COMPARISON OF COAT PROTEIN-MEDIATED AND GENETICALLY-DERIVED RESISTANCE IN CUCUMBERS TO INFECTION BY CUCUMBER MOSAIC-VIRUS UNDER FIELD CONDITIONS WITH NATURAL CHALLENGE INOCULATIONS BY VECTORS

During three consecutive growing seasons, transgenic cucumbers of the cultivar Poinsett 76 possessing the coat protein gene of a non-aphid transmissible strain of cucumber mosaic virus (CMV) were compared with the non-transformed plants of the same cultivar and CMV-resistant Marketmore 76. Unique to this study, a low percentage of CMV-infected cucumbers provided the major source of virus, which was naturally spread by the indigenous aphid populations. Monitoring of test plants by visual inspection and ELISA provided a dynamic evaluation on the resistance of transgenic plants throughout the plant growth cycle. Eight weeks after transplanting, the critical period when plants were bearing fruit, the percentage of infection in transgenic Poinsett 76 and Marketmore 76 plants averaged less than 5 %, in contrast to about 72 % in non-transformed plants. Trials were terminated 13 weeks after field transplanting, when plants had entered the senescence stage. At this time, ELISA demonstrated an appreciable level of CMV infection in transgenic lines (35%) and a much higher amount in Marketmore 76 (62%), while an average of 85% of the non-transformed Poinsett 76 tested positive. Fruit yields and vegetative growth of transgenic lines averaged better than those of non-transformed plants of the same cultivar.