Biological control of damping‐off of sugar beet by Pseudomonas putida applied to seed pellets

Pseudomonas putida 40RNF applied to seed pellets reduced the occurrence of Pythium damping‐off of sugar beet. A density of 6 × 10 7 40RNF per pellet reduced Pythium damping‐off from 70 to 26% when seeds were sown in artificially infested soil (250 propagules Pythium ultimum per g dry soil). The efficacy of 40RNF was dependent on its density in the seed pellet (in the range 2 × 10 4 –6 × 10 8 per pellet) and on the number of propagules of Pythium in soil. 40RNF declined to or stabilized at approximately 1 × 10 6 per pellet 3 days after planting, and this was independent of the inoculum density. This indicated that the crucial steps resulting in damping‐off of sugar beet caused by Pythium ultimum must occur within 3–4 days of sowing. 40RNF reduced pericarp colonization by P. ultimum by 43% 48 h after planting and caused a 68% decrease in the number of sporangia of P. ultimum in the surrounding soil (0.0–5.0 mm). P. putida 40RNF also reduced pre and post‐emergence damping‐off (from 69.5 to 37.5%) caused by indigenous populations of Pythium species in an infested soil and this was as effective as the fungicide hymexazol (69.5 to 40%).