CHARACTERIZATION OF THE HYPHAL SWELLING GROUP OF PYTHIUM - DNA POLYMORPHISMS AND CULTURAL AND MORPHOLOGICAL-CHARACTERISTICS

The hyphal swelling (HS) group of Pythium species and P. ultimum were studied for cultural and morphological characteristics, restriction fr agment length polymorphisms of the amplified internal transcribed spac er (ITS) region in nuclear rDNA, and random amplified polymorphic DNA (RAPD) analysis of genome DNA. The shape of sporangia was spherical to subspherical or lemoniform and averaged 18.1-23.0 mu m. All isolates could grow at 5 to 35 degrees C, and the rate at the optimal temperatu re, 30 degrees C, was 29-34 mm/24 h. The size of the ITS region amplif ied by polymerase chain reaction and the banding patterns after digest ion with the restriction enzymes showed no variation between the HS gr oup and P. ultimum. No difference in banding patterns was shown betwee n the HS group and P. ultimum by RAPD analysis with each of three prim ers. Isolates examined were from Japan, and results should be confirme d from other regions.