Leptosphaeria maculans

Examine under 10X-40X magnification, looking for loose growing silver brownish white mycelium. Infected seeds will have black pycnidia growing that are relatively large (~250um), with papilla, sometimes developed as a neck. The pycnidia will have a pink to purple or amethyst exudate, containing the pycnidiospores. Pycnidiospores are colorless, cylindrical, one celled and occasionally guttulate. Plenodomus biglobosa cannot be visually differentiated from L. maculans. DNA testing is required to differentiate these two fungi, or subsequent testing on Czapeck agar. The perithecia of Stemphylium looks similar and could be confused with pycnidium, but these are larger, more rounded and do not have any exudate.