Multilocus genetic structure, characterization, and relationships of Populus × canadensis cultivars

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Abstract
The genotypes of 21 clones of 18 Populus × canadensis Moench cultivars ('Baden 431', 'Blanc du Poitou', 'Canada Blanc', 'DN44', 'Dorskamp 925', 'Eugenei', 'Gelrica', 'Grandis', 'Heidemij', 'I-55/56', 'I-132/56', 'I-262', 'Jacometti', 'Ostia', 'Regenerata', 'Robusta', 'Steckby', and 'Zurich 03/3') were determined for 31 allozyme loci coding for 9 enzyme systems in root tips. Horizontal starch gel electrophoresis was used to assay the enzymes. All clones had allozyme gene and allele contribution from both P. deltoides Marsh, and P. nigra L. The interclonal allozyme variability was controlled by nine loci. 'Canada Blanc' and 'Ostia' shared the same 31-locus genotypes, whereas each of the remaining 19 clones, including 3 clones of 'Robusta' and 2 clones of 'Jacometti', had unique multilocus genotypes. On average, unique genotypes differed from each other at 3.59 loci. Principal-component analysis of the clonal genotypes at 9 variable loci indicated 4 loci (Idh-2, Idh-3, Mdh-4, and Idh-1) to be the most discriminating among the clones. The first two principal components accounted for 48% of the total variance in the nine loci. Clones on the principal component analysis ordination (principal components 1 and 2) were separated into 3 groups; 14 belonged to one group and 5 to a second group. 'Blanc du Poitou' was widely separated from all others. 'Canada Blanc' and 'Steckby' showed the highest genetic interrelationships. Three 'Robusta' clones and two 'Jacometti' clones were in the same group., The interrelationships among the clones based on allozyme genotypes were in general agreement with their speculated origin and (or) morphology.Key words: Populus × canadensis, allozymes, multilocus genotypes, clone–cultivar identification, clone relationships.