Differences in cerato‐ulmin production between the EAN, NAN and non‐aggressive subgroups of Ophiostoma ulmi

Abstract

A test of comparative in vitro cerato‐ulmin wilt toxin production in the aggressive and non‐aggressive subgroups of the Dutch elm disease pathogen Ophiostoma ulmi was carried out by turbidity and ELISA methods. Ten non‐aggressive, ten EAN aggressive and ten NAN aggressive isolates were tested from a range of geographical sources. In liquid shake cultures the non‐aggressive isolates produced the greatest and the NAN aggressives the least mean biomass. Despite considerable variation in cerato‐ulmin production by individual isolates in three separate experiments, both the turbidity and ELISA methods showed a clear separation of the non‐aggressive and aggressive subgroups. Non‐aggressive isolates produced little or no cerato‐ulmin (ELISA range of means 0–56.0 ng/ml) and EAN and NAN aggressive isolates moderate to high levels (EAN 1.6–89.0 × 104 ng/ml and NAN 0.2–300 × 104 ng/ml). In the aggressive isolates no correlation was detected between cerato‐ulmin production and either biomass or pathogenicity to clonal Commelin elm. The role of cerato‐ulmin in the pathogenicity of O. ulmi is discussed.