Screening for fluorescent pseudomonades,isolated from the rhizosphere of tomato,for antagonistic activity toward <Emphasis Type="Italic">Clavibacter michiganensis</Emphasis> subsp<Emphasis Type="Italic">. michiganensis</Emphasis>

Bacterial canker of tomato, caused by Clavibacter michiganensis subsp. michiganensis, continues to be a problem for tomato growers in the Souss-Massa Draa valley, South of Morocco. Assuming that biological control is an alternative for the management of this disease, a total of 303 fluorescent pseudomonads strains isolated from roots and rhizospheric soil of tomato plants were in vitro tested against C. michiganensis subsp. michiganensis. Fluorescent pseudomonads strains which showed the highest antagonistic properties were thereafter investigated for their ability to colonize tomato roots. Our results showed that fluorescent pseudomonads are more represented in rhizospheric soils. However, the most efficient fluorescent pseudomonads isolates were found in the rhizoplane soil and the endorhizosphere. Among 42 spontaneous antibiotic resistant mutants obtained by treatment of the wild-type isolates with five antibiotics (rifampicine, nalidixic acid, ampicilline and chloramphenicol), 28 completely colonized the roots of all tomatoes seedlings used in this investigation. The 42 wild type isolates were then used for in vivo screening with the cotyledon test. Using this test, eight isolates from 42 tested induced a significant decrease of disease incidence and disease symptoms. The eight efficient isolates were then tested for their effectiveness in the protection of tomato plants in pots under greenhouse conditions. Results obtained showed that all tested isolates applied as seed and root treatments reduced significantly (P ≤ 0.001) the incidence of bacterial canker.     

Expression of putative virulence factors in the potato pathogen Clavibacter michiganensis subsp. sepedonicus during infection

The Gram-positive bacterium Clavibacter michiganensis subsp. sepedonicus is the causal agent of bacterial wilt and ring rot of potato. So far, only two proteins have been shown to be essential for virulence, namely a plasmid-encoded cellulase CelA and a hypersensitive response-inducing protein. We have examined the relative expression of CelA and eight putative virulence factors during infection of potato and in liquid culture, using quantitative real-time PCR. The examined putative virulence genes were celB, a cellulase-encoding gene and genes encoding a pectate lyase, a xylanase and five homologues of the Clavibacter michiganensis subsp. michiganensis pathogenicity factor Pat-1 thought to encode a serine protease. Six of the nine assayed genes were up-regulated during infection of potato, including celA, celB, the xylanase gene, and two of the pat genes. The pectate lyase gene showed only slightly elevated expression, whereas three of the five examined pat genes were down-regulated during infection in potato. Interestingly, the two up-regulated pat genes showed a noticeable sequence difference compared to the three down-regulated pat genes. These results reveal several new proteins that are likely to be involved in Clavibacter michiganensis subsp. sepedonicus pathogenicity.     

Molecular characterisation of Fusarium oxysporum causing rot diseases in small cardamom (Elettaria cardamomum Maton)

Incidence of root rot and foliar yellowing, rhizome rot, panicle wilt and stem rot diseases of small cardamom (Elettaria cardamomum Maton) are caused by Fusarium oxysporum Schlecht., and were surveyed in the high ranges of Idukki district, Kerala during 2010–2011. The diseases were noticed in different areas to varying degrees. Root rot was found to be most severe, followed by pseudostem rot, rhizome rot and panicle wilt. The Fusarium infections were prevalent throughout the year (January–December) and varied from 1.5 to 10.6%. Even though the pathogen was isolated from different plant parts, during pathogenicity studies, all the isolates could cross-infect other plant parts too. Twenty different isolates of F. oxysporum were obtained from diseased samples, and five morphologically distinct isolates were analysed with Randomly Amplified Polymorphic DNA (RAPD) markers to study the genetic variability, if any, among them. PCR amplification of total genomic DNA with random oligonucleotide primers generated unique banding patterns, depending upon primers and isolates. Nine oligunucleotide primers were selected for the RAPD assays, which resulted in 221 bands for the five isolates of F. oxysporum. The number of bands obtained was entered into an NTSYS, and the results showed moderate genetic variability among F. oxysporum isolates causing root rot, rhizome rot, panicle wilt and pseudostem rot, collected from different locations. The dendrogram of different isolates into groups resulted in one major cluster at 0.61 similarity index comprising of four isolates (CRT 3, CRR 3, CPW 2 and CSR 1) and one isolate (CRT 5) formed in a separate cluster. Among the five isolates of F. oxysporum, CRT 5 was entirely different from the other four isolates. The isolates also differ according to the geographical area, as revealed from the genetic variability observed in different root rot isolates (CRT 3 and CRT 5). It is inferred that despite moderate variability, F. oxysporum, infecting small cardamom in Idukki district of Kerala, consists of a single clonal lineage.     

