This is a long shot, but aside from laboratory testing, is there another way to tell if a tulip with stripes is a striped cultivar, or infected with a virus? The bulbs were planted many (~20) years ago. Sorry for the photo quality, it bloomed a couple weeks ago and is past its prime.
If no reply here, one possible course of action is to contact (or visit) the library at the Denver Botanic Gardens. If they maintain a collection of historical plant catalogues, you can browse and compare against what might have been for sale at the time.
