Resistance in hybrid aspen to pathogens

Wide-scale plantations of aspen (Populus tremula) and hybrid aspen (P. tremula x Populus tremuloides) have recently been established in Nordic and Baltic countries after the forest industry has become interested in aspen fibre. As the number of aspen stands increases, the fungal diseases will become economically and ecologically important. Neofabraea populi was recorded for the first time in Fennoscandia early in 1960’s and subsequent observations of the disease were made later in 1970’s. In 2000’s, serious damage was observed in second generation of hybrid aspen in Finland. Since conditions in dense cop-pice stands are probably favourable for the spread of N. populi, the fungus could pose a potential threat for short-rotation coppices of hybrid aspen. To study the variation in the resistance of hybrid clones, artificial inoculations were made. The bark of a total of 100 trees (10 clones) was wounded and inocula were placed under the bark. The reactions of the trees and the advance of the cankers were recorded; resistance was considered to be expressed as healing of the cankers. In conclusion, hybrid aspen clones, despite of the fact that the original selection was based on only yield and fibre characteristics, show variability in resistance. A promising observation was made by combin-ing the results from separate trials; the best-growing clone is one of the most resistant ones. Thus it seems likely that there are possibilities to select for both growth and resis-tance traits in breeding