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Nature and Control of the Aspergillus Black Mold Disease of Onions in New York 2002

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Project Leader: Dr. James W. Lorbeer, Professor

Department of Plant Pathology

Cornell University, Ithaca

Cooperator(s): J. W. Tuffley, Research Technician

Department of Plant Pathology

Cornell University, Ithaca

And Orange County Onion Growers

Type of grant: Biological control and pest biology

Project location: The findings of the study could be applied in all areas of New York as well as nationally and internationally wherever onions are grown.

Abstract: Onion seedlings became infected with Aspergillus niger either when seed harboring the fungus was planted in soil free of the fungus or when seed not harboring A. niger was planted in soil artificially infested with the fungus. A. niger was detected in the roots, basal plates, cotyledons, and leaves of the infected seedlings. Onion plants grown from seedlings infected with A. niger from both seedborne and soilborne sources were detected to harbor the fungus in a symptomless manner in tissues of the plants until they became mature. Either prior to harvest, at harvest, or after harvest the plants and/or resulting bulbs exhibited symptoms of black mold. Physiological changes in the plants as they mature and or environmental conditions such as high temperatures and moisture levels at maturity most likely can regulate the change of A. niger from the endophytic symptomless nature to the production of black mold symptoms. Propagule levels of A. niger in fields (organic soil) cropped to onions differed substantially between fields, perhaps due to different cultural procedures and/or cropping patterns. These differences along with the use of seed either free of A. niger or contaminated with the fungus could lead to divergent levels of black mold in onions grown on the different fields. Studies involving cooling and drying of onion bulbs to prevent expression of black mold symptoms as well as temperature regulation of onion seedling infection by soilborne inoculum of A. niger in miniculture studies are still to be finalized.

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