PhD

The study entitled “Purification and immunodetection of banana bract mosaic virus” was conducted in College of Agriculture, Vellayani, Thiruvananthapuram during 2000-2003.
Survey conducted in Thiruvananthapuram district revealed that banana bract mosaic virus (BBrMV) is widely prevalent in different taluks of the district. Zero to 100 per cent variation was observed for disease incidence and per cent disease index was significantly different between taluks. The disease was found to increase with progress of time. Studies on varietal reaction revealed that none of the commonly cultivated varieties were resistant to BBrMV. Symptomatological studies showed that the characteristics symptoms of banana bract mosaic disease were longitudinal irregular reddish streaks on pseudostem, chlorosis of leaves, necrotic streaks on petiole and bract, travellers’ palm appearance, severe reduction in bunch size and formation of malformed fingers. Mechanical transmission of BBrMV through different means, graft transmission and soil transmission were unsuccessful. The aphid Pentalonia nigronervosa Coq. was identified as efficient vector of BBrMV (40 per cent transmission) with pre-acquisition fasting of one hour and acquisition threshold of 30 minutes.
Carbohydrate content was less in BBrMV infected plants compared to healthy at all stages of analysis except at bract stage. The phenol content was more in infected banana plants at six months after planting and flag leaf stage whereas it was higher in healthy plants at three months after planting and at bract stage. Content of OD-phenol, protein, activity of peroxidase, polyphenol oxidase and phenylalanine ammonialyase were found to be more in banana bract mosaic virus infected plants.
Electrophoretic analysis of BBrMV infected samples through SDS-PAGE revealed the presence of three extra bands (of virus) with molecular weight of 31, 32 and 39 kDa. Electrophoretic analysis of isozymes through native gel revealed the production of peroxidase isozyme in infected plants and the over expression of polyphenol oxidase isozyme in plants infected with BBrMV. Bioassay of endogenous growth regulators showed that the content of auxin, cytokinin and gibberlic acid was less in BBrMV infected fruits compared to healthy.
The virus, BBrMV was purified from infected young leaf and the antiserum was developed in New Zealand white rabbit by giving intramuscular injection of partially purified virus. Titre of antiserum was tested using DAC-ELISA and it was determined as 1 : 1024. Electron microscopic studies of infected plant sample revealed that the virus particles were long flexuous rods with an average size of 725 x 12 nm. Detection of BBrMV infected plant parts was done using various immunological techniques like chloroplast agglutination, microprecipitin, Ouchterlony’s agar gel double diffusion test, DAC-ELISA and dot immuno binding assay and all were found to be efficient for the detection of BBrMV.
Germplasm collection at Banana Research Station, Kannara were screened for banana bract mosaic disease resistance and found that varieties with ‘A’ genome were found to be more susceptible to the disease compared to those with ‘B’ genome. Screening of varieties at Instructional Farm, Vellayani showed that all of the commonly cultivated varieties were susceptible to BBrMV. For the production of virus free planting material meristem culture technique was attempted using meristems of BBrMV infected suckers. Virus free nature of the developed plants was confirmed through DAC-ELISA and it was found that about 100 per cent plants developed through meristem culture were free of BBrMV. Based on the survey and screening of germplasm collection, it was concluded that strict phytosanitation and use of virus free planting materials, preferably meristem cultured plants will help to manage the disease to a great extent.