Agronomic Management of Indigenous Mycorrhizas

Many of the advantages conferred to plants by arbuscular mycorrhiza (AM) are associated to the ability of AM plants to explore a greater volume of soil through the extraradical mycelium. Sieverding (1991) estimates that for each centimetre of colonized root there is an increase of 15 cm3 on the volume of soil explored, this value can increase to 200 cm3 depending on the circumstances. Due to the enhancement of the volume of soil explored and the ability of the extraradical mycelium to absorb and translocate nutrients to the plant, one of the most obvious and important advantages resulting from mycorrhization is the uptake of nutrients. Among of which the ones that have immobilized forms in soil, such as P, assume particular significance. Besides this, many other benefits are recognized for AM plants (Gupta et al, 2000): water stress alleviation (Augé, 2004; Cho et al, 2006), protection from root pathogens (Graham, 2001), tolerance to toxic heavy metals and phytoremediation (Audet and Charest, 2006; Göhre and Paszkowski, 2006), tolerance to adverse conditions such as very high or low temperature, high salinity (Sannazzaro et al, 2006), high or low pH (Yano and Takaki, 2005) or better performance during transplantation shock (Subhan et al, 1998). The extraradical hyphae also stabilize soil aggregates by both enmeshing soil particles (Miller e Jastrow, 1992) and producing a glycoprotein, golmalin, which may act as a glue-like substance to adhere soil particles together (Wright and Upadhyaya, 1998). Despite the ubiquous distribution of mycorrhizal fungi (Smith and Read, 2000) and only a relative specificity between host plants and fungal isolates (McGonigle and Fitter, 1990), the obligate nature of the symbiosis implies the establishment of a plant propagation system, either under greenhouse conditions or in vitro laboratory propagation. These techniques result in high inoculum production costs, which still remains a serious problem since they are not competitive with production costs of phosphorus fertilizer. Even if farmers understand the significance of sustainable agricultural systems, the reduction of phosphorus inputs by using AM fungal inocula alone cannot be justified except, perhaps, in the case of high value crops (Saioto and Marumoto, 2002). Nurseries, high income horticulture farmers and no-agricultural application such as rehabilitation of degraded or devegetated landscapes are examples of areas where the use of commercial inoculum is current. Another serious problem is quality of commercial available products concerning guarantee of phatogene free content, storage conditions, most effective application methods and what types to use. Besides the information provided by suppliers about its inoculum can be deceiving, as from the usually referred total counts, only a fraction may be effective for a particular plant or in specific soil conditions. Gianinazzi and Vosátka (2004) assume that progress should be made towards registration procedures that stimulate the development of the mycorrhizal industry. Some on-farm inoculum production and application methods have been studied, allowing farmers to produce locally adapted isolates and generate a taxonomically diverse inoculum (Mohandas et al, 2004; Douds et al, 2005). However the inocula produced this way are not readily processed for mechanical application to the fields, being an obstacle to the utilization in large scale agriculture, especially row crops, moreover it would represent an additional mechanical operation with the corresponding economic and soil compaction costs. It is well recognized that inoculation of AM fungi has a potential significance in not only sustainable crop production, but also environmental conservation. However, the status quo of inoculation is far from practical technology that can be widely used in the field. Together a further basic understanding of the biology and diversity of AM fungi is needed (Abbott at al, 1995; Saito and Marumoto, 2002). Advances in ecology during the past decade have led to a much more detailed understanding of the potential negative consequences of species introductions and the potential for negative ecological consequences of invasions by mycorrhizal fungi is poorly understood. Schwartz et al, (2006) recommend that a careful assessment documenting the need for inoculation, and the likelihood of success, should be conducted prior to inoculation because inoculations are not universally beneficial. Agricultural practices such as crop rotation, tillage, weed control and fertilizer apllication all produce changes in the chemical, physical and biological soil variables and affect the ecological niches available for occupancy by the soil biota, influencing in different ways the symbiosis performance and consequently the inoculum development, shaping changes and upset balance of native populations. The molecular biology tools developed in the latest years have been very important for our perception of these changes, ensuing awareness of management choice implications in AM development. In this context, for extensive farming systems and regarding environmental and economic costs, the identification of agronomic management practices that allow controlled manipulation of the fungal community and capitalization of AM mutualistic effect making use of local inoculum, seem to be a wise option for mycorrhiza promotion and development of sustainable crop production

