COMPARISON OF RESISTANCE LEVEL TO TOMATO YELLOW LEAF CURL VIRUS AMONGCOMMERCIAL CULTIVARS AND BREEDING LINES

The effect of tomato yellow leaf curl virus (TYLCV) on total yield and yield components of various resistant F-1 tomato cultivars and new br eeding lines was evaluated in the field. Seeds of the F-1 hybrids 8484 , 3761, Fiona, and Tyking and the new breeding lines TY172 and TY197 w ere sown in an insect-proof greenhouse. When the seedlings reached the first-leaf stage, they were inoculated with TYLCV by means of the whi tefly vector Bemisia tabaci. Noninoculated plants of the same cultivar or line which were exposed to nonviruliferous whiteflies served as co ntrols. After a short recovery period, the plants were transplanted to the field. The inoculated plants of each cultivar or line were compar ed with their respective control, noninoculated plants, in terms of to tal yield, average fruit weight and number, and plant fresh weight. Di sease symptom development and virus accumulation in the inoculated pla nts were monitored. There were substantial differences among the diffe rent entries tested in the extent of yield loss relative to the corres ponding noninoculated control plants as well as viral DNA accumulation levels. Plants of TY172 and TY197 suffered the least relative yield l oss and contained the lowest level of viral DNA. Therefore, these two lines exhibited the highest level of resistance. These results clearly demonstrate the ability of the various resistant tomato cultivars and lines to inhibit the effects of the virus, even following inoculation at a very early stage of plant development.