The objective of modelling large-scale dissemination of Pseudomonas syringae was to build a predictive model of epidemic risk of in France.

A model is under development to estimate the connectivity of geographic sites based on air mass trajectories that bring rainfall (in relation with the life history of the bacterium with the water cycle). This will be compared to the history of spread of kiwifruit canker due to P. syringae that emerged in France in 2010.

The importance of the air mass trajectory was shown for Pseudomonas syringae in precipitation (88 rain and snow samples collected in southeast and central France). Main results are:

• the occurrence of P. syringae in precipitation was correlated with the chemical characteristics of the precipitation (conductivity, pH) as well as the associated air mass trajectory
• the structure of the P. syringae population consisted of three distinct genetic groups related to the location and type of precipitation in which the sample came from
• the phenotypic characteristics of strains (ice nucleation activity, traits related to pathogenic potential) differed if they were collected form snow or rain.

In contrast, the presence of B. cinerea in these same precipitation events was indifferent to the trajectory of the air mass and there was no difference between rain and snow in the aggressiveness of the strains of B. cinerea that they carried. This striking contrast illustrates the specificity of each model and illustrates the interest in such comparative studies of different models as a means to highlight this specificity.

Monteil, C., Bardin, M., Morris, C. E. 2014. Features of air masses associated with the deposition of Pseudomonas syringae and Botrytis cinerea by rain and snowfall. ISME Journal, 8 (11), 2290-2304. DOI : 10.1038/ismej.2014.55https://hal.inrae.fr/hal-02637810