Loading...
![Thumbnail Image](assets/images/Collection.png)
Theses
Browse
5 results
Search Results
ThesisItem Open Access Plant growth promoting rhizobacteria mediated induced systemic resistance against bacterial wilt in ginger(College of Horticulture, Vellanikkara, 2007) Reshmy, Vijayaraghavan; KAU; Koshy, AbrahamThe pathogen causing bacterial wilt of ginger was isolated and identified as Ralstonia solanacearum biovar III based on its cultural, morphological and biochemical characters coupled with pathogenicity. Rhizosphere microflora of ginger from different locations of Thrissur, Waynad and Palakkad districts were isolated. Altogether, 163 rhizobacterial isolates were selected from these areas and their antagonistic activity against the pathogen assessed. Out of 163 isolates, only 45 showed antagonistic reaction. Further, study of these antagonists based on zone of inhibition resulted in selection of 20 isolates. The effect of these 20 isolates in promoting the growth of ginger was studied in pot culture in comparison with three reference cultures of P. fluorescens and B. subtilis. Result of this experiment revealed that only 11 isolates including the two reference cultures of P. fluorescens had growth promoting effect as evidenced in terms of yield and yield attributing characters of ginger. Factors which impart growth promotion in ginger by these isolates were assessed by estimating the inhibition zone, vigour index, hydrogen cyanide, indole acetic acid, ammonia production and ‘P’ solubilzation and based on that, PGPR index of the isolates was worked out. In addition to that, production of salicylic acid, antibiotics and siderphore by the isolates, the secondary metabolites which are known to play a role in disease suppression were assessed. The isolates varied in their ability to produce salicylic acid. Isolates RB-22 followed by RB-11, RB-144 and RB-66 produced more number of antibiotics which include pyoluteorin, pyrrolnitrin, 2,4DAPG etc. Similarly, isolate RB-22 and RB-11 produced maximum siderophores. The potential of these 11 rhizobacterial isolates in imparting resistance against the disease was assessed in another pot culture experiment by estimating phenol, proteins and amino acid content of ginger upon challenge inoculation. Here also, the isolates showed a profound effect on growth and yield of ginger especially by those plants bacterized with RB-11. There was no natural incidence of bacterial wilt in plants treated with RB-11 and RB-22. Upon challenge inoculation also, plants bacterized with RB-11 showed the least incidence. In general, rhizobacterial treated plants contained more amount of phenol, protein and amino acids than untreated ones. Upon challenge inoculation with the pathogen, the rate of increase of these compounds in rhizobacteria treated plants was more than that of control during different intervals of observations. A third pot culture experiment was conducted to assess the effect of rhizobacterial treatments on defense related enzymes of ginger upon challenge inoculation. Here, eight most promising ones including the reference cultures were used. In general, the study revealed more activity of peroxidase (PO), polyphenol oxidase (PPO) and phenylalanine ammonia lyase (PAL) in rhizobacterial treated plants that too after challenge inoculation. Native PAGE analysis revealed six isoforms of PO and four isoforms of PPO in a majority of the rhizobacterial treated plants whereas only three were noticed in control. Similarly, difference in the protein profile of rhizobacterial treated plants and control was noticed. Chlorophyll, NPK and oil and oleoresin content varied among treatments where the highest was observed in rhizobacterial treated plants. An attempt was made to elucidate the molecular mechanism of induced systemic resistance (ISR) in ginger by synthesizing cDNA and was subjected to RAPD assay. However, no conclusive evidence on ISR was observed. The compatibility of eight rhizobacterial isolates including the two reference cultures with antibiotics, fungicides, insecticides and fertilizers were assessed which revealed variation in their sensitivity. Moreover, mutual compatibility of the rhizobacterial isolates and compatibility with Trichoderma spp. were also studied and it was observed that all bacterial isolates were mutually compatible. However, Pseudomonas aeruginosa, P. fluorescens (RB-66) and the reference culture of P .fluorescens (P.f2) were found incompatible with the Trichoderma spp. The promising six rhizobacteria isolates were identified based on cultural, morphological and biochemical characters and also in comparison with that of reference culture of P. fluorescens. They were tentatively identified as Pseudomonas aeruginosa (RB-22), Pseudomonas fluorescens (RB-82, RB-66, RB-11) and the remaining two, RB-144 and RB-77, as non-fluorescent Pseudomonads.ThesisItem Open Access Characterization and management of viral diseases of black pepper(Piper nigrum L.)