VIEW ARTICLE

Vector Relations

The Aphid Salivary Gland Basal Lamina as a Selective Barrier Associated with Vector-Specific Transmission of Barley Yellow Dwarf Luteoviruses. F. E. Gildow, Department of Plant Pathology, Pennsylvania State University, University Park 16802; S. M. Gray, USDA/ARS, Department of Plant Pathology, Cornell University, Ithaca, NY 14853. Phytopathology 83:1293-1302. Accepted for publication 21 July 1993. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1993. DOI: 10.1094/Phyto-83-1293.

The inability of virions of the MAV barley yellow dwarf luteovirus to penetrate the extracellular basal lamina surrounding the accessory salivary glands of some nonvector aphid species suggests that the basal lamina may possess a selective function that regulates vector-specific luteovirus transmission. When Sitobion avenae and Rhopalosiphum padi were fed for 2 wk on either MAV- or RPV-infected oats and then examined by electron microscopy, virions of both the transmitted MAV and the nontransmitted RPV were observed penetrating the salivary basal lamina of S. avenae. When R. padi were examined, virions of transmitted RPV consistently were observed in the salivary basal lamina; however, virions of nontransmitted MAV were not observed in the salivary basal lamina of 50 aphids examined from five experiments. When 0.5–2 ng of purified MAV was injected into individual aphids and the aphids were examined by transmission electron microscopy after a 24-h feeding on oats, virions were observed in salivary basal lamina of S. avenae and of Metopolophium dirhodum, but MAV virions were rarely observed in R. padi, R. maidis, or in Schizaphis graminum. Virions per unit basal lamina length were counted to determine relative affinity of MAV for salivary basal lamina. The average numbers of MAV virions in basal lamina of S. avenae, M. dirhodum, R. padi, R. maidis, and S. graminum were 47, 28, <1, 0, and <1 virions per 10 µm of basal lamina length, respectively. When purified MAV virions were treated with any of three MAV-specific monoclonal antibodies or their Fab fragments and injected into S. avenae, virions were unable to penetrate the salivary basal lamina. In addition, virions of brome mosaic virus did not penetrate the salivary basal lamina of R. padi when each aphid was injected with 30 ng of BMV. These results are consistent with the hypothesis that the accessory salivary gland basal lamina functions as a transmission barrier and that specific virus capsid-glycoprotein interactions regulate basal lamina penetration.