Impact of different cropping conditions and tillage practices on the soil fungal abundance of a Phaeozem luvico

Fungal diversity seems to be a good indicator of ecosystem disturbance and functioning. The purpose of this work was to quantify the fungal population as a sensitive indicator of the changes caused by stubble placement in two tillage systems: reduced tillage (RT) and conventional tillage (CT) with and without cropping. To this end, we determined the effect of soil disturbances such as N fertilization, tillage practice, and cropped area on the soil fungal communities of a Phaeozem luvico of the El Salado river basin (Argentina). Soil samples (at 0-10 cm depth) were collected from a field cultivated with wheat at post-harvest, before sowing and at tillering. The relative abundance of individuals of the fungal population was studied on Nash Snyder and Oxgall agar media after different treatments and assessed as colony forming units (CFU/g of soil). The diversity of the fungal population was studied by Shannon´s index (H). The tillage system showed a marked effect only at post-harvest and the number of propagules was highest under RT for both culture media. The largest values of H were found only at post-harvest when Oxgall agar was used. A significant decrease in the values of H was observed when CT and high fertilization was applied in the wheat cropped area. The relative abundance of individuals of the fungal population was different in soils under the different tillage practices

Impact of different cropping conditions and tillage practices on the soil fungal abundance of a <i>Phaeozem luvico</i>

Fungal diversity seems to be a good indicator of ecosystem disturbance and functioning. The purpose of this work was to quantify the fungal population as a sensitive indicator of the changes caused by stubble placement in two tillage systems: reduced tillage (RT) and conventional tillage (CT) with and without cropping. To this end, we determined the effect of soil disturbances such as N fertilization, tillage practice, and cropped area on the soil fungal communities of a Phaeozem luvico of the El Salado river basin (Argentina). Soil samples (at 0-10 cm depth) were collected from a field cultivated with wheat at post-harvest, before sowing and at tillering. The relative abundance of individuals of the fungal population was studied on Nash Snyder and Oxgall agar media after different treatments and assessed as colony forming units (CFU/g of soil). The diversity of the fungal population was studied by Shannon´s index (H). The tillage system showed a marked effect only at post-harvest and the number of propagules was highest under RT for both culture media. The largest values of H were found only at post-harvest when Oxgall agar was used. A significant decrease in the values of H was observed when CT and high fertilization was applied in the wheat cropped area. The relative abundance of individuals of the fungal population was different in soils under the different tillage practices.Centro de Investigaciones en Fitopatologí

Impact of different cropping conditions and tillage practices on the soil fungal abundance of a <i>Phaeozem luvico</i>

Fungal diversity seems to be a good indicator of ecosystem disturbance and functioning. The purpose of this work was to quantify the fungal population as a sensitive indicator of the changes caused by stubble placement in two tillage systems: reduced tillage (RT) and conventional tillage (CT) with and without cropping. To this end, we determined the effect of soil disturbances such as N fertilization, tillage practice, and cropped area on the soil fungal communities of a Phaeozem luvico of the El Salado river basin (Argentina). Soil samples (at 0-10 cm depth) were collected from a field cultivated with wheat at post-harvest, before sowing and at tillering. The relative abundance of individuals of the fungal population was studied on Nash Snyder and Oxgall agar media after different treatments and assessed as colony forming units (CFU/g of soil). The diversity of the fungal population was studied by Shannon´s index (H). The tillage system showed a marked effect only at post-harvest and the number of propagules was highest under RT for both culture media. The largest values of H were found only at post-harvest when Oxgall agar was used. A significant decrease in the values of H was observed when CT and high fertilization was applied in the wheat cropped area. The relative abundance of individuals of the fungal population was different in soils under the different tillage practices.Centro de Investigaciones en Fitopatologí

Composition and dynamics of the fungal population in a typical Phaeozem luvico in Argentina

he decomposer soil community maintains the arable soil ecosystem for the nutrient turnover. Here, we studied the dynamics of the soil fungal populations in a typical Phaeozem luvico in Argentina and related it to the management practices. Soil samples (at 0–10cm depth) were collected from a field cultivated with wheat, at different sampling times: at post-harvest, before sowing, and at tillering. The relative abundance of individuals in the population on Nash Snyder and Oxgall agar media was assessed as colony forming units (CFU). The fungal population was classified by numerical taxonomy at the different sampling times. The highest values of CFUg−1of soil were found at post-harvest under reduced tillage and differed significantly from those at conventional tillage. The generaTrichoderma,Fusarium,Aspergillus,Penicillium, andFusarium oxysporumwere present in the largest number of samples and discriminated the fungal community between times. This discrimination could be related to alterations in the availability of carbon sources during stubble degradation at post-harvest and before sowing and were of lesser importance at tillering

