Hadas, R., Official Seed Testing Laboratory, Volcani Center, Bet Dagan 50250, Israel
Pearlsman, M., Dept. of Virology, ARO, Volcani Center, Bet Dagan 50250, Israel
Gefen, T., Official Seed Testing Laboratory, Volcani Center, Bet Dagan 50250, Israel
Lachman, O., Dept. of Virology, ARO, Volcani Center, Bet Dagan 50250, Israel
Hadar, E., Hazera Ltd., Brurim, M.P. Snikmim 79836, Israel
Sharabany, G., Hazera Ltd., Brurim, M.P. Snikmim 79836, Israel
Antignus, Y., Dept. of Virology, ARO, Volcani Center, Bet Dagan 50250, Israel

An indexing system for detecting Tomato mosaic virus (ToMV) in commercial tomato seed lots is described. Factors associated with the procedure were analyzed and the following standard two-step working scheme is proposed: (i) mass screening by ELISA for the presence of the virus; (ii) evaluation of virus infectivity within the infested seed lots. A threshold of 10 ng ml-1 was determined for detection of purified ToMV by either ELISA or plant inoculation. Nicotiana tabacum cv. Xanthi NN was found to be a highly sensitive local lesion assay plant for the detection of ToMV. A positive ELISA threshold (1.3 times above the non-specific background) was set for seed samples taken from commercial seed lots by testing the same samples by both ELISA and a bioassay.