Search Results

You are looking at 1 - 10 of 11 items for

  • Author or Editor: R. Velazhahan x
  • Refine by Access: All Content x
Clear All Modify Search

Downy mildew, caused by Peronosclerospora sorghi is one of the important diseases affecting maize (Zea mays L.) production worldwide. Several downy mildew resistant maize lines have been identified. However, variability in the degree of resistance among maize genotypes to P. sorghi has been reported. In the present study the molecular basis of resistance of maize to P. sorghi was studied by using differential-display reverse transcription PCR (DDRT-PCR) technique. Maize seedlings of downy mildew resistant (MAI 756) and susceptible (CM 500) cultivars at two-leaf stage were inoculated with P. sorghi and leaf samples were collected at 0, 3 and 5 days after inoculation and analyzed for differentially expressed cDNAs using cDNA-RAPD approach. A total of 17 cDNA fragments corresponding to transcripts that showed alterations during the defence response of maize to P. sorghi were identified. Genes involved in signal transduction and several genes with unknown functions were found to be upregulated in maize after infection by P. sorghi. Among 35 random primers tested, OPD-05 has identified a differentially expressed cDNA coding for serine/threonine kinase protein in resistant maize genotype. Constitutive and high level expression of serine/threonine kinase gene was observed in the uninoculated plants of resistant genotype, whereas no expression of this gene was observed in uninoculated plants of susceptible genotype. However, the transcript level was induced 3 days after inoculation in the susceptible genotype and slightly reduced 5 days after inoculation. This study represents the first identification of maize serine/threonine kinase gene that is upregulated following infection by P. sorghi.

Restricted access

Twenty strains of Pseudomonas fluorescens were evaluated for their potential in promoting plant growth and in the control of late leaf spot caused by Cercosporidium personatum in groundnut under greenhouse conditions. Seed treatment with P. fluorescens strain Pf1 recorded the highest germination percentage and the maximum plant height. Seed treatment with P. fluorescens Pf1 significantly controlled late leaf spot disease of groundnut and increased the pod yield. When the treated seeds were sown in soil, the antagonist colonized well in the groundnut rhizosphere. P. fluorescens Pf1 showed the maximum production of indole acetic acid in in vitro.

Restricted access

Seed extracts of 50 plant species belonging to different families were evaluated for their ability to inhibit growth of Trichoderma viride in vitro. Of the various seed extracts, the seed extracts of Harpullia cupanioides (Roxb) belonging to Sapindaceae family exhibited very high antifungal activity. The seed extract of H. cupanioides strongly inhibited the growth of Rhizoctonia solani, Curvularia lunata, Colletotrichum musae and Alter­naria alternata. Seed extract of H. cupanioides retained its antifungal acti­vity even after heating at 100 °C for 10 min or autoclaving at 121 °C for 20 min. For partial purification of antifungal proteins, H. cupanioides seed extract was subjected to ammonium sulphate fractionation followed by gel filtration on Sephadex G-200 column. The fractions from sephadex G-200 were individually tested for their antifungal activity against T. viride. SDS-PAGE analysis of the fractions from Sephadex-G200 column indi­cat­ed that the fractions with antifungal activity contained a 68-kDa band as well as other low molecular weight protein bands. The N-terminal amino acid sequence of the 68-kDa protein (13 residues) was determined by Edman degradation. However, comparison with sequences in the GenBank database (Swiss Prot) did not reveal any homology with known protein sequences.

Restricted access

Changes in activities of phenylalanine ammonia-lyase,chitinase,ß-1,3-glucanase and phenolic content in rice leaves were measured at different times after treatment of leaves with Pseudomonas fluorescens strain Pf1.When rice leaves were sprayed with P.fluorescens,substantial increase in the phenylalanine ammonia-lyase activity was observed 1 day after treatment.Following increase of the first enzyme of the phenylpropanoid pathway,phenolic content of rice leaves also increased to a maximum at 4 days after P.fluorescens treatment.Chitinase activity increased in rice leaves in response to application of P.fluorescens and the maximum enzyme activity was observed 3 days after treatment.ß-1,3-Glucanase activity also increased significantly from 1 day after P.fluorescens treatment and continued to increase through 7 days.A five-fold increase in glucanase activity was observed 7 days after P.fluorescens treatment.