Pectolytic Bacteria Associated with Soft Rot of Calla Lily (Zantedeschia spp.) Tubers

Soft rot is the most important disease on calla lily in Poland. The isolation of the presumptive pathogen from symptomatic tubers on nutrient agar yielded bacteria with different colony morphology. Of 41 isolates collected, 10 showed pectolytic activity on crystal violet pectate medium and caused soft rot on potato slices. All pectolytic bacteria appeared to be Gram‐negative rods producing typical soft rot on inoculated leaf petioles of calla lily. Bacteria with colonies which morphologically resembled those used for inoculation were re‐isolated from diseased petioles. Their identification was based on phenotypic characters and sequence of the gene fragment coding 16S rRNA. It was found that, in addition to Pectobacterium carotovorum subsp. carotovorum, soft rot of calla lily can be caused by Pectobacterium carotovorum subsp. atrosepticum, Pseudomonas marginalis, Pseudomonas veronii and Chryseobacterium indologenes. The latter two are described for the first time as plant pathogens. The pectolytic activity of all identified bacteria, except that of P. carotovorum subsp. atrosepticum, was lower than that of P. carotovorum subsp. carotovorum, but strains of P. veronii showed a higher activity than P. marginalisand C. indologenes species.     

Biocontrol of bacterial soft rot of calla lily by elicitor HarpinXoo and N-acyl homoserine lactonase (AttM)

Bacterial soft rot caused by Pectobacterium carotovorum subsp. carotovorum is a serious plant disease in Zantedeschia spp. (also called calla lily). In this study, two independent genes (a N-acyl homoserine lactonase gene attM from Agrobacterium tumefaciens and a hypersensitive response and pathogenicity gene hrf1 from Xanthomonas oryzae pv. oryzae), transcribed by a strong and constitutive Escherichia coli promoter P _lpp , respectively, were cloned into plasmid pUC19, and was transformed into E. coli, creating strain JM109/pPHA. The result of sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS–PAGE) assay showed that both genes (hrf1 and attM) were successfully expressed in one plasmid system in strain JM109/pPHA. The expressed Harpin_Xoo (Hrf1) and AttM protein had the ability of inducing hypersensitive response (HR) in nonhost tobacco and degrading the N-acyl homoserine lactones (AHLs) produced by P. carotovorum subsp. carotovorum, respectively, whereas Harpin_Xoo and AttM protein did not seem to interfere with the normal growth of this pathogen. In planta, strain JM109/pPHA could significantly reduce the soft rot disease severity on dormant tubers (control efficiency: 92.8%) or potted plants (control efficiency: 92.4%) of calla lily. We have first demonstrated the both biocontrol effects of Harpin_Xoo and AttM proteins (also described as Quorum interference) on the bacterial soft rot disease of calla lily, caused by P. carotovorum subsp. carotovorum. This work provided a potential way to control this serious plant disease.     

Colonization of peanut roots by biofilm-forming Paenibacillus polymyxa initiates biocontrol against crown rot disease

Aim: To investigate the role of biofilm‐forming Paenibacillus polymyxa strains in controlling crown root rot disease. Methods and Results: Two plant growth‐promoting P. polymyxa strains were isolated from the peanut rhizosphere, from Aspergillus niger‐suppressive soils. The strains were tested, under greenhouse and field conditions for inhibition of the crown root rot pathogen of the peanut, as well as for biofilm formation in the peanut rhizosphere. The strains’ colonization and biofilm formation were further studied on roots of the model plant Arabidopsis thaliana and with solid surface assays. Their crown root rot inhibition performance was studied in field and pot experiments. The strains’ ability to form biofilms in gnotobiotic and soil systems was studied employing scanning electron microscope. Conclusion: Both strains were able to suppress the pathogen but the superior biofilm former offers significantly better protection against crown rot. Significance and Impact of the Study: The study highlights the importance of efficient rhizosphere colonization and biofilm formation in biocontrol.     

