SSR-based analysis of clonality, spatial genetic structure and introgression from the Lombardy poplar into a natural population of Populus nigra L. along the Loire River

Abstract

A scarcity of favourable habitats and introgression from exotic cultivars are two major threats to black poplars (Populus nigra L.) in Europe. Natural vegetative propagation contributes to maintenance of the species in areas where seedling recruitment is limited. Exhaustive sampling of all mature trees in a natural P. nigra stand (413 individuals at recorded positions), genotyping at 11 SSR loci, and a standardized analysis framework resulted in a precise description of clonality in terms of (a) frequency, (b) spatial growth form, and (c) impacts on the overall spatial genetic structure (SGS). The high proportion of replicated genotypes detected resulted in a genotypic richness (R) of 0.47. Up to 18 ramets were found per multilocus lineage (MLL), but 95% of MLLs contained fewer than five ramets (Pareto index β=1.07). No significant difference in vegetative propagation potential was found between genders. Uneven spatial distribution of ramets, with clustering of clonal ramets (aggregation index A c =0.62) and near-zero intermingling between MLLs (clonal dominance index D c = 0.99), resulted in a 'phalanx' clonal growth form, explaining most of the SGS observed over short distances (0-20 m, Sp=0.0324). Although they did not exhibit the typical columnar shape of the Lombardy poplar (P. nigra var. italica), five trees were found to be probable F 1 hybrids of this old and widely distributed cultivar.

Genetic structure of the old black poplar population along the bank of the Vistula River in Poland

“…1), which is in agreement with previous genetic studies of Populus nigra employing a variety of genetic marker systems [13][14][15][16][17][18]. All nSSR loci were highly polymorphic.…”

“…High levels of clonal diversity in black poplar were previously reported by Legionnet et al [20] in six natural stands located in different regions of France. However, others have indicated that asexual regeneration strategies play an important role in the maintenance of P. nigra populations (e.g., [15,17,21,22]). …”

Sex-specific pattern of spatial genetic structure in dioecious and clonal tree species, Populus alba L.

“…Based on dominance index, we inferred that the ramets of both sexes presented a rather clumped occurrence within a genet, a pattern defined as the phalanx strategy of growth, commonly found in many woody species (Peterson and Jones 1997) including species from Populus (Namroud et al 2005;Chenault et al 2011;Cristobal et al 2014). Spatial analysis also detected the non-random distribution of individuals (ramets) of both sexes in space (Table 2).…”

“…(Petzold et al 2013). In Populus nigra L., Sakai and Burris (1985) reported a greater number of ramets in females, while Chenault et al (2011) reported similar genet sizes in males and females. Matsushita and Tomaru (2012) suggested a lack of significant sex-dependent differences in clone sizes measured with the number of ramets in the shrub Lindera trilobata Thunb.…”

“…Dispersal capabilities of clonally derived individuals depending on the clonal growth mode and architecture may interfere with the spatial organization of genetic information in a population affecting local SGS. Some empirical studies suggest that clonality may indeed strengthen SGS (Reusch et al 1999;Setsuko et al 2004;Chenault et al 2011;Peng et al 2015). Recent meta-analysis on SGS pattern in clonal and non-clonal tree species suggested also that clonal species may display significantly higher SGS in their populations (Dering et al 2015).…”