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

New Record of Bipolaris cynodontis: An Emerging Human Pathogen Causing Superficial Mycosis in North India

Superficial mycosis, a common fungal infection affecting people worldwide are prevalent in the tropical and subtropical countries, mostly caused by the dermatophytes but nowadays, there is an increase in the incidence of these infections being caused by non-dermatophytic fungi and yeasts. Among non-dermatophytes, Bipolaris species, usually known to cause diseases in plants, have also emerged as potent human pathogens in the past years. Reports on Bipolaris species associated with clinical human skin samples are rare worldwide with no reports on B. cynodontis as a causal agent of superficial human skin mycoses from India. We report the first case of superficial mycosis caused by B. cynodontis that affected the feet of a 19-year-old female student from Jammu district, Jammu and Kashmir, India. Thus, the causal agent described in the research communication constitutes a new addition to the list of pathogenic non-dermatophytes associated with human skin.

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.

Serological detection and immunogold localization of cross-reactive antigens shared by Camellia sinensis and Exobasidium vexans

AIMS

Pathogenicity of Exobasidium vexans, causal agent of blister blight of tea, was studied in 30 commercially cultivated tea varieties by analysing the antigenic patterns of host and pathogen using immunological techniques.

METHODS AND RESULTS

Whole plant inoculation of tea varieties with E. vexans showed that T-78 and T-17/1/54 were most susceptible and most resistant respectively. Antigen preparations from tea varieties, pathogen, nonpathogen (Fusarium oxysporum) and of nonhosts (Glycine max, Leucaena leucocephala and Oryza sativa) were compared by indirect enzyme-linked immunosorbent assay and dot-immunobinding assay using polyclonal antibodies raised against the pathogen, nonpathogen, susceptible and resistant tea varieties. Cross-reactive antigens (CRA) were found among susceptible varieties and E. vexans isolates but not in resistant varieties, nonhosts or nonpathogen. Indirect staining of antibodies using fluorescein isothiocyanate indicated CRA were concentrated mainly around epidermal and mesophyll cells in compatible host (T-78). This was substantiated by ultrastructural studies using gold-labelled antibodies through transmission electron microscopy which showed specific localization in the chloroplasts and host cytoplasm.

CONCLUSION

Pathogenicity of E. vexans to different tea varieties is therefore related to the level of antigenic similarity between host and pathogen.

SIGNIFICANCE AND IMPACT OF THE STUDY

Immunological methods proved to be valuable in screening commercially cultivated tea varieties against E. vexans.