Expansión de la agricultura : la tragedia del éxito

Fil: Ghers, Claudio M. Universidad de Buenos Aires. Facultad de Agronomía; ArgentinaEl éxito económico-social de las nuevas tecnologías, fundamentalmente aplicadas al\ncultivo de soja, creó una expansión epidémica con consecuencias trágicas que resultan\nen transformaciones donde la homogenización y los efectos masivos de acumulación y\ndominio se hacen evidentes

Ozone Exposure of a Weed Community Produces Adaptive Changes in Seed Populations of Spergula arvensis

Tropospheric ozone is one of the major drivers of global change. This stress factor alters plant growth and development. Ozone could act as a selection pressure on species communities composition, but also on population genetic background, thus affecting life history traits. Our objective was to evaluate the consequences of prolonged ozone exposure of a weed community on phenotypic traits of Spergula arvensis linked to persistence. Specifically, we predicted that the selection pressure exerted by high ozone concentrations as well as the concomitant changes in the weed community would drive population adaptive changes which will be reflected on seed germination, dormancy and longevity. In order to test seed viability and dormancy level, we conducted germination experiments for which we used seeds produced by S. arvensis plants grown within a weed community exposed to three ozone treatments during four years (0, 90 and 120 ppb). We also performed a soil seed bank experiment to test seed longevity with seeds coming from both the four-year ozone exposure experiment and from a short-term treatment conducted at ambient and added ozone concentrations. We found that prolonged ozone exposure produced changes in seed germination, dormancy and longevity, resulting in three S. arvensis populations. Seeds from the 90 ppb ozone selection treatment had the highest level of germination when stored at 75% RH and 25 °C and then scarified. These seeds showed the lowest dormancy level when being subjected to 5 ºC/5% RH and 25 ºC/75% followed by 5% RH storage conditions. Furthermore, ozone exposure increased seed persistence in the soil through a maternal effect. Given that tropospheric ozone is an important pollutant in rural areas, changes in seed traits due to ozone exposure could increase weed persistence in fields, thus affecting weed-crop interactions, which could ultimately reduce crop production.Fil: Landesmann, Jennifer Brenda. Consejo Nacional de Invest.cientif.y Tecnicas. Centro Cientifico Tecnol.conicet - Patagonia Norte. Instituto de Invest.en Biodiversidad y Medioambiente;Fil: Gundel, Pedro Emilio. Consejo Nacional de Invest.cientif.y Tecnicas. Oficina de Coordinacion Administrativa Pque. Centenario. Instituto D/inv.fisiologicas y Eco.vinculadas A L/agric;Fil: Martinez Ghersa, M. Alejandra. Consejo Nacional de Invest.cientif.y Tecnicas. Oficina de Coordinacion Administrativa Pque. Centenario. Instituto D/inv.fisiologicas y Eco.vinculadas A L/agric;Fil: Ghersa, Claudio Marco. Consejo Nacional de Invest.cientif.y Tecnicas. Oficina de Coordinacion Administrativa Pque. Centenario. Instituto D/inv.fisiologicas y Eco.vinculadas A L/agric

Identificación molecular del endosimbionte secundario Hamiltonella defensa en el pulgón amarillo de los cereales, Metopolophium dirhodum

255-258This is the first report of the association between the rose-grain aphid Metopolophium dirhodum, a potentially important cereal pest and the facultative symbiont Hamiltonella defensa. The infection with this gamma-proteobacterium was determined by PCR in laboratory-reared and field-collected specimens of an Argentinian population of the aphid. Partial bacterial 16S, IGS and 23S rRNA genes were sequenced and compared to other available Hamiltonella sequences by phylogenetic analysis. The present study provides new information on previously unknown M. dirhodum microbiota

Neotyphodium endophyte transmission to Lolium multiflorum seeds depends on the host plant fitness

