Abstract:

Systematic studies of the biological characteristics were carried out on 17 Frankia strains isolated from the root nodules of actinorhizal plants Casuarina in Fujian and Guangzhou, including morphology, culture, physiological group, nutrient utilization, nitrogenase activity and host specificity. The observations by microscopy demonstrated that all the strains tested showed a typical Frankia morphology, with filamentous hyphae, multilocular sporangia borne terminally, laterally, or in an intercalary position on branching hyphae. Terminal or lateral borne vesicles were generally formed on lack of nitrogen, the isolates FCc^AC04、FCe75、FCc92 and FCg77 formed occasionally terminal vesicles in presence of nitrogen. Variations in hypha diameter, sporangia and vesicle numbers were noted between media and isolates. The specialized reproducrive torulose hyphae were found in strains FCc64、FCc92、FCe33. The Frankia isolates whether from the same species or a single plant had a quite difference on clonal shape, color and pigment. Fifteen Frankia isolates were found to fall into three physiological groups, two isolates were belonged to group A, eight were group B and five were group AB. There was no apparent correlation of physiological groups with pattern on utilization of carbon, nitrogen and organic acids. Nearly all the isolates were likely to utilize NZ amine, sodium acetate, sodium propionate and Tween-80, but potassium nitrate and sodium benzoate, sodium succinate, sodium citrate used by different strains. Cellulase, pectinase had not been found in all isolates but proteinase was produced in some strains cultured. All strains tested grew well in the media lack of nitrogen and did not produce the cellulase. Nitrogenase activity of strains was monitored in culture and varied greatly among isolates. The inoculation expriment result showed that the strains from Casuarina not only had ability to infect Casuarina, but also to infect Myrica rubra, Elaeagnus angustifoli and Alnus cremastogym. And it reflected that Frankia in roots of Casuarina in China might have a wide diversity.

Key words: Casuarina, Frankia, Biological characteristics, Physiological group, Host specificity