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  • Author or Editor: R. Viswanathan x
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Production of secondary metabolites such as siderophores, indole acetic acid, salicylic acid and antibiotics phenazine, pyocyanine and 2,4-diacetyl phloroglucinol by Pseudomonas spp. associated with induced systemic resistance (ISR) activity in sugarcane against red rot disease was assessed. Many of the strains have been found to produce these metabolites and antibiotics in the culture medium. The antibiotics were separated and identified by thin layer chromatography by running the purified metabolites from the reference strains. The bacterial strains varied in their capability to produce the metabolites. The purified compounds were tested for their antifungal activity against the red rot pathogen Colletotrichum falcatum. Most of the purified metabolites have completely arrested conidial germination and mycelial growth of the fungus. The results suggest that the metabolites production may play a role in antagonism/induced systemic resistance against the pathogen.

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Forty Colletotrichum musae isolates were recovered from ten different banana cultivars (Musa spp.) exhibiting the symptoms of both crown rot and anthracnose. The isolates were characterized morphologically and with molecular tools. Based on morphological characters in culture, the 40 C. musae isolates were included in four groups. Group I consisted of fast growing isolates with pinkish to light orange mycelia; group II included isolates with sparse, slow growing, suppressed, light orange mycelia; group III consisted of isolates with dense, fast growing, orange mycelia; and group IV included isolates with profuse cottony mycelia, mostly white to very light orange colour. Twelve isolates of C. musae were further selected and tested with RAPD primers for their genetic diversity. The RAPD dendrogram grouped the 12 isolates of C. musae in three clusters. Based on RAPD patterns, the similarity index (SI) within C. musae isolates ranged from 41.66 to 100%. Thus, the RAPD analysis revealed a high genetic variability in C. musae isolated from different banana cultivars. This might explain the differences in cultural characteristics of different isolates.

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Authors: M. Krishnaratnam, B. Viswanathan and R. Ramaswamy

Abstract  

The characteristics of uncatalyzed bromate oscillator are altered in presence of -irradiation. These alterations could not be accounted for in terms of substrates acting as scavengers for hydrogen atoms. The alteration of the effective activity of the key species in presence of -irradiation can also account for the changes observed in the oscillation characteristics.

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Treatment of acibenzolar-S-methyl (bionTM), salicylic acid and the saprophytic bacterium Pseudomonas fluorescens exhibited induced systemic resistance in Sorghum bicolor (cv. Rio) to Sugarcane mosaic virus (SCMV) isolates from sugarcane. The treatments significantly slowed down the SCMV titre in plants during the initial growth phase. The enhanced induction of total phenols, phenylalanine ammonia lyase (PAL), peroxidase (PO) and polyphenol oxidase (PPO) might have contributed for the induced systemic resistance triggered by various biotic and abiotic inducers. More induction of PO and PPO isozymes were noticed upon application of these inducers. In the present studies, there was a significant decrease of SCMV titre as evidenced by ELISA in these treatments. Among the treatment methods, foliar application was highly effective in case of the abiotic elicitors bion and salicylic acid whereas with P. fluorescens seed treatment was effective.

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Authors: M. Krishnaratnam, K. Sudhakar Rao, B. Viswanathan and R. Ramaswamy

Abstract  

The oscillatory characteristics of a catalyzed bromate system is altered by gammairradiation. The alterations observed are probably due to the activation of the reduced form of the metal ion catalyst under gamma-irradiation. However, these alterations could not be accounted for in terms of an effective concentration of bromate acting as a quenching agent under gamma-irradiation conditions as reported in the literature.

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Authors: P. Malathi, P. Padmanaban, R. Viswanathan, D. Mohanraj and A. Ramesh Sundar

The control of sugarcane red rot was studied in model experiments with carbendazim and thiophanate methyl. In axenic cultures carbendazim inhibited the pathogen more efficiently than thiophanate methyl (MIC 1 and 100 mgL-1, respectively). However, under greenhouse conditions, the reverse picture was revealed. Carbendazim, the metabolite of thiophanate methyl, exhibited lower efficacy against red rot disease than its precursor. Fungicides applied before infection reduced the disease incidence and improved both germination of setts and plant survival. Soaking of sugarcane setts in a 0.25% suspension of fungicides for 24 h before planting was found to be more effective in controlling debris-borne infection than soaking for 1 h period at elevated doses. The persistence of effects both on disease incidence and on promoting plant growth can be observed up to 60 days after planting (DAP).

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Authors: S. Obayd, B. Rao, S. Bendre, R. Viswanathan, S. Chaudhari, S. Kanetkar and S. Ogale

Abstract  

High-Tc superconductor YBa2Cu3O7 was irradiated by thermal neutrons. Significant effects on the critical temperature were found. The changes were also investigated by X-ray diffraction technique.65Cu (n, )66Cu was the only reason for the degradation in superconducting properties. The existence of an isotope effect is argued.

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