Virus Diseases of Peanut

Biocontrol of tomato wilt by plant growth-promoting rhizobacteria

PGPR-induced defense responses in the tea plant against blister blight disease

Involvement of secondary metabolites and extracellular lytic enzymes produced by Pseudomonas fluorescens in inhibition of Rhizoctonia solani, the rice sheath blight pathogen

Twenty isolates of fluorescent pseudomonads were evaluated for their ability to control damping-off in tomato (Lycopersicon esculentum) and hot pepper (Capsicum annuum). These isolates were characterized as Pseudomonas fluorescens and Pseudomonas putida. Two isolates, PFATR and KKM 1 belonged to P. putida and the remaining 18 isolates belonged to P. fluorescens. Among these isolates, P. fluorescens isolate Pf1 showed the maximum inhibition of mycelial growth of Pythium aphanidermatum and increased plant growth promotion in tomato and hot pepper. P. fluorescens isolate Pf1 was effective in reducing the damping-off incidence in tomato and hot pepper in greenhouse and field conditions. Isolate Pf1 was further tested for its ability to induce production of defense-related enzymes and chemicals in plants. Earlier and increased activities of phenylalanine ammonia lyase (PAL), peroxidase (PO) and polyphenol oxidase (PPO) were observed in P. fluorescens Pf1 pretreated tomato and hot pepper plants challenged with Pythium aphanidermatum. Moreover, higher accumulation of phenolics was noticed in plants pretreated with P. fluorescens isolate Pf1 challenged with Pythium aphanidermatum. Thus, the present study shows that in addition to direct antagonism and plant growth-promotion, induction of defense-related enzymes involved in the phenyl propanoid pathway collectively contributed to enhance resistance against invasion of Pythium in tomato and hot pepper.

Enhancing resistance of tomato and hot pepper to Pythium diseases by seed treatment with fluorescent pseudomonads

Foliar application of a plant growth-promoting rhizobacterium, Pseudomonas fluorescens strain Pf1 significantly controlled late leaf spot and rust diseases of groundnut (Arachis hypogaea L.) under greenhouse conditions. Groundnut plants, when sprayed with P. fluorescens strain Pfl, showed increase in activity of phenylalanine ammonia-lyase 1 day after application and the maximum enzyme activity was detected at 3 days after treatment. An increase in phenolic content was observed 1 day after P. fluorescens treatment. Also chitinase and β-1,3-glucanase activities increased significantly 1 day after P. fluorescens treatment and maximum activities were reached 4 days later. Application of P. fluorescens to groundnut leaves induced accumulation of a 23-kDa thaumatin-like protein (TLP) and a 30-kDa glucanase. The induction of 23-kDa TLP was detected only in treated leaves and not in roots, stems and petioles of the groundnut plants. The 30-kDa glucanase started to accumulate 1 day after treatment and the level of the protein continued to increase throughout the experimental period of 4 days. Both TLP and glucanase were found in the intercellular fluid of P. fluorescens-sprayed groundnut leaves.

Induction of pathogenesis-related proteins, phenolics and phenylalanine ammonia-lyase in groundnut by Pseudomonas fluorescens

Glasshouse and field trials were conducted to determine the efficacy of a talc-based powder formulation of Pseudomonas fluorescens strain Pf1 in controlling groundnut leaf spot ( Cercosporidium personatum ) and rust ( Puccinia arachidis ). Seed treatment with the talc-based powder formulation of the bacterium alone effectively reduced the severity of leaf spot and rust. When the treated seeds were sown in soil, the antagonist moved to the rhizosphere and multiplied well in it. Foliar application with the powder formulation effectively controlled the groundnut leaf spot and rust. P. fluorescens multiplied well in the phyllosphere after foliar application of powder formulation. Combined application of the P. fluorescens formulation to seed and foliage effectively controlled leaf spot and rust, and increased the pod yield in greenhouse and field tests.

Biological Control of Groundnut Late Leaf Spot and Rust by Seed and Foliar Applications of a Powder Formulation of Pseudomonas fluorescens

The potential of Pseudomonas fluorescens for the management of groundnut (Arachis hypogaea) root rot caused by Macrophomina phaseolina was evaluated under greenhouse and field conditions. Various strains of P. fluorescens isolated from the rhizosphere of groundnut were screened for their ability to inhibit mycelial growth of M. phaseolina. Among the various strains tested in vitro, five strains were found to inhibit the mycelial growth of M. phaseolina. Talc-based powder formulations of the effective strains of P. fluorescens were developed and evaluated for their efficacy in the management of groundnut root rot under greenhouse conditions. Seed treatment or soil application of powder formulation of P. fluorescens strain Pf1 effectively reduced groundnut root rot when compared to other strains. Seed treatment with Pf1 powder formulation exhibited a similar level of control to the soil application with P. fluorescens or soil drenching with carbendazim. Seed treatment with P. fluorescens reduced the root rot incidence from 88.8 % (with non-bacterized seeds) to 33.3 %. Four field trials were conducted over a 2-year period to determine the efficacy of seed treatment with powder formulation of Pfl in checking groundnut root rot. Seed treatment with powder formulation of Pf1 resulted in significant reduction in root rot incidence and increase in pod yield in all field trials. Ten strains of P. fluorescens were tested for their ability to produce HCN, salicylic acid, siderophore and lytic enzymes. The strain Pf1 that showed maximum in vitro antagonism produced more HCN, salicylic acid, siderophore and 3-1,3-glucanase in vitro when compared to other strains, The results suggest that more than one mechanism might be involved in suppression of M. phaseolina by P. fluorescens.

Biological control of root rot of groundnut with antagonistic Pseudomonas fluorescens strains.

Pseudomonas fluorescens mediated systemic resistance against late leaf spot of groundnut.

Twenty strains of Pseudomonas fluorescens were evaluated for their potential in promoting plant growth and in the control of late leaf spot caused by Cercosporidium personatum in groundnut under greenhouse conditions. Seed treatment with P. fluorescens strain Pf1 recorded the highest germination percentage and the maximum plant height. Seed treatment with P. fluorescens Pf1 significantly controlled late leaf spot disease of groundnut and increased the pod yield. When the treated seeds were sown in soil, the antagonist colonized well in the groundnut rhizosphere. P. fluorescens Pf1 showed the maximum production of indole acetic acid in in vitro.

T. Marimuthu

Papers

Induction of pathogenesis-related proteins, phenolics and phenylalanine ammonia-lyase in groundnut by Pseudomonas fluorescens

Biological Control of Groundnut Late Leaf Spot and Rust by Seed and Foliar Applications of a Powder Formulation of Pseudomonas fluorescens

Biological control of root rot of groundnut with antagonistic Pseudomonas fluorescens strains.

Pseudomonas fluorescens mediated systemic resistance against late leaf spot of groundnut.

Role of Fluorescent Pseudomonads in Plant Growth Promotion and Biological Control of Late Leaf Spot of Groundnut