Characterization of Pythium spp. from soil samples in Illinois

Pythium root rot is widely distributed in major soybean (Glycine max) production areas throughout the world. There are many species of Pythium described on soybean and other crops, although not all species are pathogenic on these crops. The objectives of this study were to isolate and identify Pythium isolates obtained from field soils across Illinois and evaluate their pathogenicity on soybean seedlings. Soil samples were collected from 12 corn-soybean rotation fields in six Illinois counties. All isolates of Pythium were recovered through a baiting technique, identified to the species taxon using morphological and molecular techniques, and evaluated using an in vitro pathogenicity assay on soybean seedlings. Twenty-seven species of Pythium were identified, and P. cryptoirregulare, P. irregulare, P. sylvaticum, P. ultimum var. sporangiiferum and P. ultimum var. ultimum were highly pathogenic on soybean seedlings.