MSc

The study, “Management of foliar blight of amaranthus using plant growth promoting rhizobacteria (PGPR) and a chemical activator Acibenzolar-S- Methyl” was conducted at the Department of Plant Pathology, College of Agriculture, Vellayani. Four proven PGPR isolates viz., Pseudomonas fluorescens strain PN026R, Pseudomonas putida strain 89B61, Bacillus pumilus strain SE34 and Bacillus subtilis strain GB03 and a chemical activator ActigardTM 50WG containing the active ingredient Acibenzolar-S-Methyl (ASM) were used for the study. Disease suppression and plant growth promotion studies were performed using these PGPR isolates and ASM. In vitro studies were conducted to check whether the bioagents are having a direct antagonistic effect on the pathogen. Dual culture plate assay was performed in four different media. It was noted that the antagonism showed by these rhizobacteria ranged from slight antagonism to a zone of more than 5 mm. The range of antagonism even by same antagonist varied in different media. The mycelial growth inhibition of the pathogen by different concentration of ASM in the medium was also noticed.
A screening experiment was conducted to assess the involvement of ISR by different PGPR and the chemical activator individually and in combination against the disease caused by R. solani in amaranthus var. Arun. Sterile potting mixture was used in the study. The minimum disease severity was observed for combined treatment with GB03 and ASM. Plants treated with PN026R, GB03 and the consortium of bacteria showed same disease severity of 8.33%. Observations on plant growth promotion were also taken. Based on the effect on disease suppression and plant growth promotion two PGPR strains were selected for further pot culture studies viz., GB03 and PN026R. PN026R+ASM, GB03 and ASM treatments recorded the lowest disease incidence. The minimum disease severity was recorded for uninoculated control. GB03 and PN026R+ASM recorded same disease severity. Maximum shoot length and shoot fresh weight was observed for the treatment with PN026R+ASM.
The total phenol content and the different enzyme activities were also recorded in this experiment. Changes in the levels of PAL, PO and PPO were recorded at one, five and ten days after inoculation with the pathogen. After five days of inoculation the maximum phenol content was recorded for PN026R. Treatment with ASM alone showed maximum PAL activity five days after inoculation. There was a progressive increase in peroxidase activity from one day after inoculation to ten days after inoculation in the plants treated with PN026R, PN026R+ASM and GB03.
Plant Growth promotion experiments were also carried out using the four PGPR strains and ASM. The maximum shoot length was recorded for the treatment with SE34 followed by PN026R, consortium of bacteria+ASM and the control. The maximum root length was recorded for GB03+ASM.
The results of the study indicate that PN026R showed better growth promotion and ISR activities. PN026R can also be used in combination with ASM which helps to compensate the adverse effects of ASM.