April 2012 issue of the Cornell Flower Bulb Research Program Research Newsletter:
Over five years, we exposed bulbs of 91 tulip cultivars to 10 ppm ethylene in flowing air streams at 20C in October-November and forced. About 35% of the cultivars were substantially resistant to ethylene. About 51% of the cultivars were consistently damaged by ethylene. The remaining 15% of cultivars showed an inconsistent response to ethylene. It is unknown whether similar results would be seen with ethylene exposure earlier in the season (e.g., July-September). These results should be interesting for dry sales firms, export companies, tulip breeders, growers and forcers.