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  • Author or Editor: R. Aggarwal x
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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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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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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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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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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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Abstract  

Instrumental neutron activation analysis (INAA) was employed to determine concentrations of 19 elements (As, Ba, Br, Ce, Co, Cr, Cs, Fe, K, La, Mn, Na, Nd, Rb, Sc, Sm, Th, Yb and Zn) in a large number (55) of tea samples (from market as well as virgin tea leaves) from different locations in India (Assam, Darjeeling, Munnar and Kangra). The results obtained in the present work are compared with those reported in literature. The concentration levels, their variations with collection locations and the correlations among different elements in these samples are discussed.

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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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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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Abstract  

Experimental evaluation on the use of239Pu spike in Isotope Dilution-Thermal Ionization Mass Spectrometry (ID-TIMS),238Pu spike in Isotope Dilution Alpha Spectrometry (IDAS) and233U as a Non-Isotopic Diluent in Alpha Spectrometry (N-IDAS), for determing plutonium concentration in samples with burn-up values in the range of 1,000–10,000 MWD/TU is done. Precision is determined by analyzing replicate aliquots from different samples using each of the three spikes. Accuracy is established by comparing the results with those obtained by using well recognized spike242Pu in ID-TIMS. It is shown that the use of239Pu spike with the latest generation thermal ionization mass spectrometers gives the best precision (0.2%), whereas the precision values of 0.5 and 1% can be obtained by using238Pu and233U spikes, respectively, on a routine basis. Reasons for the difference in the precision values are discussed, along with the merits and drawbacks on the use of different spike isotopes.

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Abstract  

An experimental evaluation of the recently available passivated ion-implanted detectors, which appear promising for high resolution -spectrometry, is presented in terms of % tail contribution per unit -activity ratio, peak to valley ratio, and resolution /FWHM/. The two IPE detectors with areas of 20 mm2 and 450 mm2 were used for comparing these parameters. It is seen that the smaller area detector provides a better resolution for single nuclide sources, but there is no significant difference for sources containing nuclides with close lying -energies, e.g.,239Pu,240Pu. Further, the large area detector gives less tail contribution and should be preferred to minimize the error in -activity ratio determinations. However, the small area detector offers a possibility of qualitative or semiquantitative determination of nuclides with close lying -energies.

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