Shelf-life of a biocontrol Pseudomonas putida applied to sugar beet seeds using commercial coatings

Pseudomonas putida 40RNF is a putative biological control agent (BCA) of Pythium damping-off of sugar beet. The survival of 40RNF during commercial seed treatment and its subsequent shelf-life (i.e. long-term viability and biocontrol activity) were assessed. Two methods were used to apply 40RNF to sugar beet seeds: incorporation into film-coats sprayed on to pre-pelleted seeds and incorporation into the pellet material prior to pelleting. Only 7.1% of applied 40RNF survived film-coating, but an initial concentration of 7 X 10(8) ensured that 83.3% of a pre-deter mined target rate of 6 X 10(7)/pellet was achieved. After 52 weeks of storage at 4 degrees C, the numbers of 40RNF had declined by one to two orders of magnitude, with a decrease of approximately 50% in disease control, After 52 weeks at 18-20 degrees C, 40RNF was below detectable limits (<100/pellet), yet the biocontrol activity of the seed treatments was not reduced. The survival of 40RNF during incorporation into the pellet material was poor (<0.2% of those applied, i.e. 5 x 10(5) pellet). However, bacterial viability and biocontrol efficacy were maintained at 100% of the control value for 24 weeks when stored at 18-20 degrees C. The results indicate that commercial seed treatments and the storage of pellets at ambient temperatures has potential for the introduction of bacterial BCAs into the spermosphere.