Isolation, culture, and behavior of Frankia strain HFPCgI4 from root nodules of Casuarina glauca

Casuarina glauca (Casuarinaceae) is an important introduced tree species in Egypt, valued for windbreaks, land stabilization, and soil improvement associated with actinomycete-induced root nodules that fix atmospheric nitrogen. A strain of Frankia designated HFPCgI4 was isolated from root nodules collected in Egypt and its characteristics assessed both in pure culture and in symbiosis. Strain CgI4 grows well in synthetic nutrient medium with added NH4 +or, in the absence of combined N in the medium, forms vesicles and fixes dinitrogen adequate for growth. Hyphae, vesicles, sporangia, and spores characteristic of the genus Frankia were observed. This strain shows spontaneous spore release when grown in media lacking N. When tested for infectivity on actinorhizal host plants grown in unacrated water culture, CgI4 nodulates several species of Casuarina that fix atmospheric dinitrogen. Other genera in the Casuarinaceae, namely, Allocasuarina and Gymnostoma, were not nodulated under these conditions. Species of the genus Myrica and Comptonia peregrina (Myricaceae) were effectively nodulated by CgI4. The isolate may have use as an inoculant for forest plantations using species of Casuarina sensu stricta.