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Although it is currently eradicated from the United States, Plum pox virus (PPV) poses an ongoing threat to U.S. stone fruit production. Although almond ( Prunus dulcis ) is known to be largely resistant to PPV, there is conflicting evidence about its potential to serve as an asymptomatic reservoir host for the virus and thus serve as a potential route of entry. Here, we demonstrate that both Tuono and Texas Mission cultivars can be infected by the U.S. isolate PPV Dideron (D) Penn4 and that Tuono is a transmission-competent host, capable of serving as a source of inoculum for aphid transmission of the virus. These findings have important implications for efforts to keep PPV out of the United States and highlight the need for additional research to test the susceptibility of almond to other PPV-D isolates., Competing Interests: The author(s) declare no conflict of interest.

Plum pox virus (PPV) is a significant pathogen of Prunus worldwide and is known for having a broad experimental host range. Many of these hosts represent epidemiological risks as potential wild viral reservoirs. A comparative study of the PPV reservoir capacity of three commonly found native North American species, western choke cherry ( Prunus virginiana var. demissa ), black cherry ( Prunus serotina ), and American plum ( Prunus americana ) was conducted. Pennsylvania isolates of PPV-D were transmitted from the original host peach ( Prunus persica cv. GF305) to all three species. Viral accumulation and transmission rates to alternative hosts and peach were monitored over the course of five vegetative growth and cold induced dormancy (CID) cycles. The three alternative host species demonstrated differences in their ability to maintain PPV-D and the likelihood of transmission to additional alternative hosts or back transmission to peach. Western choke cherry had low (5.8%) initial infection levels, PPV-D was not transmissible to additional western choke cherry, and transmission of PPV-D from western choke cherry to peach was only possible before the first CID cycle. Black cherry had intermediate initial infection levels (26.6%) but did not maintain high infection levels after repeated CID cycles. Conversely, American plum had a high level (50%) of initial infection that was not significantly different from initial infection in peach (72.2%) and maintained moderate levels (15 to 25%) of infection and PPV-D transmission to both American plum and peach through all five cycles of CID. Our results indicate that American plum has the greatest potential to act as a reservoir host for Pennsylvania isolates of PPV-D.

Soybean dwarf virus (SbDV) exists as several distinct strains based on symptomatology, vector specificity, and host range. Originally characterized Japanese isolates of SbDV were specifically transmitted by Aulacorthum solani. More recently, additional Japanese isolates and endemic U.S. isolates have been shown to be transmitted by several different aphid species. The soybean aphid, Aphis glycines, the only aphid that colonizes soybean, has been shown to be a very inefficient vector of some SbDV isolates from Japan and the United States. Transmission experiments have shown that the soybean aphid can transmit certain isolates of SbDV from soybean to soybean and clover species and from clover to clover and soybean with long acquisition and inoculation access periods. Although transmission of SbDV by the soybean aphid is very inefficient, the large soybean aphid populations that develop on soybean may have epidemiological potential to produce serious SbDV-induced yield losses.