Estudios preliminares de biocontrol de mancha en red de la cebada en semilla, con cepas de Trichoderma spp. Ensayos in vitro

La “mancha en red” de la cebada, producida por el hongo Drechslera teres (Sacc.) Shoem. (teleomorfo Pyrenophora teres Drechsler) es una enfermedad endémica en la Argentina, llegando a tener una prevalencia del 76 % e incidencia del 100%, presentándose desde el estado de plántula hasta la cosecha. Produce pérdidas en el rendimiento del 20% y disminuye el peso y cantidad de granos/mt2 . La semilla infectada y el rastrojo son las principales fuentes de inóculo de la enfermedad. Las semillas constituyen el agente más eficiente de diseminación y el medio más seguro para la supervivencia de los patógenos cumpliendo un rol fundamental en sus ciclos de vida. La asociación de los patógenos con las semillas, les asegura la obtención de nutrientes en el momento de la germinación y emergencia de las plántulas (Reis et al., 1999). D. teres, se transmite de la semilla infectada a los órganos aéreos para dar continuidad a su ciclo de vida, con una tasa de transmisión del 21%, por esto el tratamiento de semilla es la clave para impedir la introducción de éste patógeno en los lotes de cultivo.Centro de Investigaciones de Fitopatologí

Estudios preliminares de biocontrol de mancha en red de la cebada en semilla, con cepas de Trichoderma spp. Ensayos in vitro

La “mancha en red” de la cebada, producida por el hongo Drechslera teres (Sacc.) Shoem. (teleomorfo Pyrenophora teres Drechsler) es una enfermedad endémica en la Argentina, llegando a tener una prevalencia del 76 % e incidencia del 100%, presentándose desde el estado de plántula hasta la cosecha. Produce pérdidas en el rendimiento del 20% y disminuye el peso y cantidad de granos/mt2 . La semilla infectada y el rastrojo son las principales fuentes de inóculo de la enfermedad. Las semillas constituyen el agente más eficiente de diseminación y el medio más seguro para la supervivencia de los patógenos cumpliendo un rol fundamental en sus ciclos de vida. La asociación de los patógenos con las semillas, les asegura la obtención de nutrientes en el momento de la germinación y emergencia de las plántulas (Reis et al., 1999). D. teres, se transmite de la semilla infectada a los órganos aéreos para dar continuidad a su ciclo de vida, con una tasa de transmisión del 21%, por esto el tratamiento de semilla es la clave para impedir la introducción de éste patógeno en los lotes de cultivo.Centro de Investigaciones de Fitopatologí

Formation of Lewia infectoria, the teleomorph of Alternaria infectoria, on wheat in Argentina

The trapping of pseudothecia carrying asci with mature ascospores of Lewia infectoria (teleomorph of Alternaria infectoria) from wheat stubble under natural field conditions in Buenos Aires Province, Argentina, is reported for the first time. The production of mature pseudothecia in culture is also reported. Monosporic isolates of A. infectoria, obtained from infected wheat plants in Argentina, produced conidia within a week and ascomata with fully mature ascospores within 7 months when stored on slants of PCA at 4°Cin darkness. The anamorph exhibited the sporulation pattern of Alternaria infectoria species-group, and was identified by its axenic colony morphology and the prominence of its secondary conidiophore structure. Critical examination of the teleomorph revealed it to be Lewia infectoria. The presence of the teleomorph has implications in the long-distance dispersal of A. infectoria and on resistance breeding programs. This is the first confirmed report of the sexual stage of A. infectoria in Argentina.Centro de Investigaciones en Fitopatologí

Alternaria infectoria species-group associated with black point of wheat in Argentina

Regional surveys are being conducted in Argentina to assess the presence of wheat (Triticum aestivum) pathogens on grains across the main cropping area. During 2001 and 2002, grain samples with a dark brown or blackish discoloration around the embryo end, known as black point, were observed on several cultivars across the wheat region of Buenos Aires Province.Centro de Investigaciones de Fitopatologí

