Solani AG Research Articles

Characterization and pathogenicity of Rhizoctonia SPP. isolated from vegetable crops grown in greenhouses in Samsun province, Turkey

A total of one hundred and five isolates of Rhizoctonia belonging to 7 anastomosis groups (AGs) were obtained from the diseased roots and rhizosphere soils of bean, cucumber, eggplant, pepper and tomato plants grown in greenhouses in Samsun province (Black Sea region, Turkey) during the period 2011–2012. The isolates of Rhizoctonia spp. were examined for their cultural characteristics, anastomosis groups and pathogenicity. Of these, 83.8% were multinucleate Rhizoctonia solani (AG-2, AG-4, AG-5 and AG-6) and 16.2% were binucleate Rhizoctonia (AG-A, AG-E and AG-F). Sixty five of the isolates belonged to AG-4 which was the most frequent group (61.9%) in all greenhouses surveyed. Numbers of the isolates belonging to AG-2 (7.6%), AG-5 (6.7%) and AG-6 (7.6%) were 8, 7 and 8, respectively. Seventeen isolates recovered from greenhouses surveyed were identified as binucleate Rhizoctonia AG-A (1.9%), AG-E (6.7%) and AG-F (7.6%). All isolates of Rhizoctonia spp. tested for growth rates grew at temperatures of 10, 15, 20, 25 and 30°C, whereas they were completely inhibited at 5°C. The results of pathogenicity tests showed that the differences in virulence among isolates of Rhizoctonia spp. were statistically significant ( P < 0.001). The tests on bean seedlings showed that the highest disease severity was caused by AG-4 isolates. The disease severity index (DSI) of the R. solani AG-4 isolates ranged from 3.2 to 3.8. In addition, the isolates of three AGs belonging to binucleate Rhizoctonia spp. were generally found to be moderately virulent (DSI 2.0–2.4).

Rhizoctonia solani AG4 associated with foliar blight symptoms on barley in Iran

Since June 2011, foliar blight symptoms have been observed in barley fields at Chaharmahal and Bakhtiari, Iran. The symptoms include water soaked spots progressing to elongated stripe and scald like lesions on the leaves and sheaths of barley plants. From cultural and morphological studies and phylogenetic analysis of sequences of the internal transcribed spacer region (ITS) of the ribosomal DNA, the causal agent was identified as Rhizoctonia solani AG4. Pathogenicity tests revealed that R. solani AG4 is virulent to barley. To the best of our knowledge this is the first report of R. solani AG4 causing foliar disease of barley in Iran.

Biocontrol Activities of Gamma Induced Mutants of Trichoderma harzianum against some Soilborne Fungal Pathogens and their DNA Fingerprinting.

Background Random induced mutation by gamma radiation is one of the genetic manipulation strategies to improve the antagonistic ability of biocontrol agents. Objectives This study aimed to induce mutants with more sporulation, colonization rate leading to enhanced antagonistic ability (in vitro assay) comparing to wild type (WT) and the assessment of genetic differences (in situ evaluation) using molecular markers. The superior mutants could be appropriate biocontrol agents against soil borne fungal diseases. Materials and Methods In this research sampling and isolation of Trichoderma isolates were performed from soils with low incidence of soil borne disease. T. harzianum 65 was selected and irradiation was conducted with gammacell at optimal dose 250 Gray/s. Mutants (115) were obtained from the WT. The antagonistic abilities of twenty-four mutants were evaluated using dual culture and culture filtrate tests. Results The results of in vitro assays revealed that Th15, Th11 and Th1 mutants exhibited stronger growth inhibition (GI) and colonization rate on Macrophomina phaseolina and Rhizoctonia solani AG4 compared to the wild type. Th15 and Th11 mutants exhibited stronger GI and colonization rate on Sclerotinia sclerotiorum in dual culture and culture filtrate tests and Th1 and Th11 mutants exhibited stronger GI on Fusarium grminearum in culture filtrate test. The DNA fingerprinting was carried out using RAPD and rep-PCR markers. Two (Th9 and Th17) out of the 24 mutants categorized distantly from the rest based on different polymorphism obtained by molecular markers. However, Th9 was different in GI% from Th17. RAPD analysis separated WT from mutants, Th9 from Th17 and also phenotypically superior mutants from other mutants. Meanwhile, rep-PCR analysis categorized WT isolate and mutants according to their antagonistic properties. Conclusions The latter marker (rep-PCR) appeared to be reproducible and simple to distinguish mutants from a single isolate of T. harzianum. Mutants (3 isolates) were phenotypically and genotypically distinct from WT. These mutants demonstrated a pronounced biocontrol activities against soilborne fungal phytopathogens.

