The pathogenicity level of two French Mycosphaerella grominicola field isolates (T0414 and T0251) was evaluated on Soissons wheat cultivar using two methods: detached wheat leafs assay in a climatic chamber and wheat seedlings assay in a greenhouse. Both methods revealed that chlorosis and necrosis caused by the T0414 isolate were larger than those caused by the T0251 isolate. Indeed, in the detached leaf assay, the first symptoms on leaves inoculated by T0414 were observed 12 days post inoculation and 50% of the leaves were infected on day 18, with a maximum of 84% of leaves on day 22. On the other hand, the first symptoms were observed on day 18 on leaves inoculated with T0251 with a maximum of only 10% of leaves that were infected on day 22. In addition, both methods showed that necrosis surfaces caused by T0414 were covered by large number of pycnidia, while no pycnidia were observed on the reduced necrosis caused by the T0251 isolate. To understand the pathogenicity variation between these two isolates, their ability to produce cell wall degrading enzymes, xylanases and polygalacturonases was investigated in vitro every 2 days for 20 days. The results showed similar time course for production of polygalacturonases for the two isolates, with non significant higher production for T0414. However, a peak of maximum production of xylanases by T0414 (343 +/- 52 mU mL(-1)) was observed on day 12 post inoculation, while the maximum production (265 +/- 72 mU mL(-1)) by T0251 was observed only on day 20 post inoculation. This result shows a relationship between the beginning of the appearance of symptoms on detached leaves inoculated by T0414 on day 12 and the maximum of xylanases production on the same day in enzymes assays. In conclusion, this study suggests pathogenicity variability between M. graminicola isolates and the role of xylanases in the pathogenicity of this fungus.