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Glyceollin Production Associated with Control of Phytophthora Rot of Soybeans by the Systemic Fungicide, Metalaxyl. E. W. B. Ward, Research Institute, Agriculture Canada, University Sub Post Office, London, Ontario, Canada N6A 5B7; G. Lazarovits(2), P. Stössel(3), S. D. Barrie(4), and C. H. Unwin(5). (2)(3)(4)(5)Research Institute, Agriculture Canada, University Sub Post Office, London, Ontario, Canada N6A 5B7. Phytopathology 70:738-740. Accepted for publication 24 January 1980. Copyright 1980 The American Phytopathological Society. DOI: 10.1094/Phyto-70-738.

Hypocotyls of soybean seedlings (cultivar Altona) inoculated with the compatible race 6 of Phytophthora megasperma var. sojae (Pms) developed typical spreading watersoaked lesions. When the roots of seedlings were supplied with the systemic fungicide N-(2,6-dimethylphenyl)-N-(methoxy-acetyl) alanine methyl ester (metalaxyl), the lesion development was reduced. At metalaxyl concentrations of 20 μg/ml lesions became restricted, brown, necrotic, and indistinguishable from lesions in untreated hypocotyls inoculated with the incompatible race 4 of Pms. Glyceollin production in the first 12 hr following inoculation of hypocotyls of metalaxyl-treated seedlings with Pms race 6 was similar to that in the race 4 incompatible interaction. This rate was not maintained over longer incubation periods, and maximum glyceollin levels, which were reached after 24–36 hr, usually were about two thirds as great as those present in the incompatible interaction. Metalaxyl was taken up rapidly by roots and transported to the infection site. In metalaxyl-treated seedlings, race 6 gave rise to an incompatible response even when treatment was delayed until 3 hr after inoculation.