Characterization of the Hyphal Swelling Group of Pythium: DNA Polymorphisms and Cultural and Morphological...

The hyphal swelling (HS) group of Pythium species and P. ultimum were studied for cultural and morphological characteristics, restriction fragment length polymorphisms of the amplified internal transcribed spacer (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 μm. All isolates could grow at 5 to 35°C, and the rate at the optimal temperature, 30°C, was 29-34 mm/24 h. The size of the ITS region amplified by polymerase chain reaction and the banding patterns after digestion with the restriction enzymes showed no variation between the HS group and P. ultimum. No difference in banding patterns was shown between the HS group and P. ultimum by RAPD analysis with each of three primers. Isolates examined were from Japan, and results should be confirmed from other regions.