Aniruddha Saha

A new antifungal coumarin from Clausena excavata.

A new γ-lactone coumarin, named as excavarin-A, showing antifungal activity was isolated from the leaves of Clausena excavata by bioassay guided fractionation method. The structure was elucidated by spectroscopic data analysis and identified as 7((2E)-4(4,5-dihydro-3-methylene-2-oxo-5-furanyl)-3-methylbut-2-enyloxy) coumarin. Minimum inhibitory concentration (MIC) was determined against fifteen fungal strains pathogenic against plants and human. The least MIC was recorded against the human pathogen, Candida tropicalis and the plant pathogens Rhizoctonia solani and Sclerotinia sclerotiorum. Antifungal activities against the human pathogens, Aspergillus fumigatus and Mucor circinelloides and plant pathogens, Colletotrichum gloeosporioides, Lasiodiplodia theobromae, Fusarium oxysporum and Rhizopus stolonifer were stronger than that of the standard antimicrobials.

Antifungal Activity of Some Plant Extracts Against Fungal Pathogens of Tea (Camellia sinensis.)

Abstract In an approach toward the development of ecofriendly antifungal compounds for controlling major foliar fungal diseases of tea, ethanol and aqueous extracts of 30 plants belonging to 20 different families collected from sub-Himalayan West Bengal (India) were tested against the pathogens Pestalotiopsis theae. (Saw.) Stey., Colletotrichum camelliae. Mess., Curvularia eragrostidis. (P. Hennings) Meyer, and Botryodiplodia theobromae. Patouiilard. Spore germination technique was followed for evaluation of antifungal properties. Results showed that ethanol and aqueous extracts of Allium sativum. L., Datura metel. L., Dryopteris filix-mas. (L.) Schott, Zingiber officinale. Rosc., Smilax zeylanica. L., Azadirachta indica., A. Joss. and Curcuma longa. L. recorded 100% inhibition of spore germination. The antifungal component from these plants may be used in developing novel fungicides for tea gardens.

Triterpenoids from Psidium guajava with Biocidal Activity.

In continuation of our studies on the phytochemical investigation of medicinal plants available in the foothills of Darjeeling and Teri, we report herein the isolation of two triterpenoids betulinic acid and lupeol from the leaf extract of Psidium guajava and their potential antimicrobial and phytotoxic activities. All the structures of the isolated compounds were confirmed by spectral (IR, NMR) analysis and by comparison with the literature reports.

Levels of common antigens in determining pathogenicity of Curvularia eragrostidis in different tea varieties

Aims:  Pathogenicity of Curvularia eragrostidis, a foliar fungal pathogen of tea was studied in 24 commercially cultivated tea varieties by analysing the antigenic patterns of host and pathogen with the help of immunoserological techniques.

Triterpenoids from Schleichera oleosa of Darjeeling foothills and their antimicrobial activity

Two triterpenoids, taraxerone and tricadenic acid A were isolated from the methanol extract of the outer bark of Schleichera oleosa available in Darjeeling foothills. A preliminary study on their antimicrobial activities was also performed against some fungal and bacterial species. The structure of these compounds was determined by means of chemical characterisation and IR, NMR spectral data.

Evaluation of antiserum raised againstPestalotiopsis theœ for the detection of grey blight of tea by ELISA

Polyclonal antiserum was raised against the mycelial extract ofPestalotiopsis theœ and immunoglobulin fractions were purified by ammonium sulfate fractionation and chromatography on DEAE-Sephadex. In enzyme-linked immunosorbent assay, antiserum dilution up to 1∶16000 detected homologous antigen at a 5 mg/L concentration, and at 1∶125 antiserum dilution fungal antigens could be detected at a concentration as low as 25 μg/L. In fifteen varieties of tea tested, originating from Darjeeling, UPASI and Tocklai breeding stations, absorbance values of infected leaf extracts were significantly higher than those of healthy extracts at a concentration of 40 mg/L in indirect ELISA. ELISA-positive material was detected in tea leaves as early as 12 h after inoculation withP. theœ. At antiserum dilutions up to 1∶125, the pathogen could be detected in inoculated leaf extracts up to antigen concentration of 2 mg/L. The antiserum reacted with two other isolates ofP. theœ tested but not with the antigens from mycelial extracts ofGlomerella cingulata andCorticium invisum or with extracts of tea leaves inoculated with these pathogens. The results demonstrate that ELISA can be used for early detection ofP. theœ in leaf tissues even at a very low level of infection.

