Preliminary report on the apparent breaking of resistance of a a transgenic plum by chip bud inoculation of plum pox virus PPV-S

Five transgenic clones of Prunus domestica L. containing plum pox virus (PP V) coat protein (CP) gene and one non-transformed control clone were challe nged with PPV-S in the field. Symptoms developed on C2, C3, C4, C6 and B701 46 but not C5 trees inoculated by chip budding (CBI) (2/2, 212, 1/1, 2/2 an d 2/2, positive/inoculated) in the first summer after inoculation. However, in the second year, symptoms appeared on CBI C5 trees. The presence of the virus in the plants was confirmed by enzyme-linked immunosorbent ass ay (E LISA) and reverse transcription-polymerase chain reaction (RT-P CR) amplifi cation of a fragment of viral polymerase gene. During two years, symptoms o f infection developed on 3 to 4 of 8 non-inoculated trees of clones C2, C3, C4, C6 and B70146. Eight non-inoculated C5 trees remained symptomless and ELISA-negative as of spring 1998, in spite of the presence of aphid vectors and inoculum sources.