Net blotch caused by Drechslera teres is an important disease in most barley-growing areas. To prevent the introduction of this pathogen into the field, seed treatment is recommended. The objectives of this research were to evaluate different fungicides for eradicating D. teres from the seed and the role of both infected and treated seeds in the epidemiology of the disease under field conditions. The three fungicides tested in vitro (iminoctadine, guazatine, and thiram + iprodione) were able to eliminate D. teres at the highest dose used in this study. Under field conditions, eradication of the pathogen was not achieved, but net blotch was significantly reduced.
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.
Small pieces of diseased tissue were surface sterilized with 0·5% NaOCl, plated on 2% potato dextrose agar (PDA) at pH 6, and incubated at 22 to 24 ° C. Dense, whitish mycelium developed within 72-96 h. Microconidia were abundant, globose to piriform, 0-1 septate, 4 -10 × 4·5-7 μ m, and formed on unbranched and branched monophialides. Cultures produced a fruity aroma similar to amyl acetate. Spores from 14-day-old colonies that developed on PDA were removed with 4 mL of sterile water. The pathogenicity of the fungus was tested by spraying five healthy inflorescences of tomato with a 5-mL suspension (2 × 10 5 conidia mL -1 of sterile distilled water). Another five healthy inflorescences were sprayed with sterile distilled water. The plants were placed in a growth chamber with a 12-h photoperiod at 22 ± 2 ° C and covered with polyethylene bags that were removed after 3 days when plants were moved to a glasshouse. While control flowers were healthy, all inoculated flowers showed symptoms similar to those observed previously.
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