Frequency and biodiversity of 2,4-diacetylphloroglucinol-producing bacteria isolated from the maize rhizosphere at different stages of plant growth

A Pseudomonas 2,4-diacetylphloroglucinol (DAPG)-producing population that o ccurred naturally on the roots, in rhizosphere soil of Zea mays and in the nonrhizosphere soil was investigated in order to assess the microbial diver sity at five stages of plant growth. A total of 1,716 isolates were obtaine d, and 188 of these isolates were able to produce DAPG, DAPG producers were isolated at each stage of plant growth, indicating that the maize rhizosph ere is colonized by natural DAPG producers throughout development. The freq uency of DAPG producers was very low in the first stage of plant growth and increased over time. An analysis of the level of biodiversity of the DAPG producers at the species level was performed by comparing the AluI restrict ion patterns of the 16S ribosomal DNAs (rDNAs) amplified by PCR from 167 is olates. This comparison allowed us to cluster the isolates into four amplif ied rDNA restriction analysis (ARDRA) groups, and the main group (ARDRA gro up 1) contained 89.8% of the isolates, The diversity of the 150 isolates be longing to ARDRA group 1 was analyzed by the random amplified polymorphic D NA (RAPD) technique, An analysis of RAPD patterns by a molecular variance m ethod revealed that there was a high level of genetic diversity in this pop ulation and that the genetic diversity was related to plant age. Finally, w e found that some of the DAPG producers, which originated from all stages o f plant growth, had the same genotype, These DAPG producers could be exploi ted in future screening programs for biocontrol agents.