Influence of phenolics on <i>in vitro</i> growth of <i>Frankia</i> strains

Abstract

The influence of some common plant phenolics was tested on six Frankia strains isolated from both Alnus and Elaeagnus host plants. The addition of 1 mM of different phenolics to QmodB broth significantly influenced the growth and (or) the morphological development of Frankia. Ferulic, o-coumaric, and p-coumaric acids were extremely effective in inhibiting the growth of Frankia colonies, increasing the ramification of hyphae, and decreasing the number and size of sporangia produced in vitro. However, benzoic and p-hydroxybenzoic acids did not influence the total growth of Frankia colonies but stimulated the in vitro production of spherical septate vesicles on the two strains of Frankia type N tested. The possibility that these active phenolics, which are known to be present in Alnus actinorhizae, might act as "chemical mediators" between the host cell and its endophytic Frankia is suggested.