Fil: Gundel, Pedro E. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas vinculadas a la Agricultura (IFEVA)-CONICET; Argentina.Fil: Garibaldi, Lucas Alejandro. Universidad Nacional del Comahue. Centro Regional Universitario Bariloche. INIBIOMA-CONICET. Laboratorio Ecotono; Argentina.Fil: Martínez Ghersa, María A. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas vinculadas a la Agricultura (IFEVA)-CONICET; Argentina.Fil: Ghersa, Claudio M. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas vinculadas a la Agricultura (IFEVA)-CONICET; Argentina.Fil: Garibaldi, Lucas Alejandro. Universidad de Buenos Aires (UBA). Facultad de Agronomía; Argentina.Frequency and distribution of symbiosis in nature depend both on the direct symbiont effect on the host fitness and on its efficiency to spread within host populations (transmission). For vertically transmitted Neotyphodium fungi, the attention has been centered on the endophyte effect on host grass plants but little is known about the controls of transmission. Environmental and genetic factors have been suggested as important controls of transmission efficiency. We studied the effect of these two factors on the transmission efficiency of the Neotyphodium endophyte in Lolium multiflorum plants. Plant genotype of a host population naturally endophyte-infected (95%) was manipulated by conducting controlled crosses with genetically distant plant populations. The resulting progeny was subjected to two types of factors, resource shortage and oxidative stress induced by an herbicide. Irrespective of plant genotype, high resource level increased seed yield per plant by 26-fold, spike-to-seed transmission by 12%, and plant-to-seed transmission by 10% (not significant). Although herbicide effects could be mediated indirectly by changes in plant density or directly by oxidative stress, neither plant fitness nor transmission efficiency was affected. An interesting pattern between transmission efficiency and seed yield per plant was revealed when plants (from both experiments) were plotted together. Low yielding plants, that is plants that grew under low resource level at high plant density, showed high transmission failures whereas high yielding plants, that is plants growing at low density with and without herbicide treatment, showed high transmission rates. Transmission failures may be a consequence of the endophyte cost for host plants growing under restrictive conditions, suggesting that lower transmission efficiency may partially explain previous evidence showing lower endophyte infection frequency for grasses under stressful conditions. Host plants could be penalizing the endophyte through a competition-like mechanism, instead of depressing their own fitness

Viability of Neotyphodium endophytic fungus and endophyte-infected and noninfected Lolium multiflorum seeds

Fil: Gundel, Pedro E. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas vinculadas a la Agricultura; Argentina.Fil: Martínez Ghersa, María A. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas vinculadas a la Agricultura; Argentina.Fil: Garibaldi, Lucas Alejandro. Universidad de Buenos Aires. Facultad de Agronomía; Argentina.Fil: Ghersa, Claudio M. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas vinculadas a la Agricultura; Argentina.Fil: Gundel, Pedro E. Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET); Argentina.Fil: Martínez-Ghersa, Alejandra. Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET); Argentina.Fil: Garibaldi, Lucas Alejandro. Universidad Nacional del Comahue. Centro Regional Universitario Bariloche. Laboratorio Ecotono; Argentina.Fil: Ghersa, Claudio M. Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET); Argentina.Neotyphodium endophyte fungi are vertically transmitted symbionts of cool-season grasses. The seed phase of the grass’ life cycle appears to be critical for the persistence of the fungus. Endophyte viability decreases faster than seed viability, but little is known of the effects of this endophyte on seed viability. The endophyte could affect seed viability through changes in water content. Here, we assessed the effects of the endophyte on seed viability, the differential survival of endophyte and seed, and the effects of infection on seed water content. Viability of endophyte-infected and noninfected seeds and endophyte were evaluated over a period of 729 d under 12 controlled environmental conditions. Seed viability was reduced by the infection at high temperature and high relative humidity, but not under other conditions. Moreover, endophyte viability decreased faster than seed viability only under high humidity or high temperature. Seed water content was not affected by endophyte presence. The proportion of viable infected seeds was mainly affected by the loss in endophyte viability and secondly by the differential survival of infected and noninfected seeds. Knowledge on the relative importance of these processes is critical to understand the factors affecting the efficiency of endophyte vertical transmission and the frequency of endophyte-infected plants