Selective gene silencing by viral delivery of short hairpin RNA

RNA interference (RNAi) technology has not only become a powerful tool for functional genomics, but also allows rapid drug target discovery and in vitro validation of these targets in cell culture. Furthermore, RNAi represents a promising novel therapeutic option for treating human diseases, in particular cancer. Selective gene silencing by RNAi can be achieved essentially by two nucleic acid based methods: i) cytoplasmic delivery of short double-stranded (ds) interfering RNA oligonucleotides (siRNA), where the gene silencing effect is only transient in nature, and possibly not suitable for all applications; or ii) nuclear delivery of gene expression cassettes that express short hairpin RNA (shRNA), which are processed like endogenous interfering RNA and lead to stable gene down-regulation. Both processes involve the use of nucleic acid based drugs, which are highly charged and do not cross cell membranes by free diffusion. Therefore, in vivo delivery of RNAi therapeutics must use technology that enables the RNAi therapeutic to traverse biological membrane barriers in vivo. Viruses and the vectors derived from them carry out precisely this task and have become a major delivery system for shRNA. Here, we summarize and compare different currently used viral delivery systems, give examples of in vivo applications, and indicate trends for new developments, such as replicating viruses for shRNA delivery to cancer cells

Resistance pattern in drug-resistant pulmonary tuberculosis

Background : Drug-resistant tuberculosis is an important issue for public health. There is a rise in the trend of drug-resistant tuberculosis, especially multi drug resistance (MDR), in different parts of world, India being one of the high burden countries. This study is undertaken to assess the various patterns of resistance among confirmed drug resistant pulmonary tubercular patients and to initiate second line anti tubercular treatment. Aims and Objectives : To assess various resistance patterns among confirmed drug resistant pulmonary tubercular patients and for the initiation of appropriate drug regimens in our setup. Study Design : An observational prospective study. Materials and Methods : This study was conducted at Rajiv Gandhi Institute of Chest Diseases, Bangalore between January 2005 and November 2010. A total of 309 drug resistant tuberculosis cases were studied. Sputum culture and drug sensitivity were carried out at National Tuberculosis Institute. Drug sensitivity testing done for all first line drugs, except pyrazinamide, by using LJ media. Results : In this study, out of 309 patients, MDR pattern was observed in 224 (72%), of which 20 (6.47%) had resistance only to isoniazid (INH) and rifampicin (RMP), 58 (18.7%) had resistance to INH, RMP, and either of the other first line drugs streptomycinor ethambutol and 146 (47.25%) had resistance to all first line drugs. Poly drug resistance pattern was observed in 72 (23.3%) and Mono drug resistance in 13 (4.2%). Conclusion : In the present study the most common pattern observed is MDR with predominant resistance to INH. There is a rise in the number of drug resistant tuberculosis cases, especially MDR. Hence close monitoring of drug resistant pattern is required to formulate designs of different regimens in the treatment of drug resistant tuberculosis; especially MDR-TB based on accredited laboratory reports, in a specialized center which is very much essential for the betterment of the patients and the community

