50 value of 9.7 μg/mL. Further studies found that F10 not only significantly inhibited the growth of T. cucumeris mycelia but also effectively inhibited the formation of sclerotia, and exhibited significant in vivo protective (61.1%) and curative (67.9%) activities at 200 μg/mL. Mechanism studies demonstrated that F10 can damage the integrity of the cell membrane structure, resulting in increased permeability of the cell membrane, releasing the intracellular electrolyte and inhibiting the growth of fungi. In general, this work is helpful for managing the formation and diffusion of the infection source and provides an effective method to control rice sheath blight disease infected with sclerotia of T. cucumeris.

Selection of reference genes for RT-qPCR analysis of rice with Rhizoctonia solani infection and biocontrol PGPR/KSi application.

Rhizoctonia solani (AG1 IA) is an important pathogen of rice (Oryza sativa L.) that causes rice sheath blight (RSB). Since control of RSB by breeding and fungicides have had limited success, novel strategies like biocontrol with plant growth-promoting rhizobacteria (PGPR) can be an effective alternative. Seven commonly used reference genes (RGs), 18SrRNA, ACT1, GAPDH2, UBC5, RPS27, eIF4a and CYP28, were evaluated for their stability in rice-R. solani-PGPR interaction for real-time quantitative PCR (RT-qPCR) analysis. Different algorithms were examined, Delta Ct, geNorm, NormFinder, BestKeeper, and comprehensive ranking by RefFinder, to evaluate RT-qPCR of rice in tissues infected with R. solani and treated with the PGPR strains, Pseudomonas saponiphilia and Pseudomonas protegens, with potassium silicate (KSi) alone or in combination with each PGPR strain. RG stability was affected for each treatment and treatment-specific RG selection was suggested. Validation analysis was done for nonexpressor of PR-1(NPR1) for each treatment. Overall, ACT1 was the most stable RG with R. solani infection alone, GAPDH2 with R. solani infection plus KSi, UBC5 with R. solani infection plus P. saponiphilia, and eIF4a with R. solani infection plus P. protegens. Both ACT1 and RPS27 were the most stable with the combination of KSi and P. saponiphilia, while RPS27 was the most stable with the combination of KSi and P. protegens.

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

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

Application of thifluzamide alters microbial network structure and affects methane cycle genes in rice-paddy soil.

Thifluzamide is an effective agent for controlling rice sheath blight and has a long half-life in soil. However, the effects of thifluzamide on the abundance of microbes harboring methane-cycle genes and soil microbial community assembly patterns are not well known. Thus, we conducted a three-month indoor mesocosm experiment to ascertain the effects of thifluzamide (0.05, 0.5, and 5 mg kg-1 soil; 0.05 mg kg-1 soil being recommended) on bacterial and archaeal community structure and on the abundance of methanogen genes using two typical paddy soils: sandy soil from Hangzhou (HZ) and loam sandy soil from Jiansanjiang (JSJ). The effects of thifluzamide on soil microorganisms were related to soil type. In JSJ loam sandy soil, thifluzamide significantly increased bacterial α diversity after 7-30 d and archaeal α diversity at 30 and 60 d. In HZ sandy soil, however, α diversity did not change significantly. Network analysis showed that thifluzamide-treated soils possessed more complex networks with more total nodes and links, a higher average degree of connectivity, and more keystone species. Thifluzamide application increased the number of keystone species associated with methane production in both types of paddy soil. A relatively greater number of modules were significantly negatively correlated with mcrA abundance in the HZ T10 network, but more modules were positively correlated with mcrA abundance in the JSJ T100 network. The half-life of thifluzamide varied for the different doses, i.e., from 152.0 to 419.6 d. The results reveal that methane-cycle genes, soil microbiome assembly, and interactions among microbial species all change in response to thifluzamide stress.

Baseline sensitivity of Rhizoctonia solani to four DMI fungicides.