Algunos aspectos acerca de la aparición de resistencia a herbicidas en poblaciones de malezas

Actualmente la mayor parte de las cosechas de grano en la Argentina están provistas por sistemas de producción agrícola permanente. Esto ha inducido el reemplazo de especies y la selección de fenotipos nuevos en las poblaciones de las malezas que acompañan los cultivos. Estos cambios se manifiestan a través de un incremento en las fallas en el control químico, debido a que las especies escapan, aumentan la tolerancia o resisten a los controles. En respuesta a estos problemas los agricultores han incrementado las dosis, la frecuencia de aplicación de herbicidas y el abanico de productos utilizados. Estas medidas, que apuntan a resolver las ineficiencias en el control de malezas, han acentuado en términos generales el problema de la reestructuración de las comunidades de malezas y el de la selección de poblaciones resistentes a los herbicidas. Ejemplos paradigmáticos de este proceso son la resistencia a glifosato y atrazina, dos de los herbicidas que se usan con mayor frecuencia.Fil: Ghersa, Claudio Marco. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Ferraro, Diego Omar. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Mutualism effectiveness and vertical transmission of symbiotic fungal endophytes in response to host genetic backround

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5. Vaccine development: basic considerations. Asexual blood stage vaccines: from merozoites to peptides

Asexual blood stage proliferation is responsible for the morbidity and mortality associated with malaria infection in man. These developmental stages are therefore obvious targets for the development of malaria vaccines. Several asexual blood stage components have been identified as potential candidates for the development of vaccines and some of them have been shown, following immunization, to induce at least partial protection in a variety of Plasmodium-host combinations. Studies on defined parasite components and on synthetic peptides derived from them have revealed new insights at the molecular level into parasite mechanisms involved in propagation and survival in the infected host, and into the interaction between parasite components and the host immune system. Practical application of these findings is likely to provide the basis for the design of more appropriate antigens for the development of vaccine

Daño, producción de semillas y persistencia del hongo endófito Epichloë occultans en plantas de Lolium multiflorum bajo un ataque de herbívoros lepidópteros y contaminación por ozono

