Fungus Rhizoctonia Solani Research Articles

Effectiveness of Rhizosphere Bacteria for Control of Root Rot Disease and Improving Plant Growth of Wheat (<i>Triticum </i><i>a</i><i>estivum</i> L)

Pathogenic fungus Rhizoctonia solani causes root rot disease in wheat leading to collapsing of the aerial part of the plant. To characterize antagonistic bacteria, one hundred and thirty bacterial isolates were obtained from the rhizosphere soil of wheat and these rhizobacterial isolates alongwith 72 reference strains were screened for their antagonistic interactions against R. solani under cultural conditions. Sixteen bacterial isolates inhibited the growth of R. solani and growth inhibition zone varied from 6-15 mm by different rhizobacterial isolates. Two isolates WPS3 and WPS90 caused maximum growth inhibition of the fungi. Growth inhibiton of the pathogenic fungi was also observed using culture filterates of antagonistic rhizobacterial isolates. The protein estimation of the culture filterates showed that the amount of protein excreted by different rhizobacterial isolates varied from 3.6 to 33.0 mg ml -1 of the supernatant. The loss of antagonistic activity after treatment with proteinase K and high temperature treatment indicated that excreted proteins are responsible for the antagonism. Pot house studies showed that inoculation of R. solani in wheat caused 85-90% root rot disease incidence at 60 to 90 days of plant growth. The single inoculation of rhizobacterial isolate WPS3 resulted in 131% increase of plant dry weight as compared to uninoculated control plants. The coinoculation of isolate WPS3 with R. solani enhanced 115% plant dry weight whereas coinoculation of Pseudomonas isolate WPS90 caused 98% increase in plant dry weight in comparison to control uninoculated plants at 90 days of plant growth. Coinoculation of Pseudomonas isolates WPS3 and WPS90 with R. solani also caused 88.9 and 66.7% disease control, respectively at 90 days of plant growth. Thus, Pseudomonas isolate WPS3 could be further ex- ploited for plant growth improvement under field conditions.

Elucidating the role of the phenylacetic acid metabolic complex in the pathogenic activity of Rhizoctonia solani anastomosis group 3

The soil fungus Rhizoctonia solani produces phytotoxic phenylacetic acid (PAA) and hydroxy (OH-) and methoxy (MeO-) derivatives of PAA. However, limited information is available on the specific role that these compounds play in the development of Rhizoctonia disease symptoms and concentration(s) required to induce a host response. Reports that PAA inhibits the growth of R. solani conflict with the established ability of the fungus to produce and metabolize PAA. Experiments were conducted to clarify the role of the PAA metabolic complex in Rhizoctonia disease. In this study the concentration of PAA and derivatives required to induce tomato root necrosis and stem canker, in the absence of the fungus, and the concentration that inhibits mycelial growth of R. solani were determined. The effect of exogenous PAA and derivatives of PAA on tomato seedling growth also was investigated. Growth of tomato seedlings in medium containing 0.1–7.5 mM PAA and derivatives induced necrosis of up to 85% of root system. Canker development resulted from injection of tomato seedling stems with 7.5 mM PAA, 3-OH-PAA, or 3-MeO-PAA. PAA in the growth medium reduced R. solani biomass, with 50% reduction observed at 7.5 mM. PAA, and derivatives were quantified from the culture medium of 14 isolates of R. solani belonging to three distinct anastomosis groups by GC-MS. The quantities ranged from below the limit of detection to 678 nM, below the concentrations experimentally determined to be phytotoxic. Correlation analyses revealed that isolates of R. solani that produced high PAA and derivatives in vitro also caused high mortality on tomato seedlings. The results of this investigation add to the body of evidence that the PAA metabolic complex is involved in Rhizoctonia disease development but do not indicate that production of these compounds is the primary or the only determinant of pathogenicity.

