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Department of Biotechnology
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Division of Entomology and Nematology
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Division of Plant Pathology
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    ABSTRACT: The study was taken up to assess if the media constituents played any role in governing the variable colony characteristics or pathogenicity of the bacterial wilt pathogen, Ralstonia solanacearum cultured on the widely employed Kelman medium. The effects due to the constituents 2,3,5-triphenyl tetrazolium chloride (TTC), peptone, casein hydrolysate and glucose on colony characteristics were investigated using -80°C stored culture of strain 'NH-Av01' (race 1, biovar 3) isolated from tomato. Comparing the pigment inducing TTC from two brands, its source or mode of storage/incorporation did not impart any significant effects. The source of peptone, on the other hand, displayed striking effects on the extent of colony growth, fluidity and red pigmentation depending on type, brand or batch / lot of manufacture as documented with 20 different formulations. Significant differences in the pathogenicity of isolate derived from different peptone sources in seedling-challenge assay on tomato were observed. The observations on peptone effects were endorsed with four other isolates belonging to distinct geographic locations, crops (eggplant, chilli, ginger) or races (race 1 or 4). The peptone source did not influence the pathogen-responses in biovar tests but notably altered the pattern of lawn formation and inhibition zone development during antagonistic assays. Casein hydrolysate displayed some variable effects while glucose source had no effect. This study brings to light the significant modifying effects by the peptone-constituent in Kelman medium on the physiology of R. solanacearum and the virulence of isolate and the need to consider the source of media components during culture maintenance, host-pathogen interaction studies or microbe-microbe interaction investigations.
    The Open Microbiology Journal 10/2014; 8(1):95-114. DOI:10.2174/1874285801408010095
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    ABSTRACT: Wider germplasm diversity and transferability of the antioxidant parameters is the primary requirement for the development of high antioxidant tomato cultivars. The present study was conducted to screen the tomato genotypes including hybrids, varieties, cherry tomatoes, wild species, elite germplasm lines, inter-specific hybrids and backcross populations for antioxidant activity and other quality parameters to select high antioxidant lines with good total soluble solids (TSS) for further usage in crop improvement programmes. Wild species and inter-specific hybrids between LA-1777 (Solanum habrochaites) and an elite genotype 15SBSB recorded very high antioxidant capacity (FRAP), DPPH radical scavenging ability, higher phenols and flavonoids. Inter-specific hybrids also recorded very high total soluble solids (TSS). Significantly higher total carotenoids, lycopene and vitamin C were observed in IIHR-249-1 with moderately higher TSS. Cherry tomato lines IIHR-2866, 2865 and 2864 recorded 4 to 5 times more β-carotene than the commercial hybrids/varieties. Tomato line IIHR-249-1 can be used for improving the antioxidant capacity, total carotenoids and lycopene in tomato breeding programmes. Cherry tomato lines IIHR-2866, 2865 and 2864 can be used for improving the β-carotene content. LA-1777 and inter-specific hybrids could be used for developing tomato lines rich in antioxidants as well as TSS.
    Journal of the Science of Food and Agriculture 03/2014; 94(5). DOI:10.1002/jsfa.6359
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    ABSTRACT: It is generally believed that endophytic microorganisms are intercellular inhabitants present in either cultivable or non-cultivable form primarily as root colonizers. The objective of this study was to determine whether the actively mobile micro-particles observed in the intracellular matrix of fresh tissue sections of banana included endophytic bacteria. Tissue sections (50-100 µm) from apical leaf sheaths of surface-disinfected suckers (cv. Grand Naine) displayed 'Brownian motion'-reminiscent abundant motile micro-particles under bright-field and phase-contrast (×1000), which appeared similar in size and motility to the pure cultures of endophytes previously isolated from banana. Observations on callus, embryonic cells and protoplasts with intact cell wall/plasma membrane confirmed their cytoplasmic nature. The motility of these entities reduced or ceased upon tissue fixation or staining with safranin/crystal violet (0.5 % w/v), but continued uninterrupted following treatment with actin-disrupting drugs, ruling out the possibility of micro-organelles like peroxisomes. Staining with 2,3,5-triphenyl tetrazolium chloride (TTC) confirmed them to be live bacteria with similar observations after dilute safranin (0.005 %) treatment. Tissue staining with SYTO-9 coupled with epi-fluorescence or confocal laser scanning microscopy showed bacterial colonization along the peri-space between cell wall and plasma membrane initially. SYTO-9 counterstaining on TTC- or safranin-treated tissue and those subjected to enzymatic permeabilization revealed the cytoplasmic bacteria. These included organisms moving freely in the cytoplasm and those adhering to the nuclear envelope or vacuoles and the intravacuolar colonizers. The observations appeared ubiquitous to different genomes and genotypes of banana. Plating the tissue homogenate on nutrient media seldom yielded colony growth. This study, supported largely by live cell video-imaging, demonstrates enormous intracellular colonization in bananas by normally non-cultivable endophytic bacteria in two niches, namely cytoplasmic and periplasmic, designated as 'Cytobacts' and 'Peribacts', respectively. The integral intracellular association with their clonal perpetuation suggests a mutualistic relationship between endophytes and the host.
    AoB PLANTS 02/2014; 6. DOI:10.1093/aobpla/plu002


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    Bangalore, India
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Edited by D. Kalaivanan and C. Ravindran, 01/2012; LAP Lambert Academic Publishing. ISBN: 978-3-659-12765-6
Plant Disease 12/2000; 84(12):1343. DOI:10.1094/PDIS.2000.84.12.1343B

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