There are two species causing stem canker, namely:

1. Leptosphaeria maculans (Desm.) Ces. et de Not.
2. Leptosphaeria biglobosa (Shoemaker i Brun 2001).

Taxonomic affiliation of those fungi goes as follows:

1. Order: Pleosporales
2. Class: Dothideomycetes
3. Subphylum: Ascomycotina

Those species are different as far as morphological, biochemical and genetic features are concerned as well as in pathogenicity. L. maculans is considered to be more pathogenic, because it may cause a total plant necrosis whereas L. biglobosa usually results in extensive, but superficial spots on the stem.

Leptosphaeria maculans

1. highly pathogenic, symptoms in lower parts of the plant
2. grows slower on artificial media and does not produce pigment
3. produces phytototoxic metabolites from sirodesmin group
4. many races
5. low genetical variety of isolates

Leptosphaeria biglobosa

1. less pathogenic, superficial symptoms in the middle part of the stem
2. grows faster on artificial media and produces yellowish-brown pigment
3. does not produce sirodesmin
4. no races
5. isolates are more diversified genetically