Diversity of Paenibacillus polymyxa populations in the rhizosphere of wheat (Triticum durum) in Algerian soils

The diversity of Paenibacillus polymyxa populations associated with the rhi zosphere of durum wheat was investigated in Algerian soils sampled in regio ns where wheat had been cultivated for 5 and 26 years (Hamiz, H5 and Z26), 70 years (Algiers, D70), and more than 2 000 years (Tiaret, T2000 and K2000 ). A total of 111 strains were isolated by immunotrapping and identified as P. polymyxa using an AP150CHB kit and restriction analysis of the amplifie d 16S rDNA gene. The phenotypic characteristics of the P. polymyxa populati ons were compared and the strains found not to cluster according to their o rigin. The longer the history of wheat cultivation, the lower the phenotypi c diversity and the higher the frequency of nitrogen-fixing strains. Popula tion genetic diversity, evaluated by ERIC-PCR, showed the same trends as ph enotypic diversity. The distribution of ERIC genotypes among the different populations studied were compared using Pearson's Chi-squared test. The str ains isolated in D70, 226, and H5 derived from soil populations sharing the same genetic structure, but those isolated in T2000 and K2000 each stemmed from a population with a specific genetic structure. These data suggest th at the genetic structure of P. polymyxa populations has been affected by lo ng-term wheat cultivation. (C) 2000 Editions scientifiques et medicales Els evier SAS.