Bacillus subtilis subsp. spizizenii MB29 controls alfalfa root rot caused by Fusarium semitectum

Medicago sativa L. is the most important forage legume in China. Reducing production losses caused by disease is an essential aspect of maximising alfalfa production. In the current study a Fusarium semitectum isolate collected from alfalfa roots exhibiting symptoms of root rot was proven to infect alfalfa by fulfilling Koch's postulates. A bacterial strain, MB29, also collected from alfalfa roots, was evaluated as a potential biocontrol agent against F. semitectum and a range of other alfalfa pathogens using in vitro tests. It was found that MB29 reduced the mycelia growth of all the pathogens assessed, and in the case of F. semitectum by as much as 84.47%. Furthermore, in vivo test showed that MB29 reduced the severity of rot symptoms in alfalfa seedlings resulting from F. semitectum infection. Strain MB29 was subsequently classified as Bacillus subtilis subsp. spizizenii using the Biolog MicroLog microbial identification system and sequence analysis of its 16S rDNA gene. Taken together these results indicate that B. subtilis subsp. spizizenii MB29 has great potential for the control of root rot diseases in alfalfa.     

Development of a PCR test for the detection of Curtobacterium flaccumfaciens pv. flaccumfaciens

A chromosomal DNA library of the bacterial pathogen of bean, Curtobacterium flaccumfaciens pv. flaccumfaciens NCPPB 559 was constructed in the plasmid pGEM-7Zf(+). Several clones were identified that hybridised to all Curtobacterium flaccumfaciens pathovars including: C. f. betae, C. f. flaccumfaciens, C. f. oortii, C. f. poinsettiae and, in addition, to some strains of Clavibacter michiganensis subsp. insidiosus and Clavibacter michiganensis subsp. One of these clones (pPMP-26), after subsequent digestion with restriction endonucleases EcoRI/SacI, yielded a fragment of approximately 0.2 Kb (pPMP-26D) that hybridised specifically to C. f. flaccumfaciens and not to any of the other plant pathogenic members of the order Actinomycetales or any of the other prokaryotic bean pathogens tested. This fragment was subcloned and sequenced, analysis of the resultant 198 bp sequence showed that no significant homology existed with any other sequence currently deposited in public databases. Further analysis of these data facilitated the design of PCR primers which were subsequently tested against a wide range of plant pathogenic actinomycetes and other prokaryotic bean pathogens. Results show that these primers are highly specific for all strains of C. f. flaccumfaciens with no cross-reaction to strains from any other bacterial taxa tested.     

Influence of Seed‐borne Cochliobolus sativus (Anamorph Bipolaris sorokiniana) on Crown Rot and Root Rot of Barley and Wheat

The effect of seed‐borne pathogens of wheat and barley on crown and root rot diseases of seven barley cultivars (Jimah‐6, Jimah‐51, Jimah‐54, Jimah‐58, Omani, Beecher and Duraqi) and three wheat cultivars (Cooley, Maissani and Shawarir) was investigated. Bipolaris sorokiniana and Alternaria alternata were detected in seeds of at least eight cultivars, but Fusarium species in seeds of only two barley cultivars (Jimah‐54 and Jimah‐58). Crown rot and root rot symptoms developed on barley and wheat cultivars following germination of infected seeds in sterilized growing media. Bipolaris sorokiniana was the only pathogen consistently isolated from crowns and roots of the emerging seedlings. In addition, crown rot and root rot diseases of non‐inoculated barley cultivars correlated significantly with B. sorokiniana inoculum in seeds (P = 0.0019), but not with Fusarium or Alternaria (P > 0.05). These results indicate the role of seed‐borne inoculum of B. sorokiniana in development of crown rot and root rot diseases. Pathogenicity tests of B. sorokiniana isolates confirmed its role in inducing crown rot and root rot, with two wheat cultivars being more resistant to crown and root rots than most barley cultivars (P < 0.05). Barley cultivars also exhibited significant differences in resistance to crown rot (P < 0.05). In addition, black point disease symptoms were observed on seeds of three barley cultivars and were found to significantly affect seed germination and growth of some of these cultivars. This study confirms the role of seed‐borne inoculum of B. sorokiniana in crown and root rots of wheat and barley and is the first report in Oman of the association of B. sorokiniana with black point disease of barley.     

