R. Velazhahan

Tamil Nadu Agricultural University, Koyambattūr, Tamil Nādu, India

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Publications (66)41.95 Total impact

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    ABSTRACT: The effect of elicitor from mycelial walls of Magnaporthe grisea, the rice blast fungus and α-picolinic acid, one of the toxins produced by M. grisea on induction of peroxidase (PO), polyphenol oxidase (PPO) in suspension-cultured rice (Oryza sativa L.) cells was studied. Cultured cells of blast resistant (Usen) and susceptible (CO39) rice genotypes were treated with elicitor (50 μg of glucose equivalents per ml) or α-picolinic acid (400 ppm). The cells were harvested at different time intervals and analysed for the induction of PO and PPO. PO isozyme analysis indicated that the elicitor strongly induced the activities of PO-2 and PO-3 in cultured cells of Usen 3 days after treatment. In Usen, toxin also induced the activities of PO-3 and PO-4. However, similar levels of activities corresponding to these isozymes were recorded 7 days after treatment. In CO39, the activities of PO-1 and PO-2 were induced 3 days after elicitor treatment. In contrast, the toxin suppressed the activity of PO-2. The elicitor induced the activities of PPO-1, PPO-2 and PPO-3 in both Usen and CO39. In Usen, steady increase of PPO-3 was observed and higher level of activity was recorded 5 days after treatment. In CO39, higher level of PPO-3 was observed 1 day after treatment and declined thereafter. However, the activities of PPO-1 and PPO-2 increased 3 days after treatment in CO39. In the toxin-treated cells of Usen, higher level of activity of PPO-3 was observed 3 days after treatment.
    Archives of Phytopathology and Plant Protection 12/2014; 47(20).
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    ABSTRACT: The fungus Magnaporthe grisea was isolated from the infected plants with blast-like lesions. The isolates were confirmed by PCR using primers specific for 28S rDNA of M. grisea. The Internal Transcribed Spacer (ITS) region of rDNA, which included ITS regions 1 and 2, 5.8S rRNA genes was amplified with primers ITS1 and ITS4. The PCR amplified product was approximately 550 bp in size. Analysis of nucleotide sequence of ITS regions of isolate CBECCI using NCBI-BLAST search showed 99% similarity with the sequence of Pyricularia sp. NI981 isolate from C. ciliaris. Cluster analysis using unweighted pair-group method with arithmetic average (UPGMA) clearly separated the M. grisea isolates into two groups. The isolate CBECC1, isolated from C. ciliaris clustered into a separate group (Group I) and all the remianing M. grisea isolates from GenBank database were clustered together in Group II confirming the genetic diversity among the M. grisea isolates. Sequences of the partial β-tubulin gene of M. grisea isolate CBECC1 showed 100% identities with β-tubulin gene sequences of Pyricularia sp. isolated from Cenchrus echinatus.
    03/2014; 22:122-126.
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    ABSTRACT: The genetic variability among isolates of Magnaporthe grisea collected from rice (Oryza sativa), buffel grass (Cenchrus ciliaris), finger millet (Eleusine coracana) and para grass (Brachiaria mutica) were analyzed by using Random Amplified Polymorphic DNA (RAPD) method. Analysis of the genetic coefficient matrix derived from the scores of RAPD profiles showed that minimum and maximum % similarities among the tested M. grisea isolates were in the range of 19.1 to 95.9% respectively. The phylogenetic analysis by the unweighted pair-group method with arithmetic means (UPGMA) identified two main clusters. Cluster A contained only one isolate (CBECC1 isolated from C. ciliaris) and all the other isolates were placed in Cluster B confirming high genetic diversity among the isolates of M. grisea.
    03/2014; 22:142-147.
