SUMMARY The

potential impact of transgenic plums and gra-pevines expressing viral coat protein (CP) gene con-structs on the diversity and dynamics of virus popula-tions was assessed under open and confined conditions in the frame of a research program sponsored by the European Commission. Across all field trials conducted in different locations (France, Romania, and Spain) and environments (continental and Mediterranean), trans-genic plums expressing the CP gene of Plum pox virus (PPV) and transgenic grapevines expressing the CP gene of Grapevine fanleaf virus (GFLV) had no de-tectable effect on the emergence of recombinant PPV and GFLV species over eight-ten and three years, re-spectively. Also, no statistically significant difference was found in the number and type of aphids, including viruliferous individuals, and other arthropods that visit-ed transgenic and nontransgenic plum trees. In addi-tion, Apple chlorotic leaf spot virus, Prune dwarf virus, and Prunus necrotic ringspot virus did not influence the stability of the engineered resistance to PPV in co-in-fected transgenic plums over three dormancy periods. Further, under confined conditions, no recombinant virus was found to detectable level in transgenic gra-pevines expressing the CP gene of Grapevine virus A (GVA) or Grapevine virus B (GVB) that were chal