Wheat fusarium head blight 2001 epidemic in the southern Argentinian pampas

Wheat Head Blight or Scab is frequently a destructive fungal disease caused by several Fusarium species but F. graminearum Schwabe [teleomorph Gibberella zeae (Schwein) Petch; synonym = G. saubinetii (Mont.) Sacc.] is the principal causal agent. The disease is common in humid and semi-humid wheat (Triticum spp.) cropping areas around the world. Epidemics of Fusarium head blight (FHB) seem to be increasing globally during the last two decades. In Argentina and some other countries of South America, damages have been very significant. In the USA, Canada and other wheat cropping areas, several harvests have been affected by numerous epidemics.Facultad de Ciencias Agrarias y Forestale

Alternaria infectoria species-group associated with black point of wheat in Argentina

Regional surveys are being conducted in Argentina to assess the presence of wheat (Triticum aestivum) pathogens on grains across the main cropping area. During 2001 and 2002, grain samples with a dark brown or blackish discoloration around the embryo end, known as black point, were observed on several cultivars across the wheat region of Buenos Aires Province.Centro de Investigaciones de Fitopatologí

Fusarium graminearum and deoxynivalenol contamination in the durum wheat area of Argentina

Fusarium graminearum head blight of wheat is a destructive disease of the world's wheat-growing areas. This work was performed to analyze the distribution and contamination of deoxynivalenol (DON) and its relationship with F. graminearum kernel invasion in Argentina durum wheat area during two consecutive harvests. A total of 147 samples (cultivars and lines) of durum wheat from 5 locations of the major cropping area (Southern Buenos Aires Province) were analyzed. Percentage of F. graminearum kernel infection was evaluated following the blotter test (ISTA method) and fusarotoxins were analyzed by thin layer chromatography. None of the varieties and lines were free of F. graminearum infection. In the first harvest fungal invasion was very low. From 40 samples, 55% showed DON contamination but only 4 samples (10%) were higher than 2 ppm. In the second harvest, a crop year conducive to scab development, the highest level of F. graminearum kernel invasion observed was 42% on a sample from the humid area (eastern Buenos Aires Province) DON was detected in 47 (78.2%) of 60 samples analyzed and 19 (31.6%) showed levels of DON higher than those established in the guidelines in Canada and USA for food and feedstuff. In both years all locations situated in the humid area showed levels ranging from 0 to < 8 ppm. Within the durum wheat area differences among locations were found. This analysis indicates the need for more information on the problem and distribution of Fusarium mycotoxins in durum wheat grown in Argentina.Centro de Investigaciones de Fitopatologí

Mycobiota evolution during storage of paddy, brown and milled rice in different genotypes

The rice grain is frequently infected by a series of pathogens (fungi) during its storage, producing damages to the economy and health of humans. The aim of this study was to identify the fungal genera present in different rice genotypes and to quantify their variation during storage. Paddy, brown and milled rice fractions of Nutriar, (N) H329-5(H329) and Don Ignacio genotypes were analyzed at 4, 8 and 12 months of storage. Fungi were identified based on their micromorphological characteristics and colonies. The observed genera according to their frequency were: Alternaria, Nigrospora, Epicoccum, Bipolaris, Curvularia, Cladosporium and Fusarium (field fungi) and Penicillium and Aspergillus (storage fungi). The mycobiota composition was different depending on the grain fraction and the period of storage: field fungi were located in the hulls and bran layers, while storage fungi were mainly in the endosperm. The different genotypes showed different susceptibility to contamination.O grão de arroz é, com frequência, atacado por uma série de patógenos (fungos) durante o armazenamento produzindo danos econômicos e à saúde humana. O objetivo do trabalho foi identificar os gêneros fúngicos presentes em diferentes genótipos de arroz e quantificar sua variação durante o armazenamento. Analisaram-se as frações casca, integral e polido dos genótipos Nutriar (N), H329-5 (H329) e Don Ignácio aos 4, 8 e 12 meses de armazenamento. Os fungos foram identificados por suas características micromorfológicas e suas colônias. Os gêneros observados segundo sua frequência foram: Alternaria, Nigrospora, Epicoccum, Bipolaris, Curvularia, Cladosporium e Fusarium (fungos de campo) e Penicillium e Aspergillus (fungos de armazenamento). A composição da micoflora foi diferente segundo fração de grão e tempo de armazenamento: os fungos de campo localizaram-se na casca e no farelo, enquanto os de armazenamento, no endosperma. Os diferentes genótipos apresentaram diferente suscetibilidade à contaminação

