Geographic distribution and genetic diversity of Ceanothus-infective Frankia strains

Little is known about Ceanothus-infective Frankia strains because no Franki a strains that can reinfect the host plants have been isolated from Ceonoth us spp. Therefore, we studied the diversity of the Ceonothus-infective Fran kia strains by using molecular techniques. Frankia strains inhabiting root nodules of nine Ceanothus species were characterized. The Ceanothus species used represent the taxonomic diversity and geographic range of the genus; therefore, the breadth of the diversity of Frankia strains that infect Cean othus spp, was studied. DNA was amplified directly from nodular material by using the PCR, The amplified region included the 3' end of the 16S rRNA ge ne, the intergenic spacer, and a large portion of the 23S rRNA gene. A seri es of restriction enzyme digestions of the PCR product allowed us to identi fy PCR-restriction fragment length polymorphism (RFLP) groups among the Cea nothus-infective Frankia strains tested. Twelve different enzymes were used , which resulted in four different PCR-RFLP groups. The groups did not foll ow the taxonomic lines of the Ceanothus host species. Instead, the Frankia strains present were related to the sample collection locales.