Department of Mathematics, University of Houston, 651 PGH Building, Houston TX, USA. alanavc@math.uh.edu.|Department of Mathematics, University of Houston, 651 PGH Building, Houston TX, USA. alanavc@math.uh.edu.|Department of Mathematics, University of Houston, 651 PGH Building, Houston TX, USA. alanavc@math.uh.edu.|INRA, Laboratoire des Interactions Plantes-Microorganismes (LIPM), UMR441, 24 Chemin de Borde Rouge - Auzeville, CS52627, F31326 Castanet Tolosan Cedex, France. Sylvain.raffaele@toulouse.inra.fr.