Population genetic evidence that basidiospores play an important role in the disease cycle of rice‐infecting populations of Rhizoctonia solani AG‐1 IA in Iran

The fungus Rhizoctonia solani AG‐1 IA causes sheath blight, one of the most important rice diseases worldwide. The first objective of this study was to analyse the genetic structure of R. solani AG‐1 IA populations from three locations in the Iranian Caspian Sea rice agroecosystem. Three population samples of R. solani AG‐1 IA isolates were obtained in 2006 from infected rice fields separated by 126–263 km. Each field was sampled twice during the season: at the early booting stage and 45 days later at the early mature grain stage. The genetic structure of these three populations was analysed using nine microsatellite loci. While the population genetic structure from Tonekabon and Amol indicated high gene flow, they were both differentiated from Rasht. The high gene flow between Tonekabon and Amol was probably due mainly to human‐mediated movement of infested seeds. The second objective was to determine the importance of recombination. All three populations exhibited a mixed reproductive mode, including both sexual and asexual reproduction. No inbreeding was detected, suggesting that the pathogen is random mating. The third objective was to determine if genetic structure within a field changes over the course of a growing season. A decrease in the proportion of admixed genotypes from the early to the late season was detected. There was also a significant (P = 0·002) increase in the proportion of loci under Hardy–Weinberg equilibrium. These two lines of evidence support the hypothesis that basidiospores can be a source of secondary inoculum.

Molecular characterization of the pathogenic plant fungus Rhizoctonia solani (Ceratobasidiaceae) isolated from Egypt based on protein and PCR-RAPD profiles

Twenty-one isolates of Rhizoctonia solani were categorized into three anastomosis groups consisting of AG-4-HG-I (eight isolates), AG-2-2 (nine isolates) and AG-5 (four isolates). Their pathogenic capacities were tested on cotton cultivar Giza 86. Pre-emergence damping-off varied in response to the different isolates; however, the differences were not significant. Soluble proteins of the fungal isolates were electrophoresed using SDS-PAGE and gel electrophoreses. A dendrogram of the protein banding patterns by the UPGMA of arithmetic means placed the fungal isolates into distinct groups. There was no evidence of a relationship between protein dendrogram, anastomosis grouping or level of virulence or geographic origin. The dendrogram generated from these isolates based on PCR analysis with five RAPD-PCR primers showed high levels of genetic similarity among the isolates from the same geographical locations. There was partially relationship between the genetic similarity and AGs or level of virulence or geographic origin based on RAPD dendrogram. These results demonstrate that RAPD technique is a useful tool in determining the genetic characterization among isolates of R. solani.

Reaction of faba bean genotypes to Rhizoctonia solani and resistance stability

The production of faba bean (Phaseolus lunatus) is limited due to the occurrence of Rhizoctonia canker, caused by the fungus Rhizoctonia solani. In order to select materials with potential for use in faba beans breeding programs and/or disease integrated management, 72 genotypes were evaluated and also stability of the disease resistance in relation to different pathogen isolates, inoculum densities and soil type. The seeds were sown in soil infested with the pathogen by the addition of colonized substrate (rice grains). The evaluation of genotypes was done after 15 days, using a note scale to discriminate the genotypes into five reaction classes. None of the 72 genotypes showed immunity to R. solani and only four genotypes (F-42, F-49, F-53 and F-58) behaved as highly resistant. The reactions presented by these genotypes varied according to the R. solani isolate, inoculum density and soil used. The genotype F-58 showed more stable resistance to pathogen isolates and inoculum densities. The genotype F-53 showed resistance stability in soils collected in different locations, remaining highly resistant in all situations. The genotype F-58 did not show high resistance to only one tested soil. Therefore, the genotypes F-58 and F-53 are promising sources of resistance to R. solani and should be indicated in areas infested by the pathogen.

