Effects of Frankia on field performance of Alnus clones and seedlings

Field performance of tissue cultured clones and seedlings of Alnus viridis ssp. crispa, A. glutinosa, A. incana, and A. japonica was assessed five years after outplanting in central Ontario. Half the individuals were inoculated with a mixture of four Frankia isolates prior to planting. Inoculation produced significant increases (25% to 33%) in biomass production of two clones of A. glutinosa and one of A. incana. Woody biomass increments for the first five years, averaged across all clones and seedlings, were highest in A. japonica and A. incana (4.3 and 3.7 Mg ha^–1 yr^–1, respectively). Individual tree growth improved markedly in lower slope positions, but total plot biomass did not show similar gains in downslope positions owing to higher mortality and aphid (Paraprociphilus tessellatus) infestation. Aphids occurred in 22% of Frankia-inoculated individuals, and 15% of non-inoculated individuals. The fastest growing species, A. incana and A. japonica, were most susceptible to aphid attack. Growth of the best clones of A. glutinosa and A. incana exceeded seedling growth by 51% and 76%, respectively. The high growth variation in clones of the same species with similar geographic origins and the excellent performance of tissue cultured stock suggest that rapid genetic gains in an Alnus breeding program might be obtained by clonal propagation.