Strain specificity and simultaneous transmission of closely related strains of a Potyvirus by Myzus persicae.

Potato virus Y (PVY), a Potyvirus, is transmitted by aphids in a nonpersistent manner. PVY severely affects potato production worldwide. Single and mixed infections of PVY strains, namely PVY(O), PVY(NTN), and PVY(N:O) are a common occurrence in potato systems. However, information available on the ability of aphids to simultaneously transmit multiple PVY strains, specificity associated with simultaneous transmission, and factors affecting specificity are limited. Aphid-mediated transmission experiments were conducted to test the ability of individual aphids to transmit multiple strains using a PVY indicator host. Preliminary results revealed that aphids can transmit at least two viral strains simultaneously. Subsequently, aphid-mediated transmission of three dual-strain combinations was tested using potato plants. Individual aphids transmitted two viral strains simultaneously for all three dual-strain combinations. In all aphid-mediated dual-strain infections involving PVY(NTN), the rate of PVY(NTN) infection was greater than the infection rates of the second strain and dual-strain combinations, indicating specificity associated with transmission of PVY strains. Results of aphid-mediated transmission experiments were compared with results obtained through mechanical transmission. In general, PVY infection rates from aphid-mediated transmission were lower than the rates obtained through mechanical transmission. Unlike aphid-mediated transmission, component strains in dual-strain inoculations were not eliminated during mechanical transmission. These results suggest that there may also be interference associated with aphid-mediated transmission of closely related PVY strains. Perhaps, the observed specificity and/or interference may explain the increase in the incidence of PVY(NTN) and other necrotic strains in recent years.

Within plant distribution of Potato Virus Y in hairy nightshade (Solanum sarrachoides): an inoculum source affecting PVY aphid transmission.

Potato virus Y (PVY) is vectored by several potato-colonizing and non-colonizing aphid species in a non-persistent manner and has a wide host range. It occurs naturally in several plant families. Myzus persicae and Macrosiphum euphorbiae are the most efficient potato-colonizing aphid vectors of PVY. Rhopalosiphum padi, a cereal aphid that migrates in large numbers through potato fields during the middle of the growing season, does not colonize potato plants but can transmit PVY. Hairy nightshade, Solanum sarrachoides, a prevalent annual solanaceous weed in the Pacific Northwest (PNW) of the United States, is an alternative host for PVY and a preferred host for M. persicae and M. euphorbiae. Hence, hairy nightshade plants might play an important role as an inoculum source in the epidemiology of PVY. We looked at titre accumulation and distribution of PVY(O), PVY(N:O) and PVY(NTN) in S. sarrachoides and potato after aphid inoculation with M. persicae and studied the transmission of PVY(O) and PVY(NTN), by M. persicae, M. euphorbiae and R. padi from hairy nightshade to potato plants. Virus titre at different positions on the plant was similar in S. sarrachoides and potato plants with strains PVY(O) and PVY(N:O). Titres of PVY(NTN) were similar in S. sarrachoides and potato but differences in titre were observed at different positions within the plant depending on the plant phenology. Percentage transmission of PVY(NTN) by M. persicae and M. euphorbiae was twice as high (46 and 34%, respectively) from hairy nightshade to potato than from potato to potato (20 and 14%). Percentage transmission of PVY(O) by M. persicae and M. euphorbiae was not affected by the inoculum source. No effect of the inoculum source was observed in the transmission of either PVY strain by R. padi. These results show that hairy nightshade may be an equal or better virus reservoir than potato and thus, important in the epidemiology of PVY.

Effect of an alternate weed host, hairy nightshade, Solanum sarrachoides, on the biology of the two most important potato leafroll virus (Luteoviridae: Polerovirus) vectors, Myzus persicae and Macrosiphum euphorbiae (Aphididae: Homoptera).

