Sporulation in root nodules of actinorhizal plants inoculated with pure cultured strains of Frankia

Abstract

A low level of sporulation was seen to occur consistently within root nodules produced by inoculation with specific pure cultured strains of Frankia. The three Frankia strains, UFGCeI5 from Casuarina equisetifolia, UFGCgI1 from Casuarina glauca, and UFGMuI1 from Myrica pubescens, infect and produce root nodules on a range of actinorhizal host plants. Sporulation was detected in nodules of each host plant examined when the Frankia used for inoculation was one of these three strains. The amount of sporulation that occurred in any particular nodule was so low that it required identification in thin plastic sections prepared for examination at high magnification at the light microscope level. These strains, unlike other isolates studied, appear to be genetically predisposed to sporulate in the host root nodules. All three strains also show spontaneous spore release in culture. Key words: actinorhizal plants, endosymbiont, Frankia, sporulation.