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    ABSTRACT: A total of 30 isolates of actinomycetes were isolated from the rhizosphere soils of groundnut collected from different parts of Tamil Nadu, India and tested for their inhibitory activity against Sclerotium rolfsii Sacc., the stem rot pathogen of groundnut. Among the various isolates tested in vitro, five isolates (CBE, MDU, PDK, ANR and SA) were found effective in inhibiting the mycelial growth of S. rolfsii in dual culture assay. These isolates were identified as Streptomyces sp. on the basis of standard bacteriological tests and 16S ribosomal RNA gene sequence analysis. Groundnut seeds when treated with Streptomyces sp. strains showed significant increases in root length, shoot length and seedling vigour. Talc-based powder formulations of the Streptomyces sp. strains, CBE, MDU and PDK selected on the basis of their in vitro antagonism on dual plate technique and plant-growth promoting activity were prepared and tested for their efficacy in controlling stem rot of groundnut under greenhouse and field conditions. Seed treatment and soil application of Streptomyces sp. strains CBE, MDU and PDK significantly reduced the incidence of stem rot under greenhouse and field conditions. The highest pod yield was recorded in plots treated with Streptomyces sp. strain CBE when compared to other strains.
    Archives of Phytopathology and Plant Protection 02/2014; 47(3).
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    ABSTRACT: Yellow mosaic disease is the major limitation in the production of grain legumes in India. This disease is caused by bipartite begomovirus, Mungbean yellow mosaic virus. In addition to the bipartite genomic components, the yellow mosaic disease affected urdbean plants which contain satellite like DNA-1 component called as alphasatellites. The present study has been attempted to characterise the alphasatellites associated with Mungbean yellow mosaic virus. Nucleotide sequence analysis of alphasatellites showed 98% identity with Vernonia yellow vein Fijian alphasatellite, VYVFA (JF733780). Since the sequence identity is more than 98%, the threshold value for demarcation of alphasatellites species, the alphasatellites of the present study are named as Vernonia yellow vein Fijian alphasatellite. Comparison with other, alphasatellites shared 51–55% identity with alphasatellites associated with monopartite begomovirus and it shared only 41–42% identity with an unusual alphasatellites, DNA-2. This is the first report on characterisation of alphasatellites associated with Mungbean yellow mosaic virus.
    Archives of Phytopathology and Plant Protection 01/2014; 47(2).
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    ABSTRACT: Five strains of Streptomyces sp. were evaluated in vitro for their ability of inhibiting the mycelial growth of Macrophomina phaseolina, the causal agent of root rot of mung bean (Vigna radiata L.). Among the Streptomyces sp. strains tested, PDK showed the maximum in vitro inhibition of mycelial growth of M. phaseolina and recorded an inhibition zone of 21 mm. The strains CBE, MDU, SA and ANR recorded inhibition zones of 18, 16, 13 and 11 mm, respectively. These Streptomyces sp. strains were tested for their growth-promoting efficiency on mung bean seedlings. Among them, CBE and PDK recorded the maximum increase in shoot length, root length and seedling vigour compared with control, followed by MDU. Three Streptomyces sp. strains (CBE, MDU and PDK) that showed higher levels of inhibition of growth of M. phaseolina in dual culture assay and plant growth-promoting activity were tested for their biocontrol activity against root rot under greenhouse and field conditions. Seed treatment or soil application with powder formulation of Streptomyces sp. strains CBE, MDU and PDK was effective in controlling root rot disease; but, combined application through seed and soil increased the efficacy in both the greenhouse and field trials. Among the treatments, seed treatment plus soil application with powder formulation of Streptomyces sp. strain CBE proved to be most effective, which reduced the root rot incidence from 26.8% (with non-bacterised seeds) to 4.0% in Trial I and from 32.0 to 4.9% in Trial II. The above treatment recorded the highest yield in both the field trials, and the yield increase was 78 and 74% over control in Trial I and Trial II, respectively. Isozyme analysis of the Streptomyces sp.-treated plants indicates that seed treatment plus soil application strongly induce the activities of peroxidase (PO-1 and PO-2) and polyphenol oxidase (PPO-2 and PPO-3) in mung bean. Among the three strains tested, Streptomyces sp. strain MDU- treated plants showed higher levels of activities of PO and PPO. Based on the above findings, it can be concluded that both the direct inhibition of pathogen and induced resistance might be involved in the control of root rot of mung bean by Streptomyces sp.
    Archives of Phytopathology and Plant Protection 01/2014; 47(5).
