VIEW ARTICLE

Disease Control and Pest Management

The Use of Pythium oligandrum for Biological Control of Preemergence Damping-Off Caused by P. ultimum. F. N. Martin, Former graduate research assistant, Department of Plant Pathology, University of California, Berkeley 94720, Present address: Plant Pathology Department, University of Florida, Gainesville 32611; J. G. Hancock, Professor, Department of Plant Pathology, University of California, Berkeley 94720. Phytopathology 77:1013-1020. Accepted for publication 6 January 1987. Copyright 1987 The American Phytopathological Society. DOI: 10.1094/Phyto-77-1013.

Coating sugar beet seeds with oospores of Pythium oligandrum controlled preemergence damping-off caused by P. ultimum as effectively as treating seeds with fenaminosulf. Twenty-four hours after seeds were planted in field soil naturally infested with 13 propagules of P. ultimum per gram of soil, the pathogen had colonized the seed coats of 77% of the untreated seeds but only 10% of the seeds treated with P. oligandrum. Endosperm and radicle colonization by P. ultimum was also lower for treated seeds (3 and 7%, respectively) than for untreated seeds (63 and 71%, respectively). P. oligandrum actively colonized the endosperms and emerging radicles when seeds were treated with oospores (69 and 23% of radicle length, respectively). P. oligandrum was isolated from seedling roots predominantly at the junction between the primary root and the hypocotyl and rarely from secondary roots. Scanning electron microscopy confirmed the sites of colonization. Oospore seed treatment did not control postemergence damping-off as well as fenaminosulf seed treatment but did allow greater stands than untreated seeds. Seed treatment did not affect seedling growth or influence the frequency of root infection by P. ultimum. When seeds were planted in fumigated soil, however, the root length densities of seedlings from treated seeds were lower than those from untreated seeds. No tissue necrosis or reduction in shoot growth was observed. Amending soils with low propagule densities of P. oligandrum also reduced the incidence of preemergence damping-off caused by P. ultimum. When coated on the seed surface, P. oligandrum was nonpathogenic on 12 species of economic crop plants representing six families.