R. Samiyappan

Induction of systemic resistance by plant growth promoting rhizobacteria in crop plants against pests and diseases

Abstract Plant growth promoting rhizobacteria (PGPR) belonging to Pseudomonas spp. are being exploited commercially for plant protection to induce systemic resistance against various pests and diseases. Mixtures of different PGPR strains have resulted in increased efficacy by inducing systemic resistance against several pathogens attacking the same crop. Seed-treatment with PGPR causes cell wall structural modifications and biochemical/physiological changes leading to the synthesis of proteins and chemicals involved in plant defense mechanisms. Lipopolysaccharides, siderophores and salicylic acid are the major determinants of PGPR-mediated ISR. The performance of PGPR has been successful against certain pathogens, insect and nematode pests under field conditions.

ACC deaminase from Pseudomonas fluorescens mediated saline resistance in groundnut (Arachis hypogea) plants

Aim:  To study the effect of 1‐aminocyclopropane‐1‐carboxylic acid (ACC) deaminase from Pseudomonas fluorescens against saline stress under in vitro and field conditions in groundnut (Arachis hypogea) plants.

Induction of defense-related proteins in tomato roots treated with Pseudomonas fluorescens Pf1 and Fusarium oxysporum f. sp. lycopersici

Pseudomonas fluorescens isolate Pf1 was found to protect tomato plants from wilt disease caused by Fusarium oxysporum f. sp. lycopersici. Induction of defense proteins and chemicals by P. fluorescens isolate Pf1 against challenge inoculation with F. oxysporum f. sp. lycopersici in tomato was studied. Phenolics were found to accumulate in bacterized tomato root tissues challenged with F. oxysporum f. sp. lycopersici at one day after pathogen challenge. The accumulation of phenolics reached maximum at the 5th day after pathogen challenge. In pathogen-inoculated plants, the accumulation started at the 2nd day and drastically decreased 4 days after the pathogen inoculation. Activities of phenylalanine ammonia-lyase (PAL), peroxidase (PO) and polyphenol oxidase (PPO) increased in bacterized tomato root tissues challenged with the pathogen at one day after pathogen challenge and activities of PAL and PO reached maximum at the 4th day while activity of PPO reached maximum at the 5th day after challenge inoculation. Isoform analysis revealed that a unique PPO1 isoform was induced and PO1 and PPO2 isoforms were expressed at higher levels in bacterized tomato root tissues challenge inoculated with the pathogen. Similarly, β-1,3 glucanase, chitinase and thaumatin-like proteins (TLP) were induced to accumulate at higher levels at 3-5 days of challenge inoculation in bacterized plants. Western blot analysis showed that chitinase isoform Chi2 with a molecular weight of 46 kDa was newly induced due to P. fluorescens isolate Pf1 treatment challenged with the pathogen. TLP isoform with molecular weight of 33 kDa was induced not only in P. fluorescens isolate Pf1-treated root tissues challenged with the pathogen but also in roots treated with P. fluorescens isolate Pf1 alone and roots inoculated with the pathogen. These results suggest that induction of defense enzymes involved in phenylpropanoid pathway and accumulation of phenolics and PR-proteins might have contributed to restriction of invasion of F. oxysporum f. sp. lycopersici in tomato roots.

Pseudomonas fluorescens based bio-formulation for the management of sheath blight disease and leaffolder insect in rice

Abstract The talc-based formulation of two Pseudomonas fluorescens strains (PF1 and FP7) and its mixture (with and without chitin) were tested against sheath blight and leaffolder in rice. The application of talc-formulation through seed, root, soil and foliar spray significantly reduced the sheath blight and leaffolder incidence both under greenhouse and field conditions. The mixture of two strains performed better than the individual strains. In field trials the maximum of 62.1% sheath blight and 47.7–56.1% reduction in leaffolder incidence was noticed in the mixture treatment containing chitin and its efficacy was equivalent to standard fungicide and insecticide treatments. Pseudomonas treated leaves altered the feeding behaviour of leaffolder larvae and reduced larval and pupal weight, increased larval mortality and incidence of malformed adults under in vitro. An increased population of natural enemies of leaffolder viz., hymenopterous parasitoids and predatory spider was noticed in Pseudomonas treated plots under field conditions, which, yielded 12–21% more rice.

Enhancing Resistance of Tomato and Hot Pepper to Pythium Diseases by Seed Treatment with Fluorescent Pseudomonads

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.

A new bio-formulation containing plant growth promoting rhizobacterial mixture for the management of sheath blight and enhanced grain yield in rice

Three plant growth promoting rhizobacterial (PGPR) strains, PF1,FP7 and PB2, were tested alone and in combinations for suppression ofrice sheath blight disease and promotion of plant growth underglasshouse and field conditions. The mixture of PGPR strainssignificantly reduced the sheath blight incidence when applied as eitherbacterial suspension through seed, root, foliar and soil application inglasshouse conditions, or as talc-based formulation under fieldconditions, compared to the respective individual strains. The averagemean of disease reduction was 29.2% for single strains and45.1% for mixtures. In addition to disease suppression, treatmentwith mixture of PGPR strains promoted plant growth in terms of increasedplant height and number of tillers, and ultimately grain yield. Theaverage increases in yield for single strains were 17.7%, and25.9% in case of mixture. Mixture of three PGPR strains reduceddisease and promoted growth to a level equivalent to two strainmixtures. Though seed treatment of either single strain or strainmixtures alone could reduce the disease, subsequent application to root,leaves or soil further reduced the disease and enhanced the plantgrowth. The mixture consisting of PF1 plus FP7 was the most effective inreducing the disease and in promoting plant growth and grainyield.

