Use of rifampicin-resistant bacterial biocontrol strains for monitoring survival in soil and colonisation of pea seedling roots

Abstract

Spontaneous rifampicin-resistant strains of two bacterial biocontrol agents, Bacillus subtilis and Paenibacillus polymyxa, with potential to control Aphanomyces euteiches root rot of peas, were used to assess bacterial survival in soil and colonisation of pea seedling roots. The growth and biocontrol characteristics of the rifampicin-resistant strains were similar to the wild type isolates. In two non-sterile soils (Methven and Courtenay), both bacterial strains survived at least 28 days when applied as inoculum containing high endospore numbers. However, when applied as mostly cells, no bacteria were recovered. Bacteria applied as seed coat formulations colonised both the rhizosphere and rhizoplane of the resulting pea seedlings, with higher recovery from the top 0-4 cm root section compared with the bottom 5-8 cm section. Apart from the top root section for P. polymyxa, where there was no difference in the recovery between the rhizoplane and rhizosphere, recovery of the bacteria was higher in the rhizoplane compared with the rhizosphere.