Development and evaluation of SCAR markers for a Pseudomonas brassicacearum strain used in biological control of snow mould

Biological control microorganisms have long been promoted as an alternative to conventional pesticides. Before registration of a microbial biocontrol product for commercial sale, it must be evaluated as regards potential spread and persistence after release. In this study, strainspecific sequence-characterized amplified region (SCAR) markers were developed to monitor the biocontrol candidate strain Pseudomonas brassicacearum MA250, which is effective against snow mould (Microdochium nivale). One SCAR marker, OPA2-73, was used in quantitative real-time PCR (Q-PCR) on samples from a climate chamber experiment in which winter wheat seeds were treated with the bacterium or a chemical control agent, or left untreated. The results showed that MA250 persisted for up to 3 weeks after sowing on the kernel residues and also colonized the roots of treated seedlings. Total MA250 cell numbers on biocontrol treated seedlings after three weeks were approximately 10⁶ cells, compared with the original inoculum of 10⁶–10⁷ cells per seed. Corresponding cell numbers of MA250 on chemically treated and untreated seedlings were below the detection limit. This study shows that SCAR marker OPA2-73 is a specific and sensitive tool for monitoring the biocontrol microorganism MA250 in environmental samples.