Reação de cultivares de algodoeiro a Rhizoctonia solani na fase de plântula e benefícios do tratamento de sementes com fungicidas

RESUMO O objetivo desse trabalho foi avaliar a reação de onze genótipos de algodoeiro ao fungo Rhizoctonia solani AG-4, na fase de plântula, com potencial de uso em futuros programas de melhoramento bem como os benefícios do tratamento de sementes com fungicidas para cada cultivar em estudo. O experimento foi conduzido por dois anos nas casas de vegetação da Embrapa Agropecuária Oeste, em Dourados, MS. Sementes de cada cultivar, não tratadas e tratadas com a mistura fungicida tolylfluanid + pencycuron + triadimenol (30+50+50g do i.a./100kg de sementes), foram semeadas em areia contida em bandejas plásticas, dispostas em orifícios individuais, eqüidistantes e a 3cm de profundidade. A inoculação com R. solani foi feita pela distribuição homogênea do inóculo do fungo na superfície do substrato (2,5g do inóculo do fungo/bandeja plástica com dimensões de 56x35x10cm). O fungo foi cultivado por 35 dias em sementes de aveia preta autoclavadas e trituradas em moinho (1mm). As avaliações foram realizadas com base no desenvolvimento de sintomas e sobrevivência das plântulas, utilizando os dados de emergência inicial e final, tombamento de pós-emergência e plântulas lesionadas pelo patógeno. Foi observado efeito significativo da interação cultivares x tratamento com fungicidas (P&lt;0,05). Ficou claramente demonstrada a importância do tratamento das sementes de algodoeiro com fungicidas, sendo que as melhores emergências e os menores índices de doença (tombamento e plântulas lesionadas), independente da cultivar testada, foram obtidos quando as sementes foram tratadas. Em relação as cultivares avaliadas na ausência do tratamento da sementes com fungicidas, observou-se comportamento diferenciado de alguns genótipos com relação ao ataque do fungo R. solani, merecendo destaque BRS Aroeira, seguidas de BRS Cedro, BRS Ipê e FMT 701, demonstrando uma maior tolerância destas cultivares ao ataque de R. solani em comparação às demais. Enfatiza-se que a resistência, sozinha, não é suficiente para proporcionar efetivo controle desse patógeno. Porém, pode ser útil se integrada a outras estratégias complementares de controle, como o tratamento de sementes com fungicidas, reforçando o conceito de manejo integrado de doenças.

Screening, identification, optimization of fermentation conditions, and extraction of secondary metabolites for the biocontrol of Rhizoctonia Solani AG-3

ABSTRACTIn this study a strain of Streptomyces sp. was isolated from soil and identified by 16S rRNA gene sequencing technology. The strain was screened for antibiotics production effective against biocontrol of Rhizoctonia solani AG-3 to cure the target spot disease in tobacco. For enhance production of secondary metabolites, central composite design of response surface methodology (RSM) was applied in submerged fermentation. The maximum metabolite production was using medium volume of 55 mL in 250 mL flask, agitation speed of 165 rpm, incubation temperature 30 °C, initial medium pH of 6.8 and inoculum size of 7%. Solvent extraction method was used to extract the secondary metabolites and active compounds were purified by silica gel column chromatography. The purified fractions were further investigated by gas chromatography-mass spectrophotometer (GC-MS). GC-MS analysis showed 48 compounds, among them 12 were active against pathogen. These findings indicated that the strain Streptomyces TA 1123 was a potential antagonist against R. solani AG-3.