Growth Enhancement and Disease Reduction of Soybean by 1-Aminocyclopropane-1-Carboxylate Deaminase-Producing <i>Pseudomonas</i>

Problem statement: 1-Aminocyclopropane-1-Carboxylate (ACC) deaminase-producing bacteria have been known to ameliorate the inhibiti on-effect of increase concentration of ethylene in higher plants, which can be triggered by high conce ntration of indole-3-Acetic Acid (IAA) and/or by the presence of plant pathogens. This study examine d the potential use of Pseudomonas isolates producing ACC deaminase as well as IAA to enhance soybean growth and reduce disease incidence in soil containing pathogenic fungi. Approach: Eleven promising ACC deaminase-producing isolates of Pseudomonas were retested in vitro for their ACC deaminase activity and IAA production and evaluated their potential antagonist against root-nodule bacteria. Non antagonist isolates were further tested for their ability to e nhance soybean growth and reduce disease incidence in sterile and non-sterile soils containing root-pa thogenic fungi Fusarium oxysporum , Sclerotium rolfsii and Rhizoctonia solani . Results: All isolates produced ACC deaminase as well as IAA, but 3 out of 11 isolates inhibited at least one strain of rhizobia which limit their use for soybean. The isolates increased some aspects of soybean growth, but most of the increases were not significantly different from untreated control. Most isolates sig nificantly increased the survival rates of soybean in soil containing pathogenic fungi although their ability to reduce plant weight loss varied across pathogen treatments. Conclusion: The ability of Pseudomonas producing ACC deaminase as well as IAA to increase plant growth was less significan t than that of the isolates to reduce disease incidence. The higher the destructive effect of the pathogens, the better was the ability of the isolates to reduce the disease.

Genetic diversity of Rhizoctonia solani associated with potato tubers in France

The soilborne fungus Rhizoctonia solani is a pathogen of many plants and causes severe damage in crops around the world. Strains of R. solani from the anastomosis group (AG) 3 attack potatoes, leading to great yield losses and to the downgrading of production. The study of the genetic diversity of the strains of R. solani in France allows the structure of the populations to be determined and adapted control strategies against this pathogen to be established. The diversity of 73 French strains isolated from tubers grown in the main potato seed production areas and 31 strains isolated in nine other countries was assessed by phylogenetic analyses of (i) the internal transcribed spacer sequences (ITS1 and ITS2) of ribosomal RNA (rRNA), (ii) a part of the gene tef-1α and (iii) the total DNA fingerprints of each strain established by amplified fragment length polymorphism (AFLP). The determination of the AGs of R. solani based on the sequencing of the ITS region showed three different AGs among our collection (60 AG 3 PT, 8 AG 2-1 and 5 AG 5). Grouping of the strains belonging to the same AG was confirmed by sequencing of the gene tef-1α used for the first time to study the genetic diversity of R. solani. About 42% of ITS sequences and 72% of tef-1α sequences contained polymorphic sites, suggesting that the cells of R. solani strains contain several copies of ITS and the tef-1α gene within the same nucleus or between different nuclei. Phylogenetic trees showed a greater genetic diversity within AGs in tef-1α sequences than in ITS sequences. The AFLP analyses showed an even greater diversity among the strains demonstrating that the French strains of R. solani isolated from potatoes were not a clonal population. Moreover there was no relationship between the geographical origins of the strains or the variety from which they were isolated and their genetic diversity.

Inhibition of Rhizoctonia by endospore forming bacteria indigenous to landscape planting beds

Endospore forming bacteria were collected from root samples of 35 genera of bedding plants growing in established commercial landscape beds in Central Florida. One hundred and twenty-nine bacterial strains associated with 14 species were identified using fatty acid analysis (Microbial Identification System, MIDI). All strains were evaluated for in vitro inhibition of damping off disease caused by the fungus Rhizoctonia solani. The strongest inhibition of Rhizoctonia by soluble exudates in cocultivation was observed with strains belonging to six species: B. cereus, B. pumilus, B. thuringiensis, L. sphaericus, B. amyloliquefaciens, and B. subtilis. Most strains that inhibited Rhizoctonia growth in cocultivation also inhibited growth via volatile compounds. All 129 strains were evaluated for ability to protect impatiens plants from subsequent challenge infection by Rhizoctonia solani. Certain strains of endospore forming bacteria also enhanced plant growth. It is apparent from this study that the Bacillus community associated with bedding plants in established planting beds produce soluble antifungal compounds, volatile antifungal compounds, and enhance plant growth. In developing biological control, it may be a more practical approach to promote or enhance a natural, multifaceted community of Bacillus strains within our planting beds.

