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  • Author or Editor: Nathan C. Phillips x
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The genus Allium is distributed worldwide and includes about 80 North American species, with at least 13 occurring in Utah. Our study focuses on the population dynamics of three Allium species native to Utah; Allium acuminatum, A. brandegei, and A. passeyi. In conjunction with our studies of life history, growth characteristics, demographics, and habitat, we are interested in determining the levels of genetic variation in these species. This study examines amplified fragment length polymorphism (AFLP) within and among five Allium acuminatum, four A. brandegei, and three A. passeyi populations native to Utah. These species have contrasting abundance and distribution. The study populations were selected along an elevation gradient to represent within-species habitat differences. About 10–20 plants from each of the 12 populations were genotyped using six AFLP primer combinations, which detect DNA variation within and among all three species. These data will be used to compare levels of genetic variation and isolation among populations and species.

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Three wild onion species native to the intermountain west in the United States—Allium acuminatum, A. brandegei, and A. passeyi—show horticultural potential, but little is known about patterns of genetic diversity among localized populations and geographical regions. We examined amplified fragment length polymorphisms (AFLP) within and among five Allium acuminatum, four A. brandegei, and three A. passeyi collection sites in Utah. These three congeners with contrasting abundance and distribution patterns provide an opportunity to investigate the role of geographic distance, altitude, and rarity in patterns of genetic divergence. The collection sites were selected along an altitudinal gradient to reflect ecogeographic variation. Individual plants from each of the 12 sites were genotyped using six AFLP primer combinations detecting DNA variation within and among all three species. Genetic differences between species were high enough to render comparisons among species impractical, so each species was analyzed separately for differences between populations and variability within populations. Similarity coefficients were significantly greater within collection sites versus among collection sites indicating divergence between populations. Within-population genetic diversity was not correlated with elevation for any of the three species. Analysis of molecular variance revealed that 66% (A. acuminatum), 83% (A. passeyi), and 64% (A. brandegei) of observed variation is found within populations. Genetic divergence among populations (ФST) was higher in the widely distributed species, suggesting that interpopulation gene flow may be negatively correlated with range size. Allium acuminatum and A. brandegei individuals cluster into groups corresponding strictly to collection sites based on neighbor-joining analysis of the total number of DNA polymorphisms between individual plants. Allium passeyi populations, however, had less overall genetic variation between populations. Genetic isolation by distance appeared responsible for much of the variability among populations, although there was one notable exception showing significant differences between two geographically close populations in A. acuminatum.

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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.

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