Efficacy and safety of generic azoxystrobin at controlling Rhizoctonia solani in sugar beet

Rhizoctonia solani Kühn is a major soil-borne pathogen limiting sugar beet (Beta vulgaris L.) production in the United States and other countries worldwide. There is no commercial cultivar which is immune from infection by R. solani and highly resistant cultivars typically have a yield penalty. Growers use cultivars with some levels of resistance and rely on the timely application of fungicides to control R. solani. Azoxystrobin (Quadris®) has been the most widely used fungicide for control of R. solani on sugar beet since its registration in the United States in 1997. In 2015, growers wanted to know whether generic azoxystrobin, which became available on the market and at a lower price than Quadris®, would provide effective control of R. solani. The objectives of this greenhouse study were to evaluate the efficacy and safety of generic azoxystrobins at controlling R. solani on sugar beet compared to the industry's standard Quadris. Three generic azoxystrobins – Satori®, Aframe™ and Equation™ - and two application methods - in-furrow at planting and band applications to 4-leaf stage sugar beet - were evaluated. Inoculation with R. solani AG 2-2IIIB was done after fungicide applications. To check for phytotoxicity, fungicides were applied but with mock inoculation. Plant survivors, plant height, root weight and disease severity were evaluated. Results indicated that the generic azoxystrobins were safe to use on sugar beet seeds and plants and provided similar disease control of R. solani as the industry's standard Quadris treatment. This study demonstrated under greenhouse conditions that Satori®, Aframe™ and Equation™ have the potential to be used by growers for disease management in sugar beet fields with a history of R. solani.

Genetic Characterization and Pathogenicity of Rhizoctonia solani Associated with Common Bean Web Blight in the Main Bean Growing area of Argentina

AbstractCommon bean web blight (WB), caused by the fungus Rhizoctonia solani (teleomorph Thanatephorus cucumeris), is among the endemic fungal diseases of major impact in north‐western Argentina (NWA). This study aimed to analyse the genetic and pathogenic diversity of R. solani in Salta, NWA, where 97 isolates were recovered from commercial bean cultivars and wild beans showing WB symptoms in a major bean production area. The isolates were characterized on the basis of specific primers, rDNA‐ITS sequences and morphological characteristics. All the isolates were identified as R. solani AG 2‐2WB, and they exhibited considerable intragroup variation. The phylogenetic tree generated with the ITS sequences confirmed the isolates identification. Aggressiveness of the isolates towards bean seedlings was assessed in the greenhouse. A great variability in virulence was observed among the isolates analysed. On the basis of the disease reaction on foliar tissues, the isolates were grouped into three virulence categories as follows: weakly virulent (30%), moderately virulent (38%) and highly virulent (32%). However, no correlation between virulence and geographical origin was detected. The information generated in this study provides initial data on the population variability of the WB pathogen in north‐western Argentina and represents a valuable contribution to regional breeding programmes aimed to obtain cultivars with durable resistance.

Sensitivity of Rhizoctonia solani AG-2-2 from Sugar Beet to Fungicides.

Rhizoctonia damping-off and crown and root rot caused by Rhizoctonia solani are major diseases of sugar beet (Beta vulgaris L.) worldwide, and growers in the United States rely on fungicides for disease management. Sensitivity of R. solani to fungicides was evaluated in vitro using a mycelial radial growth assay and by evaluating disease severity on R. solani AG 2-2 inoculated plants treated with fungicides in the greenhouse. The mean concentration that caused 50% mycelial growth inhibition (EC50) values for baseline isolates (collected before the fungicides were registered for sugar beet) were 49.7, 97.1, 0.3, 0.2, and 0.9 μg ml-1 and for nonbaseline isolates (collected after registration and use of fungicides) were 296.1, 341.7, 0.9, 0.2, and 0.6 μg ml-1 for azoxystrobin, trifloxystrobin, pyraclostrobin, penthiopyrad, and prothioconazole, respectively. The mean EC50 values of azoxystrobin, trifloxystrobin, and pyraclostrobin significantly increased in the nonbaseline isolates compared with baseline isolates, with a resistant factor of 6.0, 3.5, and 3.0, respectively. Frequency of isolates with EC50 values >10 μg ml-1 for azoxystrobin and trifloxystrobin increased from 25% in baseline isolates to 80% in nonbaseline isolates. Although sensitivity of nonbaseline isolates of R. solani to quinone outside inhibitors decreased, these fungicides at labeled rates were still effective at controlling the pathogen under greenhouse conditions.