In vitro antimicrobial effect of metallic nanoparticles on phytopathogenic strains of crop plants

In this research, the in vitro antimicrobial effect of zinc oxide (ZnO), copper oxide (CuO) and iron oxide (Fe₂O₃) nanoparticles (NPs)—with average sizes of 20, 46 and 30 nm, respectively—on the root rot disease caused by the fungus Fusarium oxysporum and on blight disease caused by the fungus Alternaria solani were studied. Also, bacterial diseases caused by Clavibacter michiganensis and Pseudomonas syringae that infects a wide range of plant species were assessed. Different concentrations of NPs (0, 100, 250, 500, 700 and 1,000 mg/L) were prepared on PDA agar or King's B medium in a complete randomized design with four replicates. According to the results, ZnO NPs exhibited an outstanding inhibitory effect against fungi and bacteria strains. The above results were associated with the smaller particle size. Fungi strains showed a differential sensitivity depending on the kind of NPs used. A. solani showed the highest sensitivity to ZnO NPs at 1,000 mg/L (99%), followed by CuO NPs at the same dose (95%). Fe₂O₃ NPs at all evaluated doses had no inhibitory effects on the mycelia growth of this strain, although F. oxysporum revealed greater effectiveness of the CuO NPs (96%) compared with ZnO NPs since it only inhibited 91% of the mycelial growth. The antibacterial activity was studied through optical density. C. michiganensis was found to be more sensitive to ZnO NPs because a lesser dose (700 mg/L) was required to reduce the bacterial growth (90%); in comparison, P. syringae required a dose of 1,000 mg/L to inhibit its growth (67%). CuO NPs displayed the smallest growth inhibition against the bacteria strains analysed. The antimicrobial effect of the metallic NPs that were assayed increased with higher doses.     

Pathogenicity and repulsion for toxin‐producing bacteria of dominant bacteria on the surface of American pine wood nematodes

Bacteria were isolated from the surface of two samples of American pine wood nematodes to identify methods of controlling pine wilt disease. The dominant bacterial strains were identified, and their toxicity and pathogenicity, in addition to their competitiveness with other pathogenic bacteria, were measured to ascertain how bacteria on the surface of American pine wood nematodes might be used to prevent and control pine wilt disease. The bacterial isolates show that the dominant bacteria carried by the two samples of pine wood nematodes are US4, US5, Smal‐007 and Rrad‐006. Based on routine staining, morphological observation and 16S rDNA sequence analysis, the four strains were identified as Delftia lacustris, Pseudomonas putida, Stenotrophomonas maltophilia and Rhizobium nepotum. The incubation of four dominant bacterial strains and Chinese dominant bacterial strains on the surface of aseptic nematodes and in nutrient broth showed that Smal‐007 and Rrad‐006 have strong competitiveness on the surface of pine wood nematodes. Using a bacterial culture medium to measure the propensity of pine seedlings to wilt, all the American dominant bacterial strains were shown to be less toxic than the Chinese dominant strains. If pine seedlings are inoculated with both bacterial and aseptic pine wood nematodes, American dominant bacterial strains present less pathogenicity than the Chinese dominant bacterial strains. In particular, Smal‐007 and Rrad‐006 show the lowest pathogenicity. If pine seedlings are inoculated with both bacterial and wild pine wood nematodes, American dominant bacterial strains significantly reduce the pathogenicity of wild pine wood nematodes isolated from Zhejiang Province, China. The effects of Smal‐007 and Rrad‐006 are confirmed as the most prominent. The American dominant strains Smal‐007 and Rrad‐006 satisfy two main requirements: excellent repulsion performance and low pathogenicity. Therefore, they can be used as candidate strains for biocontrol bacteria.     

Phytophthora cinnamomi Associated with Root and Crown Rot of Walnut in Turkey

Walnut decline caused by Phytophthora sp. occurred in an orchard in Sakarya province in Turkey. Affected young trees showed poor growth, leaf discolouration, root and crown rot and eventual death. A Phytophthora sp. isolated from necrotic taproots and crown tissues. The causal agent of the disease was identified as Phytophthora cinnamomi by morphological characteristics and comparing sequences of internal transcribed spacer (ITS) region. Upon conducting pathogenicity test, averaging 7.8‐cm‐long canker developed on basal stem within 2 weeks, while no cankers developed in the control plants.     

