Disease Note.

First Report of Spongospora subterranea f. sp. subterranea on Potato in Pakistan. I. Ahmad, CDRI, PARC, Islamabad, Pakistan . S. Iftikhar, and M. H. Soomro, CDRI, PARC, Islamabad, Pakistan; and U. Merz, IPS, Pathology Group, FIT, 8092 Zurich, Switzerland. Plant Dis. 80:959. Accepted for publication 19 June 1996. Copyright 1996 The American Phytopathological Society. DOI: 10.1094/PD-80-0959B.

During a survey in 1994 in the Skardu region of northern Pakistan, potato (Solanum tuberosum L.) plants with root galls and tuber lesions characteristic of powdery scab caused by Spongospora subterranea (Wallr.) f. sp. subterranea Tomlinson were found in Astak Valley. The lesions were in the early "cauliflower" stage of development, showing white, wartlike outgrowths of infected host cells. Light microscopic examination of preparations from root galls showed the presence of the characteristic spongy spore balls (40 to 80 µm diameter) with a honeycomb-like wall structure. The infested soil rated highly for the presence of zoosporangia in a bait-plant test system (1) and gave a positive reaction in an enzyme-linked immunosorbent assay (ELISA) with antiserum produced against S. subterranea f. sp. subterranea (2). Preparations from root galls also gave positive reactions in the ELISA. Because these tests, particularly in combination, are uniquely characteristic for the identification of this fungus, no futher pathogenicity tests were made. This is the first substantiated report of S. subterranea f. sp. subterranea in Pakistan.