Abstract
Three species of Pythium (P. irregulare, P. spinosum, P. ultimum var. ultimum) were identified as pathogens of root rot of tulip in Japan. The first two species were described on tulip for the first time in the world. From the results of experiments on isolation and pathogenicity, it can be concluded that P. ultimum var. ultimum is the most important pathogen, followed by P. irregulare, and P. spinosum is of minor significance.
