Avances en la investigación de la relación patogeno-hospedante y de la resistencia genética a enfermedades de la caña de azúcar en Argentina

Esta contribución presenta avances en la investigación de la variabilidad y resistencia genética con relación a “Roya marrón” y “Estría roja” de la caña de azúcar en Argentina. Resultados experimentales de la inoculación con roya en condiciones controladas permitieron postular que tanto la actividad peroxidasa basal como la tasa de su crecimiento con posterioridad a la infección serían mecanismos complementarios que favorecen la expresión de la resistencia a la enfermedad. También se investigó la diversidad molecular en poblaciones de roya con base en 538 marcadores AFLP a partir de muestreos en diferentes variedades y en una amplia faja de distribución de la enfermedad en el NOA. No se detectaron estructuras genéticas diferenciadas según orígenes, comportándose las diferentes poblaciones como una única gran población indiferenciada de uredosporos con alto grado de variabilidad genética intrínseca. Con relación a Estría roja se logró optimizar una técnica efectiva para el aislamiento, identificación y caracterización genética del agente responsable de la enfermedad. Los resultados obtenidos permitieron confirmar que Acidovorax avenae es el agente responsable de estría roja de la caña de azúcar en Argentina, siendo ésta la primera caracterización realizada en la región cañera para esta patología. Por otra parte el análisis de perfiles de REP-PCR y RAPD confirmó la presencia de al menos cuatro biotipos de la enfermedad en aislados de Salta y Tucumán. La existencia de diversidad genética entre aislamientos permite diseñar estrategias de control mediante el uso de variedades resistentes.The paper presents recent progress in the investigation of variability and genetic resistance in relation to Rust and Red stripe diseases of sugar cane in Argentina. Experimental results for rust innoculation under controlled conditions served to postulate that both basal peroxidase activity and its rate of increase after innoculation with the disease could be complementary mechanisms in the expression of resistance in different cultivars. Molecular diversity of rust populations collected in the field in North West Argentina were also investigated based on 538 AFLP markers. Samples collected in different varieties and sites indicated that rust uredospores populations correspond with a single mixed undifferentiated population with a high degree of intrinsic genetic variability. In regard to Red stripe it was possible to optimize an effective procedure for the isolation, identification and genetic characterization of the disease agent. Results permitted for the first time the identification of Acidovorax avenae as the agent responsible for the disease in Argentina. The profile analysis for REP-PC and RAPD indicated the presence of at least four different biotypes of the disease in Salta and Tucumán. The occurrence of genetic diversity among isolates permits the design of strategies for the control of the disease by means of resistant varieties.Fil: Mariotti, Jorge Alberto. Instituto Nacional de Tecnología Agropecuaria; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Machado Assefh, Cristina Renata. Universidad Nacional de Salta. Facultad de Ciencias Naturales; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Salta; ArgentinaFil: Rech, G.. Universidad Nacional de Salta. Facultad de Ciencias Naturales; ArgentinaFil: Fontana, P. D.. Instituto Nacional de Tecnología Agropecuaria; ArgentinaFil: Collavino, N. G.. Universidad Nacional de Salta. Facultad de Ciencias Naturales; ArgentinaFil: Pocoví, M. I.. Universidad Nacional de Salta. Facultad de Ciencias Naturales; ArgentinaFil: Rago, A. M.. Instituto Nacional de Tecnología Agropecuaria; ArgentinaFil: Daz, Mirta Elizabeth. Universidad Nacional de Salta. Facultad de Ciencias Naturales; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Salta; Argentin

nifH pyrosequencing reveals the potential for location-specific soil chemistry to influence N2-fixing community dynamics

A dataset of 87 020 nifH reads and 16 782 unique nifH protein sequences obtained over 2 years from four locations across a gradient of agricultural soil types in Argentina were analysed to provide a detailed and comprehensive picture of the diversity, abundance and responses of the N2-fixing community in relation to differences in soil chemistry and agricultural practices. Phylogenetic analysis revealed an expected high proportion of Alphaproteobacteria, Betaproteobacteria and Deltaproteobacteria, mainly relatives to Bradyrhizobium and Methylosinus/Methylocystis, but a surprising paucity of Gammaproteobacteria. Analysis of variance and stepwise regression modelling suggested location and treatment-specific influences of soil type on diazotrophic community composition and organic carbon concentrations on nifH diversity. nifH gene abundance, determined by quantitative real-time polymerase chain reaction, was higher in agricultural soils than in non-agricultural soils, and was influenced by soil chemistry under intensive crop rotation but not under monoculture. At some locations, sustainable increased crop yields might be possible through the management of soil chemistry to improve the abundance and diversity of N2-fixing bacteriaFil: Collavino, Mónica Mariana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Nordeste. Instituto de Botánica del Nordeste (i); Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico La Plata. Instituto de Biotecnología y Biología Molecular; ArgentinaFil: Tripp, H. James. University of California. Department of Ocean Sciences; Estados UnidosFil: Frank, Ildiko E.. University of California. Department of Ocean Sciences; Estados UnidosFil: Vidoz, María Laura. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Nordeste. Instituto de Botánica del Nordeste (i); ArgentinaFil: Calderoli, Priscila Anabel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico La Plata. Instituto de Biotecnología y Biología Molecular; ArgentinaFil: Donato, Mariano Humberto. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Laboratorio de Sistemática y Biología Evolutiva; ArgentinaFil: Zehr, Jonathan P.. University of California. Department of Ocean Sciences; Estados UnidosFil: Aguilar, Orlando Mario. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico La Plata. Instituto de Biotecnología y Biología Molecular; Argentin

