Fifty-five Phytophthora sojae isolates were collected
from soil samples and diseased soybean plants from Illinois, Indiana, Iowa,
Minnesota in 1994 and 1995. Races for the isolates were determined. DNA
of P. sojae isolates was amplified with 16 Operon
decanucleotide primers. Twenty-three of 75 amplified fragments were polymorphic.
Based on the 23 RAPD markers, a dendrogram
depicting the relatedness of the isolates was constructed using UPGMA.
The P. sojae isolates clustered into four distinct groups. The
isolates of races 3, 4 and 25 clustered into group I. The isolates of races
1, 8 and 13 clustered into group II. The isolates of race 5
clustered into group III, and the isolates of race 7 clustered into group
IV. Genetic diversity was detected among isolates of races 1,
3, 4, 5, 7 and 25 but not among isolates of races 8 and 13.