| Viral diseases have increased in commercially grown crops in the Midwest United States since the recent establishment of the soybean aphid, Aphis glycines Matsumura. In Wisconsin, Alfalfa mosaic virus (AMV) and Cucumber mosaic virus (CMV) are two nonpersistently-transmitted viruses frequently detected in infected snap bean (Phaseolus vulgaris ). Many factors, such as frequent aphid infestations, significant reservoirs of virus inoculum, and the introduction of new cultivars, may all have attributed to this increase.;A. glycines transmits viruses in many economically important crops and is suspected of contributing to current disease outbreaks in snap bean. In lab and field studies, we demonstrated that A. glycines visits non-host plants like snap bean, and is the most abundant (52% of total aphid catches) species across the agricultural landscape. Peak A. glycines activity occurred briefly (July 24 to August 11) in the summer season and coincided with the onset of disease, which further suggests A. glycines is a likely vector of snap bean viruses.;Plants along unmanaged field margins bordering commercial crops could serve as reservoirs of AMV and CMV that, via vectors like A. glycines , infects snap bean. In 2006 to 2008, a Wisconsin virus survey was conducted to develop a virus inoculum potential (VIP) index and classified alfalfa (Medicago sativa) and milkweed (Asclepias syriaca) with the greatest risk as local reservoirs of AMV and CMV, respectively.;Viral seed transmission is another potential source of primary inoculum for aphid vectors to acquire and transmit to healthy bean. Evaluation of field-collected isolates showed that AMV and CMV are transmissible through snap bean seed at rates of 0.7% and 0.5%, in the greenhouse, and 1.8% and 0.6%, under field conditions, respectively.;Successful aphid transmission of nonpersistent viruses requires specific interactions between virus, host, and aphid vector. Our research showed that aphids differed in their ability to transmit field isolates of AMV and CMV to snap bean. The soybean aphid, however, was most capable and, based on its abundance in the landscape, plays an important role in snap bean virus epidemiology. |
