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Response ofColletotrichum coccodes to fungicidesin vitro

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Abstract

Black dot is an important disease of potato that affects all plant parts. The causal agent,Colletotrichum coccodes, is commonly found on potato tubers used for seed. Our objective was to determine thein vitro sensitivity ofC. coccodes to the fungicides maneb, thiabendazole, imazalil and CGA 173506, a phenylpyrrole. These fungicides are currently used, or are being tested for use, as potato seed treatments in the United States. All four fungicides reduced radial growth, sclerotial germination and spore germination ofC. coccodes at 10 μg/ml and higher. The fungicide concentrations that inhibited radial growth by 50% were 2 μg/ml, 5 μg/ml, 35 μg/ml, and 40 μg/ml for imazalil, CGA 173506, maneb and thiabendazole, respectively. TBZ was less inhibitory than the other three fungicides and stimulated sclerotial productionin vitro. Isolates ofC. coccodes differed in their sensitivity to maneb, thiabendazole and imazalil in radial growth, but not spore and sclerotial germination, assays. On CGA 173506, radial growth of fourC. coccodes isolates was inhibited, but these isolates produced sectors which grew normally. Germination of most sclerotia from these isolates was inhibited, but some germinated and produced normal colonies in the presence of CGA 173506. OneC. coccodes isolate was resistant to this fungicide in all assays.

Compendio

El “punto negro” de la papa es una enfermedad importante del cultivo que afecta a todas las partes de la planta. El agente causal, Colletotrichum coccodes, se encuentra comunmente sobre los tubérculos utilizados para semilla. Nuestro objetivo fue determinar la sensibilidad in vitro de C. coccodes a los fungicidas maneb, thiabendazole (TBZ), imazalil y CGA 173506, un fenilpirrol. Estos fungicidas son utilizados actualmente, o están siendo probados para su utilización como tratamientos de semilla de papa en los Estados Unidos. Los cuatro redujeron el crecimiento radial, la germinación de los esclerocios y la germinación de las esporas de C. coccodes a 10 υg/cm3 y mayores concentraciones. Las concentraciones de los fungicidas que inhibieron el crecimiento radial en un 50% fueron 2 μ/cm3, 5 μg/cm3, 35 μg/cm3 y 40 μg/cm3 para imazalil, CGA 173506, maneb y thiabendazole, respectivamente. TBZ fue menos inhibitorio que los otros tres fungicidas y estimuló la producción in vitro de esclerocios. Los aislamientos de C. coccodes difieren en su sensibilidad a maneb, thiabendazole e imazalil en el crecimiento radial, pero no en las pruebas de germinación de esporas y esclerocios. Sobre CGA173506, fue inhibido el crecimiento radial de cuatro de los aislamientos de C. coccodes, pero estos aislamientos produjeron sectores que crecieron normalmente. La germinación de la mayoría de los esclerocios de estos aislamientos fue inhibida, pero algunos germinaron y produjeron colonias normales en presencia de CGA 173506. Un aislamiento de C. coccodes fue resistente a este fungicida en todos los ensayos.

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Authors and Affiliations

  1. Department of Plant Pathology, Cornell University, 14853-5908, Ithaca, New York

    Eleonora Uribe (Graduate Student) & Rosemary Loria (Associate Professor)

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  1. Eleonora Uribe
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  2. Rosemary Loria
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Uribe, E., Loria, R. Response ofColletotrichum coccodes to fungicidesin vitro . American Potato Journal 71, 455–465 (1994). https://doi.org/10.1007/BF02849099

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