|Introduction and overview of viruses seed-transmitted and non-persistently transmitted by aphids.|
S. A. TOLIN (1). (1) Virginia Polytechnic Institute and State University, Blacksburg, VA, U.S.A.
The number of viruses known to be transmitted vertically from seeds to seedlings has increased to over 200, and is dominated by about 30 members of the <i>Potyvirus</i> genus, with a few viruses in the Bromoviridae (<i>Alfalfa mosaic virus, Cucumber mosaic virus, </i>and<i> Peanut stunt virus</i>), <i>Fabavirus</i>, and <i>Carlavirus</i>. These viruses and potyviruses are also transmitted horizontally by aphids in a non-persistently or stylet-borne manner. Transmission of filamentous potyviruses is known to be mediated by interaction between specific motifs of two viral-encoded proteins, HCPro and CP, which function in attachment and release of virus particles from stylet tips. About half of the potyviruses infect and are seed-transmitted in legumes in the family <i>Fabaceae</i>, with up to three viruses infecting each of six other dicot families (<i>Asteraceae</i>, <i>Brassicaceae</i>, <i>Caricaceae</i>, <i>Cucurbitaceae</i>, <i>Rosaceae</i>, <i>Solonaceae</i>) and two monocot families (<i>Amaryllidaceae</i>, <i>Poaceae</i>). Aphids of both colonizing and non-colonizing species of host plants can usually transmit each virus, with varying efficiency. Efforts to understand pollen, ovule, and embryo infection, and manage these seed-borne viruses, will be discussed for important pathogens of lettuce and legume crops. New approaches to confirm vertical and horizontal transmission of <i>Zucchini yellow mosaic virus</i>, an emerging disease of cucurbits spread globally via infected seed, and to reveal significant genome diversity, will be discussed.