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    ABSTRACT: Rice (Oryza sativa L.,) is one of the most important cereal crops worldwide. In this study, phytoplasmas have been detected in symptomatic leaves of four varieties of rice using nested-PCR with primer pairs P1/P7 and R16F2n/R16R2, which amplified a 1.2 kb fragment of the 16S rRNA gene. The nucleotide sequence analysis of the fragment had 100 % identity among the sequences from the four varieties (GenBank Accession numbers: JX290545, JX290546, JX290547 and JX290548) and 99 % nucleotide sequence identity with 16S rRNA gene sequences of the Rice orange leaf disease phytoplasmas from the Philippines and Thailand, Maize bushy stunt phytoplasma and Wheat blue dwarf phytoplasma belonging to the ‘Candidatus Phytoplasma asteris' (16SrI) group. This is the first report of 16SrI group phytoplasmas infecting rice in India.
    Australasian Plant Disease Notes 12/2013;
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    ABSTRACT: The effectiveness of aqueous extracts of various medicinal plants in detoxification of aflatoxin B1 (AFB1) was tested in vitro by thin-layer chromatography and enzyme-linked immunosorbent assay (ELISA). Among the different plant extracts, the leaf extract of Vasaka (Adhatoda vasica Nees) showed the maximum degradation of AFB1 (≥98%) after incubation for 24h at 37°C. The aflatoxin detoxifying activity of the A. vasica leaf extract was significantly reduced by heating to 100°C for 10min or autoclaving at 121°C for 20min. Dialysis had no effect on aflatoxin detoxifying ability of A. vasica extract and the dialyzed extract showed similar level of detoxification of AFB1 as that of the untreated extract. A time course study of aflatoxin detoxification by A. vasica extract showed that 69% of the toxin was degraded within 6h and ≥95% degradation was observed after 24h of incubation. Detoxification of AFB1 by A. vasica extract was further confirmed by liquid chromatography-mass spectrometry (LC-MS) analysis. Phytochemical analysis revealed the presence of alkaloids in methanolic extract of A. vasica leaves. A partially purified alkaloid from A. vasica leaves by preparative TLC exhibited strong AFB1 detoxification activity.
    Microbiological Research 08/2013; · 1.99 Impact Factor
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    ABSTRACT: Yellow mosaic disease caused by mungbean yellow mosaic virus (MYMV) belonging to the genus Begomovirus (the family Geminiviridae) is a major constraint in cultivation of grain legumes in India. The urdbean (Vigna mungo (L.) Hepper) and mungbean (Vigna radiata (L.) R. Wilczek) samples affected with yellow mosaic disease exhibits yellow mosaic symptoms along with leaf puckering and leaf distortion in Tamil Nadu. Hence the study was performed to find out if there was any association and influence of betasatellite DNA on the symptom expression of MYMV. Full length viral clones of DNA A and DNA B were obtained through rolling circle amplification from YMD infected samples and identified as mungbean yellow mosaic virus. Interestingly, betasatellite was found to associate with MYMV, and its nucleotide sequence analysis showed its 95% identity with papaya leaf curl betasatellite (DQ118862) from cowpea. The present study represents the first report about the association of papaya leaf curl betasatellite with MYMV and represents a new member of the emerging group of bipartite begomovirus associated with betasatellite DNA. Keywords: yellow mosaic disease; grain legumes; leaf puckering; betasatellite; begomovirus.
    Acta virologica 01/2013; 57(4):405-14. · 0.76 Impact Factor
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    ABSTRACT: Aflatoxin contamination is a major problem in maize, groundnut, chillies, cotton and tree nuts. These aflatoxins are low molecular weight toxic and carcinogenic secondary metabolites produced by Aspergillus flavus, A. parasiticus and A. nomius. In the present study, a total of 11 isolates of A. flavus isolated from groundnut, maize and chilli collected from different locations of Tamil Nadu, India were tested for their ability to produce aflatoxin B1 (AFB1) in vitro by indirect competitive enzyme-linked immunosorbent assay. The results show that the isolates vary in their level of toxin production. The amount of AFB1 produced by the toxigenic isolates of A. flavus ranged from 6.6 to 108.1 ng ml−1. Among the various isolates of A. flavus, the isolate VKR produced the highest amount (108.1 ng ml−1) of AFB1. The isolates viz. CBE1, CBE2, BSR1, BSR3 and BSR4 were found to be non-toxigenic. The genetic variability among these isolates was assessed by Random amplified polymorphic DNA (RAPD) analysis. DNA fragments of between 0.15 and 3.0 kb were obtained using 13 random primers, and each isolate differed in the size and number of PCR products indicating considerable polymorphism. Cluster analysis using Unweighted Pair Group Method with Arithmetic Mean clearly separated the isolates into four main clusters confirming the genetic diversity among the isolates of A. flavus. Both toxigenic and non-toxigenic isolates were intermingled in these four groups, indicating that no relationship exists between RAPD profile and the production of aflatoxin by A. flavus.
