Nodulation of actinorhizal plants byFrankia strains capable of both root hair infection and intercellular penetration

Summary A morphological analysis of the initiation and development of root nodules ofElaeagnus angustifolia andMyrica cerifera inoculated with pure-culturedFrankia strains DDB 011610 or DDB 020110 was undertaken. From ultrastructural observations it was determined that both of theseFrankia strains can infectElaeagnus by an intercellular penetration mechanism andMyrica by the root hair infection mechanism. This indicates that both of these strains have the ability to infect host plant roots by either of two mechanisms. The reverse, thatElaeagnus orMyrica could be infected by both mechanisms, was not observed. The infection and nodule development processes of these two plants in combination with these strains were similar to observations made in previous studies (Miller andBaker 1985,Torrey andCallaham 1979). However, one exception was identified in the development of the prenodule ofMyrica when infected with strain 011610, in that endophytic hyphae developed vesicles within the cells of the prenodule. This event has not been described before for any of the actinorhizal genera and may be an indication of less than optimal compatibility between the host plant and the symbiont.Contribution no. 876 of the Battelle-Kettering Laboratory.