Wild populations as a source of germplasm for black poplar (Populus nigra L.) breeding programmes

Abstract

The aims were to explore the use of wild populations of Populus nigra for breeding and to compare crosses made between genotypes from different areas with different climates. Genetic distances ranged from 0.175 (populations growing under optimal conditions) up to 0.875 (populations growing under marginal conditions). A total of 39 trees were chosen from these populations, and in four different years 58 different parental crosses were made, from which a total of 2,277 individuals were produced for assessment as potential biomass producers. The progenies from each cross were rated according to a selection index (SI) based on three characteristics (height, leading shoot diameter and resistance to the rust Melampsora larici-populina). Sixteen of such crosses had significantly higher SI compared to the lowest SI values observed. In 19 of the crosses, it was shown that certain individual trees had made a significant contribution to lower susceptibility to rust, and in particular, two male trees used in the parental crosses were implicated as being the source of rust resistance. Selected individuals were cloned and used in a field trial with NE-42, as a control. It was found that six clones had significantly higher SI than NE-42. In crosses between trees originating from contrasting conditions, there was a higher average SI than in crosses between trees from the same conditions. However, these differences were not statistically significant. The successful clones are recommended for use in those areas where the native populations of pure black poplar are threatened by cross-pollination with allochthonous species.