Plants are expected to face novel challenges as consequence of human-driven global change. Outbreaks of pests and higher incidence of contaminants are increasing. Plants can improve tolerance to stress factors through associations with symbiotic microorganisms. Certain grasses establish persistent and asymptomatic symbioses with Epichloë fungal endophytes, which are known to confer protection against Herbivores and improve plant tolerance to abiotic stress factors. Nonetheless, accumulating evidence suggest the symbiosis outcome is context dependent. We evaluated the capacity of the endophyte fungus E. occultans in protecting the annual grass Lolium multiflorum against a spontaneous larva attack of the generalist herbivore Agrotis ipsilon under episodic exposure of plants to ozone. Symbiotic and non-symbiotic plants were individually grown outdoors and exposed to ozone at different stages resulting in four treatments: control (plant never exposed to ozone), plant exposed to ozone at vegetative stage, plant exposed to ozone at reproductive stage, and plant exposed to ozone at both stages. After the last exposure, there was an outbreak of A. ipsilon larvae. We evaluated herbivore damage, seed production per plant, and endophyte transmission to the seeds. Frequency of attacked plants was irrespective of both the endophyte and ozone exposure. However, the damage level per plant was only reduced by the endophyte. Seed production was slightly lower in endophyte-symbiotic plants and not affected by ozone. Interestingly, herbivore damaged and undamaged endophyte-symbiotic plants contributed equally to seed production. However, in plants exposed to ozone once at vegetative or reproductive stage, endophyte-free undamaged plants had higher seed production than endophyte-free damaged plants. Ozone treatments did not affect the transmission efficiency of endophytes to the seeds. Mean endophyte transmission efficiency per plant was 95%. Medium doses of ozone seem to have undetectable effects on grass-endophyte symbiosis, not affecting the defensive mutualism nor the persistence of the symbiont across generations.Las plantas enfrentan nuevos desafíos debido al cambio global impulsado por las actividades humanas. Mientras los brotes de plagas y la incidencia de contaminantes están en aumento, las plantas pueden mejorar su tolerancia al estrés asociándose con microorganismos. Ciertas gramíneas establecen simbiosis persistentes y asintomáticas con endófitos fúngicos Epichloë, y así obtienen protección contra herbívoros y tolerancia al estrés abiótico. No obstante, los resultados de la simbiosis dependen del contexto ecológico. Evaluamos la capacidad del hongo endófito E. occultans para proteger el pasto anual Lolium multiflorum contra un ataque de larvas del herbívoro generalista Agrotis ipsilon bajo exposición episódica de las plantas al ozono. Cultivamos plantas simbióticas y no-simbióticas en macetas y las expusimos a ozono en diferentes etapas, resultando en cuatro tratamientos: control (nunca expuesta al ozono), planta expuesta al ozono en etapa vegetativa, planta expuesta al ozono en etapa reproductiva y planta expuesta al ozono en ambas etapas. Luego, hubo un brote de larvas de A. ipsilon. Evaluamos el daño causado por las larvas, la producción de semillas por planta y la transmisión del endófito a las semillas. La frecuencia de plantas atacadas fue independiente de la presencia del endófito y del ozono. Sin embargo, el nivel de daño por planta sólo fue afectado y reducido por el endófito. La producción de semillas fue ligeramente menor en las plantas con endófito y no afectada por el ozono. Curiosamente, las plantas simbióticas dañadas y no-dañadas presentaron igual producción de semillas. No obstante, las plantas no-simbióticas no-dañadas produjeron más semillas que las dañadas cuando fueron expuestas una vez a ozono en etapa vegetativa o reproductiva. El ozono no afectó la eficiencia de transmisión de los endófitos a las semillas, la cual fue, en promedio, 95%. El ozono, en dosis medias, parece tener efectos indetectables sobre la simbiosis planta-endófito.Fil: Gundel, Pedro Emilio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; Argentina. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Recursos Naturales y Ambiente; ArgentinaFil: Bigaxzoli, Fernando. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Métodos Cuantitativos y Sistemas de Información; ArgentinaFil: Freitas, Priscila P.. Ministry For Primary Industries; Nueva ZelandaFil: Landesmann, Jennifer Brenda. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; Argentina. Universidad Nacional del Comahue. Centro Regional Universitario Bariloche. Laboratorio de Ecotono; ArgentinaFil: Martínez Ghersa, María Alejandra. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; Argentina. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Recursos Naturales y Ambiente; ArgentinaFil: Ghersa, Claudio Marco. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; Argentina. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Recursos Naturales y Ambiente; Argentin

Mutualism effectiveness and vertical transmission of symbiotic fungal endophytes in response to host genetic background

838-849Certain species of the Pooideae subfamily develop stress tolerance and herbivory resistance through symbiosis with vertically transmitted, asexual fungi. This symbiosis is specific, and genetic factors modulate the compatibility between partners. Although gene flow is clearly a fitness trait in allogamous grasses, because it injects hybrid vigor and raw material for evolution, it could reduce compatibility and thus mutualism effectiveness. To explore the importance of host genetic background in modulating the performance of symbiosis, Lolium multiflorum plants, infected and noninfected with Neotyphodium occultans, were crossed with genetically distant plants of isolines (susceptible and resistant to diclofop-methyl herbicide) bred from two cultivars and exposed to stress. The endophyte improved seedling survival in genotypes susceptible to herbicide, while it had a negative effect on one of the genetically resistant crosses. Mutualism provided resistance to herbivory independently of the host genotype, but this effect vanished under stress. While no endophyte effect was observed on host reproductive success, it was increased by interpopulation plant crosses. Neither gene flow nor herbicide had an important impact on endophyte transmission. Host fitness improvements attributable to gene flow do not appear to result in direct conflict with mutualism while this seems to be an important mechanism for the ecological and contemporary evolution of the symbiotum