Abstract

Seeds from five populations of Rhododendron vaseyi A. Gray (pinkshell azalea), representing the entire distribution of the species, were germinated at 25C (77F) or an 8/16-hr thermoperiod of 30/20C (86/68F) with daily photoperiods at each temperature of 0 (total darkness), 8, 12, or 24-hr (continuous light). Germination was recorded every 3 days for 30 days. Responses to light and temperature of all populations were similar. Light was required for germination regardless of temperature. As photoperiod increased, germination increased for all populations with the alternating temperature partially compensating for the light requirement. The highest cumulative germination for all populations ranged from 51 to 67% and was achieved at 30/20C with a 24-hr photoperiod. These germination percentages, although at a moderate level, were due in part to rigorous cleaning and grading of seeds collected across a broad range of plants and growing conditions prior to initiation of the study, suggesting seed viability of R. vaseyi is inherently low.