Impact of Plant-Associated Bacteria on the In Vitro Growth and Pathogenic Resistance against of Different Aspen () Genotypes.

Aspens ( and its hybrids), economically and ecologically important fast-growing trees, are often damaged by , a rot-causing fungus. Plant-associated bacteria can be used to increase plant growth and resistance; however, no systematic studies relating the activity of symbiotic bacteria to aspen resistance against have been conducted so far. The present pioneer study investigated the responses of two and two × genotypes to in vitro inoculations with, first, either sp. or sp. bacteria (isolated originally from hybrid aspen tissue cultures and being most closely related to and , respectively) and, in the subsequent stage, with . Both morphological parameters of in vitro-grown plants and biochemical content of their leaves, including photosynthesis pigments and secondary metabolites, were analyzed. It was found that both × genotypes, whose development in vitro was significantly damaged by , were characterized by certain responses to the studied bacteria: decreased shoot development by both sp. and sp. and increased phenol content by sp. In turn, these responses were lacking in both genotypes that showed in vitro resistance to the fungus. Moreover, these genotypes showed positive long-term growth responses to bacterial inoculation, even synergistic with the subsequent fungal inoculation. Hence, the studied bacteria were demonstrated as a potential tool for the improved in vitro propagation of fungus-resistant aspen genotypes.