(College of Agriculture, Vellayani, 2010) Ayisha, R; KAU; Joseph, P JA detailed survey was undertaken to study the occurrence and distribution of viral diseases in black pepper in Thiruvananthapuram and Kollam districts of Kerala. Disease incidence (DI) and per cent disease index (PDI) were determined during survey which showed that per cent DI varied between 0-57 and PDI between 0-18. The disease was prevalent in both the districts. Most of the local cultivars and improved varieties were susceptible to the disease. The characteristics symptoms of disease were chlorotic spots on emerging younger leaves, vein clearing, scattered chlorotic flecks followed by chlorotic mottling along veins leading to interveinal chlorosis and characteristic twisting and curling of leaves. The infected leaves were also observed to be small, crinkled, and brittle with reduced internodal length, leading to typical stunting of plants. Most of the diseased plants were found to be infected with both Cucumber mosaic virus (CMV) and Pepper yellow mottle virus (PYMo V). The presence of these viruses was confirmed through conducting enzyme linked immunosorbent assay (ELISA) on representative samples collected from different locations. The virus was not mechanically transmitted to healthy pepper seedlings. However the virus was found to be transmitted through grafting, insect vectors and also through seeds. The mealy bug, Ferrisia I virgata was found to be the efficient vector although aphid, Toxoptera aurantii, was also found to be transmitting the virus. Thermal inactivation point was recorded at a range of 40-450C and dilution end point between 10-3 and 10-4 for CMV. Host range studies revealed that virus could be readily transmitted to other species in Piperaceae family as well to some of the weed hosts. The virus was partially purified and antiserum was produced with a titre of 1:128. Identification and serological characterization of the virus was done using ELISA and DIBA. Molecular detection of the virus was also performed using PCR and a PCR product of amplicon size 500 bp and 300 bp were obtained for primers specific to CMV and banana streak virus (BSV) respectively. The pathophysiological studies revealed that virus infected plants showed increased phenol, carbohydrate and protein content. The chlorophyll content was found to be less in infected samples. The activity of defence related enzymes like peroxidase, polyphenol oxidase and phenylalanine ammonialyase were found to be more in infected plants. Electrophoretic analysis of virus infected samples through SOS-PAGE revealed the presence of two novel proteins in diseased samples. Analysis of isozymes through native gel revealed the production of an additional isoform of peroxidase and over expression of polyphenol oxidase in infected plants. In screening of varieties for the source of resistance Panniyur, 2, 3 and 4 were found moderately resistant and Karimunda was highly susceptible. Piper colubrinum showed resistance to the virus. Meristem culure attempted was unsuccessful and could not be used as a viable strategy for eliminating the virus infecting black pepper as the meristems were seen contaminated with the pepper badnavirus.ThesisItem Open Access Strain improvement and production technology of milky mushroom (Caiocybe indica P. and C.)(Kerala Agricultural University;Thiruvananthapuram, 2006) Heera, G; KAU; Suharban, M.ThesisItem Open Access Disease management and growth improvement in chilli and tomato using Trichoderma spp. and fluorescent pseudomonads(Kerala Agricultural University;Thiruvananthapuram, 2005) Rini, C.R.; KAU; Sulochana, K.K.ThesisItem Open Access Characterisation and management of bitter gourd distortion mosaic virus(Kerala Agricultural University;Thrissur, 2006) Zacharia, Reeny Mary; KAU; Mathew, Sally K.