Diseño de un programa de seguimiento de poblaciones de cánidos silvestres en ambientes esteparios de la Patagonia, Argentina

Wildlife management decisions should be based on solid baseline information, with monitoring populations as a necessary activity whenever the management objective is maintaining abundance at a previously stated level. Developing a monitoring program requires careful experimental and statistical considerations in order to get confidence about its capability in detecting predefined trends. Our objective was to develop a monitoring program for two canid species (the Grey Fox Pseudalopex griseus and the Culpeo Fox P. culpaeus), based on visitation indices to bait stations. Using MONITOR software we estimated the sampling effort necessary to detect a 50% decrease in their populations during the next 5 years (annual rate of –12,94%) and during the next 10 years (annual rate of –6,70%), with a minimum power of 80%. We assume that the environmental cost of making a Type II error (failing to detect a real population trend) is greater than that of making a Type I error (sounding a false alarm) and used three alpha levels 0.05, 0.10 and 0.15. We also tested an increasing sampling effort (number of bait stations lines), and activating them during one, two and up to three times in a single year. We fed the MONITOR program with the mean visitation index to the 20 transects activated on several occasions during the previous year in the study area. In order to detect a 50% decrease over the next 5 years, any monitoring program should be based on at least two annual replicates of the bait stations. A monitoring program accessible to the protected area manpower and financial resources and considering the conservation status of the target species would be one developed to detect a 50% decrease over the next 10 years, activating 16 lines once a year, during two or three consecutive nights and an alpha of 0.10. We also discuss alternatives to use only the first nigh of visit in order to assimilate bait stations to scent stations and make these results comparable with other studiesin Patagonia, Argentina. Monitoring programs like the one presented here would be valuable to help managers when deciding about harvest quotas for the fur trade, or anticipating conflicts and solutions with sheep rangers by detecting increasing trends in Culpeo populations. La gestión de la fauna silvestre debe basarse en sólida información de base. Ello incluye el seguimiento de poblaciones para ayudar a mantenerlas en tamaños próximos a aquellos previamente fijados. El desarrollo de programas de seguimiento requiere de una considerable planificación y evaluación estadística antes de su implementación. El objetivo de nuestro trabajo fue desarrollar un programa de seguimiento para dos especies de cánidos silvestres en Patagonia: el zorro colorado (Pseudalopex culpaeus) y el zorro gris (P. griseus). Tratamos de averiguar, utilizando el programa MONITOR, cual debería ser el esfuerzo de muestreo anual para detectar una disminución del 50% de la población actual en los próximos 5 años (esto es una tasa anual de –12,94%), o en los próximos 10 años (una tasa anual de –6.70%), satisfaciendo una potencia mínima del 80%. El trabajo de campo se realizó en el área protegida “Monumento Natural Bosques Petrificados”, Provincia de Santa Cruz, Argentina. Como estimador de la abundancia de los zorros se utilizaron las visitas a líneas de estaciones de cebado. El costo ambiental de cometer un error de Tipo II es mayor que el de cometer uno de Tipo I, por lo que utilizamosalternativamente tres niveles de α: 0.05, 0.10 y 0.15. Probamos también un esfuerzo de muestreo (número de líneas de estaciones de cebado) creciente, activándolas una, dos y hasta tres veces por año. Como valores iniciales para alimentar el programa MONITOR utilizamos la media y desviación estándar del índice de visita a cada una de las 20 líneas que se instalaron en el área de estudio. Para detectar una disminución del 50% en cinco años cualquier programa de seguimiento poblacional deberá basarse al menos en dos repeticiones anuales de las estaciones de cebado. Un programa de seguimiento accesible a las disponibilidades del área protegida sería aquel diseñado para detectar una disminución del 50% en diez años (-6.7% anual), con un α de 0.10 y un esfuerzo de 16 líneas, activadas una vez por año y revisadas durante dos o tres noches consecutivas. Se proponen alternativas para utilizar solo la primer noche de muestreo, de forma que los resultados sean luego comparables con los de experiencias de estaciones de olor en otras regiones de la Patagonia. La puesta en marcha de programas como el aquí presentado servirán para la toma de decisiones a organizaciones encargadas de la gestión de la fauna silvestre, autorizando o prohibiendo extracciones destinadas al mercado peletero. Servirían también para conocer a tiempo incrementos poblacionales, permitiendo así tomar medidas preventivas tendentes a disminuir conflictos con la actividad ganadera.&nbsp

nifH pyrosequencing reveals the potential for location-specific soil chemistry to influence N₂-fixing community dynamics

