Powdery mildew was introduced into a Station greenhouse in 1968, apparently with seed of Glycine falcata (PI 246.591). This accession was very susceptible; there was abundant conidia production. The mildew spread to G.max and, before control measures could be instituted, varietal differences in resistance and susceptibility were observed.
Buzzell, R. I. and Haas, J. H.
"Research Notes: Agriculture Canada,"
Soybean Genetics Newsletter: Vol. 2
, Article 5.
Available at: http://lib.dr.iastate.edu/soybeangenetics/vol2/iss1/5