Hairy nightshade, Solanum sarrachoides (Sendtner), is a ubiquitous weed in potato agro-ecosystems and nonagricultural lands of southeastern Idaho and the Pacific Northwest. This weed increases the complexity of the Potato leafroll virus (PLRV) (Luteoviridae: Polervirus)-potato pathosystem by serving as aphid and virus reservoir. Previous field studies showed higher densities of green peach aphid, Myzus persicae (Sulzer), and potato aphid, Macrosiphum euphorbiae (Thomas), the two most important vectors of PLRV, on S. sarrachoides compared with potato plants in the same fields. Some of the S. sarrachoides plants sampled in these surveys tested positive for PLRV. Viral infections can alter the physiology of plant hosts and aphid performance on such plants. To understand better the potential effects of S. sarrachoides on the PLRV-potato-aphid pathosystem, the life histories of M. persicae and M. euphorbiae were compared on virus-free and PLRV-infected S. sarrachoides and potato. Individual nymphs of each aphid species were held in clip cages on plants from each treatment to monitor their development, survival, and reproductive output. Nymphal survival for both aphids across plant species was higher on S. sarrachoides than on potato, and, within plant species, it was higher on PLRV-infected plants than on noninfected plants. With a few exceptions, similar patterns occurred for fecundity, reproductive periods, adult longevity, and intrinsic rate of increase. The enhanced performance of aphids on S. sarrachoides and on PLRV-infected plants could alter the vector population dynamics and thus the PLRV-disease epidemiology in fields infested with this weed.

Effect of mixed viral infections (potato virus Y-potato leafroll virus) on biology and preference of vectors Myzus persicae and Macrosiphum euphorbiae (Hemiptera: Aphididae).

Mixed viral infections of heterologous viruses such as Potato virus Y (family Potyviridae, genus Potyvirus, PVY) and Potato leafroll virus (family Luteoviridae, genus Polerovirus, PLRV) are a regular occurrence in Idaho's potato, Solanum tuberosum (L.), cropping systems. An increased number of plant samples from Idaho's potato fields over the past 2 yr has serologically tested positive for both PVY and PLRV via double antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) and exhibited more severe symptoms than singly-infected plants (PVY or PLRV). Several studies have extensively examined the mixed infection phenomenon but to the best of our knowledge, none have examined the effect of such infections on vector biology and preference. Laboratory studies were conducted to examine the effect of mixed viral (PVY-PLRV) infection on the fecundity and preference of two of the most efficient PVY and PLRV vectors, the green peach aphid, Myzus persicae (Sulzer), and the potato aphid, Macrosiphum euphorbiae (Thomas) (Hemiptera: Aphididae). M. persicae and M. euphorbiae adults were clip-caged (one adult per cage) to leaflets of PVY, PLRV, PVY-PLRV-infected, and noninfected potato plants. The number of nymphs produced in all four treatments was recorded after 96 h. M. persicae and M. euphorbiae fecundity was significantly higher on mixed infected plants than on singly infected plants or noninfected plants. Preference of alatae and apterae of M. persicae and M. euphorbiae was determined with the use of settling bioassays. Both alatae and apterae of M. persicae and M. euphorbiae preferentially settled on PVY-PLRV-infected plants than on singly infected plants (PVY or PLRV) or noninfected plants.

Evaluation of hairy nightshade as an inoculum source for aphid-mediated transmission of potato leafroll virus.

Potato leafroll virus (PLRV) causes one of the most serious aphid-transmitted diseases affecting yield and quality of potatoes, Solanum tuberosum (L.), grown in the United States. The green peach aphid, Myzus persicae (Sulzer), is considered to be by far the most efficient vector of this virus. Even the most strict aphid control strategy may not prevent the spread of PLRV unless measures also are taken to keep virus source plants within and outside the crop at a minimum. Hairy nightshade, Solanum sarrachoides (Sendtner), is one of the preferred weed hosts for green peach aphid. The potential of this weed as an aphid reservoir and virus source and its spread or perpetuation were investigated. With the use of double antibody sandwich enzyme-linked immunosorbent assay, it was confirmed that green peach aphid can transmit PLRV to hairy nightshade and that aphids can become viruliferous after feeding on infected hairy nightshade plants. Transmission from hairy nightshade to potato is 4 times the rate of potato to potato or potato to hairy nightshade. The green peach aphid preferred hairy nightshade over potato plants and reproduced at a higher rate on hairy nightshade than on potato. Therefore, a low level of PLRV-hairy nightshade infection could enhance the disease spread in the field.