Variation in production of phomodiol and phomopsolide B by Phomopsis spp

Naming Phomopsis spp. based on the identity of their host plant has been a common practice. Taking this into account, we compared production of two secondary metabolites by Phomopsis isolates among isolates from a single plant genus and isolates from various plant genera. Phomopsis spp. growing endophytically in willow twigs were isolated from seventeen of the seventy-three trees of Salix species sampled at seven sites in England and New Jersey, USA. No correlations appeared to exist between presence of the fungus and host plant species or geographical location. Fifty-two of these Phomopsis isolates from willows, as well as eight from other nonwillow plants, were fermented in both malt and millet media to assay for the production of the Phomopsis secondary metabolites phomopsolide B and phomodiol. Phomopsolide B was almost universally produced by the isolates from willows, while it was produced by only one of the nonwillow isolates. Phomodiol production varied among all isolates. Isolates obtained from the same tree also varied in production of these metabolites. A high degree of flask-to-flask variability in production of these metabolites by a single isolate was found, which suggested that the presence or absence of a metabolite was more meaningful than the absolute amount produced.