Phylogeny and synonymous codon usage pattern of Papaya ringspot virus coat protein gene in the sub-Himalayan region of north-east India

Sub-Himalayan West Bengal is favorable for the production of several fruits and vegetables. Papaya is one of the common plants cultivated in the area. Most of the papaya plants of the area are susceptible to Papaya ringspot virus (PRSV). Coat protein genes of 6 PRSV isolates of the area were sequenced following RT-PCR. Phylogenetic study of the PRSV isolates showed about 80%-90% similarity with Cuban isolates. The codon usage pattern of our isolates was also analyzed, along with several other isolates. PRSV isolates of our study showed a preference for 8 putative optimal codons. Correspondence analysis of the genes of different isolates along the first 2 major axes were done, as the first 2 axes contributed more in shaping codon usage pattern. In the phylogenetic tree constructed by the neighbour-joining method, our isolates clustered together with the east Indian, north Indian, and Bangladeshi isolates. The diversity and codon usage pattern of the PRSV isolates of different regions were studied, and it was observed that the codon usage pattern of PRSV isolates is probably influenced by translational selection along with mutational bias.

Biotransformation of 16-oxacleroda-3,13(14)E-dien-15-oic acid isolated from Polyalthia longifolia by Rhizopus stolonifer increases its antifungal activity

Abstract Biotransformation of the antifungal compound 16-oxocleroda-3,13(14)E-dien-15-oic acid (1) isolated from Polyalthia longifolia leaves was achieved by Rhizopus stolonifer in broth medium containing the substrate at the sublethal concentration of 0.06 mg ml−1. A novel derivative, 18-hydroxy-16-oxocleroda-3,13(14)E-dien-15-oic acid (2) was isolated after 4 d of incubation. Minimum inhibitory concentration (MIC) was determined against 11 fungal pathogens of clinical and agricultural importance. The biotransformed compound showed lower MIC values than the natural parent compound. The study showed that the fungus R. stolonifer has the potential to hydroxylate a natural fungicidal clerodane diterpene at allylic position to produce a novel hydroxylated derivative with enhanced antifungal activity.

Molecular Detection and Diversity Analysis of Some Potyviruses Associated with Mosaic Diseases of Papaya, Common Bean and Potato Growing in Sub-Himalayan West Bengal

Molecular Detection and Diversity Analysis of Some Potyviruses Associated with Mosaic Diseases of Papaya, Common Bean and Potato Growing in Sub-Himalayan West Bengal. Environmental condition of sub- Himalayan West Bengal and Brahmaputra valley of Assam is conducive to year round production of vegetables and fruit crops. The crops of the region are also proving to viral diseases. Several symptoms of viral diseases are found in the fields of sub-Himalayan West Bengal. Mosaic symptoms one of the important disease symptom of the area. Mosaic symptoms containing samples of papaya, common bean and potato of the region were studied for causal pathogenic viruses of the crops. As most the symptoms matched with potyvirus symptoms found elsewhere. The detection of the viruses was made by universal potyvirus primers. Analysis of the viruses was also made for identification of the viruses. .

Evaluation of the biocontrol efficacy of a Serratia marcescens strain indigenous to tea rhizosphere for the management of root rot disease in tea

The aim of the present study is to evaluate plant growth promoting and biocontrol efficacy of a Serratia marcescens strain ETR17 isolated from tea rhizosphere for the effective management of root rot disease in tea. Isolated bacterial culture ETR17 showed significant level of in vitro antagonism against nine different foliar and root pathogens of tea. The phenotypic and molecular characterization of ETR17 revealed the identity of the bacterium as Serratia marcescens. The bacterium was found to produce several hydrolytic enzymes like chitinase, protease, lipase, cellulase and plant growth promoting metabolites like IAA and siderophore. Scanning electron microscopic studies on the interaction zone between pathogen and antagonistic bacterial isolate revealed severe deformities in the fungal mycelia. Spectral analyses (LC-ESI-MS, UV-VIS spectrophotometry and HPLC) and TLC indicated the presence of the antibiotics pyrrolnitrin and prodigiosin in the extracellular bacterial culture extracts. Biofilm formation by ETR17 on polystyrene surface was also observed. In vivo application of talc-based formulations prepared with the isolate ETR17 in tea plantlets under green house conditions revealed effective reduction of root-rot disease as well as plant growth promotion to a considerable extent. Viability studies with the ETR17 talc formulation showed the survivability of the isolate up to six months at room temperature. The sustenance of ETR17 (concentration of 8-9x108 cfu g-1) in the soil after the application of talc formulation was recorded by ELISA. Safety studies revealed that ETR17 did not produce hemolysin as observed in pathogenic Serratia strains. The biocontrol strain reported in this study can be used for field application in order to minimize the use of chemical fungicides for disease control in tea gardens.