Antimicrobial activities ofStreptomyces pulcher,S. canescens andS. citreofluorescens against fungal and bacterial pathogens of tomatoin vitro

Thirty-seven actinomycete species isolated from fertile cultivated soils in Egypt were screened for the production of antimicrobial compounds against a variety of test organisms. Most of the isolates exhibited antimicrobial activities against Gram-positive, Gram-negative, and acid-fast bacteria, yeasts and filamentous fungi, with special attention to fungal and bacterial pathogens of tomato. On starch-nitrate agar, 14 strains were active againstFusarium oxysporum f.sp.lycopersici (the cause ofFusarium wilt), 18 againstVerticillium albo-atrum (the cause ofVerticillium wilt), and 18 againstAlternaria solani (the cause of early blight). In liquid media, 14 isolates antagonizedPseudomonas solanacearum (the cause of bacterial wilt) and 20 antagonizedClavibacter michiganensis ssp.michiganensis (the cause of bacterial canker). The most active antagonists of the pathogenic microorganisms studied were found to beStreptomyces pulcher, S. canescens (syn.S. albidoflavus) andS. citreofluorescens (syn.S. anulatus). The antagonistic activities ofS. pulcher andS. citreofluorescens against pathogenic bacteria in liquid media under shaking conditions. The optimum culture conditions were determined.     

Isolation,identification, and antifungal activity of a Gamair complex formed by <Emphasis Type="Italic">Bacillus subtilis</Emphasis> M-22, a producer of a biopreparation for plant protection from mycoses and bacterioses

A metabolic complex, Gamair, has been isolated from Bacillus subtilis strain M-22, a producer of a biopreparation for plant protection from diseases of various etiologies. Gamair was shown to possess a broad spectrum of activity against phytopathogenic bacteria (including Pseudomonas corrugata, Erwinia carotovora, Clavibacter michiganensis subsp. michiganensis, and Xantomonas campestris pv. vesicatoria), and fungi (Fusarium, Verticullum, Ascochyta, Colletotrichum, Rhizoctonia, Sclerotinia, Septoria, and other genera). Using NMR and IR spectroscopy, it was shown that the complex of active compounds is a mixture of the following fractions: Gamair A (close to bacillin), and Gamair B-D (mediocin type hexaene-like) antibiotics. The chemical and biological properties of the above fractions were investigated. In field trials using tomato plants, it was demonstrated that the biological efficacy of Gamair against bacterial wilt, stem core necrosis, and vegetable's mild rot reached 70–90%, whereas the harvest increase was 25-35%.     

Biological Control of Phytophthora Root Rots on Alfalfa and Soybean with Streptomyces

A collection of 53 antibiotic-producing Streptomyces isolated from soils from Minnesota, Nebraska, and Washington were evaluated for their ability to inhibit plant pathogenic Phytophthora medicaginis and Phytophthora sojae in vitro. Eight isolates having the greatest pathogen-inhibitory capabilities were subsequently tested for their ability to control Phytophthora root rots on alfalfa and soybean in sterilized vermiculite and naturally infested field soil. The Streptomyces isolates tested significantly reduced root rot severity in alfalfa and soybean caused by P. medicaginis and P. sojae, respectively (P < 0.05). On alfalfa, isolates varied in their effect on plant disease severity, percentage dead plants, and plant biomass in the presence of the pathogen. The same eight isolates of Streptomyces were also tested for inhibitory activities against each other and against three strains of Bradyrhizobium japonicum and two strains of Sinorhizobium meliloti isolated from soybean and alfalfa, respectively. Streptomyces isolates clustered into two major compatibility groups: isolates within the same group were noninhibitory toward one another in vitro. The compatibility groups corresponded with groupings obtained based upon inhibition of B. japonicum and S. meliloti strains.     

Mutability in Pseudomonas viridiflava as a programmed balance between antibiotic resistance and pathogenicity

