The aim of this study was to evaluate in vitro the mycelial susceptibility of Trichoconiella padwickii to different active ingredients through average median concentration IC50 calculation. Inoculum disks were seeded on bean agar at different concentrations (0.1; 1; 10; 30, 50; 100 and 1000 mg/l) of various fungicides. After seven days the colony diameter was measured. The data obtained were fitted to nonlinear regression models. Susceptibility was classified using the scale proposed by Edgington. The results show that the pathogen is very sensitive to products that act on the respiratory chain (quinone outside inhibitors QoI and succinate dehydrogenase inhibitors SDHI) and cell membrane (multi-site contact activity), and moderately sensitive to those products interfering with cell division (methyl benzimidazole carbamates MBC), synthesis of nucleic acids (phenylamides PA) and osmotic signal transduction (multi-site contact activity). This work is the first record on the sensitivity of T. padwickii.

El objetivo de este trabajo fue evaluar in vitro la sensibilidad micelial de Trichoconiella padwickii a diferentes principios activos por medio del cálculo de la concentración inhibitoria media (CI50). Para ello se realizaron siembras de discos de inóculo en agar poroto con distintas concentraciones (0,1; 1; 10; 30, 50; 100 y 1.000 mg/l) de diversos fungicidas. A los 7 días se midió el diámetro de crecimiento de la colonia (cm). Los datos obtenidos se ajustaron a modelos de regresión no lineal. La sensibilidad se clasificó utilizando la escala de Edgington. Los resultados obtenidos demuestran que el patógeno es muy sensible a los productos que actúan sobre la cadena respiratoria (quinone outside inhibitors QoI y succinate dehydrogenase inhibitors SDHI) y la membrana celular (multisitio), y moderadamente sensible a los que interfieren en la división celular (metil benzimidazol carbamatos MBC), en la síntesis de ácidos nucleicos (fenilamidas PA) y en la transducción de la señal osmótica (actividad multisitio). Este trabajo es el primer antecedente sobre la sensibilidad in vitro de T. padwickii a principios activos fungicidas.

Disease severity evaluation is an important decision support for adoption of strategies and tactics for disease control. The most commonly used method to assess disease severity is visual, but the problem is repeatability, due to subjectivity and imprecision of estimates. For Puccinia sorghi, a threshold of action of 1% severity was determined, so high precision is required in disease quantification. The aim of this study was to compare different assessment methods and analyze their association. Two diagrammatic scales were used to estimate severity, the Peterson and Amorim scales. Pustules were counted with the naked eye and with a 20x magnification hand lens. Software for disease quantification, Assess 2.0, was used to determine actual percentage area and lesion count. No significant differences were found between naked-eyed count and with magnifier. Lesion count with Assess 2.0 gave an imprecise result. Significant differences were found between diagrammatic scales. Compared with Assess 2.0, severity using Peterson was 2% higher, showing widely scattered differences (R²=0.48). Overestimation with visual scales was suggested, especially at low severity levels. Counting pustules was more objective, precise and reproducible. Thus, a calibration curve was constructed (R²=0.79), which will allow calculation of severity from counting pustules.

Four seed health methods (Blotter test, potato glucose agar, bean agar and malt agar) were evaluated for detection of Microdochium oryzae in rice seed, cultivar Fortuna, from Corrientes, Argentina. Data of seed incidence were submitted to analysis at the 5 % significance level. The highest incidence of M. oryzae in seeds were detected on bean agar. Thus, this method should be recommend for detection and studies of transmission and control of M. oryzae in rice seeds.

En ensayos conducidos en laboratorio, fueron evaluados cuatro métodos (Papel de filtro, Agar papa glucosado, Agar poroto y Agar extracto de malta), considerándose su eficiencia y sensibilidad para detectar Microdochium oryzae en semillas de arroz, variedad Fortuna. Los datos obtenidos fueron sometidos al análisis de varianza y las medias comparadas por con el test de Tukey. Entre los métodos probados, las mayores incidencias de M oryzae fueron detectadas en las semillas sembradas en medio conteniendo agar poroto. En ensayos de relevamiento sanitarios, cuantificación de la transmisión y de control, se debería usar preferencialmente este medio.

