Abstract
Aspens (Populus tremula and its hybrids), economically and ecologically important fast-growing trees, are often damaged by Phellinus tremulae, 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 Phellinus tremulae have been conducted so far. The present pioneer study investigated the responses of two Populus tremula and two P. tremula × P. tremuloides genotypes to in vitro inoculations with, first, either Pseudomonas sp. or Paenibacillus sp. bacteria (isolated originally from hybrid aspen tissue cultures and being most closely related to Pseudomonas oryzihabitans and Paenibacillus tundrae, respectively) and, in the subsequent stage, with Phellinus tremulae. 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 Populus tremula × P. tremuloides genotypes, whose development in vitro was significantly damaged by Phellinus tremulae, were characterized by certain responses to the studied bacteria: decreased shoot development by both Paenibacillus sp. and Pseudomonas sp. and increased phenol content by Pseudomonas sp. In turn, these responses were lacking in both Populus tremula 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.
Highlights
Forest trees and their wood quality are threatened by pathogenic fungi [1,2]; one of the most pressing problems in forestry, today, is the selection of tree genotypes for increased growth and better resistance to phytopathogens [3,4]
The present study showed that bacteria from the genera Paenibacillus and Pseudomonas can be applied for the growth promotion of in vitro-propagated Populus plants, but the particular outcome largely depends on a specific genotype and was temporally variable, with the enhancements becoming statistically significant in the second-stage trials and not after the first stage
Our results indicate that higher chlorophyll a/b ratio and carotenoid concentration was related to better rooting in genotype A-37, inoculated with Pseudomonas sp., in the first-stage trials
Summary
Forest trees and their wood quality are threatened by pathogenic fungi [1,2]; one of the most pressing problems in forestry, today, is the selection of tree genotypes for increased growth and better resistance to phytopathogens [3,4]. More attention has recently been paid to potentially beneficial interactions between symbiotic bacteria and woody plants. Endophytic bacteria can promote resistance to stress and pathogens, at the same time stimulating nutritional processes in their hosts, affecting overall growth [5,6,7,8]. Plant growth promoting bacteria are being more widely used in agriculture, as an eco-friendly alternative to chemical fertilizers and pesticides [7,12]; the potential application of such beneficial bacteria in forestry has not yet been sufficiently explored [13].
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