The effect of heterogeneity on invasion in spatial epidemics: from theory to experimental evidence in a model system.

Heterogeneity in host populations is an important factor affecting the ability of a pathogen to invade, yet the quantitative investigation of its effects on epidemic spread is still an open problem. In this paper, we test recent theoretical results, which extend the established “percolation paradigm” to the spread of a pathogen in discrete heterogeneous host populations. In particular, we test the hypothesis that the probability of epidemic invasion decreases when host heterogeneity is increased. We use replicated experimental microcosms, in which the ubiquitous pathogenic fungus Rhizoctonia solani grows through a population of discrete nutrient sites on a lattice, with nutrient sites representing hosts. The degree of host heterogeneity within different populations is adjusted by changing the proportion and the nutrient concentration of nutrient sites. The experimental data are analysed via Bayesian inference methods, estimating pathogen transmission parameters for each individual population. We find a significant, negative correlation between heterogeneity and the probability of pathogen invasion, thereby validating the theory. The value of the correlation is also in remarkably good agreement with the theoretical predictions. We briefly discuss how our results can be exploited in the design and implementation of disease control strategies.

Bioactive metabolites from Phoma species, an endophytic fungus from the Chinese medicinal plant Arisaema erubescens

Through bioassay-guided fractionation, the EtOAc extract of a culture broth of the endophytic fungus Phoma species ZJWCF006 in Arisaema erubescens afforded a new α-tetralone derivative, (3S)-3,6,7-trihydroxy-α-tetralone (1), together with cercosporamide (2), β-sitosterol (3), and trichodermin (4). The structures of compounds were established on the basis of spectroscopic analyses. Compounds 1, 2, and 3 were obtained from Phoma species for the first time. Additionally, the compounds were subjected to bioactivity assays, including antimicrobial activity, against four plant pathogenic fungi (Fusarium oxysporium, Rhizoctonia solani, Colletotrichum gloeosporioides, and Magnaporthe oryzae) and two plant pathogenic bacteria (Xanthomonas campestris and Xanthomonas oryzae), as well as in vitro antitumor activities against HT-29, SMMC-772, MCF-7, HL-60, MGC80-3, and P388 cell lines. Compound 1 showed growth inhibition against F. oxysporium and R. solani with EC₅₀ values of 413.22 and 48.5 μg/mL, respectively. Additionally, compound 1 showed no cytotoxicity, whereas compound 2 exhibited cytotoxic activity against the six tumor cell lines tested, with IC₅₀ values of 9.3 ± 2.8, 27.87 ± 1.78, 48.79 ± 2.56, 37.57 ± 1.65, 27.83 ± 0.48, and 30.37 ± 0.28 μM, respectively. We conclude that endophytic Phoma are promising sources of natural bioactive and novel metabolites.

