Rapid Assay for Systemic Fungicides Against Phytophthora Rot of Soybeans. G. Lazarovits, Research Institute, Agriculture Canada, University Sub Post Office, London, Ontario, Canada N6A 5B7. C. H. Unwin, and E. W. B. Ward, Research Institute, Agriculture Canada, University Sub Post Office, London, Ontario, Canada N6A 5B7. Plant Dis. 64:163-165. Accepted for publication 19 September 1979. Copyright 1980 American Phytopathological Society. DOI: 10.1094/PD-64-163.

A procedure for screening systemic fungicides for activity against Phytophthora megasperma var. sojae on soybean (Glycine max) is described. Roots of etiolated seedlings were soaked for 24 hr in solutions or suspensions of test compounds. Seedlings were then placed horizontally in trays and inoculated by placing droplets of a zoospore suspension from a compatible race of the fungus on the upper part of the hypocotyl. The trays were closed to maintain humidity, and disease development was recorded after 24 hr. Control ranged from complete (restriction of the fungus to the area beneath the droplet with light flecking of surface cells), through partial (varying degrees of browning and spreading), to nil (tissue was water-soaked and spread of the fungus unrestricted as in untreated hypocotyls). Ridomil (CGA 48988) and Chevron RE 26745 were the most effective of the compounds tested and Aliette the least. The procedure is rapid, simple, requires relatively small amounts of test compound, and gives uniform results.