Enrichment and diversity of plant-probiotic microorganisms in the rhizosphere of hybrid maize during four growth cycles.

The population dynamics of naturally-occurring antibiotic producing and nitrogen fixing rhizobacteria, as well as of arbuscular mycorrhizal fungi (AMF) was investigated for a hybrid of maize (Lo964 x Lo1016) in comparison to its two parental lines (Lo964 and Lo1016), during four successive 5-week-long growth cycles in the same pot. Beneficial rhizobacteria, such as nitrogen fixers and 2,4-diacetylphloroglucinol (DAPG)- and pyrrolnitrin (PRN)- producers, as well as AMF were stimulated in the hybrid rhizosphere earlier than in those of the two parental lines. In fact, they were molecularly detected in all rhizospheric samples of the hybrid, independently of the cycle, whereas for the parental lines positive detections occurred only for samples collected after at least two growth cycles. Interestingly, a PCR-MPN approach on rhizospheric DNA samples indicated that, when detected, beneficial rhizobacteria reached similar density in all maize genotypes. Concerning the AMF, even if the three maize genotypes were cultivated in the same soil, it appears that each maize genotype stimulates the AMF population differently. Both the hybrid and the Lo964 line were able to select, in the observed time period, their own adapted phylogenetic AMF subgroups (Glomus A for the hybrid, Archeospora for Lo964), whereas the Lo1016 line was not.