S. Umesha

Bacterial wilt of tomato in Karnataka and its management by Pseudomonas fluorescens

Field surveys undertaken in major tomato growing districts of the Karnataka state, located in southern part of India, revealed a high incidence of bacterial wilt caused by Ralstonia solanacearum and it is one of the most destructive bacterial diseases of economically important crops. Across all the tomato cultivars under evaluation, the disease incidence in plants ranged from 9% to 39% whereas the incidence in seeds ranged from 4% to 18%. The effects of tomato seed treatments with Pseudomonas fluorescens in the control of bacterial wilt under greenhouse conditions revealed that the treatments protected plants against soil-borne infections of the bacterial wilt organism. Seed treatment with antagonistic P. fluorescens strain significantly improved the quality of seed germination and seedling vigour. The disease incidence was significantly reduced in plants raised from P. fluorescens treated seeds followed by challenge inoculation with R. solanacearum. Periodic field surveys for the incidence of bacterial wilt of tomato could be recommended to monitor the populations of the bacterial wilt pathogen. Workable measures are presented that could lead to the reduction of the prevalence of this serious disease in affected fields of the small farm-holders.

Biocontrol of downy mildew disease of pearl millet using Pseudomonas fluorescens

Pseudomonas fluorescens was tested against pearl millet downy mildew disease by treating seeds with a pure culture and formulated in talc powder. The bioagent was also tested as a foliar spray to pearl millet under greenhouse and field conditions. Treated seeds increased seedling vigour and inhibited sporulation of downy mildew pathogen. P. fluorescens controlled downy mildew disease both by seed treatment and foliar application, but efficacy was significantly higher when seed treatment was followed by a foliar application. Seed treatment was better than foliar application alone.

Assessment of membrane stabilizing activity from honey. An in-vitro approach

BACKGROUND esent study was conducted to evaluate Manoflora (MF), Polyflora (PF), Polyflora forest (PFf), and Processed (Pro) honey varieties to compare the in-vitro anti-inflammatory effects of aqueous honey samples in dose dependent manner. In-vitro anti-inflammatory activity was evaluated using membrane stabilization assay of RBCs at different aqueous honey concentrations. Material and method. The present investigation carried out for selected varieties of honey against erythrocytes exposed to both heat and hypotonic lyses and inhibition of membrane damage was compared to the standard drug acetylsalicylic acid. Results. Membrane damage was inhibited in both the model hemolysis of erythrocytes in vitro in a concentration dependent manner. Hypotonic solution inducing damage was inhibited by aqueous honey sample in ascending order ranged from 8.25% to 97.76% at 10 to 50 mg/ml and standard drug acetylsalicylic acid showing hemolysis protection 96.09% at 100 μg/ml concentration. In heat induced hemolysis model aqueous honey sample exhibited its protecting property during external stress condition in all samples ranged from 0.44% to 21.23% at 10 to 50 mg/ml and acetylsalicylic acid showed 39.38% at 100 μg/ml concentration. Among the variety PFf showed highest protecting nature for hypotonic solution induced lyses (97.76%) and heat induced hemolysis (21.23%) at 50 mg/ml respectively. Conclusion. With these investigations data conclude that the model exhibits marked anti-inflammatory effect. Future research is to be carried out to identify the molecules responsible in honey and its mechanism. METHODS present study was conducted to evaluate Manoflora (MF), Polyflora (PF), Polyflora forest (PFf), and Processed (Pro) honey varieties to compare the in-vitro anti-inflammatory effects of aqueous honey samples in dose dependent manner. In-vitro anti-inflammatory activity was evaluated using membrane stabilization assay of RBCs at different aqueous honey concentrations. Material and method. The present investigation carried out for selected varieties of honey against erythrocytes exposed to both heat and hypotonic lyses and inhibition of membrane damage was compared to the standard drug acetylsalicylic acid. RESULTS Membrane damage was inhibited in both the model hemolysis of erythrocytes in vitro in a concentration dependent manner. Hypotonic solution inducing damage was inhibited by aqueous honey sample in ascending order ranged from 8.25% to 97.76% at 10 to 50 mg/ml and standard drug acetylsalicylic acid showing hemolysis protection 96.09% at 100 μg/ml concentration. In heat induced hemolysis model aqueous honey sample exhibited its protecting property during external stress condition in all samples ranged from 0.44% to 21.23% at 10 to 50 mg/ml and acetylsalicylic acid showed 39.38% at 100 μg/ml concentration. Among the variety PFf showed highest protecting nature for hypotonic solution induced lyses (97.76%) and heat induced hemolysis (21.23%) at 50 mg/ml respectively. CONCLUSIONS With these investigations data conclude that the model exhibits marked anti-inflammatory effect. Future research is to be carried out to identify the molecules responsible in honey and its mechanism involved.

