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  • Author or Editor: R. Aggarwal x
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Ascochyta blight (Ascochyta rabiei) is one of the most devastating diseases of chickpea. The biocontrol potential of fungal antagonists, Chaetomium globosum, Trichoderma viride, Acremonium implicatum were explored under in vitro and in vivo. A. implicatum isolate-1 overgrew the host mycelium and caused lysis, while A. implicatum isolate-2 produced inhibition zone. C. globosum profusely overgrew the mycelium of A. rabiei and T. viride showed overgrowth and profuse sporulation. Bioassay with culture filtrates of all the antagonists resulted in significant inhibition of pycnidiospore germination and reduction in colony development of A. rabiei. Syringe filtered culture filtrate when amended in liquid broth medium also significantly reduced the mycelial growth. Bioassay of culture filtrates under glass house conditions, although brought reduction in disease development in both pre- and post-inoculation sprays, but C. globosum was the most effective antagonist causing 73.12% reduction in disease index when used as post inoculation spray. Under in vitro conditions C. globosum caused 48.59% reduction in colony diameter and 70.86% reduction in pycnidiospore germination.

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Chaetomium globosum Kunze Ex. Fries has been identified as a potential antagonist of Bipolaris sorokiniana and Ascochyta rabiei. Nine isolates of this biocontrol agent were characterized based on RAPD technique using 40 random primers of OPB and OPM series, out of which 24 primers gave a total of 356 amplification products, showing 91% polymorphism. RAPD analysis revealed that C. globosum isolates taken under study formed genetically two distinct clusters, with isolates Cg2, Cg3 and Cg4 in one cluster and the remaining isolates in another cluster, which in turn was grouped separately into two subclusters separating isolates Cg6 and Cg8 from Cg1, Cg5, Cg7 and Cg9. Similarity matrix indicated that Cg1 and Cg2 were genetically distinct as they showed only 29.4% similarity followed by Cg2 and Cg7 showing 31.1% similarity, while isolates Cg7 and Cg9 were found to be genetically similar with 68.9% similarity index.

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Tropospheric ozone (O3) adversely affects growth and productivity of crops and also influences crop—pathogen interactions. Adverse effects of O3 on crops can be mitigated by antioxidants application. In the present study through lab and field experiments impact of O3 and antioxidants treatment to wheat was assessed on growth of Bipolaris sorokiniana (BS-75 strain) pathogen responsible for Spot blotch disease, pathogenesis related (PR) proteins and chitinase content. Results showed that growth of Bipolaris was significantly higher in elevated ozone (EO3) exposed plants as compared to control plants. Antioxidants — ascorbic acid (AA), tagetes extract (T) and quercetin (Q) application on culture media and wheat plants, respectively, retarded the growth of Bipolaris sorokiniana. Among the three antioxidants minimum growth of Bipolaris was observed in AA-treated plants as compared to control plants. Reduction in chitinase activity and PR proteins content due to EO3 treatment in wheat plants was 18% and 78%, respectively, as compared to control plants. Increase in chitinase activity and PR proteins content due to antioxidants treatment in wheat plants was 45% and 60%, respectively, as compared to control plants.

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Abstract  

A method based on the geometric progression decrease of the counts in the far tail of the alpha spectrum is described for the simultaneous determination of plutonium, americium and curium by alpha spectrometry. For evaluating the precision and accuracy, synthetic mixtures were prepared from solutions of enriched isotopes and sources were prepared by direct evaporation method using tetraethylene glycol /TEG/ as a spreading agent and electropolished stainless steel discs as the backing material. Precision and accuracy of about 1% is demonstrated in the determination of244Cm/239Pu,241Am/239Pu,244Cm/233U,241Am/233U and239Pu/233U alpha activity ratios using a 450 mm2 silicon surface barrier detector.

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Abstract  

The glass-forming tendency and specific heat in ice cold water-quenched Ge1−xSnxSe2.5 glassy alloys with 0<x<0.6 were investigated by means of differential scanning calorimetry. The heat of fusion ΔH f, the heat ΔH c associated with the crystallization of an amorphous phase and the glass transition temperatureT g were deduced from the DSC curves. The composition dependence of glass forming ability,T g and crystallization behavior has been discussed.

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Abstract  

Experimental evaluation of a commonly used silicon surface barrier detector and of the recently introduced passivated ion implanted detector for alpha spectrometry is reported in terms of FWHM, peak to valley ratio, tail parameter and % tail contribution per unit alpha activity ratio using electrodeposited sources of plutonium prepared on platinum backing material. For this purpose, detectors of nearly the same diameter were employed (100 mm2 silicon surface barrier detector with a diamater of 1.13 cm and 80 mm2 passivated ion implanted silicon detector with a diameter of 1.01 cm). It is shown that the recently introduced passivated ion implanted detectors give smaller tailing effects. But there is no significant difference between the two detectors used in the present work w.r.t. FWHM and peak to valley ratios. Further, it is observed that the peak to valley ratio can be used to get an idea about240Pu/239Pu and241Am/238Pu alpha-activity ratios in the sample.

