Detection of Pythium ultimum Using Polymerase Chain Reaction with Species-Specific Primers

This study was conducted to sequence the rDNA internal transcribed spacer (ITS) region of Pythium ultimum and Pythium group HS, design species-specific primers for polymerase chain reaction (PCR), and detect P. ultimum from diseased seedlings using PCR. The sequence of the ITS region of P. ultimum was identical with that of Pythium group HS. The results support the reports that the HS group is an asexual strain of P. ultimum. Using PCR, the primer pair K1+K3, designed on portions of the sequence of the ITS region, amplified isolates of P. ultimum and the HS group but not isolates of 20 other Pythium species. DNA extracts from damped-off seedlings were not amplified, but a 10-fold dilution of the extracts with Tris-EDTA (TE) buffer diluted the inhibitors and allowed PCR amplification. The primer pair used detected P. ultimum from a single diseased seedling.