    Archives of Phytopathology and Plant Protection 01/2013; 46(18).
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    ABSTRACT: The coat protein (CP) gene of Tobacco streak virus (TSV) from sunflower (Helianthus annuus L.) was amplified, cloned and sequenced. A 421 bp fragment of the TSV coat protein gene was amplified and a gene construct encoding the hairpin RNA (hpRNA) of the TSV-CP sequence was made in the plasmid pHANNIBAL. The construct contains sense and antisense CP sequences flanking a 742 bp spacer sequence (Pdk intron) under the control of the constitutive CaMV35S promoter. A 3.6 kb Not I fragment containing the hpRNA cassette (TSV-CP) was isolated from pHANNIBAL and sub-cloned into the binary vector pART27. This chimeric gene construct was then mobilized into Agrobacterium tumefaciens strain LBA4404 via triparental mating using pRK2013 as a helper. Sunflower (cv. Co 4) and tobacco (cv. Petit Havana) plants were transformed with A. tumefaciens strain LBA4404 harbouring the hpRNA cassette and in vitro selection was performed with kanamycin. The integration of the transgene into the genome of the transgenic lines was confirmed by PCR analysis. Infectivity assays with TSV by mechanical sap inoculation demonstrated that both the sunflower and tobacco transgenic lines exhibited resistance to TSV infection and accumulated lower levels of TSV compared with non-transformed controls.
    Biologia Plantarum 12/2012; 56(4):735-741. · 1.69 Impact Factor
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    ABSTRACT: Suspension-cultured rice cells showed an appreciable amount of chitinase activity when the cultured cells were treated with an elicitor isolated fromRhizoctonia solani, the rice sheath blight pathogen. A fivefold increase in chitinase activity was observed 24 h after elicitor treatment. The elicitor-inducible chitinase was purified by ammonium sulfate fractionation, chitin affinity chromatography and gel filtration. Its molecular weight is 35 kDa and it has an isoelectric point of 8.3. The 35 kDa basic chitinase inhibited mycelial growth ofR. solani in vitro. Morphological changes appeared within 1 h following exposure of mycelium to the chitinase. The hyphal tip showed marked swelling and subsequently lysis was also observed.
    Phytoparasitica 04/2012; 28(2):131-139. · 0.72 Impact Factor
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    ABSTRACT: Red rot disease of sugarcane caused by Colletotrichum falcatum Went is one of the most destructive diseases of sugarcane (Saccharum officinarum L.) worldwide. The pathogen spreads primarily through infected sugarcane setts and hence the use of disease-free setts is essential to prevent the disease. In order to develop immunological method for detection of C. falcatum, two proteins with molecular weights of 27 kDa and 45 kDa were purified from the mycelium of C. falcatum race Cf 05 and used as antigen source to raise polyclonal antibodies in NewZealand white rabbit. The developed polyclonal antibodies were tested for detection of C. falcatum by enzyme-linked immunosorbent assay (ELISA) and immunoblot analysis. The polyclonal antibodies specifically detected C. falcatum in extracts from infected plants, both in immunoblot and ELISA. The ELISA results showed that the developed polyclonal antibodies were highly specific to C.falcatum. The developed antibodies were very sensitive and could detect C.falcatum proteins even at a dilution of 1:50,000. Higher ELISA absorbance values were recorded even at an antigen dilution of 1:500. In western blot analysis, protein bands with molecular weights of 27 kDa and 45 kDa reacting to antisera raised against 27 kDa and 45 kDa mycelial proteins of C. falcatum, respectively, were detected in protein samples from red rot infected canes. The high specific reactivity and sensitivity of the antisera indicate its potential suitability for ELISA-based detection of C. falcatum.
    Archives of Phytopathology and Plant Protection 04/2012; 45(7):823-830.
