Diseases caused by geminiviruses are widespread in the tropical-subtro
pical tomato production areas. Tomato yellow mosaic geminivirus (ToYMV
) is a member of the whitefly-transmitted subgroup (III), which is vec
tored by the whitefly Bemisia tabaci. Several accessions of Lycopersic
on con chilense, L. hirsutum, and L. peruvianum var. glandulosum were
identified that exhibit tolerance or a high degree of resistance to a
Venezuelan isolate of ToYMV in field and greenhouse studies using mech
anical inoculation and viruliferous vectors. Polymerase chain reaction
analysis showed that viral DNA is present in infected plants and abse
nt in resistant ones. Mechanical and insect transmission gave differen
t results in some species or cultivars, suggesting a distinct mechanis
m for resistance.