Differential isolatoion of Pythium species from soil by means of selective media,temperature, and pH.

Pythium aphanidermatum, with an optimum temperature for growth at 35C, grew welland was readily isolated from soil on pimaricin-vancomycin medium (MPVM) when incubated for 24h at 38-40C. The pH of the medium affected recovery; maximum numbers developed above pH 6.0. Other Pythium spp. were recovered on MPVM at 20-25C, but were excluded by incubation at 38-40C. These Pythium spp. included P. ultimun, P. paroecandrum, P. irregular, P. mamillatum, and an unidentified Pythium sp. These species grew well and were readily siolated from soil on gallic acid medium (GAM) when incubated for 24-8h at 20 C.P. aphanidermatum and P. myriotylum grew from mycelium on GAM, but their oospores did not germinate nor could they be isolated from soilon this medium. P. myriotylum grew well on MPVM, but was only rarely isolated, evenfrom soils with known high potential for disease caused by P. myriotylum. Propagules of Pythium were enumerated by a plate-dilution frequency method or by a smearplateethod is valuable for studies on the ecology, survival, and inoculum potential in soils with mixed populations of P. aphanidermatum and other Pythium spp.