Genetic tests for daylength insensitivity have been run using PI 297,550 reported to be day-neutral by Polson (1972), as source material. Segregating material was grown under long days at various times from 1973 to 1979, either in a growth cabinet (Buzzell et al., 1974) or in a greenhouse with daylength 27 extended to 20 hours with incandescent light. Material was classified at 35 to 42 days after planting as either non-flowering, sensitive (S), or flowering, insensitive (I).