Diversity in the susceptibility of Botrytis cinerea strains to the biological control agent Pseudomonas helmanticensis

Abstract: The strain Pseudomonas helmanticensis CT22 isolated from tomato stem in a tomato greenhouse in Bejaia (Algeria) has shown a good protective efficacy against Botrytis cinerea in controlled conditions but its effect against various strains of B. cinerea was not assessed. In this study, we evaluated the diversity in the sensitivity of sixty two strains of B. cinerea strains to P. helmanticensis CT22 both in vitro and on tomato. In vitro effect of the biocontrol agent is variable according to the strain of B. cinerea, both in dual culture assay or in volatile assay. Due to the very high level of efficacy against all tested strains of B. cinerea on detached tomato stem when P. helmanticensis CT22 was applied at 107 CFU/ml, the dose of application was reduced 10-fold at 106 CFU/ml. In this condition, the protective efficacy of the biocontrol agent is significantly influenced by B. cinerea strains with protection levels ranging from 24% to 100%. These results suggest a diversity in the sensibility of the different strains of B. cinerea to the biological control agent and emphasize the importance to consider several strains of a given plant pathogen species when screening a biocontrol agent.