Radha Prasanna

Evaluation of fungicidal activity of extracellular filtrates of cyanobacteria--possible role of hydrolytic enzymes.

A set of seventy axenised and unicyanobacterial isolates belonging to the genus Anabaena were evaluated for biocidal activity against a set of phytopathogenic fungi. Among them, 35 Anabaena strains showed zone of inhibition against one or more fungi. The extracellular filtrates from 4 and 8 weeks old cultures of these Anabaena strains were further evaluated in terms of hydrolytic enzymes, proteins and IAA employing standard methods. Significant differences were also observed among the strains in terms of their FPase, chitosanase and xylanase activity, while low and relatively similar values of CMCase, cellobiase and protease activity were recorded in the strains analyzed. IAA production was also observed in all the strains. Comparative evaluation of activity of hydrolytic enzymes and antifungal activity revealed that such enzymes may contribute to the fungicidal activity of the cyanobacterial strains, besides other bioactive compounds, including IAA, which are established promising traits for biocontrol agents. This study is a first time report on the production of hydrolytic enzymes by these oxygenic photosynthetic prokaryotes, which can be potential candidates for the development of biocontrol agent(s) against selected phytopathogenic fungi. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Influence of diverse rice soil ecologies on cyanobacterial diversity and abundance

Cyanobacteria comprise a large group of structurally complex and ecologically significant gram-negative prokaryotes which flourish in rice paddies, and play a major role in sustaining the fertility of this ecosystem. This study aimed to characterize the abundance of cyanobacteria in various rice ecologies of India, identify the isolates and determine diversity indices in relation to the genera wise distribution. Average population counts (measured as MPN) of various locations clearly brought out the tremendous diversity among the locations sampled. Soil samples from Jeypore (Orissa state) recorded highest diversity and 20 cyanobacterial forms, spanning 9 genera were isolated. Nostoc and Anabaena were found to be the dominant genera in all the locations, in terms of their abundance and exhibited highest diversity indices. Our results suggest the need for practical utilization of these organisms towards developing region-specific inocula–which can establish better in their niche and provide maximum benefits to the crop.

Cyanobacteria as potential options for environmental sustainability — promises and challenges

Cyanobacteria represent an ancient group of photosynthetic prokaryotes, whose ubiquity, metabolic flexibility and adaptive abilities have made them a subject of research worldwide. These structurally simple organisms combine in themselves interesting facets of plant and bacterial metabolism, which is amenable to genetic exploitation. Despite their globally recognized significance in the sustenance of fertility in rice based cropping systems, they have not been tapped for their extraordinary repertoire of activities, especially their beneficial role as biological agents in remediation and amelioration of soil and water environment and as sinks for greenhouse gases. The information available on these aspects and future lines of research for more efficient utilization of these microorganisms is presented.

Physiological characterization of the cultured and freshly isolated endosymbionts from different species of Azolla

Abstract Freshly separated and cultured symbionts of six species of Azolla — A .xa0 microphylla , A .xa0 filiculoides , A .xa0 caroliniana , A .xa0 rubra , A .xa0 mexicana , and A .xa0 pinnata —were examined for selected physiological attributes including pigments—chlorophyll, phycobiliproteins; macromolecular components—proteins, sugars and selected enzymes involved in N and P metabolism. These were then compared with the observations recorded for free living strains of Anabaena variabilis and Nostoc sp. The amount of chlorophyll a , proteins, sugars and ammonia excreted was observed to be significantly higher in freshly separated symbionts while their cultured counterparts exhibited higher activities of N-assimilation enzymes. The similarity of the symbionts to free living strains with respect to certain attributes and significant variation in others, provides a lot of interesting information on this symbiotic association and underlines the critical role played by host factors in the metabolic capabilities of the symbionts.

Comparative Performance of Three Carrier Based Blue Green Algal Biofertilizers for Sustainable Rice Cultivation

ABSTRACT Nitrogen fixing cyanobacteria or blue green algae are ecologically significant inputs in rice cultivation in the tropics. Field experiments were conducted to compare the efficiency of two newly developed carrier based blue green algal (BGA) biofertilizers (wheat straw and multani mitti), with the traditional soil based BGA biofertilizer, on the grain yield of rice for a period of three years. Treatments included five levels of nitrogenous fertilizer urea and their interaction with the three types of BGA biofertilizers, on the grain yield of rice variety ‘PNR 381’. Highest grain yields were obtained with the application of multani mitti based biofertilizer along with 90 kg N/ha, although maximum percent increase in yield over control (37.97%), when applied along with 60 kg N/ha. The straw based and soil based biofertilizer treatments showed highest yields when supplemented with 90 and 120 kg N/ha, respectively. This investigation clearly emphasizes the need for supplementing chemical fertilizers with the newly developed BGA biofertilizers in rice cultivation for maximizing crop productivity, reducing inputs of chemical fertilizers and sustaining soil fertility.

Growth potential and biocide tolerance of non-heterocystous filamentous cyanobacterial isolates from rice fields of Uttar Pradesh, India

Abstract. Twenty-eight non-heterocystous filamentous cyanobacterial strains were isolated from different locations in the rice fields of Uttar Pradesh. These strains belonged to seven genera, namely Pseudanabaena, Limnothrix, Phormidium, Microcoleus, Plectonema, Lyngbya and Oscillatoria. A wide variation was observed in these strains with respect to dry weight, generation time and tolerance to biocides. Lyngbya palmarum and Oscillatoria acuminata showed maximum biomass (dry weight), while Pseudanabaena frigidum, Phormidium foveolarum, O. acuminata, Lyngbya palmarum and Lyngbya spiralis showed a significantly shorter generation time as compared to other strains studied. An interesting feature observed was that these non-heterocystous filamentous cyanobacteria possessed a remarkable tolerance to the biocides 2,4-dichlorophenoxyacetic acid, Malathion and Dimecron, at doses much higher than those recommended for rice crops.

Growth, Nutritional, and Yield Parameters of Wetland Rice as Influenced by Microbial Consortia Under Controlled Conditions

ABSTRACT A pot culture experiment was undertaken under controlled conditions in the National Phytotron Facility to investigate the interactive effect of microbial inoculants—blue-green algae (BGA), Azospirillum, phosphate-solubilizing bacterium (PSB) Pseudomonas striata, vesicular-arbuscular mycorrhizal fungus (VAMF), and Azolla, individually and in combination with chemical fertilizers and/rock phosphate on the wetland rice (Oryza sativa L.) cultivar ‘PNR 381’. The microbial inoculants—BGA, PSB, VAMF, and Azospirillum—positively interacted with one another, resulting in significant improvement in yield and nutritional parameters. Application of biofertilizers also substantially improved soil (peat) fertility status by increasing the nitrogen (N), phosphorous (P), and organic carbon content. The biofertilizer combination BGA + PSB + VAMF + Azospirillum was best for improved growth and yield traits, nutritional status of rice, and sustained soil (peat) fertility. Azolla, which is a highly competitive organism, suppressed the growth of the other four inoculants. The inclusion of VAMF and PSB was observed to significantly improve the zinc nutrition of the paddy and the P utilization of the applied rock phosphate. A basal dose of nitrogenous fertilizer was essential for deriving maximum benefits from applied inoculants, thereby underlying the supplementary/complementary role of biofertilizers in efficient nutrient management in agriculture.