Cultural characteristics, pathogenicity predictions, and pathogenicity tests for some isolates of Ceratocystis ulmi

Ceratocystis ulmi isolates of known pathogenicity were culturally characterized on a defined synnema production medium (SPM) and American elm wood disks. More aggressive isolates generally produced more synnemata and mycelial pigment on SPM and more synnemata on the wood disks than less aggressive ones. There was no relationship between pathogenicity and radial growth or aerial mycelium production on SPM. Multivariate discriminant analyses on synnema and pigment production and radial growth on SPM and univariate discriminant analyses on synnema production on the wood disks accurately classified the isolates of known pathogenicity into their respective pathogenicity classes. Isolates of unknown pathogenicity also were characterized on SPM and elm wood disks, and pathogenicity predictions made for them using discriminant analyses. Five isolates predicted to be less aggressive were selected for pathogenicity testing, and four were less pathogenic in American elm than a known more aggressive isolate.