Cambio en la sensibilidad al fungicida Tebuconazol en las poblaciones de Zymoseptoria Tritici (Quaedvlieg & Crous) patógeno de la septoriosis de la hoja del trigo

La septoriosis de la hoja del trigo, producida por Zymoseptoria tritici (Quaedvlieg &amp;amp; Crous), necrosa el área fotosintética disminuyendo el rendimiento final. En Argentina la aplicación de fungicidas es una práctica común de control y los triazoles y las estrobilurinas son los más frecuentes. Los triazoles son activos inhibidores del ergosterol que abunda como parte constitutiva de la membrana de la célula fúngica. No obstante, el uso genera grados de tolerancia en el patógeno obligando a la utilización de mezclas de principios activos. El objetivo fue: evaluar la pérdida de sensibilidad al efecto del fungicida tebuconazol en las poblaciones de aislados de Zymoseptoria tritici de la región triguera argentina. Se cuantificaron: a) la tasa de crecimiento de las colonias fúngicas de 46 aislados creciendo en APG sólido con fungicida incorporado, en relación a los mismos creciendo en medio de cultivo sin el fungicida y b) el porcentaje de eficiencia del fungicida para cada uno de los aislados. El análisis de Kruskal Wallis categorizó a los aislados en dos tipos de respuesta: 1-tolerantes, que superan el efecto inhibidor del fungicida; 2- que no superan el crecimiento en presencia del fungicida. La experiencia internacional explica la tolerancia al fungicida por alteraciones genéticas producidas en el gen CYP51, responsable en el patógeno de la sensibilidad al químico. El siguiente avance será diagnosticar la presencia de los genotipos alterados para recomendar el uso adecuado de los principios activos.Trabajo presentado por el Centro de Investigaciones de Fitopatología (CIDEFI

Importancia del grano de trigo en la epidemiologia de la mancha de la hoja producida por Septoria tritici

Varias enfermedades del trigo se producen por hongos transmitidos por la semilla. Promueve la sobrevivencia del patógeno e inicia el inóculo para el nuevo cultivo. Los antecedentes no precisan la importancia de la semilla en la transmisión de la mancha de la hoja del trigo. El objetivo es definir el rol de la semilla en la epidemiología de la enfermedad

Septoriosis del trigo en la Argentina: observaciones prácticas para el manejo de la enfermedad

El rendimiento del trigo se ve afectado por “la mancha de hoja del trigo”, o “septoriosis ” producida por el hongo hemibiótrofo Mycosphaerella graminicola (Fuckel) Schroeter in Cohn (anamorfo Septoria tritici Rob. ex Desm.). Es un serio problema en el sur de Chile y de Uruguay y en la Argentina, en las provincias de Córdoba y Buenos Aires. Los daños a nivel mundial oscilan entre 31 y 54 % y entre 17 y 50 % en Argentina, dependiendo del estado fenológico y el grado de ataque en el que ocurre la infección. No hay dudas acerca de la importancia del manejo integrado de la enfermedad, especialmente con temas como la sanidad de la semilla, el manejo de los rastrojos y el uso consciente de fungicidas. El objetivo de esta presentación es: Sumar conocimientos para la aplicación racional de medidas de control. Para ello se definió: (i) la presencia de S. tritici en la semilla y su vinculación en la transmisión de la enfermedad y (ii) las condiciones ambientales asociadas a la dinámica del inóculo aéreo. Partiendo de semillas de trigo que provenían de plantas con alta severidad a la mancha de la hoja del trigo, se diseñó una estrategia basada en la técnica convencional de PCR para detectar el hongo S. tritici. Se comprobó la ausencia del patógeno en capas internas del pericarpio y/o endosperma. Se demostró la inhibición parcial o total de la germinación del cariopse y los patógenos que la generaron. Con la técnica tradicional de transmisión en speedling se cuantificaron los patógenos que aparecieron en el coleoptile o la plántula. Con la técnica de Elekes, se sometió la semilla previamente humedecida e incubada a 20°C a un período de 8 h a -20°C para inhibir la actividad de las enzimas que impedían que el patógeno transmitida por ella, se manifieste. Luego de una desinfección superficial se incubaron las mitades longitudinales de las semillas en medio Papavizas. Las otras mitades se conservaron en eppendorf y luego en freezer a -20°C hasta su procesado por PCR. La suma de evidencias aseguran que el patógeno no se transmite hacia la plántula por el grano de trigo contrariamente a lo ocurrido con Stagonospora nodorum, aunque la amplificación del ADN de los granos y la posterior secuenciación de los fragmentos sugiere que trazas de hifas o conidios deben alcanzar su superficie por el elevado nivel de infección en el periodo vegetativo - reproductivo del cultivo. Para tratar el segundo objetivo, se cuantificó la abundancia relativa de ascosporas y picnidiosporas en el campo durante dos periodos. Se generó una aproximación empírica útil para predecir la eliminación de altas cantidades de esporas reproductivas y vegetativas que indiquen la probabilidad de generar una nueva epidemia. Una asociación positiva de las picnidiosporas con la intensidad de la lluvia ocurrió cuando esta varió entre 20 a 43mm/h 30 días antes del exudado, al igual que las T mayores de 14°, entre los 7-60 días previos. Para que se desarrolle una epidemia en invierno las temperaturas deben ir en aumento de 7 a más de 14°C especialmente al final del macollaje en el periodo de elongación. La captura de picnidios estuvo directamente relacionada con la HR mayor del 90% 60 días antes de la misma ó con los mm de lluvia acumulados 60 días antes de la eliminación; también con las temperaturas mayores de 14°C 60 días previos a la expulsión. La eliminación de las ascoporas se relacionó con una disminución de la radiación 30 días antes de la expulsió

