VIEW ARTICLE

Ecology and Epidemiology

Population Dynamics of Laetisaria arvalis and Low-Temperature Pythium spp. in Untreated and Pasteurized Beet Field Soils. S. B. Martin, Postdoctoral research associate, Department of Plant Pathology, New York State Agricultural Experiment Station, Cornell University, Geneva 14456; H. C. Hoch(2), and G. S. Abawi(3). (2)(3)Associate professors, Department of Plant Pathology, New York State Agricultural Experiment Station, Cornell University, Geneva 14456. Phytopathology 73:1445-1449. Accepted for publication 18 May 1983. Copyright 1983 The American Phytopathological Society. DOI: 10.1094/Phyto-73-1445.

Addition of Laetisaria arvalis was highly effective in suppressing reproduction of Pythium ultimum in pasteurized and untreated field soils planted to table beets (Beta vulgaris). The number of germinable propagules of P. ultimum reached a maximum of approximately 300 and 6,500 per gram in pasteurized soils amended and nonamended, respectively, with L. arvalis. Addition of L. arvalis to field soil similarly reduced buildup of germinable propagules of low-temperature Pythium spp. In one test, in field soil infested with 455 germinable propagules of low-temperature Pythium spp. per gram of soil, a maximum of approximately 500 and 2,000 propagules per gram in L. arvalis-amended and nonamended soils, respectively, occurred after 3-wk of incubation. The number of sclerotia of L. arvalis was lower in field soil infested with Pythium spp. than in pasteurized soil, but was still relatively high (30 sclerotia per gram of soil) after 16 wk. Significantly greater emergence, lower postemergence damping-off, and subsequently greater survival of table beet seedlings was obtained in soils amended with L. arvalis in comparison to similar treatments lacking L. arvalis. Soils that were planted repeatedly to table beets developed suppressiveness that was characterized by reduced numbers of P. ultimum propagules, increased numbers of L. arvalis sclerotia, and lower seedling disease incidence.