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Evaluation of Several Actinomycetes and the Fungus Hyphochytrium catenoides as Biocontrol Agents for Phytophthora Root Rot of Soybean. A. B. Filonow, Former Research Associate, Department of Botany and Plant Pathology, Michigan State University, East Lansing 48824-1312. J. L. Lockwood, Professor, Department of Botany and Plant Pathology, Michigan State University, East Lansing 48824-1312. Plant Dis. 69:1033-1036. Accepted for publication 10 April 1985. Copyright 1985 The American Phytopathological Society. DOI: 10.1094/PD-69-1033.

Soybean seed (cultivar Corsoy) were coated with Actinoplanes missouriensis, A. utahensis, Amorphosporangium auranticolor, Micromonospora sp., and Hyphochytrium catenoides in 1% carboxymethyl cellulose + 1% soluble starch (w/v). Treated seed were planted in a loam soil naturally infested with Phytophthora megasperma f. sp. glycinea (P. m. glycinea) in a greenhouse. In some experiments, the soil was supplemented with 400 oospores per gram. After 1 mo, stands of plants from seed coated with A. missouriensis, A. utahensis, or Micromonospora sp. were significantly (P = 0.05) greater than those from uncoated seed in three of four experiments. Surviving plants from seed coated with these microorganisms in many cases also had increased root and shoot weights and reduced root rot severity. Amorphosporangium auranticolor was effective in one experiment, but H. catenoides provided no protection against Phytophthora root rot. Aqueous suspensions of the five microorganisms were also applied to soil and incubated for 1 and 3 wk. Two-day-old soybean (cultivar Corsoy) seedling baits for P. m. glycinea were incubated in 10-fold dilutions of treated and untreated soil. Seedling decay at the greater soil dilutions was significantly (P = 0.05) reduced by A. missouriensis and A. utahensis in one experiment and by all five hyperparasites in a second experiment compared with that in untreated soil, suggesting that the hyperparasites had reduced P. m. glycinea inoculum in soil.