Assessment of Cultural, Biochemical and Genetic Characteristics of Frankia Isolates, Their Nodulation and Symbiotic Nitrogen Fixation With Casuarina Trees

Abstract

The microsymbiont Frankia genus belongs to the order of filamentous bacteria, the actinomycetales, family Frankiaceae, is Gram-positive bacteria fixing atmospheric nitrogen which forms symbiotic association with actinorhizal Casuarina glauca. C. glauca is an important introduced tree species in Egypt, valued for windbreaks and shelterbelt; land stabilization and soil improvement.The present study concerned with the phenotypic, ecological and genetic characters; symbiotic competence and host specificity of some local Frankia isolates with Casuarina trees. ** Sixteen native Frankia pure isolates were isolated from root nodules of Casuarina trees, collected from different ecological Egyptian soils and their characteristics assessed in comparison with foreign reference Frankia isolates. ** Frankia isolates were grown well in synthetic nutrient medium. Vegetative hyphae, vesicles; sporangia and reproductive torulose hyphae (RTH) were observed.According to their physiological properties and plasmids number it was found that the isolated Frankia were identified as fifteen different Frankia isolates belonging to Frankia Casuarina. The characterization of Frankia isolates at DNA level revealed that existence of a large diversity with the exception of two isolates that were completely identical in all parameters using RFLP analysis. ** Inoculation of Casuarina seedlings with the various local Frankia isolates induced nodulation (nodules number and dry weights) and enhanced their vegetative growth parameters (stem lengths, branches and shoots dry weight) over the foreign reference strain. ** Some environmental factors included resistance to different antibiotics, neutral salinity and various C-sources utilization were investigated well in comparison with imported foreign reference strain. ** Performance symbiotic N2-fixation of various indigenous Frankia isolates were judged by the percent shoots and roots N-content and N-uptake (mg/seedling) of Casuarina seedlings cultivated in both calcareous and sandy soils. Efficacy of Casuarina seedlings to N2-fixation was significantly increased upon inoculation with the most local Frankia isolates, which resulted in augmentation of N-content and uptake over the reference strain. ** Highly efficient, native indigenous Frankia isolated from Kafr El-Sheikh and those from Ismailia regions identified as salinity tolerant, characterized by well intrinsic antibiotics resistance, showed greatly response to different C-sources and displayed highly symbiotic competence and effectiveness on Casuarina glauca, which surpassed the imported foreign reference Frankia strain. Therefore, such isolates were strongly recommended to be applied as inocula for Casuarina species grown in Egyptian soils.The obtained data clearly emphasize the importance of isolation of proper Frankia strains for high compatible, resistant processed inocula for Casuarina cultivated under ecological conditions similar to initial from which they were isolated i.e. initial niches.