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    ABSTRACT: Red rot, caused by Colletotrichum falcatum Went, is one of the most important diseases of sugarcane (Saccharum officinarum L.). The pathogen shows a great diversity in virulence as a number of pathotypes are known to occur in nature. In the present study, the toxin producing ability and genetic variability among isolates of C. falcatum collected from major sugarcane growing areas of Tamil Nadu, India were analysed. The C. falcatum isolates differed significantly in their ability to produce toxin in vitro. The toxin from C. falcatum isolate Cf 671a induced the maximum electrolyte leakage (300 μS) from sugarcane leaf tissues. The genetic relatedness of the isolates of C. falcatum differing in toxin production potential was investigated by using RAPD analysis. Analysis of the genetic coefficient matrix derived from the scores of RAPD profiles showed that minimum and maximum percent similarities among the tested C. falcatum isolates were in the range of 19 to 95% respectively. The phylogenetic analysis by the UPGMA identified two main clusters. Cluster A contains only one isolate (Cf 98061) and all the other isolates were placed in Cluster B confirming high genetic diversity among the isolates. No correlation was observed between clustering of the C. falcatum isolates in the dendrogram and their toxin producing abilities.
    Archives of Phytopathology and Plant Protection 01/2012; 45(16).
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    ABSTRACT: Red rot disease of sugarcane caused by Colletotrichum falcatum is one of the most destructive diseases of sugarcane (Saccharum officinarum) worldwide. The pathogen spreads primarily through infected sugarcane setts and hence the use of disease‐free planting materials is essential for preventing disease development in the field. In the present study a polymerase chain reaction (PCR) assay was developed for accurate and sensitive detection of C. falcatum in planting materials. Randomly amplified polymorphic DNA (RAPD) analysis identified a 566 bp PCR fragment that was specific to C. falcatum. The DNA sequence of this fragment was determined and used to design oligonucleotides amplifying a 442 bp sequence characterised amplified region (SCAR). The specificity of the SCAR primers was evaluated using purified DNA from C. falcatum and other Colletotrichum spp. as templates in PCR. The results indicated that the SCAR primers were highly specific to C. falcatum since the 442 bp fragment was amplified only from DNA of isolates and races of C. falcatum but not from any other Colletotrichum spp. tested. The detection sensitivity of C. falcatum was 0.1 ng for genomic DNA of C. falcatum and 5 ng for DNA extracted from infected sugarcane tissue. This new PCR‐based assay is a convenient tool for detection of this important pathogen in seed canes to ensure production of sugarcane.
    Annals of Applied Biology 01/2012; 160(2). · 2.15 Impact Factor
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    ABSTRACT: A total of 60 maize genotype samples from different agroclimatic regions of India were collected. Fresh harvest of these maize samples comprising some commercial maize genotypes and some land races were kept under ambient storage conditions for 9 months duration at grain moisture ranges from 14% to 10.5% with a view to identifying the least contaminated maize genotype with aflatoxin. The purpose of this study was to identify the maize genotypes which can survive in ambient storage conditions with minimum spoilage. The response of various maize genotypes for AFB1 accumulation was variable in similar storage conditions. Promising genotypes which showed lower accumulation of AFB1 were identified: Shaktiman-1 (A QPM variety) by showing the lowest concentration of AFB1 (0.30 ppb) followed by KMH-1701 (0.40 ppb); HQPM-1 (0.50 ppb); and QPM-2-136 (0.60 ppb), whereas the most highly toxic sample was Mon - 4 (62.42 ppb) at grain moisture ranges from 12.6 to 11.1%. During the study it has been observed that Shaktiman-1 and other QPM genotypes showed minimum levels of AFB1. Further, it was confirmed by western blot analysis by comparing the resistant and susceptible genotype under artificially inoculated grains with Aspergillus flavus and uninoculated maize grains. It was observed that more chitinase activity was found in shaktiman-1, when the grains were artificially inoculated with A. flavus. The thickness of the seed coat and Aleuron layer was maximum in (90-100 m) in Shaktiman compared to that of Pro-311 (80-85 m). It was observed that the thickness of seed coat may act as a barrier for mold contamination and as a result the storage spoilage is minimised.
    Archives of Phytopathology and Plant Protection 04/2011; 44(6).
