Genetic structure and introgression in riparian populations of Populus alba L.

Abstract

White poplar (Populus alba) is a widespread species of the northern hemisphere. Introgressed populations or hybrid zones with the related species of the European aspen (Populus tremula) have been suggested as potential venues for the identification of functionally important variation for germplasm conservation, restoration efforts and tree breeding. Data on the genetic diversity and structure of introgressed P. alba are available only for sympatric populations from central Europe. Here, clonality, introgression and spatial genetic patterns were evaluated in three riparian populations of P. alba along the Ticino, Paglia‐Tevere and Cesano river drainages in Italy. Samples of all three populations were typed for five nuclear microsatellite markers and 137 polymorphic amplified fragment length polymorphisms. Microsatellite‐based inbreeding co‐efficients (F _IS) were significantly positive in all three populations. Genetic diversity was consistently highest in Ticino, the population with the highest level of introgression from P. tremula. Population differentiation (F _ST) was low between the Ticino valley in northern Italy and the Cesano valley in central Italy and between the central Italian populations of Cesano and Paglia‐Tevere, consistent with a role of the Appenine mountain range as a barrier to gene flow between adjacent drainage areas. Introgression was not the primary determinant of within‐population spatial genetic structure (SGS) in the studied populations.

Keywords:

• Populus
• hybridisation
• introgression
• microsatellite
• amplified fragment‐length polymorphism

Acknowledgements

We are grateful to Joan Cottrell for providing reference samples of P. tremula and to Berthold Heinze for helpful and stimulating discussions. S. Castiglione’s research was supported by the Italian Ministry of Environment, Land and Sea Protection (Ministero dell’Ambiente e della Tutela del Territorio e del Mare) within the research project “Research and development in biotechnology applied to the protection of the environment”, in collaboration with The People’s Republic of China. C. Lexer’s research on within‐species variation for genomic isolation in European Populus is supported by grant NE/E016731/1 of the Natural Environment Research Council (NERC) in the UK.