Pyramiding transgenic resistance in elite indica rice cultivars against the sheath blight and bacterial blight

Elite indica rice cultivars were cotransformed with genes expressing a rice chitinase (chi11) and a thaumatin-like protein (tlp) conferring resistance to fungal pathogens and a serine-threonine kinase (Xa21) conferring bacterial blight resistance, through particle bombardment, with a view to pyramiding sheath blight and bacterial blight resistance. Molecular analyses of putative transgenic lines by polymerase chain reaction, Southern Blot hybridization, and Western Blotting revealed stable integration and expression of the transgenes in a few independent transgenic lines. Progeny analyses showed the stable inheritance of transgenes to their progeny. Coexpression of chitinase and thaumatin-like protein in the progenies of a transgenic Pusa Basmati1 line revealed an enhanced resistance to the sheath blight pathogen, Rhizoctonia solani, as compared to that in the lines expressing the individual genes. A transgenic Pusa Basmati1 line pyramided with chi11, tlp, and Xa21 showed an enhanced resistance to both sheath blight and bacterial blight.

Induced systemic resistance by fluorescent pseudomonads against red rot disease of sugarcane caused by Colletotrichum falcatum

Abstract Certain strains of fluorescent Pseudomonas spp. were studied for their plant growth promoting attributes and induced systemic resistance (ISR) against red rot pathogen Colletotrichum falcatum Went in sugarcane. The fluorescent pseudomonad (FPs) strains were applied three times in the field, initially as a sett treatment while planting and two soil applications in the field using talc-based formulations. The ISR effect in the treated canes was assessed by artificial inoculation of the pathogen in the cane stalks. Some Pseudomonas strains significantly reduced red rot disease intensity in the sugarcane stalks. The Pseudomonas- mediated ISR was significantly higher in the disease susceptible cultivars than in the moderately resistant and moderately susceptible cultivars. When five Pseudomonas strains were evaluated for their efficacy against the disease in an endemic location, isolates CHAO, EP1 and Pf1 significantly reduced disease incidence. The tested strains significantly improved vegetative sett germination and crop growth in the field. Less pathogen induced invertase enzyme activity was recorded in cane tissues from bacteria treated stalks, and higher juice characters viz. sucrose per cent and sugar yield as compared to the untreated stalk tissues, after pathogen inoculation. The efficacy of certain Pseudomonas strains against red rot pathogen, enhanced the yield of cane and sugar and this suggests that these bacterial strains may have a role to play in the management of red rot disease in sugarcane.

Plant growth promoting bacteria enhance water stress resistance in green gram plants

Plant growth promoting bacterial (PGPB) strains Pseudomonas fluorescens Pf1 and endophytic Bacillus subtilis EPB5, EPB22, EPB 31 were tested for their capacity to induce water stress related proteins and enzymes in green gram (Vigna radiata) plants. Among the different bacteria used, P. fluorescens Pf1 increased the vigour index, fresh weight and dry weight of green gram seedlings in vitro. Quantitative and qualitative analyses of stress-related enzymes indicated the greater activity of catalase and peroxidase in green gram plants bacterized with P. fluorescens Pf1 against water stress when compared to untreated plants. The greater accumulation of proline was recorded in Pf1 treated plants compared to untreated plants. The pot culture study revealed the greater resistance to water stress by green gram plants treated with P. fluorescens Pf1 compared to untreated plants. The greater activity of stress-related enzymes in green gram plants mediated by PGPB could pave the way for developing drought management strategies.

Risk assessment of insecticides used in rice on miridbug, Cyrtorhinus lividipennis Reuter, the important predator of brown planthopper, Nilaparvata lugens (Stal.).

The green miridbug, Cyrtorhinus lividipennis, an important natural enemy of the rice brown planthopper (BPH), Nilaparvata lugens plays a major role as a predator in suppressing the pest population. The study assessed the impact of certain potential insecticides used in the rice ecosystem on the miridbug predator and brown planthopper through contact toxicity. Eleven insecticides, including neonicotinoids, diamides, azomethine pyridines, carbamates, pyrethroids, organophosphates and cyclodienes were selected to test their toxicities against the nymphs of C. lividipennis and N. lugens. Median lethal concentration (LC(50)) was determined for each insecticide using an insecticide-coated vial (scintillation) residue bioassay, which revealed BPMC as the highly toxic chemical with an LC(50) of 0.003mga.iL(-1) followed by ethofenprox and clothianidin with LC(50) of 0.006mga.iL(-1) at 48 HAT against C. lividipennis and ethofenprox as the highly toxic chemical with an LC(50) of 0.009mga.iL(-1) followed by clothianidin with an LC(50) of 0.211mga.iL(-1) at 48h after treatment (HAT) against N. lugens. Among the insecticides tested, the cyclodiene compound, endosulfan had the lowest acute contact toxicity (LC(50)=66.65mga.iL(-1) at 48 HAT) to C. lividipennis. Among the insecticides tested, endosulfan, chlorpyriphos, acephate and methyl parathion are regarded as safer to C. lividipennis based on selectivity ratio, hazard quotient and probit substitution method of risk assessments.