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    ABSTRACT: Extraction of antimicrobial compounds from medicinal mushrooms, namely, Auricularia polytricha (Jew's ear), Lentinulla edodes (Shiitake) and Volvariella volvacea (paddy straw), has been done with different solvent systems (chloroform, ethyl acetate, ether and methanol) and tested against a wide range of phytopathogens by filter paper disk assay. All the three basidiomycetes inhibited the phytopathogens tested so far. This enumeration was based on the number of organisms inhibited and the diameter of inhibitory zones produced. From the results obtained, it could be observed that ethyl acetate was the best solvent for extracting antimicrobial substances from these medicinal mushrooms. Thin layer chromatography revealed the presence of several compounds with different Retention Factor (RF) values. Sodium dodecyl sulphate–polyacrylamide gel electrophoresis profiling of V. volvacea showed the presence of several antimicrobial proteins with various molecular weights. Western blotting revealed the presence of thaumatin-like glycoproteins of molecular weight more than 45 kDa.
    Archives of Phytopathology and Plant Protection 01/2011;
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    ABSTRACT: Induction of phenolics, peroxidase (PO), polyphenol oxidase (PPO), chitinase and thaumatin-like proteins (TLP) in leaves of chilli (Capsicum annuum L.) in response to foliar application with a biocontrol agent Burkholderia sp. strain TNAU-1 was studied. Chilli plants, when sprayed with Burkholderia sp. strain TNAU-1 showed increase in phenolic content one day after application and the maximum accumulation was observed seven days after treatment. Three new peroxidase isozymes (PO-1, PO-2 and PO-3) were induced in chilli leaves upon treatment with Burkholderia sp. strain TNAU-1. The activity of all the peroxidases was at the maximum level three days after treatment and subsequently decreased. Protein extracts obtained from Burkholderia sp. strain TNAU-1 treated plants exhibited a major polyphenol oxidase (PPO-1) one day after treatment. The activity of PPO-1 subsequently decreased, but continuously present throughout the experimental period of 15 days. Western blot analysis of protein extracts from Burkholderia sp. strain TNAU-1 treated chilli leaves revealed that two TLPs with sizes of 23 and 25 kDa and a chitinase with an apparent molecular weight of 28 kDa were induced three days after treatment.
    Brazilian Journal of Plant Physiology 12/2010; 23(4):261-266.
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    ABSTRACT: Induction of acquired resistance and pathogenesis related proteins in intact plant leaves and the potentiation of pathogen signals in plant cell cultures by elicitors is mediated by different signaling pathways. We show here, the induction of PR proteins, the most widely used marker of acquired resistance, in tomato cells in response to Alternaria solani elicitors. The crude glycoprotein elicitor preparation from A. solani was used to detect the possible induction of pathogenesis -related proteins chitinase (PR-3), thaumatin like proteins (PR-5) and -1,3 glucanase in suspension -cultured cells and leaves of tomato cultivar CO 3. Western blot analysis revealed the presence of 23 kDa thaumatin like protein and 44 kDa chitinase in elicitor treated suspension -cultured cells and leaves of tomato. The biochemical approach described in this paper with tomato should provide the basis for further efforts concentrating on the isolation and characterization of elements involved in perception and in the early steps of intracellular signal transduction.
    Scientific Research and Essay. 08/2009; 4:685-689.
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    ABSTRACT: The fungus Peronosclerospora sorghi [Weston and Uppal (Shaw)] infects both sorghum and maize and incites downy mildew disease. Pathogenic and molecular variability among isolates of P. sorghi from sorghum and maize has been reported. In the present study we developed a DNA sequence characterized amplified region (SCAR) marker for identification of isolates of P. sorghi from maize by using polymerase chain reaction (PCR). The random amplified polymorphic DNA (RAPD) primer OPB15 consistently amplified a 1,000 base pairs (bp) product in PCR only from DNA of P. sorghi isolates from maize and not from isolates of sorghum. The PCR-amplified 1,000-bp product was cloned and sequenced. The sequence of the SCAR marker was used for designing specific primers for identification of maize isolates of P. sorghi. The SCAR primers amplified a 800bp fragment only from genomic DNA of maize isolates of P. sorghi. The SCAR primers developed in this study are highly specific and reproducible, and proved to be powerful tool for identification of P. sorghi isolates from maize.
    World Journal of Microbiology and Biotechnology 01/2009; 25(12):2129-2135. · 1.35 Impact Factor