Fusarium graminearum and deoxynivalenol contamination in the durum wheat area of Argentina

Fusarium graminearum head blight of wheat is a destructive disease of the world's wheat-growing areas. This work was performed to analyze the distribution and contamination of deoxynivalenol (DON) and its relationship with F. graminearum kernel invasion in Argentina durum wheat area during two consecutive harvests. A total of 147 samples (cultivars and lines) of durum wheat from 5 locations of the major cropping area (Southern Buenos Aires Province) were analyzed. Percentage of F. graminearum kernel infection was evaluated following the blotter test (ISTA method) and fusarotoxins were analyzed by thin layer chromatography. None of the varieties and lines were free of F. graminearum infection. In the first harvest fungal invasion was very low. From 40 samples, 55% showed DON contamination but only 4 samples (10%) were higher than 2 ppm. In the second harvest, a crop year conducive to scab development, the highest level of F. graminearum kernel invasion observed was 42% on a sample from the humid area (eastern Buenos Aires Province) DON was detected in 47 (78.2%) of 60 samples analyzed and 19 (31.6%) showed levels of DON higher than those established in the guidelines in Canada and USA for food and feedstuff. In both years all locations situated in the humid area showed levels ranging from 0 to < 8 ppm. Within the durum wheat area differences among locations were found. This analysis indicates the need for more information on the problem and distribution of Fusarium mycotoxins in durum wheat grown in Argentina.Centro de Investigaciones de Fitopatologí

Manchado del grano de arroz: efecto de la fertilización nitrogenada

El manchado del grano de arroz o pecky rice causa pigmentación del grano y reducción de la germinación del mismo. Está asociado a una gama de microorganismos. Este trabajo evaluó el comportamiento de cinco cultivares de arroz a esta patología, bajo diferentes condiciones de fertilización nitrogenada. Se aisló e identificó la micoflora asociada. Se realizó un ensayo en campo en Los Hornos (Buenos Aires, Argentina) con los cinco genotipos, bajo tres niveles de nitrógeno, en un diseño de bloques completos al azar con cuatro repeticiones. Se caracterizaron visualmente los síntomas, cuantificándose la incidencia de la enfermedad y el porcentaje de germinación. Con ambos parámetros se realizó un ANOVA utilizando como fuente de variación los tratamientos, los cultivares y los bloques. Se compararon las diferencias encontradas a través del test de Tukey (p&lt;0,05). Para el análisis de sanidad se utilizó el método del blotter test, realizado sobre 200 semillas por parcela. Se observó interacción fertilización x genotipo en la variable porcentaje de incidencia. El porcentaje de germinación disminuyó significativamente en la dosis mayor de nitrógeno. Las distintas especies fúngicas inhibieron en distinta proporción la germinación del grano en extremos que van desde un 100 % para Bipolaris oryzae (B.de Haan) Shoem. hasta un 23,2 % en el caso de Epicoccum sp. La presencia de hongos se incrementó con la dosis de N aplicada.Pecky or grain discoloration of rice reduced germination and caused kernel pigmentation. Several microorganisms are associated. This article evaluates the response of 5 rice genotypes under different nitrogen fertilisation. The mycoflora involved was isolated and identified. A field assay in Los Hornos (Buenos Aires, Argentina) with the 5 cultivars, under three levels of N, in a complete aleatorized design with four blocks was performed. Symptoms were characterized visually and disease incidence and germination percentage was quantified. An ANOVA test to evaluat both parameters was done using cultivars, treatments and blocks as the source of variation. Differences were compared by Tukey test (p&lt;0,05). For seed health, the blotter test was carried out using 200 seeds per plot. Interaction fertilisation x genotype was performed for incidence percentage variable. The grain germination percentage decreased significatively with the higher doses of nitrogen. It was inhibited in variable proportion by different fungi with a range between 23,2 % in the case of Epicoccum sp. to 100 % for Bipolaris oryzae (B. de Haan) Shoem. Fungal presence was higher with the N dosis applied