Role of phenazines and cyclic lipopeptides produced by pseudomonas sp. CMR12a in induced systemic resistance on rice and bean.

Pseudomonas sp. CMR12a produces two different classes of cyclic lipopeptides (CLPs) (orfamides and sessilins), which all play a role in direct antagonism against soilborne pathogens. Here we show that Pseudomonas sp. CMR12a is also able to induce systemic resistance to Magnaporthe oryzae on rice and to the web blight pathogen Rhizoctonia solani AG2-2 on bean. Plant assays with biosynthesis mutants of Pseudomonas sp. CMR12a impaired in the production of phenazines and/or CLPs and purified metabolites revealed that distinct bacterial determinants are responsible for inducing systemic resistance in these two pathosystems. In rice, mutants impaired in phenazine production completely lost their ability to induce systemic resistance, while a soil drench with pure phenazine-1-carboxamide (PCN) at a concentration of 0.1 or 1 μM was active in inducing resistance against M. oryzae. In bean, mutants that only produced phenazines, sessilins or orfamides were still able to induce systemic resistance against Rhizoctonia web blight, but a balanced production of these metabolites was needed. This study not only shows that Pseudomonas sp. CMR12a can protect rice to blast disease and bean to web blight disease, but also displays that the determinants involved in induced systemic resistance are plant, pathogen and concentration dependent.

Evidência de que o fungo Rhizoctonia solani AG-1 IA adaptado à Urochloa na Colômbia mantém ampla gama de hospedeiros incluindo o milho

RESUMO O fungo Rhizoctonia solani grupo de anastomose AG-1 IA emergiu como patógeno importante associado à queima foliar, podridão do coleto e morte de pastagens do gênero Urochloa (braquiária) na América do Sul. Neste estudo objetivou-se determinar se a adaptação de R. solani AG-1 IA à Urochloa spp. na Colômbia promoveu diferenças fenotípicas de agressividade a hospedeiros distintos. Testou-se a hipótese de que as populações do patógeno adaptadas à Urochloa não são hospedeiro-especializadas e, desta forma, não estão geneticamente isoladas, mantendo assim ampla gama de hospedeiros, incluindo as fabáceas feijão caupi e soja. Determinou-se, também, se dois grupos de isolados obtidos de populações de R. solani AG-1 IA amostradas de Urochloa na Colômbia tinham potencial adaptativo para emergir como patógeno do milho. Além do nível de agressividade da doença em diferentes hospedeiros, determinou-se os componentes de evolutibilidade como o coeficiente de variância genotípica (IG), de variância ambiental (IE) e a herdabilidade (h2). Concluiu-se que: i) A adaptação de R. solani AG-1 IA à Urochloa spp. não promoveu diferenças fenotípicas de agressividade em hospedeiros distintos e, desta forma, o patógeno mantêm ampla gama de hospedeiros; ii) A população de R. solani AG-1 IA de Urochloa híbrido Mulato da Colômbia tem potencial adaptativo para emergir como patógeno do milho.