A dataset of 87 020 nifH reads and 16 782 unique nifH protein sequences obtained over 2 years from four locations across a gradient of agricultural soil types in Argentina were analysed to provide a detailed and comprehensive picture of the diversity, abundance and responses of the N₂-fixing community in relation to differences in soil chemistry and agricultural practices. Phylogenetic analysis revealed an expected high proportion of Alphaproteobacteria, Betaproteobacteria and Deltaproteobacteria, mainly relatives to Bradyrhizobium and Methylosinus/Methylocystis, but a surprising paucity of Gammaproteobacteria. Analysis of variance and stepwise regression modelling suggested location and treatment-specific influences of soil type on diazotrophic community composition and organic carbon concentrations on nifH diversity. nifH gene abundance, determined by quantitative real-time polymerase chain reaction, was higher in agricultural soils than in non-agricultural soils, and was influenced by soil chemistry under intensive crop rotation but not under monoculture. At some locations, sustainable increased crop yields might be possible through the management of soil chemistry to improve the abundance and diversity of N₂-fixing bacteria.Facultad de Ciencias ExactasInstituto de Biotecnologia y Biologia MolecularFacultad de Ciencias Naturales y MuseoLaboratorio de Sistemática y Biología Evolutiv

The discovery of Stromatolites developing at 3570 m above sea level in a high-altitude volcanic lake Socompa, Argentinean Andes

We describe stromatolites forming at an altitude of 3570 m at the shore of a volcanic lake Socompa, Argentinean Andes. The water at the site of stromatolites formation is alkaline, hypersaline, rich in inorganic nutrients, very rich in arsenic, and warm (20-24°C) due to a hydrothermal input. The stromatolites do not lithify, but form broad, rounded and low-domed bioherms dominated by diatom frustules and aragonite micro-crystals agglutinated by extracellular substances. In comparison to other modern stromatolites, they harbour an atypical microbial community characterized by highly abundant representatives of Deinococcus-Thermus, Rhodobacteraceae, Desulfobacterales and Spirochaetes. Additionally, a high proportion of the sequences that could not be classified at phylum level showed less than 80% identity to the best hit in the NCBI database, suggesting the presence of novel distant lineages. The primary production in the stromatolites is generally high and likely dominated by Microcoleus sp. Through negative phototaxis, the location of these cyanobacteria in the stromatolites is controlled by UV light, which greatly influences their photosynthetic activity. Diatoms, dominated by Amphora sp., are abundant in the anoxic, sulfidic and essentially dark parts of the stromatolites. Although their origin in the stromatolites is unclear, they are possibly an important source of anaerobically degraded organic matter that induces in situ aragonite precipitation. To the best of our knowledge, this is so far the highest altitude with documented actively forming stromatolites. Their generally rich, diverse and to a large extent novel microbial community likely harbours valuable genetic and proteomic reserves, and thus deserves active protection. Furthermore, since the stromatolites flourish in an environment characterized by a multitude of extremes, including high exposure to UV radiation, they can be an excellent model system for studying microbial adaptations under conditions that, at least in part, resemble those during the early phase of life evolution on Earth.Instituto de Biotecnologia y Biologia Molecular (IBBM

Dynamics of Seed-Borne Rice Endophytes on Early Plant Growth Stages

Bacterial endophytes are ubiquitous to virtually all terrestrial plants. With the increasing appreciation of studies that unravel the mutualistic interactions between plant and microbes, we increasingly value the beneficial functions of endophytes that improve plant growth and development. However, still little is known on the source of established endophytes as well as on how plants select specific microbial communities to establish associations. Here, we used cultivation-dependent and -independent approaches to assess the endophytic bacterrial community of surface-sterilized rice seeds, encompassing two consecutive rice generations. We isolated members of nine bacterial genera. In particular, organisms affiliated with Stenotrophomonas maltophilia and Ochrobactrum spp. were isolated from both seed generations. PCR-based denaturing gradient gel electrophoresis (PCR-DGGE) of seed-extracted DNA revealed that approximately 45% of the bacterial community from the first seed generation was found in the second generation as well. In addition, we set up a greenhouse experiment to investigate abiotic and biotic factors influencing the endophytic bacterial community structure. PCR-DGGE profiles performed with DNA extracted from different plant parts showed that soil type is a major effector of the bacterial endophytes. Rice plants cultivated in neutral-pH soil favoured the growth of seed-borne Pseudomonas oryzihabitans and Rhizobium radiobacter, whereas Enterobacter-like and Dyella ginsengisoli were dominant in plants cultivated in low-pH soil. The seed-borne Stenotrophomonas maltophilia was the only conspicuous bacterial endophyte found in plants cultivated in both soils. Several members of the endophytic community originating from seeds were observed in the rhizosphere and surrounding soils. Their impact on the soil community is further discussed