Seed Transmission in the Potyviridae

Viral pathogens comprise approximately half of the emerging diseases in plants, and plant introductions (including the international movement of seed) are considered to be one of the most important contributing factors to the emergence of these pathogens. For the most part plant viruses are incapable of surviving outside of host tissue making their long-term propagation dependent on their hosts. Thus infected seeds are an effective strategy that not only allows for pathogen survival from one season to the next, but also for their dispersal. The Potyviridae, as the largest plant virus family, is often considered to be the most economically important and its members rank among the most successful plant pathogens. Seed transmission within the Potyviridae family is not uncommon, however the exact mechanism of viral entry into the germ line is currently unknown, and the genetic basis of seed transmission has yet to be completely elucidated. Seed transmission rates are influenced by complex interactions among a variety of factors including the host cultivar, the virus isolate, environmental conditions, the timing of infection, vector characteristics, and viral synergism. Seed transmission can have an enormous effect on the epidemiology of crop pathogens due in part to the ecology of plant viruses which are often secondarily disseminated via insect vectors with the effect that extremely low frequencies of seed transmission can result in devastating epidemics. This is compounded by the fact that vertically infected seedlings often do not exhibit symptoms of viral infection. Given the potential for seed transmitted viral pathogens to initiate epidemics, it is vital to understand how seed transmission rates translate into epidemics. In addition, as seed transmission is a means of dispersal for these viral pathogens, effective phytosanitary measures to control the spread of these pathogens are crucial.