Thank you very much, tuckerg, I am glad to see that someone does not seem to think as another person in this forum told me : "that I trying to inform you that you are making groundless assumptions".
I was also happy to find this morning that two other plant pathologists from Minnessota (on the web) give the same type of information as mine :
http://www.na.fs.fed.us/spfo/pubs/h...non/non_all.htm
Best regards