Bacillus amyloliquefaciens SB14 from rhizosphere alleviates Rhizoctonia damping-off disease on sugar beet

The use of biocontrol strains recently has become a popular alternative to conventional chemical treatments. A set of bacteria isolated from sugar beet rhizosphere and from roots and shoots of apple and walnut were evaluated for their potential to control sugar beet seedling damping-off caused by R. solani AG-4 and AG2-2.The results of in vitro assays concluded that three isolates, SB6, SB14, SB15, obtained from rhizosphere of sugar beet and five isolates, AP2, AP4, AP6, AP7, AP8, obtained from shoots and roots of apple were the most effective antagonists that inhibited the mycelial growth of both R. solani isolates. Combination of several biochemical tests and partial sequencing of 16S rRNA and gyrBgenes revealed that eight efficient bacterial isolates could be assigned to the genus Bacillus and all could tolerate high temperatures and salt concentrations in their vegetative growth. The potential biocontrol activity of the eight bacterial antagonists were tested in greenhouse condition. The results indicated that four strains,B. amyloliquefaciens SB14, B. pumilus SB6,B. siamensis AP2 and B. siamensisAP8 exerted a significant influence on controlling of seedling damping-off and performed significantly better than others.However, the treatment of the seeds with bacteria was most effective when the isolate SB14 was used, which significantly controlled damping-off disease by 58% caused by R. solani AG-4 and by 52.5% caused by R. solani AG-2-2. This indicates that the use of beneficial bacterial native to the host plant may increase the success rate in screening biocontrols, because these microbes are likely to be better adapted to their host and its associated environmental conditions than are strains isolated from other plant species grown in different environmental conditions. We can infer from the results reported here that sugar beet plantsmay recruitbeneficial microbes to the rhizosphere to help them solve context-specific challenges.

Carbon Source-Dependent Effects of Anaerobic Soil Disinfestation on Soil Microbiome and Suppression of Rhizoctonia solani AG-5 and Pratylenchus penetrans.

The effect of carbon source on efficacy of anaerobic soil disinfestation (ASD) toward suppression of apple root infection by Rhizoctonia solani AG-5 and Pratylenchus penetrans was examined. Orchard grass (GR), rice bran (RB), ethanol (ET), composted steer manure (CM), and Brassica juncea seed meal (SM) were used as ASD carbon inputs, with plant assays conducted in natural and pasteurized orchard soils. Subsequent studies investigated the effect of GR application rate used in ASD on control of these pathogens. In general, apple root infection by R. solani AG-5 was significantly lower in ET, GR, RB, and SM ASD treatments compared with the control. Among different ASD treatments, apple seedling growth was significantly greater when GR or SM was used as the carbon input relative to all other ASD treatments. R. solani AG-5 DNA abundance was significantly reduced in all ASD treatments, regardless of amendment type, compared with the control. In independent experiments, ASD-GR was consistently superior to ASD-CM for limiting pathogen activity in soils. ASD treatment with a grass input rate of 20 t ha(-1) provided superior suppression of P. penetrans but grass application rate did not affect ASD efficacy in control of R. solani AG-5. The soil microbiome from ASD-GR-treated soils was clearly distinct from the control and ASD-CM-treated soils. In contrast, composition of the microbiome from control and ASD-CM-treated soils could not be differentiated. Comparative results from pasteurized and nonpasteurized soils suggest that there is potential for GR based ASD treatment to recruit microbial elements that persist over the anaerobic phase of soil incubation, which may functionally contribute to disease suppression. When ASD was conducted with GR, microbial diversity was markedly reduced relative to the control or ASD-CM soil suggesting that this parameter, typically associated with system resilience, was not instrumental to the function of ASD-induced soil suppressiveness.

Comprehensive analysis of microRNA-Seq and target mRNAs of rice sheath blight pathogen provides new insights into pathogenic regulatory mechanisms.