Lytic activity in pearl millet: its role in downy mildew disease resistance

Sclerospora graminicola causes downy mildew disease in susceptible pearl millet. Molecular basis of downy mildew disease resistance has been studied. Coleoptile region has been shown earlier to be the most susceptible site for attack by the pathogen. Lytic activity is differentially expressed in the coleoptile region of 3-day-old pearl millet seedlings of resistant and susceptible cultivars. Significantly higher levels of lytic factors were measured in the coleoptile region of resistant cultivars (100%) than in that of susceptible cultivars (20%). Both constitutive and inducible lytic factors were observed in different resistant cultivars, and they were able to lyse the pathogen. The level of lytic activity correlated well with the degree of resistance as evaluated by field screening studies. The present study, therefore, proposes that lytic factors found in the coleoptile region of the pearl millet seedling, are responsible for the lysis of the pathogen in the resistant plant, and may therefore provide resistance to downy mildew disease. This study also provides a simple method to evaluate downy mildew resistance in pearl millet cultivars.

Identification and genetic diversity of bacterial wilt pathogen in brinjal

Ralstonia solanacearum is the causal agent of bacterial wilt disease of solanaceous crops, which is a severe obstacle to the production of brinjal along with other crops. R. solanacearum strains are isolated from different fields of Karnataka, India, and are characterised to determine the distribution and diversity of soil-borne pathogen. The isolated strains of R. solanacearum showed maximum identity as biovar 2. The genetic diversity was analysed among the isolated strains compared with worldwide sequence deposited with NCBI, by 16S rDNA sequence through phylogenetic orientation. This comparison confirms that isolates were originated from Asia and are different from American and European strains. Among our isolates 65% of variation was recorded with that of R. solanacearum in Asian strains. Sequence analysis also confirms the isolated strains as R. solanacearum with 99% homology with BLAST programme. Hence, the present study reports on the rapid identification of R. solanacearum which overcomes conventional diagnostics and helps in early and rapid disease diagnosis. Here, we determined genetic diversity and relationship of R. solanacearum complex of India with other countries using 16S rDNA sequences.

Anti-inflammatory and antinociceptive effect of Pachygone ovata leaves

Abstract Context: Pachygone ovata (Poir.) Miers ex Hook. F. et Thoms (Menispermaceae) is a rich source of bioactive bisbenzylisoquinoline and aporphine alkaloids. Objective: This study investigates the in vitro and in vivo anti-inflammatory and antinociceptive potential of Pachygone ovata leaves. Materials and methods: Lipoxygenase (LOX) assay for anti-inflammatory activity was conducted using MeOH, EA, H and Aq extracts; followed by alkaloid isolation. The anti-inflammatory potential was determined using carrageenan-induced paw oedema and formalin tests for evaluation of Pachygone ovata analgesic effect. Different doses (100, 300 and 400 μg/kg) were administered orally to Wistar rats for a period of one week, once daily. Results: MeOH and EA extract efficiently inhibited LOX (IC50 1.43 and 2.15 μg/mL, respectively). MeOH extract had better inhibiting capacity (57%) than indomethacin (51%) in carrageenan induced rats. MeOH extract (300 μg/kg) significantly reduced the increased levels of nitric oxide (8 ± 0.57 M), total leukocyte count (4.5 ± 0.05 cells 103/cells) and C-reactive protein (55 ± 0.45 mg/mL). There was a decrease in various serum biochemical markers (ALT, AST). Histopathological studies revealed reduction in oedema and decreased cellular infiltration on supplementation with MeOH extract. Furthermore, MeOH extract (300 μg/kg) and alkaloid fraction (400 μg/kg) effected both phases (neurogenic and inflammatory) of formalin injected models. Discussion and conclusion: Inflammatory mediators play a key role in inflammation; therefore, keeping it in control is of utmost importance. The usefulness of Pachygone ovata leaves on pain and inflammation has been described, probably due to its effect on inflammatory mediators and high alkaloid content.

