Seeds provide an ideal medium for the survival of viruses, especially when suitable host plants are in short supply. Irrespective of their transmission frequency, which may vary from less than I percent to 100 percent, seed-transmitted viruses have significant impact on disease epidemics. A low rate of virus transmission coupled with secondary spread by animal vectors may lead to disease epidemics in a new area, while a high rate of transmission may cause virus self-extinction as a result of poor development of flowers and seeds. More than 100 plant viruses are reported to have seed-based transmission (Mink. 1993: Van den Heuvel et al.. 1999).