Mutable bacterial cells are defective in their DNA repair system and often have a phenotype different from that of their wild‐type counterparts. In human bacterial pathogens, the mutable and hypermutable phenotypes are often associated with general antibiotic resistance. Here, we quantified the occurrence of mutable cells in Pseudomonas viridiflava, a phytopathogenic bacterium in the P. syringae complex with a broad host range and capacity to live as a saprophyte. Two phenotypic variants (transparent and mucoid) were produced by this bacterium. The transparent variant had a mutator phenotype, showed general antibiotic resistance and could not induce disease on the plant species tested (bean). In contrast, the mucoid variant did not display mutability or resistance to antibiotics and was capable of inducing disease on bean. Both the transparent and mucoid variants were less fit when grown in vitro, whereas, in planta, both of the variants and wild‐types attained similar population densities. Given the importance of the methyl‐directed mismatch repair system (MMR) in the occurrence of mutable and hypermutable cells in human bacterial pathogens, we investigated whether mutations in mut genes were associated with mutator transparent cells in P. viridiflava. Our results showed no mutations in MMR genes in any of the P. viridiflava cells tested. Here, we report that a high mutation rate and antibiotic resistance are inversely correlated with pathogenicity in P. viridiflava, but are not associated with mutations in MMR. In addition, P. viridiflava variants differ from variants produced by other phytopathogenic bacteria in the absence of reversion to the wild‐type phenotype.     

Monitoring of pathogenic and non‐pathogenic Fusarium oxysporum strains during tomato plant infection

Monitoring of pathogenic strains of Fusarium oxysporum (Fox), which cause wilt and rots on agricultural and ornamental plants, is important for predicting disease outbreaks. Since both pathogenic and non‐pathogenic strains of Fox are ubiquitous and are able to colonize plant roots, detection of Fox DNA in plant material is not the ultimate proof of an ongoing infection which would cause damage to the plant. We followed the colonization of tomato plants by strains Fox f. sp. radicis‐lycopersici ZUM2407 (a tomato foot and root rot pathogen), Fox f. sp. radicis‐cucumerinum V03‐2g (a cucumber root rot pathogen) and Fox Fo47 (a well‐known non‐pathogenic biocontrol strain). We determined fungal DNA concentrations in tomato plantlets by quantitative PCR (qPCR) with primers complementary to the intergenic spacer region (IGS) of these three Fox strains. Two weeks after inoculation of tomato seedlings with these Fox strains, the DNA concentration of Forl ZUM2407 was five times higher than that of the non‐compatible pathogen Forc V03‐2g and 10 times higher than that of Fo47. In 3‐week‐old plantlets the concentration of Forl ZUM2407 DNA was at least 10 times higher than those of the other strains. The fungal DNA concentration, as determined by qPCR, appeared to be in good agreement with data of the score of visible symptoms of tomato foot and root rot obtained 3 weeks after inoculation of tomato with Forl ZUM2407. Our results show that targeting of the multicopy ribosomal operon results in a highly sensitive qPCR reaction for the detection of Fox DNA. Since formae speciales of Fox cannot be distinguished by comparison of ribosomal operons, detection of Fox DNA is not evidence of plant infection by a compatible pathogen. Nevertheless, the observed difference in levels of plant colonization between pathogenic and non‐pathogenic strains strongly suggests that a concentration of Fox DNA in plant material above the threshold level of 0.005% is due to proliferation of pathogenic Fox.     

Pythium and Phytopythium species associated with weeds collected in vegetable production fields in Brazil

This study aimed to identify Pythium and Phytopythium species from weeds collected in vegetable fields and test their pathogenicity. Weeds with symptoms of damping-off, root rot or wilt were sampled in the Brazilian states of Ceará, Goiás and Pernambuco, as well as in the Distrito Federal, for isolation and identification of the causal agents. Once isolated, colonies with typical Pythium and Phytopythium characteristics grew in selective V8 medium. Procedures for species identification included morphology and amplification of the ITS and Cox II regions, which were compared with other accessions available at GenBank. The phylogenetic relationships among the isolates and pathogenicity to their original hosts were evaluated. Six Pythium species were identified: P. aphanidermatum, P. oopapillum, P. orthogonon, P. ultimum var. ultimum, P. myriotylum and P. sylvaticum, and two species of Phytopythium, Phy. chamaehyphon and Phy. oedochilum. In the pathogenicity tests, the 10 weed hosts showed symptoms of damping-off or root rot after inoculation, with exception of Portulaca oleraceae in which none of the isolates was pathogenic. Therefore, common weeds in vegetable fields areas can host different Pythium and Phytopythium species and play an important role in the epidemiology of vegetable diseases, in particular on pathogen survival and population increase.     

First Report of Rhizoctonia solani AG 8 on Wheat in Turkey

A survey was conducted in Ankara and Eskisehir provinces of Turkey for determining anastomosis groups and pathogenicity of Rhizoctonia species associated with root and crown rot of wheat. Pathogenicity tests revealed that Rhizoctonia solani AG 8 caused the common symptoms of damping‐off and stunting.