Bacterial blight pathogen concentration in cotton seeds; its role in seed quality parameters of fuzzy and acid delinted seeds

Abstract The adverse effects of increasing concentration of Xanthomonas axonopodis pv. malvacearum on cotton seed quality parameters, seedling dry weight and on defense-related enzyme, Phenylalanine Ammonia Lyase (PAL) were studied. Different concentrations of pathogen (1×102 to 1×108 CFU/ml) were treated on both fuzzy and acid delinted seeds and subjected to the standard blotter method to study the effect of the pathogen on seed quality parameters. The seedling symptom test following the roll towel method, the modified germination test to study the blight incidence and the field emergence test were carried out to discover the field planting value and disease incidence under laboratory and field conditions. From these experiments, it was found that the decrease in the seed quality parameters like seed germination, seedling vigour, and the dry weight of seedlings when X. axonopodis pv. malvacearum concentration was increased. Whereas the bacterial blight incidence increased with an increase in pathogen concentration, in both greenhouse and field conditions. Phenylalanine ammonia lyase activity was found to increase along with the pathogen concentrations, but total phenol content decreased as pathogen concentration increased. The effect of X. axonopodis pv. malvacearum load on seed quality parameters, PAL enzyme activity of fuzzy and acid delinted cotton seeds are discussed in the present study.

Selection of downy mildew resistant somaclones, from a susceptible B line of pearl millet.

Plants regenerated from seed-derived callus of a PNMS 6B line of pearl millet (Pennisetum glaucum (L.) R. Br.) were evaluated for their resistance induced by somaclonal variation for downy mildew disease caused by Sclerospora graminicola (Sacc.) Schroter. Among the 201 lines regenerated, only 3 lines consistently proved highly resistant (free from disease incidence) for up to 5 generations; whereas, 17 lines were resistant (disease incidence ranging from 1 to 9%). Resistance was confirmed by testing the plants under both laboratory and field conditions. The plants were evaluated for their agronomic traits.

Microbial Biotechnology and Sustainable Agriculture

Abstract Agriculture forms a significant portion of the economies of world and therefore can contribute toward major continental priorities such as eradicating poverty, hunger, rapid industrialization, economic diversification, sustainable resource, investments, and environmental management. Biotechnology is the rapidly growing segment and has diversified applications in sustainable agriculture. This chapter discusses the role of biotechnology, agroecology, and plant–microbial interaction for sustainable agriculture. For the growing world population, an intensive agricultural production is necessary to satisfy food requirements. Agricultural microbiology is presented as a synthetic research field responsible for knowledge transfer from general microbiology and microbial ecology to the agricultural biotechnology. A fundamental knowledge of the genetics, molecular biology, ecology, and evolution of symbiotic interactions could enable the development of microbe-based sustainable agriculture. Undoubtedly, getting biased rhizosphere opens new opportunities for future agricultural developments based on exploiting the beneficial microbial services to reduce the inputs of agrochemicals, thereby reaching sustainable environmental and economical goals.

Cocculus hirsutus extract inhibits the Xanthomonas oryzae pv. oryzae, the bacterial leaf blight pathogen in rice

Plant-derived natural bactericides and their possible applications in agriculture to control plant bacterial diseases has intensified as this approach has enormous potential to inspire and influence modern agro-chemical research. Naturally occurring and biologically active plant products such as essential oils and organic extracts could be a source of alternative classes of natural biopesticides to serve as templates for new and more effective compounds in controlling plant pathogenic micro-organisms. In the present study, the efficacy of six plants extracts from different solvent system were tested for their antibacterial activity aganist Xanthomonas oryzae pv. oryzae both in vitro and in vivo. Among these extracts, Cocculus hirsutus leaf chloroform extract exhibits significant antibacterial activity against X. oryzae pv. oryzae. Data obtained from the experiments such as minimum inhibitory concentration, effect of C. hirsutus leaf chloroform extract on the incidence of X. oryzae pv. oryzae, phytotoxicity test and effect of C. hirsutus leaf chloroform extract on seed germination and seedling vigour, along with the in vivo experiments under greenhouse conditions showed significant improvement over controls. Thus, the present study demonstrated that the C. hirsutus leaf chloroform extract posses antibacterial activity against bacterial leaf blight pathogen of rice.