Control of damping-off of safflower by bacterial seed treatment

Among 665 strains of rhizosphere bacteria isolated from plant samples in southern Alberta, 23 strains were antagonistic to Pythium sp. 'group G', a sterile form of Pythium ultimum causing damping-off of safflower. Fifteen of these antagonistic strains were identified at the species level and tested for efficacy as seed-treatments for safflower in soil naturally infested with P. ultimum var. ultimum. Erwinia carotovora, strains 6-7, 6-9-3, and 18-6; E. rhapontici, strains 16-5, 16-7, 17-8, and 18-7; Pseudomonas putida, strain 15-2-3; and P. fluorescens, strains 1-2, 3-3, 6-9-2, and 7-3, significantly (P < 0.05) reduced pre-emergence damping-off and increased seedling emergence in safflower. Bacillus polymyxa strain 5-8; B. subtilis, strain 16-8; and Erwinia herbicola, strain 2-2 were ineffective. Seed treatment with B. polymyxa, strain 5-8; E. rhapontici, strains 17-8 and 18-7; and P. fluorescens, strains 7-3 and 6-9-2 increased seedling height of safflower. The potential of antagonistic strains of rhizosphere bacteria as biocontrol agents for pythium damping-off of safflower is discussed.