On further propagation on EMS2 plants of two of these first passage progenies (derived, respectively, from the SN3 and LA4 isolates) a high infection rate was noted (92%) and a mutation at position 105 of the VPg was detected in these second passage progenies, suggesting that RB variants were probably already present, although in low proportion, in the first passage progenies. Here, RB1 is linked to infection.