Fate and behaviour of a seed-applied Pseudomonas brassicacearum strain in a winter wheat field trial,as determined by analysis with SCAR markers

The fate and behaviour of the seed-applied biocontrol strain Pseudomonas brassicacearum MA250 in a field trial with winter wheat was determined using sequence-characterised amplified region (SCAR) markers. Samples of belowground plant parts from healthy and withered (due to snow mould infection) seedlings were collected approximately one and seven months after sowing, which was performed in early autumn. DNA was extracted from roots and remaining parts of seeds with adhering soil, and the abundance of the strain was determined in quantitative real-time PCR (qPCR) assays. The results show that the introduced strain persisted over the whole trial-period of seven months. On termination of the trial (after seven months) the belowground plant parts of each plant housed 10⁶–10⁷ cells, substantially less than the original approximately 10⁹ cells inoculated onto the seed. In healthy seedlings, there was a shift in cell numbers from seeds to roots between the samplings, suggesting colonisation of the roots during this time. The results show that with sufficient attention given to analytical control measures and the possibility of resident background populations, SCAR markers in combination with qPCR provide valuable information regarding the fate and behaviour of biocontrol micro-organisms under field conditions.