A set of 78 Rhizoctonia solani isolates from Shanghai, China, were examined for their sensitivity in vitro to four demethylase inhibitor (DMI) fungicides, epoxiconazole, difenoconazole, hexaconazole, and tebuconazole, by the mycelial growth rate method. The isolates were very sensitive to the four DMI fungicides. The ranges and means of the EC50 values were 0.004-0.045 and 0.014 ± 0.007 μg ml-1 for epoxiconazole, 0-0.103 and 0.010 ± 0.016 μg ml-1 for difenoconazole, 0.001-0.078 and 0.011 ± 0.013 μg ml-1 for hexaconazole, and 0.001-0.210 and 0.034 ± 0.035 μg ml-1 for tebuconazole, respectively. The frequency distribution of the EC50 values showed a normal curve for epoxiconazole and an approximately unimodal curve for difenoconazole, hexaconazole, and tebuconazole. There was no correlation between the sensitivities of the R. solani population to any two of the four fungicides (r < 0.3). In field trials, in 2015 and 2016, the control efficacies of hexaconzole, epoxiconazole, and tebuconazole were >90.0% at 75 g.a.i. ha-1 , 80.0%-90.0% at 75 g.a.i. ha-1 and 80.0%-90.0% at 97 g.a.i. ha-1 , respectively; these values are significantly higher (p < 0.05) than those obtained in this study for difenoconazole (65.0%-70.0% at 80 g.a.i. ha-1 ) and jinggangmycin (68.0%-71.0% at 150 g.a.i. ha-1 ). These results show that sensitivity data can be used to monitor and detect any variations in the sensitivity of the R. solani population to these four DMI fungicides, and demonstrate that epoxiconazole, hexaconazole, and tebuconazole are likely to be good alternatives to jinggangmycin for controlling rice sheath blight.

Lauric Acid Induces Apoptosis of Rice Sheath Blight Disease Caused by Rhizoctonia solani by Affecting Fungal Fatty Acid Metabolism and Destroying the Dynamic Equilibrium of Reactive Oxygen Species

Rice sheath blight, caused by Rhizoctonia solani, is one of the major rice diseases. In order to better understand the inhibitory mechanism of lauric acid on the disease, RNA sequencing (RNA-Seq) was used to analyze the transcriptome changes in Rhizoctonia solani treated with lauric acid for 3 h, 6 h, 18 h, and 24 h, including 2306 genes; 1994 genes; 2778 genes; and 2872 genes. Based on gene ontology (GO) enrichment and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses, we found that protein processing in endoplasmic reticulum (KO04141), carbon metabolism (KO01200), and starch and sucrose metabolism were significantly enriched. Most oxidoreductase, dehydrogenase, reductase, and transferase genes are downregulated in this process. Lauric acid can affect ergosterol content, mitochondrial membrane potential collapse, hydrogen peroxide content, electrolyte leakage, reactive oxygen species balance, and can induce endoplasmic reticulum (ER) stress. Lauric acid also increased the expression levels of ER chaperone glucose regulatory protein Grp78 (BIP), protein disulfide isomerase (PDI), and Calpain (CNX), and decreased the expression levels of HSP40, HSP70, and HSP90 genes. Lauric acid affected the ergosterol content in the cell membrane of R. solani, which induces ER stress and increases the BiP level to induce the apoptosis of Rhizoctonia solani. These results indicated that lauric acid could be used to control rice sheath blight.

Characterisation of rice-associated antagonistic pseudomonads and their application in combination with plant resistance inducer molecules for the control of sheath blight disease of rice

ABSTRACT Rice sheath blight caused by Rhizoctonia solani AG1-IA is one of the most important diseases of high-yielding rice (Oryza sativa L.) cultivars in rice-growing areas of the world including Iran. This study aimed to determine the efficacy of native fluorescent pseudomonads in combination with plant defence activators in controlling rice sheath blight disease. Sampling was done from local and high-yielding rice cultivars grown in Mazandaran province, Iran. A total of 291 fluorescent strains were isolated and screened for antagonism against R. solani. The isolates Ps-275, Ps-128, Ps-287, Ps-240 and Ps-243 reduced the disease symptoms up to 53.1­%, 49.3%, 44.76%, 40.83% and 35.7­%, respectively, only when applied in combination with potassium silicate at the booting stage of rice growth. The isolate Ps-3 reduced the disease symptoms when applied alone and in combination with oxalic acid by 60.5% and 58.7%, respectively. Multilocus sequence analysis of house-keeping genes, rpoD, oprI and oprL identified the most effective antagonistic isolates, Ps-275, Ps-3 and Ps-287, as endemic Pseudomonas strains affiliated with the P. protegens, P. mosselii and P. aeruginosa (sub) groups, respectively. These strains significantly inhibited the growth of R. solani AG1-IA in vitro and reduced the disease symptoms at the booting stage of the rice plant as well.

Novel Citral-thiazolyl Hydrazine Derivatives as Promising Antifungal Agents against Phytopathogenic Fungi.

