Variabilité génotypique de l'aptitude à la fixation symbiotique de l'azote chez Acacia cyanophylla Lindl.

Abstract

Genotypic variability of the symbiotic nitrogen fixation ability on Acacia cyanophylla Lindl. The phenotypic and functional characteristics of four rhizobium strains isolated from nodules of Acacia cyanophylla Lindl., syn. Acacia saligna (Labill.) H. Wendl., and the inoculated host-plant genetic variability were evaluated. The evaluation used permitted the ranking of the tested rhizobium strains and seedlots according to their performance. The growth pattern of these strains indicated that A. cyanophylla was able to nodulate and fix N2 with slow- and fast-growing rhizobium strains. The acetylene reduction activity test reflected a variable effectiveness of the strains depending on their site of isolation. Strains RFH383 and RFH483 were more effective than RFH183 and RFH283. The high antibiotic resistance acquisition by RFH183 and RFH283 strains seemed to be inversely related to their effectiveness. Acacia cyanophylla seedlings from five seedlots displayed a high variability regarding their growth, nodulation, and ability to fix nitrogen. The ability to fix nitrogen was greater in the seedlings from KL seedlot than those from EN, KR, and TZ seedlots. The qualitative assessment of the seedlots using correspondence factorial analysis showed that the seedlings from KL seedlot preformed better than those from KR and TZ. The seedlings from TN and EN seedlots displayed an intermediate behaviour pattern. Seed origin seemed to affect the growth, nodulation, and nitrogen fixation of inoculated A. cyanophylla. The behaviour of this species and that of its associated rhizobium strains appeared to be very sensitive to variations in site characteristics. Results suggested that the association between plants derived from KL seedlot and RFH383 strain may represent the best partnership allowing the improvement of symbiotic nitrogen fixation.Key words: Acacia cyanophylla, rhizobium, nodulation, N2 fixation, genotypic variability, correspondence factorial analysis.