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Synergistic Effect of Pythium ultimum and the Additive Effect of P. aphanidermatum with Heterodera schachtii on Sugarbeet. E. D. Whitney, Research Plant Pathologist, ARS, USDA, U.S. Agricultural Research Station, Salinas, California 93901; Phytopathology 64:380-383. Accepted for publication 28 September 1973. DOI: 10.1094/Phyto-64-380.

The effect of Pythium ultimum and Heterodera schachtii in combination was synergistic on the preemergence and postemergence damping-off of sugarbeet, but a synergistic effect occurred only rarely on the root rot of sugarbeet. The increased damping-off appeared to be associated with the increased growth of the fungus around the infection centers because the number of centers remained constant whether or not the nematode was present. This observation is consistent with the fact that the period of susceptibility to the fungus was not lengthened by nematode infection. The effect of P. aphanidermatum and the nematode in combination was additive for both damping-off and root rot of sugarbeet.