| Systematic studies were carried out on Frankia strains isolated from the root nodules of actinorhizal plants in Fujian. The main results were as follows.1. The root nodules were collected from twenty-two different geographical sites in Fujian. They belonged to four families Betulaceae, Casuarinaceae, Elaeagaceae and Myricaceae, including nine species of Alnus cremastogyne, A.formosana, A.traboculosa, Casuarina.glauca, C.equisetifolia, C.cunninghamian.,Elaeagnus.oldhami,E.glabra and Myrica rubra. Eighty-six isolates were obtained and the nodulation experiment indicated that the isolates were all infective Frankia strains. An initial attempt was made to set up Frankia strainbank of Fujian and to conserve these strains.2. More than thirty strains obtained were studied on the biological characteristics, including morphology, culture, physiological type, nutrient utilization, nitrogenase activity, host specificity and the growth response to various salt-stress. The effects of nodulation and nitrogen fixation of Casuarina-Frankia symbiont on different water stress was also estimated.(1) 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 laterally borne vesicles were occasionally formed on lack of nitrogen for the Frankia isolates from Alnus^ Casuarina and Elaeagnus, the isolates FCe75% FCc92> FCg77 from Casuarina and most isolates from Myrica formed terminal vesicles in rich nitrogen. Variations in hyphae diameter, sporulation and vesicle numbers were noted between media and also between isolates. The specialized reproductive torulose hyphae wrere found in strains FCc64> FCc92, FCe33 from Casuarina and FMr^ FMr43 from Myrica.(2) Comparison of culture characteristics in liquid media and on solid slants was made between the isolates. The Frankia isolates whether from the same species or a single plant had a quite difference on clone shape, clone color and growth rates.(3) Thirty-one Frankia isolates were found to fall into three type physiological groups (A, B and AB). Four Frankia isolates belonged to group A, twenty were group B, and seven belonged to groups AB. There was no apparent correlation of physiological types with pattern on utilization of simple inorganic or organic ammonia and organic acid salts. 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 occurred with different strains. Six carbohydrate utilization patterns were observed among the isolates tested.(4) Nitrogenase activity of twenty-seven isolates was monitored in media lacking combined nitrogen, and no acetylene reduction activity and vesicles were found in three strains FCc93 ^ FCe23 >, FMr43.(5) Fifty-nine pure cultured isolates were inoculated with seedlings of C.cunninghamiana, C.equisetifolia, C.glauca, E.angustifolia, H.rhamnoides and M.rubra to determine the host specificity groups (HSG). All strains separated two HSP: Casuarina group and Myrica-Alnus-Elaeagnus group. Frankia strains in Casuarina group came from Casuarina only and strains in Myrica-Alnus-Elaeagnus group can infect the seedlings of Myrica, Casuarina and Elaeagnus.(6) The DNA region comprising the 3' end of the 16S rDNA, the IGS, and the 5' part of the 23S rDNA (i.e.,rrn region) were amplified from Frankia strains isolated from C.cunninghamiana, C.equisetifolia C.glauca, M.rubra and A.cremastogyne and living in nodules of C.cunninghamiana, C.collina, C.glauca, M.rubra, A.cremastogyne and A.traboculosa. PCRs products were analyzed by using a set of restriction endonucleases. Two distinct geneticgroups, Casuarina group and Myrica-Alnus group, were recognized on the basis of thses restriction patterns. All strains isolated or living in Casuarina were assigned to Casuarina group, strains isolated... |
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