Introgression was studied in the offspring of P. nigra and P. × Canadensis female trees using 3 enzymatic
patterns (6-PGD, LAP, and GPI). Our investigations were aimed at the offspring from open pollination and controlled pollination by the pollen mixture from 3 clones of P. nigra and 3 clones of P. × Canadensis. The rate of introgression in P. nigra offspring from open pollination was 0.67%. Introgression in 3 offsprings of P. nigra from controlled pollination was 7.14%. In P. × Canadensis the heterozygous: homozygous phenotype ratio in 2 offsprings from open pollination was 1:1; it documents prevailing fertilization by P. nigra pollen. After fertilization by the pollen mixture, this segregation ratio was 1:1 (6-PGD; GPI) or 3:1 (LAP). The offspring of P. × Canadensis maternal components are assumed to have a major share in introgression.
