The competitivity, persistence and dispersal of Frankia strains in mine spoil planted with inoculated Alnus rubra

Polymorphisms in Frankia DNA sequences corresponding to part of the 16s rDN A were amplified by a PCR-based technique. The technique generated a sequen ce-specific "gene signature" that facilitated discrimination between two Fr ankia strains in nodules from Alnus rubra. Analysis of nodules from randomi sed plots of A. rubra, specifically inoculated 10 years earlier with the tw o strains or with a crushed nodule preparation, provided evidence for diffe rential persistence of the two strains. Frankia UGL 013103 was detected in 28 nodules from trees inoculated originally with this strain whereas DDB010 210 was not detected in any nodule from the specifically inoculated trees n or from other trees in the experimental plot. Strain UGL013103 was also fou nd in 10% of samples from control plots (uninoculated prior to planting). U nidentified strains were detected in the remainder of nodule samples. Possi ble origins for these were from Alnus glutinosa trees, planted out with the experimental plot 6 years after establishment, from the crushed nodule pre parations used to inoculate alders in some plots or from nursery soil carri ed over with outplants. Both strains were detected in nodules formed on pla nts grown in soil samples collected from an alder-free area immediately adj acent to the experimental plot. This suggests that the competitive pressure s for survival of these strains, in the absence of alders as a host, were l ower than within the experimental plot.