Comparison of Resistance Level to Tomato Yellow Leaf Curl Virus Among Commercial Cultivars and Breeding Lines.

The effect of tomato yellow leaf curl virus (TYLCV) on total yield and yield components of various resistant F1 tomato cultivars and new breeding lines was evaluated in the field. Seeds of the F1 hybrids 8484, 3761, Fiona, and Tyking and the new breeding lines TY172 and TY197 were sown in an insect-proof greenhouse. When the seedlings reached the first-leaf stage, they were inoculated with TYLCV by means of the whitefly vector Bemisia tabaci. Noninoculated plants of the same cultivar or line which were exposed to nonviruliferous whiteflies served as controls. After a short recovery period, the plants were transplanted to the field. The inoculated plants of each cultivar or line were compared with their respective control, noninoculated plants, in terms of total yield, average fruit weight and number, and plant fresh weight. Disease symptom development and virus accumulation in the inoculated plants were monitored. There were substantial differences among the different entries tested in the extent of yield loss relative to the corresponding noninoculated control plants as well as viral DNA accumulation levels. Plants of TY172 and TY197 suffered the least relative yield loss 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.