14 15Disentangling the role of epidemiological factors in plant pathogen emergences is a 16 prerequisite to identify the most likely future invaders. An example of emergence was 17 recently observed in France: in 10 years, "classic" (CL) strains of Watermelon mosaic virus 18 (WMV) were displaced at a regional scale by newly introduced "emerging" (EM) strains. 19Here we analyse a 3 years dataset describing the co-dynamics of CL and EM strains at field 20 scale using state-space models estimating jointly (i) probabilities of primary and secondary 21 infection and (ii) probabilities of over-infecting with a CL [EM] strain a plant already infected 22 with an EM [CL] strain. Results especially indicate that it is more than 3 times less probable 23 for a CL strain to over-infect an EM infected plant than for an EM strain to over-infect a CL 24 infected plant. To investigate if these asymmetric interactions can explain the CL/EM shift 25 observed at regional scale, an exploratory model describing WMV epidemiology over several 26 years in a landscape composed of a reservoir and a cultivated compartment is introduced. In 27 most simulations a shift is observed and both strains do coexist in the landscape, reaching an 28 equilibrium that depends on the probabilities of over-infection. 29 30 31