To determine optimum germination temperatures and effective dormancy-breaking procedures, field-grown (1983-85) seeds of `Bandera' Rocky Mountain penstemon (Penstemon strictus Benth), `Cedar' Palmer penstemon (Penstemon palmeri Gray), and firecracker penstemon (Penstemon eatonii Gray) were subjected to various cold stratification and incubation temperature treatments. Increased germination following an 8-week stratification occurred in seed lots containing dormant seeds, but a 2-week stratification generally failed to break dormancy. Older (1983) seeds of `Bandera' and `Cedar' penstemon germinated to full viability without stratification. All species showed a marked decrease in germination percentage above 20C; 15C consistently produced maximum germination after 4 weeks. At 15C, mean times to 90% of total germination were 11, 22, and 29 days for `Bandera', `Cedar', and firecracker penstemon, respectively. Transfer of seeds failing to germinate at warm temperatures (25 and 30C) to 15C and applying 720 μm gibberellic acid (GA3) solution was effective in breaking primary dormancy of firecracker penstemon and secondary dormancy of `Bandera' penstemon. Our findings suggest that incubation below 20C, combined with 8 weeks of stratification or the use of after-ripened seed, may improve seed propagation efforts for these species.
Phil S. Allen and Susan E. Meyer
Nathan C. Phillips, Daniel T. Drost, Bill Varga, Leila Shultz and Susan E. Meyer
Seed germination timing strategies and seedling growth characteristics in wild populations have evolved in response to their life history, ecology, and habitat. In this study, we examined the ecophysiological aspects of seed germination and growth in three Allium species native to the Intermountain West (A. acuminatum, A. brandegei, and A. passeyi). Three populations of each species were studied along an elevation gradient resulting in low, mid, and high elevation sites for each species. We investigated seed dormancy patterns within and among species and their relation to habitat. Seeds collected at the study sites were subjected to cold (3 °C) moist stratification in low light to simulate the natural winter environment under snow. Stratification periods ranged from 0 to 24 weeks. After stratification, seeds were placed in lighted growth chambers at 8 °C to simulate the natural spring environment. Germination was observed for 4 weeks. Germinated seeds were then grown at either 12 °C or 16 °C until leaf senescence. Destructive sampling occurred at 2, 4, and 8 weeks. Bulb mass and water content were also assessed after leaf senescence. In the germination experiment, all species responded favorably to cold moist stratification, suggesting physiological seed dormancy. Germination percentages among species varied greatly with 98% germination in A. acuminatum, but only 33% in A. brandegei. Seedling survival and growth varied among species and in response to growing temperature. Observed patterns in seed germination and growth are typical of survival strategies in other spring ephemerals. Seed dormancy traits and seedling growth characteristics in these species have evolved to allow optimal success for their specific habitat.