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Not AvailableThe aim of the present investigation was to study the spatio-temporal variability of the microbial activities in coastal saline soils (locally called Khazan) of Goa, India (west coast region). The coastal soil salinity is a major constraint for reduced crop yields and abandonment of farming in these areas. Three replicated global positioning based soil samples (0–0.20 m depth) from each of four salinity groups i.e. non-saline (EC=0.08±0.06 dS m−1), weakly saline (EC=2.04±0.06 dS m−1), moderately saline (EC=3.50±0.57 dS m−1) and strongly saline (EC=5.49±0.49 dS m−1) during three seasons–monsoon, post-monsoon and pre-monsoon were collected. Soil microbial activity in terms of soil microbial carbon (MBC), MBC as a fraction of soil organic carbon (SOC) (MBC/SOC), basal soil respiration (BSR), metabolic quotient (qCO2) and soil enzyme activities–dehydrogenase, phosphatase and urease was tested. In all the seasons, the soil cationic composition depended significantly (p monsoon > during pre-monsoon season. The mean MBC and MBC/SOC of non-saline soils were 1.61 and 2.28 times higher than that of strongly saline soils, whereas qCO2 of strongly saline soils was 2.4 times higher than that of non-saline soils. This indirectly indicates the salinity stress on the soil microorganisms. Irrespective of season, the soil enzyme activities decreased significantly (p<0.05) with increasing salinity levels. Suitable countermeasures needs to be taken up to alleviate the depressive salinity effect on the microbial and activity for the sustainable crop production in the coastal saline soils of Goa, India.Indian Council of Agricultural Researc

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Not AvailableSoil quality (SQ) under any agriculture system is greatly influenced by source of nutrients, type of soil, crop, and their management practices. In this regard, a field experiment was conducted under lowland rice production system for 5 years to assess the effect of nutrient management with organic and inorganic nutrient on soil quality. The nutrient management practices studied were: FYM: farmyard manure (10 t ha−1), Verm: vermicompost (5 t ha−1), GE: Gliricidia and Eupatorium (each 5 t ha−1), PW: Paddy straw and water hyacinth (each 5 t ha−1), SR: Dhaincha (10 t ha−1), RDF-NPK: recommended dose of fertilizers (100:50:50 NPK kg ha−1), and control. The effect of different nutrient management practices on the soil properties, grain yield, sustainable yield index, and soil quality index were evaluated. The nutrient management practices affected the soil properties, rice grain yield, and sustainable yield index significantly. Phosphatase activity, soil organic carbon, microbial biomass carbon, available phosphorus, and nitrogen were selected for minimum data set using principal component analysis. Their corresponding average contribution to the soil quality index was 70.7, 7.92, 8.67, 1.69, and 10.9%, respectively. The soil quality index obtained by integrating the minimum data set and employing non-linear scoring function varied from 0.72 (SR) to 0.99 (FYM) and it was minimum in the control (0.68). The FYM improved the SQ by 28.5 and 45.5% over RDF-NPK and control, respectively. Using organic sources of nutrients under transplanted rice improves the soil quality and sustainability by improving plant growth and soil functions.Indian Council of Agricultural Researc

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Not AvailableThe aim of the present investigation was to study the effects of salinity under low soil pH conditions on soil microbial and enzyme activities and to quantify soil organic carbon (SOC) stocks in coastal saline soils of Goa, India. Global positioning system based replicated soil samples collected from fifteen different locations showed characteristic variations in electrical conductivity (0.09–6.29 dS m-1), soil pH (4.11–6.57), exchangeable sodium (Na) (7.40–23.2 meq 100 g-1) and exchangeable sodium percentage (48.3–85.7 %). Exchangeable Na was the most dominant cation among all the cations analyzed at all the sites. The total SOC stock of the study sites varied significantly (p \ 0.05) and ranged from 4.27–24.3 Mg C ha-1. The soil microbial activity measured in terms of basal soil respiration, soil microbial biomass carbon (Cmb), Cmb as a fraction of SOC and enzyme activities related to dehydrogenase, phosphatase and urease showed a decline with increasing salinity levels. On the contrary, metabolic quotient increased with increasing salinity. The results of the study suggest that salinity under low soil pH has a depressive effect on the soil microbial and enzyme activity. Alleviation of the depressive effect of salinity on microbial activity needs to be addressed through suitable interventions and countermeasures for sustainable crop production in coastal acid saline soils of Goa.Indian Council of Agricultural Researc

