Positive correlations between in vitro growth rate and pathogenesis in Ophiostoma ulmi

In vitro radial growth rate was found to be positively correlated with pathogenicity in two experiments involving NAN aggressive isolates of O. ulmi. One of the correlations was detected in a sample of B mating‐type, but not in equivalent A mating‐type isolates. Another was detected in a sample of pathogenic phase, but not in comparable saprophytic phase isolates. The significance of these results for the vascular wilt syndrome and population biology of O. ulmi is discussed.