Abstract
Silver scurf, caused byHelminthosporium solani, and black dot, caused byColletotrichum atramentarium, are pathogens of tuber periderm whose presence in Colorado was only recently reported. A field survey conducted in September 1977 revealed thatC. atramentarium was more prevalent (21.8% tuber infection) and had a wider distribution thanH. solani (5.4% tuber infection). A greater incidence of both pathogens was observed on thin skinned tubers of chipping cultivars (49.0% infection) than on thicker skinned tubers of table stock cultivars (9.1% infection). Conidial development ofH. solani is tretic, pleurogenous, and requires 17–21 hours per conidium. Conidial septations appear while conidial elongate, and require 3–5 hours per septum. Light microscopy revealed that at least 11 conidia per conidiophore are produced in culture in 54 hours at 20–25 C (68–77 F) and humidity >90%. Scanning electron microscopy showed that fructifications ofH. solani (conidiophores-conidia) arise from beneath infected tuber periderm. Histological studies indicate some peridermal loosening and sloughing. Heavy deposition of unidentified compounds was observed in infected periderm, and hyphae were restricted to periderm cells. Fresh weight loss of tubers naturally infected withC. atramentarium was significantly greater than fresh weight loss of nearly noninfected (< 1% surface area infected) control tubers. Periderm infected with eitherH. solani orC. atramentarium appeared similar, i.e. shriveled, suggesting infections from either pathogen may result in increased fresh weight loss through alteration of the periderm.
Resumen
Helminthosporium solani causante de la costra plateada yColletotrichum atramentarium del punteado negro, son patógenos del peridermo del tubérculo cuya presencia ha sido recientemente reportada en el estado de Colorado-USA. Una inspección de campo realizada en Septiembre de 1977 reveló queC. atramentarium fue más prevalente (21.8% de infection de tubérculo) y de distribución más amplia queH.solani (5.4%). Una mayor incidencia de ambos patógenos se observó en los cultivares de piel delgada usados para hojuelas (chips) (49.0% de infección) que en los de piel gruesa que se usan para consumo de mesa (9.1% de infección). El desarrollo de las conidias deH. solani es terético, pleurógeno y requieren de 17 a 21 h. para su formación. Las septaciones se desarrollan a medida que las conidias se van alargando y requieren de 3 a 5 h. por septa. La microscopía de luz reveló que en medio de cultivo, entre 20 y 25 C (68–77F) y más de 90% de humedad se forman por lo menos ll conidias por conideóforo a las 54 h. La microscopía electrónica de exploración demostró que las fructificaciones deH. solani (conidias y condióforos) emergen de debajo del peridermo de los tubérculos infectados. Estudios histológicos demuestran que el peridermo so afloja y se desgarra. En el peridermo infectado se observó una abundante deposición de compuestos no identificados y las hifas se encontraron restringidas a las células peridérmicas. La pérdida de peso fresco de los tubérculos infectados porC. atramentarium en forma natural fue significativamente mayor que la de los tubérculos control que casi no presentaban infección (< 1% de area de la superficie afectada). Tanto los tubérculos infectados conH. solani como conC. atramentarium mostraron el peridermo similarmente arrugado, lo que sugiere que las infecciones por ambos patógenos pueden dar como resultado un incremento en la pérdida de peso fresco, debido a la alteración del peridermo.
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Former Graduate Teaching Assistant, Dept. of Botany and Plant Pathology, Colorado State University.
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Hunger, R.M., McIntyre, G.A. Occurrence, development, and losses associated with silver scurf and black dot on Colorado potatoes. American Potato Journal 56, 289–306 (1979). https://doi.org/10.1007/BF02855598
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DOI: https://doi.org/10.1007/BF02855598