The interference between tomato yellow leaf curl geminivirus (TYLCV) and tomato mosaic
tobamovirus (ToMV), has great effect on concentration and infectivity of both viruses in infected plants as well
as on tomato yield. Using polymerase chain reaction (PCR), nucleic acid hybridization (NASH), enzyme-linked
immunosorbant assay (ELISA) and biological assay, it was found that TYLCV or ToMV had high
concentration in inoculated tomato plants. While, it had low concentration in TYLCV inoculated tomato plants
when inoculated at the first, followed by ToMV inoculation, 15 days later or when the two viruses were
inoculated at once. Also, low virus concentration was obtained when tomato plants inoculated with ToMV at
first followed by TYLCV inoculation 15 days later. Concerning the external symptoms, it was found that the
reduction of TYLCV external symptoms were in ascending order when ToMV, TYLCV or both viruses were
inoculated at first. In addition, it was observed that, ToMV was suppressed in all treatments followed by
increase with plant age. In contrary to that of TYLCV, ToMV symptoms increased in descending order
respectively. The distribution of TYLCV was existent in all parts of inoculated plants. The height and yield of
tomato plants also affected by the interference between the two viruses in which this affect depended on which
virus was inoculated at first. In general, the effect of two viruses on decreasing tomato yield was more than
when the two viruses were found individually.