To develop new antifungal agents against phytopathogenic fungi, a series of citral-thiazolyl hydrazine derivatives were designed, synthesized, and characterized by FT-IR, 1H NMR, 13C NMR, and HRMS. Antifungal activity results showed that most synthetic compounds exhibited broad-spectrum antifungal activities against six phytopathogenic fungi in vitro. Notably, compounds b and c15 exhibited remarkable antifungal activity against Colletotrichum gloeosprioides, Rhizoctonia solani, Phytophthora nicotianae var. nicotianae, Diplodia pinea, Colletotrichum acutatum, and Fusarium oxysporum f. sp. niveum, which were all superior to the positive control tricyclazole. Structure-activity relationship (SAR) studies demonstrated that introducing electron-withdrawing groups such as F on the benzene ring exhibited outstanding antifungal activities against all the tested fungi. Furthermore, compound b could effectively control rice sheath blight and showed higher curative activities against R. solani than validamycin·bacillus in vivo. In addition, the in vitro cytotoxicity results indicated that compound b possessed moderate cytotoxicity activity, and all citral-thiazolyl hydrazine derivatives exhibited lower or no cytotoxicity to the LO2 and HEK293 cell lines. In addition, the acute oral toxicity test showed that compound b had moderate toxicity (level II) with an LD50 value of 310 mg/kg bw (95% confidence limit: 175-550 mg/kg bw). Finally, a preliminary action mechanism study showed that causing obvious malformation of mycelium and increasing cell membrane permeability are two of the potential mechanisms by which compound b exerts antifungal activity. The present work indicates that some of these derivatives may serve as novel potential fungicides, and compound b is expected to be the leading structure for the development of new antifungal agents.

Validamycin treatment significantly inhibits the glycometabolism and chitin synthesis in the common cutworm, Spodoptera litura.

Validamycin, as a broadly applied antibiotic, has been used to control rice sheath blight disease. Furthermore, validamycin was considered as an insecticide to control agricultural pests. Insight into the mechanism of validamycin's action on insects can provide molecular targets for the control of agricultural pests. In this study, a toxicological test analysis revealed that Spodoptera litura larval growth and development was significantly inhibited and the pupation rate was significantly reduced with the increase of the concentration of validamycin. According to the NMR-based metabolomic analysis, a total of 15 metabolites involved in glycolysis and tricarboxylic acid cycle (TCA) pathways were identified. Additionally, trehalase activities, glucose and chitin contents were significantly downregulated, but the trehalose content was upregulated after exposure to validamycin. Reverse transcription quantitative PCR analysis revealed that the expression level of genes involved in glycolysis, TCA and chitin synthesis were upregulated after treating with validamycin. Further chitin staining also confirmed that chitin content was downregulated at 12h after validamycin treatment. Our results indicated that validamycin worked via two different molecular mechanisms, one through inhibiting glycometabolism and the other by inhibiting chitin synthesis in S. litura. The information lays a theoretical foundation for further control of S. litura.

Isolation and evaluation of the biocontrol potential of Talaromyces spp. against rice sheath blight guided by soil microbiome.

Rice sheath blight caused by Rhizoctonia solani is the major disease of rice that seriously threatens food security worldwide. Efficient and eco-friendly biological approaches are urgently needed since no resistant cultivars are available. In this study, fallow and paddy soils were initially subjected to microbiome analyses, and the results showed that Talaromyces spp. were significantly more abundant in the paddy soil, while Trichoderma spp. were more abundant in the fallow soil, suggesting that Talaromyces spp. could live and survive better in the paddy soil. Five Talaromyces isolates, namely, TF-04, TF-03, TF-02, TF-01 and TA-02, were isolated from the paddy soil using sclerotia of R. solani as baits and were further evaluated for their activity against rice sheath blight. These isolates efficiently parasitized the hyphae and rotted the sclerotia even at higher water contents in the sterilized sand and the soil. Isolate TF-04 significantly promoted rice growth, reduced the severity of rice sheath blight and increased the rice yield under outdoor conditions. Defence-related genes were upregulated and enzyme activities were enhanced in rice treated with isolate TF-04. Our research supplies a microbiome-guided approach to screen biological control agents and provides Talaromyces isolates to biologically control rice sheath blight.

Synthesis, Antimicrobial Activity, and Molecular Docking of Benzoic Hydrazide or Amide Derivatives Containing a 1,2,3‐Triazole Group as Potential SDH Inhibitors

