Growth of Frankia in the rhizosphere of Betula pendula, a nonhost tree species

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Abstract
The growth of Frankia in the rhizosphere of Betula pendula was studied to understand the favourable effect of this nonhost species on Alnus-nodulating Frankia in soil. Axenic Betula pendula and Alnus incana seedlings were inoculated with Frankia strains. The development of Frankia in the rhizosphere was examined by light and scanning electron microscopy. Some Frankia strains grew in the rhizosphere of Betula pendula seedlings without addition of a carbon and energy source. In addition to hyphae and sporangia, vesicles were also formed. Growth (if any) was more local and less abundant in the rhizosphere of Alnus incana seedlings. Frankia strains were grown in defined medium supplemented with tryptophan. Indole-3-ethanol was detected in the culture solution by gas chromatography – mass spectrometry. Key words: Alnus incana, Betula pendula, Frankia, indole-3-ethanol.