Sporulation of Helminthosporium solani and Infection of Potato Tubers in Seed and Commercial Storages. D. A. Rodriguez, Research Assistant, Department of Plant Pathology, North Dakota State University, Fargo 58105. G. A. Secor, Professor, N. C. Gudmestad, Professor, and L. J. Francl, Associate Professor, Department of Plant Pathology, North Dakota State University, Fargo 58105. Plant Dis. 80:1063-1070. Accepted for publication 5 June 1996. Copyright 1996 The American Phytopathological Society. DOI: 10.1094/PD-80-1063.

Silver scurf has become a major reason for rejection of fresh and processing potatoes in recent years. Control of the disease by chemical or cultural practices or resistant cultivars has been difficult. Observations have shown spread and increase of disease of potatoes in storage, but this has not been extensively studied. The objective of this study was to document Helminthosporium solani conidia production, dispersal, and tuber infection in potato storages. Spore samplers placed in seed, processing, and table stock storages collected conidia ranging from 0 to 12,000 conidia per day in seed and table stock storages (4°C), and from 0 to 24,000 conidia per day in processing storages (10°C). Conidia were detected soon after tubers entered storage and increased progressively during the storage period, with the maximum conidia numbers found during the time of tuber handling. Greenhouse-produced minitubers placed in storages for 1, 2, 3, or 4 weeks were infected by H. solani spores. Infection was significantly higher in those exposed for 4 weeks than in those exposed for 1 week. Results document the buildup of H. solani spores throughout the storage period, and that this inoculum is important in disease epidemiology. Control of this inoculum could lead to disease reduction.