Comparison of application methods to prolong the survival of potential biocontrol bacteria on stored sugar-beet seed

Abstract

To develop bacterial inoculation treatments on sugar-beet seed that will maintain a commercially acceptable degree of viability for a minimum of 4 months storage at ambient temperature. Single rifampicin-resistant (Rif(+)) strains of both Gram-positive and negative bacterial isolates (mostly pseudomonads) were applied in turn to sugar-beet seed in a comparative study by seed soaking, encapsulation in alginate, pelleting using an inoculated peat carrier or seed priming. The treated seed was assessed for bacterial survival over a time course by plating out homogenized samples onto a selective medium. Priming inoculation offered a significant improvement over all the other application strategies tested. After pelleting with fungicides and drying at 40 degrees C, Pseudomonas marginalis/putida P1W1 maintained populations of >6.6 log(10) CFU g(-1) seed during 4 months storage at 15 degrees C. Subsequent experiments verified a stabilized population under these storage conditions with commercial pellets at <7% moisture content. An inoculation method was established which allowed the survival on seed of a Gram-negative bacterium at ambient temperature with little loss in viability. This has promising implications for the delivery of beneficial bacteria, especially Gram-negative strains, on sugar beet.