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Not AvailableTo study the fertility status of coastal saline soils of Goa (locally called ‘Khazan’) global positioning system based soil samples were collected from two districts of Goa. Three replicate samples per location were collected. In general, the soils had acidic soil reaction (pH ≤ 6.57). Electrical conductivity of the soils varied from 0.09 dS m-1 to 6.29 dS m-1. Exchangeable sodium was the most dominant cation among all the cations and resulted in ESP ranging from 48.3%-84.5%. Unlike other parts of salt-affected soils in the country, this is a unique situation where acidity and salinity occur simultaneously. Soils were found deficient in soil available nitrogen (N) (104 to 150 kg ha-1) and low to medium in soil available phosphorus (P) (1.94 to 20.0 kg ha-1) and medium to high in soil available potassium (K) (126 to 1588 kg ha-1), respectively. Soil available micronutrients status was found in sufficiency ranges. The results of the study showed conducive fertility status of soils for plant growth, but acidity and salinity exerts a stress resulting in poor crop productivity. The preliminary information could be useful for deciding the management practices to overcome poor physical condition of the soils, deciding nutrient management practices and achieving higher crop productivity.Not Availabl

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Not AvailableNot AvThe effect of medium-term (5 years) application of organic and inorganic sources of nutrients (as mineral or inorganic fertilizers) on soil organic carbon (SOC), SOC stock, carbon (C) build-up rate, microbial and enzyme activities in flooded rice soils was tested in west coast of India. Compared to the application of vermicompost, glyricidia (Glyricidia maculate) (fresh) and eupatorium (Chromolaena adenophorum) (fresh) and dhaincha (Sesbania rostrata) (fresh), the application of farmyard manure (FYM) and combined application of paddy straw (dry) and water hyacinth (PsWh) (fresh) improved the SOC content significantly (p < 0.05). The lowest (p < 0.05) SOC content (0.81%) was observed in untreated control. The highest (p < 0.05) SOC stock (23.7 Mg C ha−1) was observed in FYM-treated plots followed by recommended dose of mineral fertilizer (RDF) (23.2 Mg C ha−1) and it was lowest (16.5 Mg C ha−1) in untreated control. Soil microbial biomass carbon (Cmb) (246 μg g−1 soil) and Cmb/SOC (1.92%) were highest (p < 0.05) in FYM-treated plot. The highest (p < 0.05) value of metabolic quotient (qCO2) was recorded under RDF (19.7 μg CO2-C g−1 Cmb h−1) and untreated control (19.6 μg CO2-C g−1 Cmb h−1). Application of organic and inorganic sources of nutrients impacted soil enzyme activities significantly (p < 0.05) with FYM causing highest dehydrogenase (20.5 μg TPF g−1 day−1), phosphatase (659 μg PNP g−1 h−1) and urease (0.29 μg urea g−1 h−1) activities. Application of organic source of nutrients especially FYM improved the microbial and enzyme activities in flooded and transplanted rice soils. Although the grain yield was higher with the application of RDF, but the use of FYM as an organic agricultural practice is more useful when efforts are intended to conserve more SOC and improved microbial activity.ailableIndian Council of Agricultural Researc

Endophytes and Plant Secondary Metabolite Synthesis: Molecular and Evolutionary Perspective

The distribution of endophytes (fungal and bacterial) is ubiquitous and almost without exception; the endophytes have been reported from all tissues, including leaves, stems, roots, flowers and fruits. As typical symptomless organisms, in contrast to their pathogenic counterparts, they pose a serious challenge in explaining their continued maintenance in plants. How do plants tolerate them? And how do the endophytes contain the plant defences? But a more intriguing and enigmatic issue with many endophytes is the fact that they mimic the production of specific plant associated secondary metabolites (e.g. taxol, camptothecin and rohitukine) in culture, independent of the host tissue. Several theories including the possibility of horizontal gene transfer from the respective hosts have been proposed, but none has so far been supported. In this paper, we critically review studies on endophytes producing plant secondary metabolites and explore the possible molecular mechanisms. By analysing the pathway genes for a few major metabolites, including taxol and camptothecin, we show that a far more intricate molecular mechanism might be involved in the production of the secondary metabolites by the endophytes. We show that these molecular mechanisms could have arisen through the evolutionary interactions of the endophytes with their respective host plants. We discuss these findings in the context of the current interest in harnessing endophytes as alternative sources of plant secondary metabolites