Evaluation of transgenic tomato plants expressing the coat protein gene of cucumber mosaic virus strain WL under field conditions

Transgenic tomato plants expressing the coat protein (CP) gene of cucumber mosaic virus (CMV) strain WL, a member of CMV subgroup II, were evaluated for resistance to CMV infections under field conditions for 2 years. Three transgenic inbred lines, two hemizygous and one homozygous, and one transgenic hybrid were field tested. CMV subgroup I strain Fny was used as challenge inoculum. Disease incidence was assessed by monitoring symptom development, enzyme-linked immunosorbent assays (ELISA), and bioassays on indicator hosts. The four transgenic tomato lines exhibited a high level of resistance to CMV infections, since all 747 transgenic plants remained symptomless throughout the crop cycle. Moreover, CMV could not be detected by ELISA nor recovered from uninoculated leaves of transgenic plants. These developed to normal height, and showed a 17-fold increase in productivity along with a 44% increase in fruit weight compared with nontransformed control plants. Since our transgenic CMV-resistant homozygous tomato line also has resistance to TMV that is conferred by the Tm-2(2) gene in the parental cultivar, it can be used as a breeding germ plasm to develop commercial hybrids resistant to both CMV and TMV, two important viruses that affect tomato crops.