MicroRNAs (miRNAs) are ∼22 nucleotide non-coding RNAs that regulate gene expression by targeting mRNAs for degradation or inhibiting protein translation. To investigate whether miRNAs regulate the pathogenesis in necrotrophic fungus Rhizoctonia solani AG1 IA, which causes significant yield loss in main economically important crops, and to determine the regulatory mechanism occurring during pathogenesis, we constructed hyphal small RNA libraries from six different infection periods of the rice leaf. Through sequencing and analysis, 177 miRNA-like small RNAs (milRNAs) were identified, including 15 candidate pathogenic novel milRNAs predicted by functional annotations of their target mRNAs and expression patterns of milRNAs and mRNAs during infection. Reverse transcription-quantitative polymerase chain reaction results for randomly selected milRNAs demonstrated that our novel comprehensive predictions had a high level of accuracy. In our predicted pathogenic protein-protein interaction network of R. solani, we added the related regulatory milRNAs of these core coding genes into the network, and could understand the relationships among these regulatory factors more clearly at the systems level. Furthermore, the putative pathogenic Rhi-milR-16, which negatively regulates target gene expression, was experimentally validated to have regulatory functions by a dual-luciferase reporter assay. Additionally, 23 candidate rice miRNAs that may involve in plant immunity against R. solani were discovered. This first study on novel pathogenic milRNAs of R. solani AG1 IA and the recognition of target genes involved in pathogenicity, as well as rice miRNAs, participated in defence against R. solani could provide new insights into revealing the pathogenic mechanisms of the severe rice sheath blight disease.

De novo Transcriptome Analysis of Rhizoctonia solani AG1 IA Strain Early Invasion in Zoysia japonica Root.

Zoysia japonica brown spot was caused by necrotrophic fungus Rhizoctonia solani invasion, which led to severe financial loss in city lawn and golf ground maintenance. However, little was known about the molecular mechanism of R. solani pathogenicity in Z. japonica. In this study we examined early stage interaction between R. solani AG1 IA strain and Z. japonica cultivar “Zenith” root by cell ultra-structure analysis, pathogenesis-related proteins assay and transcriptome analysis to explore molecular clues for AG1 IA strain pathogenicity in Z. japonica. No obvious cell structure damage was found in infected roots and most pathogenesis-related protein activities showedg a downward trend especially in 36 h post inoculation, which exhibits AG1 IA strain stealthy invasion characteristic. According to Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) database classification, most DEGs in infected “Zenith” roots dynamically changed especially in three aspects, signal transduction, gene translation, and protein synthesis. Total 3422 unigenes of “Zenith” root were predicted into 14 kinds of resistance (R) gene class. Potential fungal resistance related unigenes of “Zenith” root were involved in ligin biosynthesis, phytoalexin synthesis, oxidative burst, wax biosynthesis, while two down-regulated unigenes encoding leucine-rich repeat receptor protein kinase and subtilisin-like protease might be important for host-derived signal perception to AG1 IA strain invasion. According to Pathogen Host Interaction (PHI) database annotation, 1508 unigenes of AG1 IA strain were predicted and classified into 37 known pathogen species, in addition, unigenes encoding virulence, signaling, host stress tolerance, and potential effector were also predicted. This research uncovered transcriptional profiling during the early phase interaction between R. solani AG1 IA strain and Z. japonica, and will greatly help identify key pathogenicity of AG1 IA strain.

The impacts of natural antioxidants on sclerotial differentiation and development in Rhizoctonia solani AG-1 IA

Rhizoctonia solani AG-1 IA, the pathogen of rice sheath blight (RSB), causes severe economic losses in all rice-growing countries or regions. The sclerotia produced by R. solani AG-1 IA play an important role in the disease cycle of RSB. In this study, the influences of three natural antioxidants (quercetin, morin and catechol) on sclerotial differentiation and development in R. solani AG-1 IA were investigated. Our results showed that quercetin, morin and catechol at lower concentration caused significant inhibitory effects on sclerotial differentiation as compared with thiourea, one of the most commonly used synthetic antioxidants and an effective inhibitor of sclerotial differentiation reported previously. Specifically, 0.30 mmol/L quercetin, 0.50 mmol/L morin and 1.80 mmol/L catechol resulted in 15 days, 11 days and 7 days delay of sclerotial differentiation, respectively; 0.14 mmol/L quercetin, 0.17 mmol/L morin and 1.00 mmol/L catechol caused 45 %, 32 %, and 33 % decrease of sclerotial dry weights, respectively, when compared with the untreated control. These potent antioxidative effects demonstrate that natural antioxidants have obvious advantages over the commonly used synthetic antioxidant, thiourea. Thus, natural antioxidants may have great potentials in effectively controlling RSB and related plant diseases caused by other sclerotium-producing fungi. In addition, our results also provide strong evidences to support the theory that sclerotial differentiation in sclerotium-producing fungi is induced by oxidative stress.

