Characterization of the Alfalfa Pollen Virome

Vertical transmission of plant pathogenic viruses is an important component of viral persistence, survival, and spread in agricultural production systems. This type of transmission is of considerable economic significance as it can cause major crop losses by serving as the initial focus of infection for future epidemics. Vertical transmission occurs when a virus is passed on to offspring either by direct invasion of the developing seed embryo from infected mother plants or through infected pollen grains after fertilization. We have recently demonstrated via high-throughput sequencing that mature seeds of the agriculturally important forage crop alfalfa (Medicago sativa L.) are associated with a broad range of viruses, some of which could potentially spread over long distances via seed. With the exception of the alfalfa mosaic virus, little is currently known about viral transmission through alfalfa pollen and its subsequent impact on the disease epidemiology of the crop. The objective of this study was to screen pollen from diverse alfalfa genotypes for pathogenic viruses and assess their risk of transmission. The pollen was collected from alfalfa genotypes selected for fungal disease resistance and agronomic performance in the USDA ARS pre-breeding program in Prosser, WA.