THE BLACKLEG FUNGUS OF RAPESEED: HOW MANY SPECIES?

The blackleg fungus (Leptosphaeria maculans, asexual stage Phoma lingam) causes widespread destruction among cruciferous crops and can be particularly devastating for rapeseed (Brassica napus L. and B. rapa L.). Crop losses caused by P. lingam, in Canada alone, exceed thirty million dollars annually.
Three strains of the pathogen have been characterized on the basis of virulence, host range, and cultural tests: a highly virulent strain, a weakly virulent strain, and a strain causing disease only on stinkweed (Thlaspi arvense L.). Varieties of spring rapeseed and canola (B. napus L. and B. rapa L.) commercially available for oilseed production in Canada are susceptible to both highly and weakly virulent strains of blackleg.

Virulent isolates of the blackleg fungus are readily recognized by their biosynthesis of epipolythiodioxopiperazines and a depsipeptide.
No characteristic metabolites appear to have been isolated from weakly virulent isolates until recently.
Because the chemical characterization of weakly virulent isolates might lead to the isolation of useful markers, it was of interest to examine the chemistry of those isolates.

We have recently reported the chemical structures of several metabolites produced by weakly virulent isolates of the blackleg fungus.
Further studies on the secondary metabolite profile of these isolates have shown an intriguing relationship between P. lingam and another Phoma spp, also a pathogen of crucifers.
This relationship was further supported by molecular genetic characteristics and pathogenicity tests.
The results of these studies will be presented and their implication on grouping the weakly virulent isolates of P. lingam will be discussed.

ISHS Brassica Symposium – IX Crucifer Genetics Workshop

M.S.C. Pedras, J.L. Taylor, V.M. Morales

Leptosphaeria maculans, Phoma lingam, blackleg disease, phytotoxins, polyketides

https://doi.org/10.17660/ActaHortic.1996.407.56