Resistance of transgenic tomato to cucumber mosaic cucumovirus under fieldconditions

Since the summer of 1993, transgenic tomato plants expressing the coat prot ein (CP) genes of cucumber mosaic cucumovirus have been tested under field conditions to assess the level of resistance and agronomic performance. Tri als were performed in different areas in Italy and the target virus in the majority of tests was spread naturally by the indigenous aphid populations. Twenty-three homozygous lines of variety UC82B, transformed to contain fou r different CP genes of CMV, were evaluated. The lines were preselected for CP expression, single gene copy, and virus resistance in growth chamber ex periments. In general, CMV resistance was confirmed under field conditions though resistance in the field was less effective than what was observed in growth chamber experiments. The resistance observed in multi-year and mult i-location experiments is of commercial value for several of the most resis tant lines. Engineered resistance upon transfer to Italian varieties by bre eding or direct transformation will be used in tomato production in Italy o r elsewhere.