Detection, symptoms and symptomless transmission of Drechslera avenae (teleomorph Pyrenophora avenae) from seed were investigated. The present study reported that the D. avenae is frequently found in oat (Avena sativa) seed in Argentina. The prevalence of the seed lot infected was 54%. The incidence of seeds infected by D. avenae in the various seed lots from different regions ranged from 0 to 52% (overall mean of 7%). Besides conidia on conidiophore and immature pseudothecia, D. avenae produced small, spherical to pear-shape picnidia containing tiny conidia, on the seed surface. The pathogen was efficiently transmitted at a rate of 55% from seed to coleoptile tips in symptomless seedlings and at 12.5% to plumules. The importance of the infected seed and its epidemiological role are discussed.

El presente trabajo tuvo como objetivos detectar y cuantificar a Drechslera avenae en muestras de semillas y evaluar su transmisión hacia los coleoptiles y plúmulas de la avena (Avena sativa). Un total de trece muestras resultaron infectadas por D. avenae, representando un 54% de prevalencia. Los valores máximos y mínimos de infección obtenidos fueron 0 y 52% con un promedio de 7%. Sobre las semillas, D. avenae produjo además de conidióforos, conidios y pseudotecios inmaduros, picnidios pequeños, esféricos y con forma de pera conteniendo conidios diminutos. El patógeno fue detectado en los coleoptiles, sin síntomas en las plúmulas con una eficiencia de transmisión del 55%. La tasa de transmisión sintomática fue del 12,5%. Se discuten la importancia de la semilla infectada y su papel epidemiológico.

Net blotch is the most important barley (Hordeum vulgare) disease in Argentina. The seed chemical treatment is an important measure to avoid the introduction and dispersion of D. teres. The objectives of the present study were: 1) to evaluate in vitro the fungicide iprodione in different dosages and its mixtures with triticonazole and thiram and to compare them to the most common fungicides used (tebuconazole and flutriafol), and 2) to study under field conditions, the best treatment achieved in vitro. Seed treatment studies indicated that the fungicides used in Argentina such as tebuconazole and flutriafol were less effective against D. teres than iprodione (50 g i.a.), iprodione + triticonazole, and iprodione + thiram. The number of focuses of primary infection, incidence, severity, and agronomic yield in paired plots with iprodione + triticonazole and without fungicide were measured in field. Differences in the valued of these variables were significant among parcels indicating the importance of seed infection in the epidemiology of the disease. It concludes that the mixture of iprodione + triticonazole was effective against D. teres both in vitro and un the field significantly decreasing the incidence of net blotch epidemic.

La mancha en red de la cebada (Hordeum vulgare) es la enfermedad más importante de este cultivo en la Argentina. El tratamiento químico de semillas es una medida importante de control para impedir la introducción y dispersión de Drechslera teres. Los objetivos de este trabajo fueron 1) evaluar la fungitoxicidad específica in vitro de diferentes dosis del fungicida iprodione y sus mezclas con thiram y triticonazole y compararlos con los fungicidas más utilizados (flutriafol y tebuconazole), y 2) valorar a campo, el mejor tratamiento obtenido in vitro. Los resultados mostraron que los fungicidas actualmente en uso en Argentina fueron menos eficientes en el control de D. teres que el iprodione sólo (50 g i.a.) o en mezcla con triticonazole y thiram. En parcelas apareadas con iprodione + triticonazole versus testigo se evaluaron el número de focos de infección primaria, incidencia, severidad y el rendimiento agronómico. Las diferencias entre tratamientos fueron significativas indicando la importancia epidemiológica de la semilla infectada. Se concluye que la mezcla de iprodione + triticonazole fue eficiente en el control de D. teres en semilla, in vitro y a campo, permitiendo disminuir significativamente la epidemia de la mancha en red.