Frankia nodulating Alnus glutinosa and Casuarinaceae in Tunisia

The capacity of some Tunisian soils to induce nodulation on Casuarina spp. and Alnus glutinosa was investigated through survey at fields and by plant-trapping bioassay. Frankia nodules were detected only in the north of Tunisia in some experimental forest stations for Casuarinaceae, and in natural endemic A. glutinosa stands. Frankia genetic diversity was assessed by PCR-RFLP of nifD-K region and, for Casuarinaceae, also of 16S-23S rDNA internal transcribed spacers, amplified from DNA directly extracted from root nodules. Restriction patterns showed that one and two haplotypes of Frankia colonise Casuarinaceae and A. glutinosa, respectively. Frankia in nodules of Casuarinaceae were found to be closely related to the group 1 of Casuarinaceae nodulating strains previously identified in Australia, corroborating the hypothesis of a recent introduction of these strains into Tunisia, probably with their hosts.