Proteomic Investigation of Rhizoctonia solani AG 4 Identifies Secretome and Mycelial Proteins with Roles in Plant Cell Wall Degradation and Virulence.

Rhizoctonia solani AG 4 is a soilborne necrotrophic fungal plant pathogen that causes economically important diseases on agronomic crops worldwide. This study used a proteomics approach to characterize both intracellular proteins and the secretome of R.solani AG 4 isolate Rs23A under several growth conditions, the secretome being highly important in pathogenesis. From over 500 total secretome and soluble intracellular protein spots from 2-D gels, 457 protein spots were analyzed and 318 proteins positively matched with fungal proteins of known function by comparison with available R.solani genome databases specific for anastomosis groups 1-IA, 1-IB, and 3. These proteins were categorized to possible cellular locations and functional groups and for some proteins their putative roles in plant cell wall degradation and virulence. The majority of the secreted proteins were grouped to extracellular regions and contain hydrolase activity.

Biosynthesis, Chemical Structure, and Structure-Activity Relationship of Orfamide Lipopeptides Produced by Pseudomonas protegens and Related Species.

Orfamide-type cyclic lipopeptides (CLPs) are biosurfactants produced by Pseudomonas and involved in lysis of oomycete zoospores, biocontrol of Rhizoctonia and insecticidal activity against aphids. In this study, we compared the biosynthesis, structural diversity, in vitro and in planta activities of orfamides produced by rhizosphere-derived Pseudomonas protegens and related Pseudomonas species. Genetic characterization together with chemical identification revealed that the main orfamide compound produced by the P. protegens group is orfamide A, while the related strains Pseudomonas sp. CMR5c and CMR12a produce orfamide B. Comparison of orfamide fingerprints led to the discovery of two new orfamide homologs (orfamide F and orfamide G) in Pseudomonas sp. CMR5c. The structures of these two CLPs were determined by nuclear magnetic resonance (NMR) and mass spectrometry (MS) analysis. Mutagenesis and complementation showed that orfamides determine the swarming motility of parental Pseudomonas sp. strain CMR5c and their production was regulated by luxR type regulators. Orfamide A and orfamide B differ only in the identity of a single amino acid, while orfamide B and orfamide G share the same amino acid sequence but differ in length of the fatty acid part. The biological activities of orfamide A, orfamide B, and orfamide G were compared in further bioassays. The three compounds were equally active against Magnaporthe oryzae on rice, against Rhizoctonia solani AG 4-HGI in in vitro assays, and caused zoospore lysis of Phytophthora and Pythium. Furthermore, we could show that orfamides decrease blast severity in rice plants by blocking appressorium formation in M. oryzae. Taken all together, our study shows that orfamides produced by P. protegens and related species have potential in biological control of a broad spectrum of fungal plant pathogens.

Host And Temperature Preferensce, Male Occurrence And Morfomentrics Offungivorous Nematode, Aphelenchus Avenae Isolates From Japan

ABSTRACT. Host and temperature preference, male accurrence, and morfomentrics of 39 isolates of Apehelenchus avenae were investigated. Of the 39 isolates, 33 were from 7 sistrict of Kyushu, 3 preference were investigated on 4 species of fungi; Botrytis cinerea, Rhizoctonia solani AG-4, Fusarium oxysporum f. sp. Melonis, and Pyitum aphanidermatum growing on 1/5 strength PDA medium. The nematodes were incubated on respective fungus mat for 30 days at 25 and 30 OC host fungi and temperatures gave rise to various levels of reproduction and male accurance. The isolates were divided into 5 groups based on their reproductivity on their host fungi at the 2 temperature regimes. Most of the isolates of A. avenae progated themselves at 25 0C on B. cinera and R. solani AG-4, was 60.850 given by Nagasaki isolates (NA3). The maximum multiplication 48.420 at 0C accured on R. solani byu Kagoshima isiolate (KA3). The occurrence of males was very low in all isolates and it occurred only at 30 0C. De Man’s value of body dimension were measured and showed no significant variation among the isolates. Besides, There were no realtions between groupings by host preference and by body dimension.