MODELO DE PONTO CRÍTICO PARA ESTIMAR DANOS CAUSADOS PELA MELA NA CULTURA DO FEIJOEIRO

No Equador, o feijão (Phaseolus vulgaris L.) é consumido quase pela totalidade da população, sendo também fonte de renda para pequenos e médios produtores. Uma das doenças mais importantes é a mela, ou podridão radicular de rizoctonia, causada pelo fungo necrotrófico Rhizoctonia solani Khun (teleomorfo Thanatephorus cucumeris Frank). Objetivou-se determinar a redução no rendimento de grãos causados pela infecção natural da mela, em diferentes cultivares de feijão, na safra agrícola 2010, no município de Quevedo, Equador. O delineamento experimental foi em blocos casualizados, com sete tratamentos e quatro repetições. O gradiente da intensidade da doença foi gerado pela variabilidade genética entre cultivares de feijoeiro. A avaliação de severidade (% de área foliar necrosada) da doença foi determinada no estádio fenológico R7 (desenvolvimento de legume). A colheita foi realizada em aos 124 dias pós-semeadura, para quantificação do rendimento. A equação da função de dano obtida foi R = 4,257.50 – 33.16 S, onde R é o rendimento de grãos e S a severidade (%) da doença, com R2 = 0.82 e p<0.0001. A equação resultante foi normalizada para 1,000 kg, sendo esta R = 1,000.0 – 7.79 S. Concluiu-se que a equação gerada da função de dano pode ser utilizada no cálculo do limiar de dano econômico (LDE), uma alternativa racional indicadora do momento para a aplicação de controle químico da mela em cultivares suscetíveis, mantendo a rentabilidade do agricultor e ser amigável com o meio ambiente.

Mungbean plants expressing BjNPR1 exhibit enhanced resistance against the seedling rot pathogen, Rhizoctonia solani

Mungbean, Vigna radiata (L.) Wilczek is an important pulse crop that is widely cultivated in semi- arid tropics. The crop is attacked by various soil-borne pathogens like Rhizoctonia solani, which causes dry rot disease and seriously affects its productivity. Earlier we characterized the non-expressor of pathogenesis related gene-1(BjNPR1) of mustard, Brassica juncea, the counterpart of AtNPR1 of Arabidopsis thaliana. Here, we transformed mungbean with BjNPR1 via Agrobacterium tumefaciens. Because of the recalcitrant nature of mungbean, the effect of some factors like Agrobacterium tumefaciens strains (GV2260 and LBA4404), pH, L: -cysteine and tobacco leaf extract was tested in transformation. The transgenic status of 15 plants was confirmed by PCR using primers for nptII. The independent integration of T-DNA in transgenic plants was analyzed by Southern hybridization with an nptII probe and the expression of BjNPR1 was confirmed by RT-PCR. Some of the T(0) plants were selected for detached leaf anti-fungal bioassay using the fungus Rhizoctonia solani, which showed moderate to high level of resistance depending on the level of expression of BjNPR1. The seedling bioassay of transgenic T(2) plants indicated resistance against dry rot disease caused by R. solani.

Preparation and fungicidal properties of (phenylthio)-acetohydroxamic acids and related compounds.

Abstract 1-Chloro-4,5-dimethoxy-2-nitrobenzene and 1-bromo-2,5-dimethoxy-4-nitrobenzene condensed readily with thioglycollic acid in alkaline medium to give the corresponding sulphides. (4,5-Dimethoxy-2-nitrophenylthio)- and (2,5-dimethoxy-4-nitrophenylthio)acetic acid, as well as the corresponding amides and hydroxamic acids, have been prepared and tested for their fungicidal properties against Aspergillus niger and Rhizoctonia solani. The (phenylthio)acetohydroxamic acids were found to be more fungicidal than the corresponding carboxylic acids against the phytopathogenic fungus Rhizoctonia solani.

Functional alteration of a dimeric insecticidal lectin to a monomeric antifungal protein correlated to its oligomeric status.

