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Author: search.filters.author.Saha, A.End date: 2009

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    Influence of culture media and environmental factors on mycelial growth, sporulation and spore germination behaviour of Curvularia eragrostidis (P. Hennings) Mayer
    (University of North Bengal, 2008-03) Saha, A.; Dasgupta, S.; Mandal, P.; Saha, D.
    Curvularia eragrostidis is a foliar fungal pathogen of young tea plants. It causes leaf spot disease of tea. Mycelial growth, sporulation and spore germination behaviour of the pathogen were studied. Six different media were tested for mycelial growth. Among these, potato carrot agar (PCA) was found best for the mycelial growth and sporulation. Maximum mycelial growth was attained after 15 days of incubation. Mycelial growth was also studied in different temperatures and pH. Optimum temperature of growth was 25 °C and best growth was obtained at pH 6.0. Glucose and peptone were best carbon and nitrogen sources respectively for growth and sporulation of the fungus. The optimum conditions of spore germination were found to be at pH 7.25 and at incubation temperature of 25 °C. Keywords: Sporulation; Curvularia eragrostidis; Mycelial growth, fungus
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    Variation of antioxidant properties and phytochemical constituents of tea cultivated under various agronomic conditions at Terai region of North Bengal
    (University of North Bengal, 2008-03) Misra, T.K.; Saha, A.; Nanda, A.K.; Mandal, P.
    The studies were conducted during 2007-2008 in three cultivars of tea (Camellia sinensis) namely, TV26, TV29 and Dangri Manipuri Jat, at tea estates of Terai, North Bengal. Commercial standard plucked tea leaves were assayed to determine antioxidants activity and related phytochemical constituents. DPPH was used to determine the antioxidant properties of bud+leaf (B+L), bud+two leaves (B+2L), bud+three leaves (B+3L) and matured leaves (L). Subsequently, total phenolics, flavonols and hydrolysable tannins were estimated using standard methods. The result showed that free-radicals scavenging potentiality and chemical composition varies significantly at different growing conditions and leaf maturation. Statistical analysis showed significant relation between antioxidant and some phytochemical composition of dry tea leaves, among which phenolics (R2 =0.904, P< 0.001), tannins (R2= 0.567, P< 0.05) and flavonols (R2= 0.314, P< 0.05) bear significant correlation. Soil physicochemical parameters like pH (R2=0.537, P< 0.05), nitrogen (R2=0.618, P< 0.01), K2O (R2=0.106, insignificant), P2O5 (R=0.730, P< 0.01), S (R2=0.157, insignificant) and soil moisture (R2=0.745, P< 0.01) influence free-radical scavenging activity in tea leaves. Antioxidant quality of tea varies with maturation stages of leaves and the pattern is specific for a selected varietes. From our observation it may be concluded that antioxidant quality is dependent on some fertility parameters of soil and maturation of leaf. These results suggests that appropriate agronomic practices and proper choice of plucking may help to preserve the tea antioxidant quality.
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    Searching for phosphate solubilizinz tungal isolates from soil
    (University of North Bengal, 2008-03) Chakraborty, B. N.; Chakraborty, U.; Saha, A.; Dey, P. L.; Sunar, K.
    A total of 354 fungal isolates were obtained from soil samples collected from forests, river basins and agricultural fields of North Bengal using serial dilution, direct soil plating, serial root washing and root maceration techniques. Cultural characteristics of the isolated fungi were studied and microscopic observations were made for identification of these isolates. All the isolates were screened for their phosphate solubilizing activities in vitro. A total of 70 fungal isolates showed phosphate solubilizing activities as detected in Pikovskaya's agar medium. Quantitative evaluation of phosphate solubilization in liquid medium supplemented with two phosphate sources (tricalcium phosphate and rock phosphate) was carried out for all the isolates showing phosphate solubilizing activity. Maximum phosphate solubilizing capacity was shown by three isolates of A. niger while A. clavatus showed minimum activity. Genomic DNA was extracted from sixteen isolates showing high activity and PCR amplification of DNA from nine isolates was done.
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    Immunotechniques: Concept and application in plant pathology
    (University of North Bengal, 2007-03) Saha, A.; Dasgupta, S.; Saha, D.
    Proper management of plant diseases requires accurate disease diagnosis and precise identification of the phytopathogens involved. Traditional and conventional methods of disease diagnosis and pathogen detection have several demerits. It takes a lot of time to diagnose a disease and to identify a pathogen accurately by traditional approaches. Moreover, results are not always conclusive because similar symptoms can be caused by different pathogens or physiological conditions and sometimes it is very difficult to distinguish closely related organisms on the basis of their morphological characters only. Thus the traditional methods normally applied for pathogen identification and disease diagnosis are less sensitive and less reliable. The need for rapid and accurate identification and diagnostic methods to identify the organisms that cause plant diseases are essential for the formulation of effective disease control strategies.