Molecular Characterization, Morphological Characteristics, Virulence, and Geographic Distribution of Rhizoctonia spp. in Washington State.

Rhizoctonia root rot and bare patch, caused by Rhizoctonia solani anastomosis group (AG)-8 and R. oryzae, are chronic and important yield-limiting diseases of wheat and barley in the Inland Pacific Northwest (PNW) of the United States. Major gaps remain in our understanding of the epidemiology of these diseases, in part because multiple Rhizoctonia AGs and species can be isolated from the same cereal roots from the field, contributing to the challenge of identifying the causal agents correctly. In this study, a collection totaling 498 isolates of Rhizoctonia was assembled from surveys conducted from 2000 to 2009, 2010, and 2011 over a wide range of cereal production fields throughout Washington State in the PNW. To determine the identity of the isolates, PCR with AG- or species-specific primers and/or DNA sequence analysis of the internal transcribed spacers was performed. R. solani AG-2-1, AG-8, AG-10, AG-3, AG-4, and AG-11 comprised 157 (32%), 70 (14%), 21 (4%), 20 (4%), 1 (0.2%), and 1 (0.2%), respectively, of the total isolates. AG-I-like binucleate Rhizoctonia sp. comprised 44 (9%) of the total; and 53 (11%), 80 (16%), and 51 (10%) were identified as R. oryzae genotypes I, II, and III, respectively. Isolates of AG-2-1, the dominant Rhizoctonia, occurred in all six agronomic zones defined by annual precipitation and temperature within the region sampled. Isolates of AG-8 also were cosmopolitan in their distribution but the frequency of isolation varied among years, and they were most abundant in zones of low and moderate precipitation. R. oryzae was cosmopolitan, and collectively the three genotypes comprised 37% of the isolates. Only isolates of R. solani AG-8 and R. oryzae genotypes II and III (but not genotype I) caused symptoms typically associated with Rhizoctonia root rot and bare patch of wheat. Isolates of AG-2-1 caused only mild root rot and AG-I-like binucleate isolates and members of groups AG-3, AG-4, and AG-11 showed only slight or no discoloration of the roots. However, all isolates of AG-2-1 caused severe damping-off of canola, resulting in 100% mortality. Isolates of Rhizoctonia AG-8, AG-2-1, AG-10, AG-I-like binucleate Rhizoctonia, and R. oryzae genotypes I, II, and III could be distinguished by colony morphology on potato dextrose agar, by PCR with specific primers, or by the type and severity of disease on wheat and canola seedlings, and results of these approaches correlated completely. Based on cultured isolates, we also identified the geographic distribution of all of these Rhizoctonia isolates in cereal-based production systems throughout Washington State.

Population genetic structure of Rhizoctonia solani AG 3-PT from potatoes in South Africa

Rhizoctonia solani AG 3-PT is an important potato pathogen causing significant yield and quality losses in potato production. However, little is known about the levels of genetic diversity and structure of this pathogen in South Africa. A total of 114 R. solani AG 3-PT isolates collected from four geographic regions were analysed for genetic diversity and structure using eight microsatellite loci. Microsatellite analysis found high intra-population genetic diversity, population differentiation and evidence of recombination. A total of 78 multilocus genotypes were identified with few shared among populations. Low levels of clonality (13–39 %) and high levels of population differentiation were observed among populations. Most of the loci were in Hardy–Weinberg equilibrium and all four populations showed evidence of a mixed reproductive mode of both clonality and recombination. The PCoA clustering method revealed genetically distinct geographic populations of R. solani AG 3-PT in South Africa. This study showed that populations of R. solani AG 3-PT in South Africa are genetically differentiated and disease management strategies should be applied accordingly. This is the first study of the population genetics of R. solani AG 3-PT in South Africa and results may help to develop knowledge-based disease management strategies.