Background Allium sativum leaf agglutinin (ASAL) is a 25-kDa homodimeric, insecticidal, mannose binding lectin whose subunits are assembled by the C-terminal exchange process. An attempt was made to convert dimeric ASAL into a monomeric form to correlate the relevance of quaternary association of subunits and their functional specificity. Using SWISS-MODEL program a stable monomer was designed by altering five amino acid residues near the C-terminus of ASAL.Methodology/Principal FindingsBy introduction of 5 site-specific mutations (-DNSNN-), a β turn was incorporated between the 11th and 12th β strands of subunits of ASAL, resulting in a stable monomeric mutant ASAL (mASAL). mASAL was cloned and subsequently purified from a pMAL-c2X system. CD spectroscopic analysis confirmed the conservation of secondary structure in mASAL. Mannose binding assay confirmed that molecular mannose binds efficiently to both mASAL and ASAL. In contrast to ASAL, the hemagglutination activity of purified mASAL against rabbit erythrocytes was lost. An artificial diet bioassay of Lipaphis erysimi with mASAL displayed an insignificant level of insecticidal activity compared to ASAL. Fascinatingly, mASAL exhibited strong antifungal activity against the pathogenic fungi Fusarium oxysporum, Rhizoctonia solani and Alternaria brassicicola in a disc diffusion assay. A propidium iodide uptake assay suggested that the inhibitory activity of mASAL might be associated with the alteration of the membrane permeability of the fungus. Furthermore, a ligand blot assay of the membrane subproteome of R. solani with mASAL detected a glycoprotein receptor having interaction with mASAL.Conclusions/SignificanceConversion of ASAL into a stable monomer resulted in antifungal activity. From an evolutionary aspect, these data implied that variable quaternary organization of lectins might be the outcome of defense-related adaptations to diverse situations in plants. Incorporation of mASAL into agronomically-important crops could be an alternative method to protect them from dramatic yield losses from pathogenic fungi in an effective manner.

Biocontrol Efficiency of Bacillus subtilis SL-13 and Characterization of an Antifungal Chitinase

The seed germination and tomato seedling tests showed that Bacillus subtilis SL-13 could promote the sprouting and seedling growth of tomato. The fresh and dry weight of tomato seedlings increased 42.86% and 18.75%, respectively. The control efficacies of the SL-13 to tomato Rhizoctonia rot were 20.65% and 35.23% in the greenhouse and field, respectively. The growth of the plant-pathogenic fungus Rhizoctonia solani was considerably inhibited in the presence of the strain SL-13 culture supernatant. The main antifungal protein was detected to be chitinase through vitro assay. The chitinase was purified with DEAE-Sepharose fast flow ion exchange column chromatography and Sephadex G-75 gel filtration for further characterization. The optimal pH and temperature for the chitinase activity were 7.0 and 50 (C, respectively. It was demonstrated that the enzyme was stable at pH 5-9 and 40-60 (C. 70% of the enzyme activity was retained when incubated at 121 (C and 0.11 MPa for 20 min, and the enzyme was not sensitive to protease K and ultraviolet radiation. Thus it is suitable for effective biological control in relatively unstable environment.

Characterization of the Biocidal Spectrum of Extracellular Filtrates of Microcystis aeruginosa.

The effect of dichloromethane (DCM) and ethyl acetate (EA) extract of a cyanobacterium, Microcystis aeruginosa was evaluated against unicellular cyanobacteria and the phytopathogenic fungus Rhizoctonia solani. Fractionation of the filtrate showed the presence of five spots of different Rf values on silica gel coated plates indicating the presence of a number of compounds in the extract. A marked reduction in growth (52%) of the fungus was recorded on the plates supplemented with cyanobacterial extract, indicating the involvement of anti-fungal metabolite(s). The extract did not show any negative influence on seed germination and growth of seedlings of wheat, rice and mung, emphasizing the suitability of the compound for use in agriculture.

Assessment of the Effects of Genetically Modified Pseudomonas spp. Expressing Chitinase on the Soil Microbial Community in the Cucumber Rhizosphere

In our previous study, a genetically-modified (GM) rhizosphere bacterium, Pseudomonas putida strain 101-97 harboring the chitinase-expression vector pKAC9-p07, showed over-production of chitinase and suppressed the damping-off of cucumber seedlings caused by the plant-pathogenic fungus Rhizoctonia solani. To assess the effects of the GM bacterium on other soil microorganisms, we monitored the microbial population in the cucumber rhizosphere after inoculation with the GM bacterium by culture-dependent and -independent methods. In the culture-dependent analysis, total bacterial and fungal populations in the cucumber rhizosphere did not differ after inoculation with either the GM bacterium or its parental strain, P. putida 101R. In the cultureindependent analysis, we determined changes in the microbial communities by PCR-denaturing gradient gel electrophoresis (DGGE). The DGGE profiles of bacterial 16S rDNA genes differed significantly depending on whether they had been inoculated with the GM bacterium or its parental strain, whereas the profiles of fungal 18S rDNA genes remained similar.

