SPORULATION OF HELMINTHOSPORIUM-SOLANI AND INFECTION OF POTATO-TUBERSIN SEED AND COMMERCIAL STORAGES

Silver scurf has become a major reason for rejection of fresh and proc essing potatoes in recent years. Control of the disease by chemical or cultural practices or resistant cultivars has been difficult. Observa tions have shown spread and increase of disease of potatoes in storage , but this has not been extensively studied. The objective of this stu dy was to document Helminthosporium solani conidia production, dispers al, and tuber infection in potato storages. Spore samplers placed in s eed, processing, and table stock storages collected conidia ranging fr om 0 to 12,000 conidia per day in seed and table stock storages (4 deg rees C), and from 0 to 24,000 conidia per day in processing storages ( 10 degrees C). Conidia were detected soon after tubers entered storage and increased progressively during the storage period, with the maxim um conidia numbers found during the time of tuber handling. Greenhouse -produced minitubers placed in storages for 1, 2, 3, or 4 weeks were i nfected by H. solani spores. Infection was significantly higher in tho se exposed for 4 weeks than in those exposed for 1 week. Results docum ent the buildup of H. solani spores throughout the storage period, and that this inoculum is important in disease epidemiology. Control of t his inoculum could lead to disease reduction.