Role of antioxidant scavenging enzymes and extracellular polysaccharide in pathogenicity of rice bacterial blight pathogen Xanthomonas oryzae pv. oryzae

In the present work, we studied the role of antioxidant scavenging enzymes of plant pathogenic bacteria:  catalase, ascorbate peroxidase and a virulence factor; extracelluar polysaccharide production in determining the virulence of Xanthomonas oryzae pv. oryzae (Xoo) isolates and its differential reaction to rice cultivars. A varied level of antioxidant scavenging activity and exopolysaccharide production was observed among 34 isolates studied, and most of the Xoo isolates with higher catalase activity also exhibited higher ascorbate peroxidase activity. The maximum level of catalase (45 µM H2O2 min-1 mg-1 protein), ascorbate peroxidase (29 µM ascorbate min-1 mg-1 proteins) activity and exopolysaccharide production (70 mg) was found in isolate Xoo32 which induced maximum lesion length on cultivar ‘Jaya’ upon clip inoculation in virulence assay. Among the 44 cultivars screened, cultivar ‘Jeerigesanna’ recorded least bacterial blight disease incidence, with 0.7 cm lesion length. The activity of catalase, ascorbate peroxidase and exopolysaccharide can be employed as bio-chemical markers in determining the virulence of Xoo under laboratory conditions.Key words: Paddy, plant pathogenic bacteria, antioxidant scavenging enzymes, exopolysaccharide,  virulence, bio-chemical markers

Role of antioxidant scavenging enzymes and extracellular polysaccharide in pathogenicity of rice bacterial blight pathogen Xanthomonas oryzae pv. oryzae

The role of antioxidant scavenging enzymes of plant pathogenic bacteria: catalase, ascorbate peroxidase and a virulence factor; extracelluar polysaccharide prodn. in detg. the virulence of Xanthomonas oryzae pv. oryzae (Xoo) isolates and its differential reaction to rice cultivars was studied. A varied level of antioxidant scavenging activity and exopolysaccharide prodn. was obsd. among 34 isolates studied, and most of the Xoo isolates with higher catalase activity also exhibited higher ascorbate peroxidase activity. The max. level of catalase (45 μM H2O2 min-​1 mg-​1 protein)​, ascorbate peroxidase (29 μM ascorbate min-​1 mg-​1 proteins) activity and exopolysaccharide prodn. (70 mg) was found in isolate Xoo32 which induced max. lesion length on cultivar 'Jaya' upon clip inoculation in virulence assay. Among the 44 cultivars screened, cultivar 'Jeerigesanna' recorded least bacterial blight disease incidence, with 0.7 cm lesion length. The activity of catalase, ascorbate peroxidase and exopolysaccharide can be employed as bio-​chem. markers in detg. the virulence of Xoo under lab. conditions

Phytochemical Screening and in Vitro Assessment of Antimicrobial and Antioxidant Potential of Andrographis Serpyllifolia-An Endemic Medicinal Plant from South India

The current study was aimed to investigate the phytochemical composition, antibacterial and antioxidant activity of A. serpyllifolia plant extracts. Phytochemical screening revealed the presence of alkaloid, tannins, steroids, terpenoids, phlobatannin, anthraquinones flavonoids, saponins and phenolic compounds. Quantitative analysis revealed the presence of saponins (4.2%) in high concentration followed by tannins (4.12%), phenolics (1.4%), alkaloids (1.2%) and flavonoids (0.98%). This study will provide phytochemical information for preparation of concentrated and effective extract of A. serpyllifolia. Petroleum ether, chloroform, benzene and methanol extracts of shade dried plant parts of A. serpyllifolia were tested for antibacterial activity against six strains of bacterial species, viz., Bacillus subtilis, Escherichia coli, Proteus, Pseudomonas aeruginosa, Klebsiella sps and Staphylococcus aureus using the standard agar disk diffusion method. All the extracts have shown significant activity against tested microbes with the inhibition zone ranged of 5.7-16.8mm. Among various solvent extracts studied petroleum ether extract showed a highest antibacterial activity followed by methanol, benzene, chloroform. Antioxidant potential of methanol extracts was determined by DPPH and ABTS free radical scavenging assay. The extracts showed a very good antioxidant property and the IC50 value was found to 268.12ìg/ml for DPPH assay and 398.46ìg/ml for ABTS assay. Ascorbic acid taken as control showed highest antioxidant power in the present study. The results suggest that A. serpyllifolia has promising antioxidant activity and could serve as potential source of natural antioxidant

Plant growth-promoting rhizobacteria mediate induced systemic resistance in rice against bacterial leaf blight caused by Xanthomonas oryzae pv. oryzae

Seven Bacillus plant growth-promoting rhizobacteria spp. were evaluated for growth promotion and induced systemic resistance in rice against Xanthomonas oryzae pv. oryzae (Xoo). The identities of colonies of X. oryzae pv. oryzae grown on mXOS and PSA medium were confirmed by PCR employing specific primers TXTF and TXT4R. Among the seven strains tested as fresh suspensions, talc and sodium alginate formulations under laboratory and green house conditions, maximum germination of 86% was recorded after seed treatments with fresh suspension of Bacillus subtilis GBO3 followed by 85% germination treated with Bacillus pumilus SE34 in comparison to only 71% germination in the untreated controls. Similarly, the maximum vigor index of 1374 was obtained by seed treatment with fresh suspensions of B. subtilis strain GBO3 followed by treatments with strain SE34 with vigor index of 1323 in contrast to an index of only 834 observed in untreated controls. Among the treatments, seed treatments with fresh suspension of seven strains resulted in better germination and vigor assessments than talc based or sodium alginate formulations. Seed treatments with fresh suspension of strain SE34 gave 71% protection, followed by B. subtilis GBO3 and B. pumilus T4 with 58% and 52% protection, respectively, compared to the untreated controls. Seed treatments with talc based formulation of SE34 gave 66% protection, while GBO3 and T4 resulted in 52% and 50% protection, respectively, with similar formulation. Seed treatment with talc and sodium alginate formulations of strain SE34 gave 58% protection followed by GBO3 with 40% protection. Seed treatment with fresh suspensions of strains SE34 and GBO3 followed by challenge inoculations with Xoo increased accumulation of phenylalanine ammonia lyase, peroxidase and polyphenol oxidase compared to untreated control seedlings. Thus, the results of the present study suggest that the PGPR strains used as fresh suspensions and powdered formulations may have commercial potential in plant growth promotion and in management of rice bacterial leaf blight disease. (C) 2011 Elsevier Inc. All rights reserved