Specificity and effectivity in nodulation by Frankia on southern hemisphere actinorhiza.

Nodulation ability was tested for Frankia strains HFPCcI3 and EL1, and Frankia sources A.t. and G.a. from Allocasaurina torulosa and Gymnostoma australianum, respectively, on A. torulosa Miq., Casuarina cunninghamiana Miq., G. australianum L. Johnson and Elaeagnus triflora Roxb. It was shown that A. torulosa and C. cunninghamiana formed nodules only with the Frankia sources obtained from their own host plant, while E. triflora formed nodules with three of the four Frankia sources tested. All nodules formed were effectively fixing nitrogen. Specific nitrogenase activity was highest in E. triflora inoculated with the Frankia strain isolated from nodules of the same species. Identification of Frankia sources in the nodules was performed by use of PCR amplification of DNA with a random primer. PCR amplification of DNA isolated from nodules of G. australianum and E. triflora inoculated with Frankia strain EL1 revealed, when compared with DNA amplified from free living Frankia strain EL1, that there was only one Frankia strain causing the observed nodules.