Virus-Vector Cell Interactions Regulating Transmission Specificity of Soybean Dwarf Luteoviruses

Transmission of soybean dwarf viruses (SbDV) indigenous to Japan (SbDV‐D) and to the eastern United States (SbDV‐Va19) were compared in vector and nonvector aphid species. Absolute vector‐specificity was maintained when Aulacorthum solani, Acyrthosiphon pisum, and Myzus persicae were allowed to feed on solutions of either virus (100 μg/ml) through Parafil© membranes. SbDVD was transmitted only by A. solani, and SbDV‐Va19 was transmitted only by A. pisum and M. persicae. Similar results were obtained when individual aphids were micro‐injected with 2 ng virus and subsequently allowed to feed on healthy plants. Ultrastructural studies of A. solani and M. persicae indicated that both SbDV‐D and SbDV‐Va20 were acquired specifically through the aphid hindgut. No difference in hindgut acquisition specificity was observed, and both A. solani and M. persicae were able to transport SbDV‐D and SbDV‐Va20 into the haemocoel by endocytotic/exocytotic pathways. When injected, SbDV was shown to be associated with only the accessory salivary glands (ASG) in aphids, indicating a high level of tissue specificity. Two different interactions with the ASG were observed for SbDV‐D and SbDV‐Va20 in A. solani and M. persicae. SbDV‐D penetrated the ASG basal lamina of A. solani, but was never observed in the basal lamina of M. persicae. The ASG basal lamina was a barrier to SbDV‐D transmission by M. persicae. SbDV‐Va19 penetrated the ASG basal lamina of both A. solani and M. persicae. However, SbDV‐Va20 was not observed in the ASG cytoplasm in A. solani, indicating that the basal plasmalemma functioned as the transmission barrier. Observations indicated that capsid protein structure, aphid basal lamina composition and cell membrane components influenced virus‐aphid interactions regulating SbDV transmission.