Flavonoid‐like compounds from seeds of red alder (Alnus rubra) influence host nodulation by Frankia (Actinomycetales)

Nitrogen‐fixing root nodules are formed by Frankia spp. (Actinomycetales) on dicotyledonous hosts such as alders (Alnus spp.). Flavonoid‐containing preparations from seed washes of red alder (Alnus rubra Bong.), and individual compounds isolated from such preparations, influenced nodulation of A. rubra by Frankia. Nodulation was enhanced by one flavonoid‐like compound, and apparently inhibited by two other such compounds. Four flavonoid‐like compounds had no significant effect on nodulation. The seven individual compounds purified from the seed washes were characterized spectrally as possible flavanones and isoflavones. Both the enhancer and the inhibitors appeared to be possible flavanones.