Restricted access

Seed extracts of pearl millet, sorghum, Japanese barnyard millet, foxtail millet, samai and proso millet were evaluated in vitro for their ability to inhibit the growth of Rhizoctonia solani, Macrophomina phaseolina and Fusarium oxysporum. Among them, seed extracts of pearl millet and sorghum were highly effective in inhibiting the growth of all three examined phytopathogenic fungi. The seed extracts were tested for the presence of thaumatin-like proteins (TLPs) by Western blot analysis using bean TLP antiserum. Results of Western blot analysis indicated the presence of a 23-kDa TLP in seeds of pearl millet, sorghum and Japanese barnyard millet. The 23-kDa TLP was more abundant in the seeds of pearl millet. The distribution of TLP in various parts of pearl millet was analyzed by Western blotting. The results indicated that the 23 kDa TLP was predominantly expressed in seeds and inflorescence of pearl millet.

Restricted access

Rice leaf sheaths were inoculated with R. solani (pathogen) and P. palmarum (non-pathogen) and were analyzed for the accumulation of pathogenesis-related (PR) proteins. Inoculation of rice plants with R. solani and P. palmarum resulted in a marked increase in activities of chitinase and b-1,3-glucanase. The levels of both enzymes were higher in incompatible interactions than in compatible interactions. Western blot analysis indicated that two proteins with molecular weights of 33 and 35 kDa cross-reacting with barley chitinase antibody were induced in rice in response to inoculation with R. solani. The appearance of these chitinases was correlated with increase in enzyme activity.

Restricted access

The antifungal activity of 30 medicinal plants belonging to different families was tested in vitro on the phytopathogenic fungus Rhizoctonia solani. The results revealed that protein extract from the galls of Quercus infectoria belonging to Fagaceae family was highly effective in inhibiting the mycelial growth of R. solani. The gall extract of Q. infectoria also inhibited the growth of other agronomically important fungal pathogens viz. Fusarium oxysporum, Cochliobolus miyabeanus, Macrophomina phaseolina, Colletotrichum gloeosporioides, Magnaporthe salvinii, Cochliobolus lunatus, Alternaria solani, Pythium aphanidermatum and Colletotrichum falcatum. A 29-kDa glycoprotein was purified from the galls of Q. infectoria by ammonium sulphate fractionation followed by gel filtration on Sephadex G-50 column. The purified protein showed the absorption maxima at 640 nm and 308 nm. The purified protein was stable even after heating at 100 °C for 10 min or autoclaving at 121 °C for 20 min. When the 29-kDa protein was treated with NaIO4 and pronase the antifungal activity was drastically reduced. The 29-kDa protein inhibited the mycelial growth of R. solani and C. miyabeanus at 2 µg level.

Restricted access

Systemic acquired resistance induced by benzo (1,2,3) thiadiazole-7-carbothioic acid S-methyl ester (BTH) in rice against bacterial leaf blight (BLB) caused by Xanthomonas oryzae pv. oryzae was studied. Rice plants (IR 50) pre-treated with BTH showed resistance to a challenge infection with Xanthomonas oryzae pv. oryzae. About 50% reduction in disease intensity was observed in plants treated with BTH at 100 µg a.i./ml. Immunoblot analysis using barley chitinase antiserum revealed the induction of a 35 kDa chitinase in rice in response to treatment with BTH. The results indicate that the BLB resistance can be induced even in genetically susceptible cultivar through application of BTH.

Restricted access

Pretreatment of rice leaves with 20 per cent cow dung water extract (CDWE) was found to reduce bacterial blight disease of rice to about 50 per cent. The suppression of the disease by the extract was not due to direct inhibition of the pathogen. Pretreatment of rice leaves with cow dung water extract as foliar spray induced the accumulation of phenolics and enhanced the activities of peroxidase, chitinase and ß-1,3-glucanase. The induced defense mechanisms might have played a role in reducing the disease.

Restricted access

Seed extract of Harpullia cupanioides was tested against infection by Tomato spotted wilt virus (TSWV), Rice tungro virus (RTV) and Cowpea aphid borne mosaic virus (CABMV). Seed extract of H. cupanioides (10%) when sprayed on test plants 24 h before virus inoculation significantly inhibited virus infections. Percentage inhibition of TSWV in local lesion host by 10% seed extract of H. cupanioides was found to be 90.9. Pre-inoculation application of 10% seed extract of H. cupanioides provided 87.5% inhibition of CABMV infection. The seed extract (10%) sprayed rice plants recorded RTV infection of 48% as against 100% in control.

Restricted access