Influence of hairy nightshade, Solanum sarrachoides (Sendtner) on the Potato leafroll virus pathosystem

Solanum sarrachoides (Sendtner), a non-native weed, is invasive of potato agro-ecosystems of the Pacific Northwest. Besides directly competing for resources with the crop it also serves as a reservoir of Potato leafroll virus (PLRV) and its most efficient vectors, the green peach aphid, Myzus persicae (Sulzer), and the potato aphid, Macrosiphum euphorbiae (Thomas). The role of S. sarrachoides as vector and virus reservoirs in PLRV-epidemiology was investigated through a series of laboratory and field experiments. Life history studies of M. persicae and M. euphorbiae on S. sarrachoides and potato with and without PLRV-infection revealed that aphids had enhanced performance on S. sarrachoides over potato and on PLRV-infected plants over non-infected plants of both hosts. Host-preference studies of winged and wingless M. persicae using settling bioassays indicated a preference for S. sarrachoides over potato and for PLRV-infected plants over non-infected plants of both hosts by this aphid. Investigations on the mechanisms of aphid host-preference led to the identification of volatile organic compounds (VOCs) and their role as olfactory cues. Emigration bioassays revealed that VOCs from S. sarrachoides and PLRV-infected plants of both hosts attracted and arrested more M. persicae than potato and non-infected plants, respectively. Qualitative and quantitative investigations of VOCs were carried out with gas chromatography and mass spectroscopy (GC-MS). GC-MS analysis indicated the presence of green leaf volatiles, nonanal and methyl salicylate and terpenoid compounds in potato. Similar VOCs except for terpenoids were detected in S. sarrachoides. A greater concentration of headspace VOCs were recorded from PLRV-infected than from non-infected S. sarrachoides. This difference was not observed in potato. Three field experiments conducted over two seasons indicated an aphid-preference for S. sarrachoides over potato. Solanum sarrachoides could play an important role in PLRV-disease epidemiology by affecting aphid populations and also by acting as an efficient PLRV-inoculum source. Host-preference studies with mixed-infected potato plants (PLRV-Potato virus Y [PVY]) revealed that winged and wingless M. persicae and M. euphorbiae exhibited increased preference for mixed-infected plants over singly-infected and non-infected plants.