Lack of competition between Frankia and Glomus for infection and colonization of roots of Casuarina equisetifolia (L.)

summary Casuarina eqisetifolia (L.) (L.) seedlings, grown with a limiting supply of mineral N and P, were inoculated with either Frankia or Glomus fasciculatum E3 and subjected to delayed inoculation with the second microsymbiont. Comparison with seedlings inoculated simultaneously with both microsymbionts showed that neither the development of nodules nor mycorrhizal colonization was delayed when seedling were pre-inoculated for periods of up to 60 d with either Glomus or Frankia, respectively. Mycorrhizal colonization was affected when inoculation with Frankia was delayed for 60 d. Thus, a 60 d delay in Frankia inoculation of Glomus-inoculated seedlings resulted in a lower percentage mycorrhizal colonization of the root system than in seedlings inoculated earlier with Frankia or simultaneously with Glomus. A similar delay in Glomus inoculation of Frankia-inoculated seedlings resulted in a 50% reduction in the colonization of the roots with Glomus 60 d after inoculation. Delayed inoculation with either microsymbiont had no long-term effect on subsequent nodulation. There was a highly significant, linear relationship between log10 (nodule number per plant/%Glomus root colonization) and the time (days) after Frankia or Glomus inoculation, indicating a high degree of coordination between nodulation, mycorrhizal colonization and seedling growth in mineral deficient conditions. These data indicate a co-operative, but not a competitive interaction between Frankia and Glomus for nodulation and mycorrhizal colonization of Casuarina.