Five strains of Frankia isolated from actinorhizae of 3 alder species were cultivated with various concentrations of neomycin in the medium. For one strain, resistance to neomycin was associated with lost of effectiveness. The ineffective strain was as infective as the parent strain. Protein and isoenzymes patterns showed that the ineffective and the parent strains were quite similar. The ineffective strain differentiated vesicles inside the infected host-cells.
Diversity of Frankia isolates originating from lobes of single nodules collected on Alnus glutinosa root systems has been analyzed using isozyme electrophoresis method. Analysis of isozyme patterns showed no divergence among strains isolated from the same nodule. Each nodule (among 10 assayed) was inhabited by a single Frankia strain.
Mots eibs Alnus Frankia Nodules pH acides Plantes fi actinorhizes Viabilit6Key words Actinorhizal plant Alnus Frankia Low pH Nodules Viability R~sum6 Vingt souches de Frankia, isol6es ~t partir de 7 esp6ces diff6rentes de plantes actinorhiziennes ont 6t6 cultiv6es sur des milieux maintenus fi des pH constants de 5; 4,8; 4,6 et 4,2. Chaque souche a 6t6 cultiv6e 2 fi 3 fois cons6cutives ~ un m6me pH. Quatorze souches ne montrent aucune croissance fi pH 5. Seules 3 souches r6sistent ~un s6jour de plusieurs semaines ~ pH 4,6. Aucune souche ne demeure viable apr6s un s6jour dans un milieu fi pH 4,2. Les 3 souches acido-r6sistantes supportent 6galement la pr6sence d'A1 + § § libre dans le milieu de culture. Une forte concentration d'H § dans le milieu stimule beaucoup la sporog6n6se.Inocul6e dans un sol acide une souche acido-r~sistante conserve une chance de survie nettement sup~rieure fi celle d'une souche neutrophile maintenue dans les m~mes conditions. Summary Twenty Frankia strains isolated from seven actinorhizal species were cultivated on media at various pH 5; 4.8; 4.6 and 4.2. Each strain was cultivated 2 or 3 times on the same pH. Fourteen strains did not grow at pH 4.6. At pH 4.2 all the strains died after few days. The 3 acido-resistant strains grew with free AI § § § in the culture medium.Inoculated in an acidic soil, the viability of an acido-resistant strain was greater than that of a neutrophilic strain.
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