Weather Conditions Associated with the Release and Dispersal of Zymoseptoria tritici Spores in the Argentine Pampas Region

The abundance ofZymoseptoria triticiascospores and conidia in a field was examined throughout two one-year periods (1998-1999 and 1999-2000) establishing the relationship between spore release and weather variables. Radiation, temperature, intensity of rainfall, and relative humidity significantly affected the dispersal of ascospores and pycnidiospores of this pathogen. Spore traps collected both types of spores, at weekly intervals, at two different stages of the wheat crop (vegetative and wheat stubble stages) and different distances from the sources. Ascospores were the predominant sources of inoculum in the field. The numbers of ascospores and pycnidiospores declined with the increase of distance from the sources. The release of pycnidiospores was associated with the increase in rainfall intensity 7 days before the released event and the increase in radiation 60 days before the same event. Relative humidity 3 and 15 days before the release event was positively correlated with ascospores release and negatively correlated with radiation and temperature in all the sampling interval. Also for the first time, a positive correlation between radiation and pycnidiospores dispersal is reported. Understanding the relationship between environment conditions and spores dispersal event could improve the control strategies of the disease.Facultad de Ciencias Agrarias y Forestale

Environmental factors affecting the release and dispersal of pycnidiospores and ascospores of Mycosphaerella graminicola

Leaf blotch of wheat, caused by Mycosphaerella graminicola is an important wheat disease that produces yield losses in different regions of the world. The objectives of this study were to examine the relative abundance of M.graminicola ascospores and conidia in a field environment throughout a period of two years and establish the relationship between their release and the climatic conditions. This inoculum posses a risk to crop production and may be important to the epidemiology of septoria diseases in the wheat producing areas of Argentina. The inoculum level of airborne spores was measured in Julio Hirschron Experimental Stattion at Los Hornos locality during October 1998 to September 1999 to September 2000. Spore traps were used to monitor both ascospores and pycnidiospores when the wheat crop was in the vegetative and debris states. Samples were taken weekly. Data of pycnidiospores in water, in petroleum jelly and ascospores in petroleum jelly wee recorded

Mineralización de los residuos de trigo provenientes de distintos sistemas de labranza: efecto sobre la pérdida de peso y dinámica del nitrógeno

En siembra directa y monocultivo los patógenos necrótrofos son más severos, porque aumentan el período de supervivencia sobre los rastrojos retenidos en el suelo. La descomposición de los residuos de cosecha depende de factores edáficos (temperatura, humedad y disponibilidad de nutrientes), químicos del rastrojo (concentración de N o la relación C/N, contenidos de lignina y carbohidratos solubles) y factores de manejo, (cantidad de rastrojo, tamaño de sus partículas (descomposición dentro o sobre el suelo) El objetivo fue investigar la pérdida de peso del rastrojo según los contenidos iniciales de nitrógeno en el suelo, trazando su dinámica