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Genetic diversity among Frankia strains nodulating members of the family Casuarinaceae in Australia revealed by PCR and restriction fragment length polymorphism analysis with crushed root nodules

Rouvier C., Prin Y., Reddell P., Normand P., Simonet P.. 1996. Applied and Environmental Microbiology, 62 (3) : p. 979-985.

DNA extracted directly from nodules was used to assess the genetic diversity of Frankia strains symbiotically associated with two species of genus Casuarina and two of the genus Allocasuarina naturally occuring in northeastern Australia. DNA from field-collected nodules or extracted from reference cultures of Casuarina-infective Frankia strains was used as the template in PCRs with primers targeting two DNA regions, one in the ribosomal operon and the other in the nif operon. PCR products were then analysed by using a set of restriction andonucleases. Five distinct genetic groups were recognized on the basis of these restriction patterns. These groups were consistently associated with the host species from which the nodules originated. All isolated reference strains had similar patterns and were assigned to group 1 along with six of eight unisolated Frankia strains from Casuarina equisetifolia in Australia. Group 2 consisted of two unisolated Frankia strains from C. equisetifolia, whereas groups 3 to 5 comprised all unisolated strains from Casuarina cunninghamiana, Allocasuarina torulosa, and Allocasuarina littoralis, respectively. These results demonstrate that, contrary to the results previous molecular studies of isolated strains, there is genetic diversity among Frankia strains that infect members of the family Casuarinaceae. The apparent high homogeneity of Frankia strains in these previous studies probably relates to the single host species from which the strains were obtained and the origin of these strains from areas outside the natural geographic range of members of the family Casuarinaceae, where genetic diversity could be lower than in Australia. (Résumé d'auteur)

Mots-clés : rflp; pcr; nodosité racinaire; variation génétique; adn; biodiversité; casuarinaceae; frankia; australie

Thématique : Génétique et amélioration des plantes

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