Characterization of sirodesmins isolated from the phytopathogenic fungus Leptosphaeria maculans

Abstract

The pathogenicity of phytopathogenic fungi is associated with phytotoxins, especially with their chemical nature and quantity. Sirodesmins are phytotoxins from the epipolythiodioxopiperazines group, produced by the fungus Leptosphaeria maculans, which are a cause of blackleg and stem canker in oilseed rape (Brassica napus L.). The aim of this work was to obtain a detailed chemical profile of sirodesmins in five fungal isolates (four from Vojvodina, Serbia, and one from the Centre for Agricultural Research, Rothamsted, UK). Sirodesmins showing different phytotoxicity on treated cotyledons of cv. Quinta were separated and detected by thin layer chromatography in all analysed isolates (L.m, C-3, St-5 and S-11) except K-113, which neither contained sirodesmin congeners nor did it exhibit activity. By use of high performance liquid chromatography coupled with tandem mass spectrometer, it was possible to identify total of 10 sirodesmins, together with their precursor-phomamide. It was found that the dominant epipolythiodioxopiperazines of the investigated L. maculans isolates were sirodesmin PL, sirodesmin C, and their de-acetylated derivatives.

Patogenost fitopatogenih gljiva povezana je sa fitotoksinima, a naročito sa njihovom hemijskom prirodom i količinom. Sirodezmini su fitotoksini iz grupe epipolitiodioksopiperazina, koje proizvodi gljiva Leptosphaeria maculans, uzročnik suve truleži korena i raka stabla uljane repice. Cilj ovog rada bila je detaljna hemijska karakterizacija sirodezmina u pet izolata gljiva (četiri iz Vojvodine i jedan iz Velike Britanije, Centar za poljoprivredna istraživanja, Rothamsted). Kod svih ispitivanih izolata (L. maculans, C-3, St-3, S-11), osim K-113 (koji nije sadržao sirodezmine niti pokazivao aktivnost) tankoslojnom hromatografijom su razdvojeni i detektovani sirodezmini koji su pokazali različitu fitotoksičnost na tretiranim kotiledonima sorte Quinta. Primenom tečne hromatografije visoke efikasnosti, kuplovane sa tandemskim masenim spektrometrom, bilo je moguće identifikovati ukupno 10 sirodezmina, kao i njihov prekursor - fomamid. Utvrđeno je da su dominantni epipolitio-dioksopiperazini ispitivanih izolata L. maculans sirodezmin PL, sirodezmin C i njihovi deacetilovani derivati.