Clone identification and structure in Populus tremula L.
Leena Suvanto, Department of Ecology and Systematics, University of Helsinki, P.O.B. 65, FIN-00014 University of Helsinki
P. tremula is a diecious tree species which can reproduce both sexually and asexually the latter being more common. Due to this, aspen has a clonal growth structure i.e. separate trees (ramets) can be members of the same genetical individual (genet or clone, Fig.1). Though aspen is a common species, not much is known about its population biology. Aspen is an important species for biodiversity, since many species are entirely dependent on it. In this study I wanted to find a tool to identify clones and to study the clonal structure of aspen.
Material and methods
Sample trees (Table 1.) were morphotyped according to their stem form, branching habit, bark colour and especially their spring foliage colour. For clone identification I sampled 1-4 ramets/morphotype and 1-8 morphotypes/ha. For the study of clone structure, I had one hectare study plots, where I sampled all aspens, which DBH was either >15cm (old growth forest) or >5cm (managed forest). DNA based clone identification was done using microsatellites (Table 2.).
The number of clones was bigger than the number of morphotypes. There were altogether 109 clones compared to the 65 morphotypes, 90 clones (49 morphotypes) and 20 clones (21 morphotypes) in Kuhmo old growth, managed and Kotinen old growth forest, respectively. In some cases several morphotypes were actually belonging to one clone. The size of the clones was really small, on average only 2-3 trees formed one clone. There were no differences between forest types or sites in the number of clones/ha or in the size of clones.
The microsatellites were a better tool than morphological methods for clone identification since they were able to identify even morphologically similar clones (Fig.2.). There was no evidence that the forest practises had affected the clone size or number. The small size of the clones may reflect their young age (Barnes 1975).
Barnes, B. (1975) Forest Sci. 21:319-328.
Dayanandan, S. Rajora, O.P. & Bawa K.S. (1998) Theor.Appl.Genet. 96:950-956.
Rahman, M.H., Dayanandan, S. & Rajora, O.P. (2000) Genome 43:293-297.
Fig.1. Single aspen clone surrounded by mixed spruce forest.
Fig.2. A gel showing one microsatellite locus (PTR1) in ten ramets of the same morpho-type. All other ramets are heterozygotes except the two most right ones, which thus clearly belong to a different clone.
Table 1. Sample areas for clone identification and clone
Table 2. The microsatellite loci used in this work.