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Bipolaris sorokiniana causes spot blotch, an important disease of wheat in Asia and America. To understand the host response to challenge by B. sorokiniana, we calculated the plant disease index (PDI) of twelve popular wheat (Triticum aestivum L.) genotypes and examined the expression levels of PR protein genes and wax synthesizing genes on an inoculation time-course using semi-quantitative reverse transcriptase polymerase chain reaction (RT-PCR). Gene expression was studied in a resistant (R) and a highly susceptible (HS) genotype selected from a PDI experiment under glasshouse conditions. A gene (β-1,3-glucanase II) was induced at 24 h post inoculation and to higher levels in the resistant genotype Chiriya-3 (PDI = 1.3) than in the highly susceptible genotype Agra Local (PDI = 40.1). Densitometry analysis showed that expression of an Actin gene was the same at all stages of inoculation due to its constitutive expression in both the resistant and susceptible genotypes, while a 7-fold increase in expression of β-1,3-glucanase II was observed 24 h post inoculation in Chiriya-3. The findings reported in the present study indicate that β-1,3-glucanase production in the B. sorokiniana infected wheat leaves may be involved in resistance to the pathogen.

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Chickpea (Cicer arietinum) seeds treated with powdered preparation of Gliocladium virens (Gv) alone @ 3 g/kg seed or in combination with vitavax (0.1%) showed colonization of G. virens on seed coat, collar region, plumule and radicle. Microscopic examination revealed that colonization of seed with mycelia and spores of antagonist started 24 h after incubation. Major portion of the seedling was covered with in 48 hrs. Population dynamics of G. virens monitored at different time inter­vals in spermosphere, rhizosphere and non-rhizosphere region in pathogen infested and non-infested soil using Trichoderma Selective Medium showed that population of G. virens increased initially up to 30 days and then gradually declined. The highest population was observed in spermosphere (7 x 105/g) followed by rhizosphere (6.3 x 104/g), when seeds treated with Gv + vitavax were sown in pathogen infested soil.

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Bipolaris sorokiniana (Sacc.) Shoemaker (Teleomorph: Cochliobolus sativus (Ito and Kuribayashi) Drechs. Ex. Dastur) is a serious necrotrophic pathogen of wheat and barley in several countries. In this paper we report on mechanism of resistance and histopathological changes that occur on pathogen attack in resistant and susceptible genotypes. Callose deposition was observed in the epidermal cell wall of resistant genotype, Pusa T3336 at 2DAI. Lignin deposition around mesophyll tissues was also strongly observed by Phloroglucinol-HCl test in Pusa T3336. Four days after inoculation (4DAI), the pathogen colonized the leaf tissues showing inter and intracellular hyphae in susceptible genotype, Agralocal. In resistant genotype, no colonization was observed. The host tissue in susceptible genotype showed degeneration away from the site of colonization and also showed loss of structural integrity thereby indicating the role of toxin in pathogenesis. Separation of plasmalemma from the cell wall was observed due to loss of electrolytes and degradation of chloroplast at 5 DAI in the susceptible genotypes was prominently seen through light microscopy.

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Karnal bunt of wheat (Tilletia indica) is an important internationally quarantined disease from food security point of view. For understanding host specificity and host-pathogen interaction, putative pathogenicity-related genes were analysed in Tilletia indica in response to host factor at different time points. Highest radial mycelia growth (3.4 cm) was recorded in media amended with susceptible host factor followed by resistant host (2.6 cm) and control (2.0 cm) at 30 days after incubation significantly. Fourteen homologous sequences of putative pathogenicity-related genes, viz. TiPmk1, TiKss1, TiHog1, TiHsp70, TiKpp2, TiCts1, TiHos2, TiChs1, TiPrf1, TiSid1, TiSsp1, TiSte20, TiUbc4 and TiUkc1, were identified in T. indica by in silico analysis. Some of the pathogenicity-related genes were highly expressed significantly in T. indica in response to susceptible host factor as compared to resistant host factor. TiPmk1, TiHog1, TiKss1 were found highly upregulated up to 26-fold (3 days), 20-fold (3 days) and 18-fold (4 days), respectively, significantly in presence of susceptible host factor. The TiCts1 and TiChs1 showed transcripts up to 26-fold (4 days) and 20-fold (3 days) in the presence of susceptible host factor. Further, the TiUbc4 and TiUkc1 were found upregulated up to 20-fold and 7-fold at 8 days and 3 days post incubation. This study provided the insight on expression of putative pathogenicity-related genes in T. indica which will help in understanding the infection mechanism and basis for further functional genomics approach.

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