Production of Phytotoxic Sirodesmins by Aggressive Strains of Leptosphaeria maculans Differing in Interactions with Oil Seed Rape Genotypes

Sirodesmins were extracted from culture filtrates of 3 aggressive strains of Leptosphaeria maculans which showed different specific interactions with the oilseed rape cultivars Quinta and Jet Neuf. Up to 8 compounds were detectable showing reactions on thin layer plates which are characteristic for sirodesmins. Sirodesmin PL, sirodesmin C, deacetylsirodesmin PL and deacetyl‐sirodesmin C were identified on the basis of their UV‐spectra, by various conversion reactions and by cochromatography with known standards. Two further compounds were tentatively identified as sirodesmin B and deacetylsirodesmin B on the basis of conversion reactions only. In the cultures of all strains sirodesmin PL was the main component, followed by deacetylsirodesmin PL, sirodesmin C, and deacetylsirodesmin C. These 4 metabolities were mainly responsible for the phytotoxic activity of all culture filtrates. They were systemically transported to leaves of root treated rape seedlings. No correlation was found between the production of the 4 main sirodesmins and the differential host parasite interactions of the 3 aggressive strains of Leptosphaeria maculans.