Main observation and conclusionThe present study was carried out in an attempt to synthesize a new class of antimicrobial agents containing a 1,2,3‐triazole motif formed by classical copper catalyzed click chemistry. Antifungal bioassay results showed that five compounds 5a, 5e, 5h, 5j, and 5k possessed a remarkable growth inhibitory activity against Botryosphaeria dothidea, Rhizoctonia solani and Gibberella zeae with EC50 values within 10.0—0.306 μg/mL. The in vitro efficacy was better than those of the commercial agrochemicals Azoxystrobin, Boscalid, and Fluxapyroxad. In vivo trials showed that compound 5l was effective for the control of rice sheath blight and wheat scab with the effects of 75% and 95%, respectively. Antifungal mechanism studies suggested that target compounds were potential succinate dehydrogenase inhibitors (SDHIs), which were proposed by the agreeable molecular docking study and restrained SDH activity (IC50 = 3.95 μg/mL, 5l). Interestingly, compounds 5r and 5s displayed good antibacterial activity against phytopathogens. In vivo screening of 5r and 5s against rice bacterial blight afforded a superior control effect (up to 51%) than those of commercial agents Bismerthiazol and Thiodiazole copper. The current studies could support some title compounds to be the lead compounds for exploring highly bioactive antimicrobial substrates, particularly the potential SDHIs.

Volatile Organic Compounds from Rice Rhizosphere Bacteria Inhibit Growth of the Pathogen Rhizoctonia solani

Rice sheath blight, a fungal disease caused by Rhizoctonia solani, seriously threatens rice production. Some of the volatile organic compounds (VOCs) produced by microbes are inhibitory to the growth of the plant pathogen, and hence may have the potential as environmentally friendly antifungal substances. However, information on the inhibitory effect of VOCs released by rice rhizosphere bacteria on R. solani is scarce. In this study, bacteria from the rice rhizosphere capable of inhibiting the growth of R. solani via releasing VOCs were screened using a double Petri dish assay. Headspace solid phase microextraction and gas chromatography mass spectrometry (GC/MS) were used to identify and quantify the VOCs. The contributions of VOCs to the inhibition of the growth of R. solani were estimated by constructing a random forest model, and were verified using pure compounds. Nine strains (i.e., Pseudomonas sp. No. 3, Enterobacter sp. No. 26, Enterobacter sp. No. 34, Pseudomonas sp. No. 35, Ralstonia sp. No. 50, Bacillus sp. No. 62, Arthrobacter sp. No. 146, Brevibacillus sp. No. 2–18, and Paenisporosarcina sp. No. 2–60) showed various inhibition on R. solani growth via VOCs. The inhibitory effect ranged from 7.84% to 100%, with Ralstonia sp. No. 50 completely inhibiting the growth of R. solani. Five VOCs (i.e., benzoic acid ethyl ester, 3-methyl-butanoic acid, 2-ethyl-1-hexanol, 3-methyl-1-butanol, and 6-methyl-5-hepten-2-one) identified by random forest model were confirmed to be toxic to R. solani when applied as a pure chemical compound. In particular, benzoic acid ethyl ester, 3-methyl-butanoic acid, and 2-ethyl-1-hexanol were lethal to R. solani. In summary, the rice rhizosphere bacteria (Ralstonia sp. No. 50) and VOCs (benzoic acid ethyl ester, 3-methyl-butanoic acid, and 2-ethyl-1-hexanol) showed potential to be used as new resources for biological control of rice sheath blight.

Field Sanitation and Foliar Application of Streptomyces padanus PMS-702 for the Control of Rice Sheath Blight.

Rice sheath blight (ShB), caused by Rhizoctonia solani Kühn AG1-IA, is one of the destructive rice diseases worldwide. The aims of this study were to develop biocontrol strategies focusing on field sanitation and foliar application with a biocontrol agent for ShB management. Streptomyces padanus PMS-702 showed a great antagonistic activity against R. solani. Fungichromin produced by S. padanus PMS-702, at 3.07 mg/l inhibited 50% mycelial growth, caused leakage of cytoplasm, and inhibited the formation of infection structures of R. solani. Fungichromin could reach to 802 mg/l when S. padanus PMS-702 was cultured in MACC broth for 6 days. Addition of 0.5% S. padanus PMS-702 broth into soil decreased the survival rate of the pathogen compared to the control. Soil amended with 0.5% S. padanus broth and 0.5% tea seed pomace resulted in the death of R. solani mycelia in the infested rice straws, and the germination of sclerotia was inhibited 21 days after treatment. Greenhouse trials revealed that S. padanus cultured in soybean meal–glucose (SMGC-2) medium after mixing with different surfactants could enhance its efficacy for inhibiting the pathogen. Of six surfactants tested, the addition of 2% tea saponin was the most effective in suppressing the pathogen. S. padanus broth after being fermented in SMGC-2, mixed with 2% tea saponin, diluted 100 fold, and sprayed onto rice plants significantly reduced ShB disease severity. Thus, S. padanus PMS-702 is an effective biocontrol agent. The efficacy of S. padanus PMS-702 for disease control could be improved through formulation.

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.