HPLC analyses of cultures of Phoma spp.: differentiation among groups and species through secondary metabolite profiles.

The metabolite profiles of 26 isolates of the blackleg fungus (Leptosphaeria maculans (Desm.) Ces. et de Not., asexual stage Phoma lingam (Tode ex Fr.) Desm.), obtained from diverse parts of the world (part of the International Blackleg Crucifer Network collection), were studied utilizing specific culture conditions, HPLC analysis, and a set of chemical markers. This fungus is the causative agent of blackleg disease of brassica oilseeds; a virulent strain of the pathogen has caused significant rapeseed (Brassica napus L., and B. rapa L.) and canola (B. napus L., and B. rapa L.) losses in Canada, and is also considered a serious agricultural problem worldwide. Effective surveys of blackleg epidemics require simple and reliable analytical methodology to differentiate among the diverse groups of isolates. The chemical analysis of phytotoxins and related secondary metabolites is perhaps one of the most discriminating and the least ambiguous methods for differentiation of Phoma blackleg isolates. Following HPLC analyses, the 26 isolates could be placed in three main groups, irrespective of country of origin: isolates producing phomamide and sirodesmins, isolates producing indolyl dioxopiperazines, and isolates producing polyketides. Discussion of the implications of our findings and suggestions for species reclassification are provided.