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 x 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 oil its density in the seed pellet (in the range 2 x 10(4)-6 x 10(8) per pellet) and on the number of propagules of Pythium in soil. 40RNF declined to or stabilized at approximately 1 x 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 ill the surrounding soil (0.0-5.0 mm). P. putida 40RNF also reduced pie 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 io 40%).