Estimating Genetic Relationships Among Southwestern Quaking Aspen Populus Tremuloides Using Random Amplified Polymorphic Dna Analysis

Poplars are model tree species in ecological and genetic studies since they are widely distributed, easy to propagate, and since more genetic and genomic resources are available for poplars than for any other woody plant genus. The poplar diversity experiment (POPDIV) has been established with European and North American aspen (Populus tremula L., P. tremuloides Michx.) planted in plots representing either a single deme only or combinations of two, four and eight demes in order to test the influence of intraspecific genetic diversity on ecosystem functions and services. In the present study, the most commonly used molecular markers, SSRs (simple sequence repeats) and AFLPs (amplified fragment length polymorphisms), were applied to conduct the genetic analysis of the POPDIV experiment. Both markers identified clonal structures in one Swedish deme and these clones are non-randomly distributed in the POPDIV experimental field. Large differences with regard to the genetic diversity within aspen demes were observed. The genetic diversity estimates based on SSR and AFLP markers showed a high correlation. The North American P. tremuloides deme had the highest level of genetic diversity; most private alleles both at SSRs and AFLPs were also observed in this deme which confirmed that it represents another species different from the European P. tremula. An analysis of molecular variance (AMOVA) revealed that most of the total genetic diversity was found within demes by both SSR and AFLP markers, but the genetic differentiation among demes was also high. Pairwise FST values between demes showed highly significant differentiation at both SSRs and AFLPs. As expected, the P. tremuloides deme was strongly differentiated from the other P. tremula demes. UPGMA dendrograms based on genetic distances obtained from both markers showed that the North American P. tremuloides deme is obviously outgrouped from the other European P. tremula demes with high bootstrap support values. The complex patterns of genetic diversity and differentiation resulted in large differences of the genetic variation within plots. Genetic diversities within plots with a given number of demes were highly variable. Across all plots, those with a single German deme and those with two demes showed the lowest and highest level of genetic diversity, respectively. The plots containing the North American P. tremuloides deme showed higher levels of genetic diversity compared to the plots including only P. tremula demes, which was obviously shown at AFLPs. For the plots with a given number of demes (1, 2, 4, 8), their average genetic diversity values were increased with increasing number of demes included within plots. However, the genetic variation within plots strongly depended on the specific mixture, and the highest diversities were observed for plots with only two demes mixed. Paternity analysis revealed different numbers of paternal trees contributed to both German single tree progenies, the deme with a high number of pollen donors showed high level of genetic diversity. The sibship reconstruction revealed a higher number of full sibling groups for the North American P. tremuloides deme compared to other demes. Across demes, the genetic diversity revealed by AFLP markers showed a positive correlation with the number of full sibling groups, indicating that the number of full sibling groups reflects the effective number of population size which directly determines the level of genetic diversity. In conclusion, the high and variable levels of genetic diversity observed within all demes need to be considered in assessments of the impact of intraspecific diversity of poplars on the diversity of the associated organisms and ecosystem functions and services. The genetic diversity in a plot strongly depends on the specific combination of demes; the number of demes included within a plot is a poor predictor of its diversity.

A rare episode of regeneration of aspen (Populus tremuloides Michx.) by seeds occurred in Yellowstone National Park (YNP), Wyoming, USA, following extensive fires that occurred in 1988. In 1997, we sampled 410 aspen seedlings from 23 local populations distributed widely across YNP to determine how genetic diversity varies with elevation, substrate, plant competition, ungulate browsing, and geographical location. We employed 132 randomly amplified polymorphic DNA (RAPD) markers based on six primers to show genetic relationships within and among the postfire aspen seedling populations. Measures of genetic variation, including estimates of percentage polymorphic loci, expected heterozygosity, and Nei's FST, indicated that most of the variation occurred within rather than among local populations. There was no indication of geographical differentiation among sampled populations based on hierarchal estimates of Nei's FST, neighbour-joining, or correlations between genetic distance and geographical distance. Even genetically distant populations shared nearly 90% of the same markers. Within plots, the amount of genetic variation decreased slightly in response to increased percentage vegetative cover, mean seedling basal diameter, and mean seedling height. Geological substrate, density of lodgepole pine (Pinus contorta var. latifolia Dougl.) seedlings, browsing intensity, and elevation were not significantly related to levels of genetic variation within the seedling plots. These data suggest that genetic variation and geographical structure among seedling populations may occur over time as the transition from seedling-dominated stands to clone-dominated stands occurs.

Poplars and willows form an important component of forestry and agricultural systems, providing a wide range of wood and non-wood products. This book synthesizes research on poplars and willows, providing a practical worldwide overview and guide to their basic characteristics, cultivation and use, issues, problems and trends. Prominence is given to environmental benefits and the importance of poplar and willow cultivation in meeting the needs of people and communities, sustainable livelihoods, land use and development.

For the last eighteen years we have been deeply involved in a cooperative effort with our Latin American colleagues in genetics, biochemistry, physiology, and molecular biology. We have been in close contact with scientists in a number of centers and have helped to organize symposia, workshops, and so forth, in an effort to accelerate their development and make their substantial work known. These symposia in Latin America have been quite successful. The fifteenth will take place in Brasilia in 1977. At the request of colleagues, we are in the process of developing a similar series in Asia. The first very successful symposium was held in Calcutta in 1973. We were most pleased when Dr. Amir Muhammed, Vice Chancellor of the University of Agriculture, Lyallpur suggested that we hold a symposium on a topic of great importance to Pakistan, Genetic Control of Diversity in Plants, under the auspices of the University of Agriculture. It is our hope that this symposium will be followed by additional ones in Pakistan as well as in other countries in the Far East. Leadership is quickly developing in the hands of outstanding scientists in these countries, and we appreciate the opportunity to cooperate with them. We are especially grateful to the Natiohal Science Foundation for makingPL- 480 funds available which made this symposium possible.