Biological Control of Rhizoctonia damping-off of Cucumber by a Transformed Pseudomonas putida Strain Expressing a Chitinase from a Marine Bacterium

To construct an effective biological control agent for plant root diseases, we isolated Pseudomonas putida strains from the rhizospheres of cucumber plants and used them as hosts of an expression vector for an antipathogenic gene. The antipathogenic gene encoded a chitinase, and was derived from the marine bacterium Alteromonas sp. strain 79401. We screened the genome of P. putida PaW8 to obtain a strong promoter for the expression of this gene. The chitinase expression vector pKAC9-p07, containing the chitinase gene and the promoter from PaW8, was introduced into P. putida strains that could survive well in the rhizosphere. The transformed P. putida strains showed chitinase production and suppressed the damping-off of cucumber seedlings in soils infected with the plant-pathogenic fungus Rhizoctonia solani. This study demonstrates a strategy for the construction of a biological control agent for practical use in the rhizosphere.

Effect of soil treatment with some biological agent on controlling damping off disease of eggplant caused by Rhizoctonia solani Kuhn

This study was conducted to evaluate the effect of soil treatment with some biocontrol agent to control eggplant seedling damping-off. The fungus Rhizoctonia solani was isolated and identified as a causal agent of seedling damping-off on eggplant.Eight Rhizoctonia solani isolates were obtained from infected root and seeding eggplants . Pathogenicity test by using cabbage seeds indicated that all isolates were pathogenic but their level of Pathogenicity was different. The isolates Rh6 and Rh7 were the most severe isolates among other isolates. البحث مستل من رسالة ماجستیر للباحث الاول Three Azotobacter chroococcum isolates were obtained from wheat rhizosphere soil and identified according to their cultural, biochemical and microscopic characters. Pathogenicity test showed that A. chroococcum had highly antagonist effect against R. solani isolates where they were inactivated the fungus growth.. Peat moss treated with biological agents was increased the germination percent and decreased the infection percent of disease. Peat moss treated with both T. harzianum and A. chroococcum was resulted 86.7%, 86.7% germination after two and five weeks respectively and use efficiency 82.6%.

Identification and localization of food-source microbial nucleic acids inside soil nematodes

Microorganisms (e.g., prokaryotes, fungi) are food sources for soil nematodes, but they can also be potential mutualists or pathogens. Understanding the linkages between microorganism and invertebrate diversity in soils requires the ability to distinguish between these microbial roles. We tested the potential of a taxon-specific fluorescent in situ hybridization (FISH) procedure for identifying and localizing microbial rRNA within the bodies of soil nematodes. Our objective was to determine whether the rate of digestion permitted detection and identification of food-source nucleic acids within the nematode digestive system (i.e., pharynges, intestines) before their breakdown. First, using laboratory cultures of Caenorhabditis elegans maintained on Escherichia coli, we were able to localize bacterial rRNA throughout the nematode pharynx with the universal bacterial-probe EUB338, although never in the intestines. Second, we applied the fungal rRNA probe FR1 to Aphelenchus avenae cultured on the fungus Rhizoctonia solani. We were unable to detect fungal rRNA within these nematodes, and it appears that this material may be digested rapidly. Next, we applied our technique to nematodes extracted directly from soils. We were able to localize bacterial rRNA within the pharynges of bacterial-feeding species of nematodes from desert soils. We also localized archaeal rRNA using the probe ARC344. Finally, application of EUB338 to desert soil nematodes revealed the presence of bacteria in the intestines of some nematodes and within the ovary of a single nematode. This technique has great potential for use in understanding the feeding behavior of bacterial-feeding soil nematodes and in studies of nematode:bacterial relationships.