Selection trials for effective N2-fixing Casuarina-Frankia combinations in Egypt

Biomass productivity and nitrogen fixation were studied for combinations of four Casuarina cultivars and four Frankia strains. Seedlings were planted in pots containing a Frankia-free, low-nutrient soil. To evaluate nitrogen fixation over the duration of the experiment, a small amount of 15N-enriched KNO3 was supplied to the pots on a weekly basis. After 56 weeks, all of the plants were harvested and dry weights determined. Plant tissue was analyzed for N concentration and 15N (atom % excess). Significant differences were observed in biomass productivity among the various host-strain concentrations. Differences were also observed in the proportion of N derived from nitrogen fixation (pNdfa) among the various host-strain combinations, and these were correlated with biomass productivity. From the results of our experiment, it is clear that performance and nitrogen fixation are related to the interaction between the host plant and the Frankia strain. If Casuarina-Frankia strain combinations are to be used, it is appropriate to conduct trials of symbiont compatibility to improve yield. © 1994.