[IUFRO RG 7.02 FORPATH] tiger blight?

We have a foliage disease of trembling aspen (Populus tremuloides) in southwestern Colorado, USA. It is beautiful, strikingly unique, appears to be causing significant impact, and has me completely baffled. The foresters who brought it to my attention are calling it "tiger blight" because of the distinctive striping (see pictures below). It is occurring mostly on suckers and saplings and lower branches of overstory trees. I was told that in one regenerating stand of suckers, it is killing 30-40% of the foliage. There is no fruiting (perhaps very early initials), but there are hyaline hyphae in the lesions. If the striping is caused by alternation between night and day (and I can't think what else would lead to the zonation), the lesions appear to expand rapidly. I put some leaves in a moist chamber to see if anything fruits. In the meantime, has anyone seen this disease before, or even similar symptoms on another species? (See attached file: tiger_4.jpg) (See attached file: tiger_5.jpg) (See attached file: tiger_group_1.jpg) Thanking you in advance, Jim Worrall US Forest Service Rocky Mountain Region Forest Health Management 216 N. Colorado St. Gunnison CO, 81230 (970) 642-1166 desk (970) 209-1332 cell (970) 642-1919 fax